GENERAL LIBRARY OF THE UNIVERSITY OF CALIFORNIA. Class ROCK DRILLS Published by the Me G raw - H ill B ook- Comp any New S\ICCC&SOT\S to theBookDepartments of tke McGraw Publishing" Company Hill Publishing' Company PutlisheM of Books for tlectrical World Jhe Engineenng" and Mining" Journal Engineering Record Power and The Engineer Electric Railway Journal American Machinist Metallurgical and Chemical Engineering ?iirFgiifig ROCK DRILLS DESIGN, CONSTRUCTION, AND USE BY EUSTACE M. WESTON Associate School of Mines, Ballarat; Reef Lecturer on Mining, Transvaal University College OF THE UNIVERSITY OF McGRAW-HILL BOOK COMPANY 239 WEST 39TH STREET, NEW YORK 6 BOUVERIE STREET, LONDON, E.C. 1910 Copyright, 1910, by the McGRAW-HiLL BOOK COMPANY GENERAL The Plimpton Press Norwood Mass. U.S.A. PREFACE IN presenting this collection of essays on rock drills, I make no claim to have treated the subjects exhaustively. Rock drills have formed the subject of numerous articles in the technical press. Various authors have dealt with the subject; but only incidentally and as a branch of other subjects. I know of no book that will, in the first place, give a description of the leading modern makes of English, Australian, and American drills of both piston and hammer types, or give such details of their actual use in metalliferous mines as would enable a novice to approach them with some previous knowledge; and, at the same time, assist the engineer and mine manager to choose machines most suited to his particular needs and to maintain and work them at their highest efficiency. This is my excuse for attempt- ing such a task, while engaged in other mining work. I have not hesitated to reprint much of the writing of others, always, I hope, with due acknowledgment. Where the facts were stated concisely and clearly I saw no object in transcribing. I had much help from H. P. Gillette's excellent book, C. LeNeve Foster's and other works on mining. I have borrowed largely from proceedings of scientific societies and from A. and Z. Daw's exhaustive work on Blasting Rock. Many thanks are due to manufacturers for much help. I have tried to write without bias in comparing the merits of various machines and devices, and the book is not an advertisement for any particular drill. I have not given much space to either rotary or gasoline drills as they scarcely come within the scope of the book. My apology to my critics, who will doubtless find many omis- sions in the book, is, that it is a collection of notes that the author himself would have been very pleased to have had in book form when recently selecting and working rock drills. My chief qualification for writing this book is, that I have had to earn my living by using many of the machines described, and more recently in superintending rock-drilling operations. For the vi PREFACE scanty and inadequate discussion of many of the problems, my excuse is, that there is much, I believe, not yet known to any one; there is much vacant ground for careful and intelligent experiment and invention. Hammer drills are only now being developed; designs are changing every month; difficulties are being overcome and some- times new ones encountered; nor has the last word been said in the design of piston drills. E. M. WESTON. OCTOBER, 1910. CONTENTS CHAPTER PAGE PREFACE v I HISTORICAL SKETCH 1 II STANDARD PISTON DRILLS 8 III HAMMER DRILLS 49 IV ELECTRIC DRILLS 85 V OPERATING ROCK DRILLS ON THE SURFACE AND UNDERGROUND 105 VI PISTON DRILLS DESIGNED TO USE AIR EXPANSIVELY . . . 122 VII PHILOSOPHY OF THE PROCESS OF DRILLING ROCK .... 129 VIII REPAIR AND MAINTENANCE OF ROCK DRILLS .... 141 IX DRILL STEEL AND DRILL BITS 150 X EXPLOSIVES AND THEIR USE 178 XI THEORY OF BLASTING WITH HIGH EXPLOSIVES 210 XII EXAMPLES OF ROCK DRILL PRACTICE, AFRICA AND AUSTRALIA 226 XIII EXAMPLES OF ROCK DRILL PRACTICE, AMERICA 269 XIV ROCK DRILL TESTS AND CONTESTS 315 XV DUST AND ITS PREVENTION 338 XVI NOTES ON THE USE OF COMPRESSED Am . . . .351 VII ROCK DRILLS HISTORICAL SKETCH HISTORY has not handed down the name of the genius who first conceived the idea of drilling a circular hole in hard rock by hammering and revolving chisels of bronze, iron, or steel, which had the length of cutting edge decreased as the depth of the hole increased to provide for wear. Such holes were drilled for building and bridge work, centuries before the invention of gunpowder. As might be expected, several nations contend for the honor of having first produced a machine driven by air or steam for boring holes in hard rock. The truth is, that, like most other inventions, the rock drill has been and is being gradually per- fected by the efforts of different men, each contributing something to the final design. Richard Trevithick, a Cornishman, invented, in 1813, a rotary, steam-driven drill for boring in limestone. The idea of fasten- ing a detachable tool to a mechanically moved piston rod dates from the invention of the steam hammer, about 1842. In 1844 Brunton, in England, suggested the employment of compressed air. for a rock borer and invented a machine he called a "wind hammer," for boring holes, as shown in Fig. 1. In 1853 William Pidding invented a hammer secured to a frame and reciprocated by steam power for rock boring. In Germany, at the same time, Schumann invented a machine for work in the Freiberg mines, which, in many features, anticipated the present type of rock drills. In France, in 1855, M. Fontainmoreau patented an improved drill for use with compressed air, which had a rotary and a for- ward movement; in the same year Mr. Bartlett patented a ma- chine tried in boring the Mt. Cenis tunnel; this drill (Fig. 2) was improved by M. Sommeiller and used in boring the tunnel. Two hundred machines had, however, to be kept on hand in order to keep sixteen in constant use. The Sommeiller machine, a true 1 2 ROCK DRILLS pneumatic percussive drill, was the first to be actually used for tunnelling (1861), and for mining at Moresuet, Belgium (1863). Americans claim, and I think rightly, that the first inventor of a machine embodying the principles of the modern rock drill was J. W. Fowle, of Boston. This drill was steam driven; the bit formed an extension of the piston rod and was fed towards the rock as the drill tool advanced. The piston was also given a slow rotary movement. The date of the patent is 1849. A recent writer in the " Mining & Scientific Press" gives the name of FIGS. 1 and 2. Brunton's "Wind Hammer" at the top, and M. Sommeil- ler's "Perforator" below. Gen. H. H. Haupt as being connected with the design of a rock drill in 1857-1861 which was of better design than those at work in the Mt. Cenis tunnel. It was improved by Taylor, and did best work in driving the St. Gothard tunnel. This drill was im- proved by Burleigh, who constructed a tunnel-drilling machine which was used in driving the Hoosac tunnel in Massachusetts, in 1866. Other names associated with the development of the rock drill are Crease, Jordan, Darlington, Beaumont, Doering, Ingersoll, Sergeant, Wood, Leyner, Holman, Stephens, and others. Fig. 3 shows the type of drill used in 1880. HISTORICAL SKETCH 3 The history of the rock drill written from another standpoint could be called the history of modern mining and of much modern engineering. It is not too much to say that without the rock drill the world would long before this have starved for its indus- trial and precious metals. The rock drill has added enormously to the wealth of the world. Mines, some of them the richest, FIG. 3. A rock drill of 1880. and quarries in hard rock, where labor was scarce and dear, have been rendered workable only by its use. The world's greed for gold, silver, lead, copper, and tin could never have been satis- fied without it. The wonderful mining undertakings of the past, the great drainage adits of Saxony and Cornwall, the deep shafts and drives in hard ground in these old mines were accomplished only by the expenditure of an amount of time and human effort 4 ROCK DRILLS that we cannot afford in these clays of large demands and large outputs. The rock drill with its hundreds of crushing blows per minute, doing the work of ten or twenty men, came to help the miner extract bodies of low-grade ore; to enable the engineer to attack problems undreamed of before; and in the Old World to pierce the Alps for his railways by the Mt. Cenis tunnel 1\ miles long; the St. Gothard tunnel 9J miles long, and the Simplon tunnel 12 miles long. In the New World great aqueducts, like the Croton, could be carried by tunneling for 34 miles, and every- where the great railroads were carried through the heart of the Alleghanies and Rockies as surely as over the Mississippi plains. In the Chicago drainage canal, 14 million cubic yards of solid rock were removed in an incredibly short space of time by their aid; and, finally, the great continents of North and South America are being rent asunder by the greatest cut in solid rock ever made by man and only possible by the aid of the percussive rock drill. Everywhere, canals, tunnels, railroads, docks, harbors, and numerous other works have been made possible, as commercial undertakings, largely by the rock drill. Twenty to thirty thou- sand rock drills are at work in the world to-day. There are about 2500 employed in the Witwatersrand field in South Africa. With- out their aid in stoping and development, the output of nearly 2J millions pounds sterling, per month, could not be maintained; financial disaster would hover over the whole civilized world, owing to a shortage of gold. Cheap roads, paving, and building, cheap rail travel and trans- portation and low-priced metals, we owe largely to the rock drills, and even in death the rock drill helps to provide our graves with head stones. This might remind us that the history of the rock drill has something of tragedy and terror connected with it. In many mining fields the standard percussive rock drill is not operated without the cost of valuable human lives. In the first place ; its use permits so many blasts that the air in the mine workings is burdened with a greatly increased proportion of the products of the combustion of high explosives. Of these carbon monoxide and nitrous acid are -active poisons rapidly producing death when present in large quantities; these gradually sap the strength and vitality when breathed during long periods, even when present in very small amounts. Adequate ventilation may deal with this trouble. The rock drill when engaged in drilling HISTORICAL SKETCH 5 holes pointed upward produces its cuttings in the form of fine dust. This dust when inhaled by the miner remains on the lungs, choking and weakening the tissues and after a time pro- duces a painful death. The life of a rock driller, engaged in development work on the Rand field in South Africa, owing to these two causes, has been stated to average not more than five years. This subject will be referred to later in discussing the problem of boring with hollow steel water jets and sprays. The following interesting chronological table is taken with the preceding figures from Messrs. Holman Brothers' catalogue. CHRONOLOGICAL TABLE AN interesting compilation of some of the most important events concerning rock drills, boring shot holes, explosives, and blasting ground. Partly com- piled by Eziha and Drinker and supplemented with additional information. From Transactions P. S., Vol. 14. A.D. 1280 Albert Magnus, the German Friar, describes an explosive powder. 1284 Roger Bacon notices the composition of an explosive powder. 1324 Berthold Schwarz is said to have invented gunpowder. 1412 Gunpowder manufactured in England. 1613 Martin Weigel, mining superintendent of Freiberg, proposed drilling and blasting in mines. 1670 German miners introduced blasting into England. 1685 Tamping with clay known in Saxony. 1687 Lumbe introduced into the Harz, tamping with clay, and straws filled with powder for firing the shot holes. 1688 Singer, of Clausthal, employed small firing tubes of hard wood. 1689 Luft, of Clausthal, used paste board cartridges. 1717 Fritsch proposed to save powder, and to break the rock by wedges driven into the bore holes. 1725 At this date the effect of simultaneous firing of several shots was known. 1749 Hungarian miners first introduced the chisel-bit drill into the Harz. For a period of one hundred and thirty-six years, from WeigePs day to this date, all drilling had been done by means of crown and cone "bits." 1759 Drilling with a chisel bit introduced into Saxony. 1760 Thumberg introduced into Sweden tamping with wedges. 1791 Le Plat used sand as a tamping. 1795 Humboldt proposed making the shot holes wider at the bottom (of a conical shape). 1811 Spangenberg, of Sahl, used wooden tamping rods, also wooden needles and soft clay for tamping. 6 ROCK DRILLS 1813 Trevithick invented a rotating boring machine, which was made at Hayle Foundry, Cornwall, and put into operation at some limestone quarries near Plymouth. 1823 Harris fired a blast by the electric spark. 1829 Needles made of a composition of lead and tin, used in the district of Ehrenfridersdorf. 1829 Moses Shaw, of New York, fired several charges of powder simultane- ously by passing an electric spark through a priming composed of the fulminiate of silver. 1831 Bickford, of Camborne, invented the safety fuse. 1834 Pischal proposed ignition of blasting powder by means of percussion. 1838 Prideaux used oxyhydrogen for deepening bore holes, and with it burnt a hole at the rate of i of an inch per minute. 1839 Hague injected water into air-compressing cylinders. 1840 Bore holes made with rotary drills at Lankowily. 1840 Cast steel borer used in the Derbyshire mines. 1844 Brunton, of Cornwall, proposed using compressed air for working drill hammers, the air after use to improve ventilation. 1845 Cast steel drills tested at Freiberg. 1846 Schonbein exhibited a sample of gun cotton at the British Association 1847 Sobrero discovered nitroglycerine. 1849 Randolph of Glasgow, introduced into an air compressor a spray of water for cooling the air during its compression. 1849 Couch, of Philadelphia, patented a "lance" percussion drill. 1850 Robert Hunt, E.R.S., made low-tension electric fuses and used them in sinking a pit of the Abercarn Colliery, South Wales, the firing of the fuses having been performed by means of an electric battery. The holes were bored in one operation, and fired simultaneously in volleys. The holes were placed so as to obtain a "sink" of ground from the blast. 1851 Fowle, of Philadelphia, patented a direct action percussion drill. 1851 Cav6, of Paris, invented a reciprocating percussion drill. 1853 Piatti proposed using compressed air in the construction of the Mont Cenis Tunnel. 1854 Bartlett's rock drill tried at the Mont Cenis Tunnel. 1854 Schumann invented his percussion power drill. 1857 Schumann's drill employed in the Freiberg Mines. 1857 Sommeiller invented a drill for use in the Mont Cenis Tunnel. 1857 Ebner employed a frictional machine for blasting. 1857 Schwarnzkopf's drill tried at Bingen. 1861 On the 1st of January, Sommeiller's perfected drill commenced to work at the Mont Cenis Tunnel. 1861 Lisbet applied his boring machine in soft rock (coal, soft lime- stone, etc.) 1862 Bornhardt's air-tight electric firing machine brought into successful use. 1863 Edward Crease introduced his rock-boring machine into the Clogan Mines, North Wales. 1863 Lowe rock drill invented. HISTORICAL SKETCH 7 1863 Sach's rock drill invented. 1863 Noble applied nitroglycerine as a blasting agent. 1864 In March, Carl Sach's machine introduced in the Altenberg Mines, Aix-la-Chapelle. 1865 Gun cotton tried at Hoosac Tunnel. 1866 Lithofracture, manufactured by Ergels, near Cologne. 1866 Nitroglycerine tried with great success in the Hoosac Tunnel. 1866 Jordan and Darlington invented the rifle-bar and ratchet wheel for turning the piston carrying the drill. 1866 The Burleigh drill successfully introduced at the Hoosac Tunnel. 1867 Jordan and Darlington invented the straight and spiral shot, and double ratchet wheel for turning the drill. 1867 Dynamite patented in England. 1867 Doering introduced his boring machine into the Tincroft Mines. 1867 Dubois and Francois rock drill invented. 1870 Beaumont and Appleby's diamond boring machinery introduced at the Croesor United Slate Quarries, North Wales. 1870 Sir George Denys, Bart, commenced driving an adit for the Old Gang Company, Yorkshire, by means of the McKean drills. 1873 The Ferroux rock drill invented. 1873 The Darlington rock drill invented. 1874 The Mowbray mica powder patented. 1874 Electric blasting introduced by Darlington into the Minerva Mines; Bonhardt's machines, the blasting stick, and wire electric fuses being employed for that purpose. 1874 Darlington invented the spinning piston. 1876 The Beaumont rock drill employed at Carn Brea. 1879 Rock drills made at the Camborne Engineering Works. 1904 The world's record for Incline Shaft Sinking by the Holman drill, S. Africa. II THE STANDARD PISTON DRILL THE standard drill consists essentially of a piston to which is attached a cutting tool. This piston reciprocates within a cylinder, and its movement is usually governed by a valve. The rear end of the cylinder contains a ratchet wheel, pawls, and rifle bar to rotate the piston and boring tool. The cylinder is mounted on a cradle in such a manner that it may be fed forward towards the rock; the cradle is attached by its seat to some rigid support. PRINCIPAL PARTS OF STANDARD DRILL Fig. 4 shows the more important portions of a well-known drill: 1, handle; 2, crosshead held by standards from the cradle FIG 4. Section of Sergeant drill, showing principal parts. not shown; 3, box on cylinder with its lines and lock nuts; 4, feed screw to move cylinder forward; 5, nuts on end of side rod; 6, buffer plate; 7, ratchet pawls and release ring; 8, rifle bar; 9, piston with packing ring 18; 10, cylinder; 11, auxiliary valve; 12, main piston air valve; 13, valve chest; 14, cradle with guides and seat; 15, front head with packing (this is not of most recent design); 16, clutch or tool holder, with U-bolt; 21, 22, pad or key; 19, packing; 20, removable bushing; 17, air port in cylinder. The accompanying Table I shows the sizes generally supplied by all makers of most standard machines. This example is taken from the Ingersoll-Rand Company's catalogue: STANDARD PISTON DRILL a io"Xo t H-w 2t2t2co3coo CO '"'O PH ^ nlao^J 1 O T3y "'"* .-th* 1 ,__, O ^ *,H QO Jr-llO'-HOO ,H .,-(1-1 GO 00 T-II-1 rl 1-H .-H T}< W c c ,2 g ^ g c ; : fl yiiniiH 1] :^a : : : :Ss ! : : ft ." > - . w 3 '^t^-i ] 03 . [ IQQ'MO) ^ M 2 cS .5.5 , '^-rt a; x3^ G S2 r r 3 'iu* J I fcfc^^o :*J J| . r ill ;-ss . o I 1 ; 5 ^^^^^^iP ;3|iiSi!PliiiiMiiJ|il I^P^sIll.a^|^ffiM^IS fsiUJUlplf^o MJQ*tS 10 ROCK DRILLS CLASSIFICATION OF PISTON DRILLS Piston rock drills may be divided, first, into two main divisions: (1) Those in which the movement of the operating fluid is controlled by a separate valve or valves, and (2), those in which the piston itself acts as a valve. Valve-operated machines may be divided into four main classes : (a) Tappet valve machines, in which the movements of the piston control those of the valve through a positive mechanical connection. (6) Air valve machines, in which the motions of the piston control that of the valve by varying air pressures on the valve surfaces, transmitted through suitable direct passages in the walls of the cylinder. (c) Corliss valve machines, in which a Corliss valve or valves is operated by tappets and levers, or by fluid pressure. (d) Auxiliary valve machines. In these machines the dis- tribution of the operating fluid to reverse the valve is controlled by a valve, or valves, which is itself positively controlled by the movements of the piston. Piston Valve Drills The piston machines, or those of the second division above mentioned, have practically become obsolete, though attempts are now being made to modify them for use as small st oping drills. In South Africa a small stoping drill of the Konomax type is being experimented with, built on this principle with devices designed to overcome previous defects. The Adelaide, Darlington, and Minerva drills were of this type. In the Darlington drill, 1 compressed air always acts through the port p, Fig. 5, in the annular space o on the front of piston, and drives it back until the passage n is opened, which allows the air to act on the larger surface on the back of pis- ton b. This drives it forward until the exhaust port e is un- covered when the cycle is repeated. From the figure it will be seen that that portion of the stroke from e to m is produced by expansion. 1 Holman Bros. Catalogues. STANDARD PISTON DRILL 11 The Adelaide drill, 1 Fig. 6, "was preceded in time by the Darlington drill, of which it may be regarded as a modification. A A represent the annular port, admitting the air all round the piston, and BI BI are ports in the piston-rod. When the latter are opposite A A, air passes down through the space C in the piston-rod to the rear end of the piston, and drives it forward FIG. 5. Darlington sloping drill. till it uncovers the port B, which puts this part of the cylinder into communication with the atmosphere. At the same time #1 BI have passed beyond the stuffing-box and part of the exhaust escapes in that direction; while this is happening the long shallow annular recess cut in the piston-rod is brought to A, the air presses on the small annular space at the front end of the piston and FIG. 6. Adelaide drill, showing principal parts. drives it back. It will be noticed that this drill uses the air expansively, for when once BI has gone past A no further supply of power is taken in. D is the rifled bar, E the ratchet wheel, H the feed-screw, and G the feed-nut, similar to the correspond- ing parts of many other machines." Advantages and Disadvantages. There is no separate valve or valve chest required; the weight can be reduced and there are 1 C. Le Neve Foster's Text Book of Ore and Stone Mining. 12 ROCK DRILLS fewer moving parts. They use air expansively. The disadvan- tages outweigh any advantages. The blow struck is generally cushioned, thus reducing their cutting efficiency, and they are not as rapid drillers as are valve machines. The piston is often weakened by having ports cut in it, and owing to the small, effective annular area, the return stroke is not powerful. Hence in holes offering side friction, or in drilling deep holes, it gives trouble. Another disadvantage is that in actual work, once the cylinder begins to wear, the air leaks, both ways past the piston, thus increasing the air consumption. Tappet Valve Drills Tappet valve drills were the earliest design made for regular work, and are now the only type really suitable for work with steam, as the condensation of the steam interferes with other valve actions. They have also special advantages for certain work which have prevented them becoming obsolete. The valve motion is positive and not affected by moisture in compressed air. The machine will keep on boring a hole that may offer great frictional resistance, where some other drills would stick. Disadvantages. These drills cannot deliver a perfectly "free" or "dead" blow. In other words, there is always some exhaust air from the front of the piston, caught between it and the cylinder by the reversal of the valve just before the forward stroke is finished. In some ground this is by no means a defect, for where the ground is dead or sticky this cushion helps to "pick the drill up" for a rapid and sure return stroke, preventing its sticking and insuring a maximum number of blows per minute. The length of stroke must be kept long enough for the movement of the piston to knock over the valve. The valve on the Rio Tin to machine is a piston, or spool valve; on other machines the valve is of the plain D-slide valve type. The Rand "giant" drill has a device to reduce the total air pressure on the back of valve; but most of the others have the full pressure of steam or air on the back of valve. This of course makes the valve take up its^own wear and form its own bearing surface, thus reducing leakage. The seats generally require periodical cleaning and are raised to give material to allow "scraping up." Where the lubrication is deficient, as it generally is, the coeffi- STANDARD PISTON DRILL 13 cient of friction may reach 25 per cent., especially in the presence of grit. Taking a valve area of 6 sq. in. exposed to 80-lb. pres- sure, it might require a force of 120 Ibs. to move the valve. This means that the blow struck by the piston is retarded to a corre- sponding degree, and in some makes the valve tends to wear its seat into an irregular surface. Some writers have contended that the turning movement of the piston is also hindered; but as the blow of the tappet occurs at the beginning and end of the stroke, while the turning movement is a positive and continuous one along all the length of the back stroke, this effect is not notice- able. As the tappet is struck 400 to 600 times per minute, the wear and stress is great. Specially hardened surfaces on pistons and tappets are needed as well as large wearing surfaces, or renew- able bushings, for the tappet to rock on. When wear takes place the throw of the valve is reduced; cushioning becomes greater and the stroke is shortened. The resistance and pressure of the tappet tends to throw increased and unequal wear on the oppo- site side of the cylinder. The drills described in the following pages are those made in America by the Ingersoll-Rand Company; the Sullivan Machinery Company, and the Chicago Pneumatic Tool Company. The English examples are the Holman drill, Stephens Climax drill, and the Rio Tinto drill. Ingersoll-Rand Drill. Regarding the design of the "Arc Valve" tappet drill, the makers state that it "is an evolution from earlier patterns in which the defects of the pioneer models are corrected. It is distinguished from other tappet types by its arc-shaped valve, moved on a circular seat by a rocking tappet, all concentric with the rocker pin." Rand "Little Giant" The following description of the Rand "Little Giant" rock drill, Fig. 7, is taken from the maker's catalogue. "The valve mechanism is made up of three pieces, the valve, the rocker, and the rocker pin. The rocker, turning on the rocker pin, is in contact with the piston at one point and projects into the valve in its upper arm, which ends in a globular form. When the piston moves, a curved surface slides under a rocker contact, pushing the rocker upward and swinging the valve in the same direction as the piston moves. On the reverse travel of the piston, this series of movements is exactly reversed. An exam- 14 ROCK DRILLS ination of the sectional view of the Little Giant reveals the follow- ing important facts: (a) "The piston does not strike the rocker. It simply slides under it gently and pushes it up. The curve of the contact sur- face of the piston is such that the. movement is the easiest possible, and the line of action, instead of being through or against the rocker pin, is such that the effort is transmitted directly to the point of contact between rocker ball and valve. There is thus no hammering action, no tendency to bind or cut on the rocker pin. The latter is simply a free support for the rocker, not a thrust bearing opposed to a hammer blow. This improved design gives the easiest and most free movement possible in all parts, with the lightest possible service on rocker, valve, pin, and piston, and with the least possible reduction of the force of the piston blow. FIG. 7. Section of "Little Giant" drill. (Rand.) (b) "The rocker is symmetrical about its vertical axis through rocker pin and ball. It is therefore reversible, and cannot be put in place 'wrong end to' by an inexperienced man. This is a refinement which will be appreciated by those who have had disastrous experiences with non-reversible rockers. It permits also the use of a straight rocker pin, instead of a taper. The holes in the cylinder for the rocker pin are lined with steel bush- ings which may be renewed when worn, and which work under exhaust pressure only. The curves at either shoulder of the piston are not identical, but so designed as to give the correct distinction between forward and return stroke. (c) "The arrangement of parts in their mutual relations and in relation to the valve is such as to secure a clean, sharp cut-off a powerful factor in air economy. (d) "The valve is held to its seat by live pressure on its upper face and thus only wears tighter with continued service. The STANDARD PISTON DRILL 15 rocker rests in a chamber which is open to the drill exhaust. Pressure cannot enter the* cylinder except through the ports and there can be no leakage loss from this cause. If, when the piston rings or cylinder bore are worn, there is a leakage of pressure past the piston, this live pressure passes directly out through the exhaust and cannot retard the action of the piston or reduce the blow, as would be the case if the ports were the exit passages used. Full stroke and full power are thus maintained under long service. (e) "This valve movement permits the correct variation in admission on the forward and back strokes, thus economizing steam or air. At the same time, the back stroke is quick and FIG. 8. Rand Model 5 shell and cylinder guides. positive, giving this drill great power in ejecting broken frag- ments and to this extent improving its cutting capacity. (/) "The arrangement of ports and the travel of the valve is such that there is a very slight cushion on the forward stroke merely enough to add life and speed to the blow, without notice- ably reducing its force. On the back stroke there is an ample cushion of exhaust steam or air which, expanding, assists in the forward stroke." Rand Model No. 5. A radical change has been made in the form of the shell guides, and the design used on the Model 5 drill, Fig. 8, is the V shape of unusually large section, providing ample wearing surfaces for any position in which the drill may be worked. The construction is such that the slides will stay in the adjustment given them, for they cannot slip when bolted 16 ROCK DRILLS down to the sharp angles of the guides. New shells are fitted with several tin liners (at the point designated in the cut), and by the removal of one of these liners both top and side wear can be taken up. These liners are held in place by dowel pins, making it impossible for them to be displaced. The Kid and No. drills, with the view of maintaining light weight, are made with solid shells, and do not have adjustable slides, although fitted with the V-shaped guides. The shells are made of malleable iron, and can be closed in by a hammer when wear takes place. Chicago Giant Rock Drill "The Chicago Giant rock drill, 1 FIG. 9. Chicago Giant rock drill unmounted. Figs. 9 and 10, manufactured by the Chicago Pneumatic Tool Company, has a shell of the adjustable type, constructed so as to provide for double side bearing for the cylinder. The shoe caps are made to take up wear in two directions with one adjust- ment. A removable cylinder stop is also provided in the lower end of the shell, to prevent the cylinder from slipping out in case the feed screw should be run out of the feed nut. To remove the cylinder from the shell, all that is necessary is to remove the stop first, then by turning the feed screw to run the cylinder down in until the feed screw is out of the feed nut. This allows the cylinder to be slipped out of the shell without dismantling the machine. 1 Engineering and Mining Journal, April 6, 1907. STANDARD PISTON DRILL 17 "The cylinder is cast from a special mixture, having a tensile strength of 35,000 to 38,000 Ibs. The upper end is extended to form a chamber for the rotating mechanism, which is of the releas- ing type. Three parts are used, and the pawls are reversible. The ratchet is of one piece with the rotating or rifle bar, which is extended on its upper end to fit into a chamber or recess into the upper head; this provides for holding the rotating bar in a central position and relieves the rotating mechanism of side strains. FIG. 10. Chicago Giant rock drill, mounted. "The valve motion is positive and is of the tappet or rocker type, modified to give a short stroke, the length of the stroke being at all times under the control of the operator. The sup- porting pin of the rocker works in renewable steel bushings and is completely enclosed, it being kept in place by caps easily remov- able but securely locked in place by the valve seat. "An oil-reservoir chamber is provided in the valve seat and communication is made between the oil reservoir and the interior of the valve chest. The oil is led through this channel into the 18 ROCK DRILLS chest where it mixes with the operating fluid and is carried by it into the interior of the machine. One filling of the oil reservoir lasts half a shift. In case the rotating mechanism should not receive sufficient lubrication from the interior, provision is made in the upper head for oiling. "The drill does its best and most economical work when operated by compressed air, but it is also a satisfactory machine when operated by steam." The Sullivan Tappet Valve Rock Drill. The makers state that the tappet valve motion possesses advantages for rock drill- ing of certain kinds, and to meet the demand for a drill contain- ing this feature the Sullivan design, shown in the accompanying illustrations, is presented. All details have been tested by long FIG. 11. Section of Sullivan tappet valve drill showing the relative posi- tion of the working parts. use, and its performance, as to speed, power economy, and dura- bility, is most satisfactory. This drill is similar in all respects, except the valve motion, to the Sullivan differential valve machine. This valve motion, as will be seen from the sectional view, Fig 11, consists of a curved rocker, whose ends rest on beveled surfaces at each end of the piston. These surfaces impart a circular movement to the rocker, causing the projection at its center to operate a flat valve, shaped like a double "D," which controls the admission of air to the drill cylinder. Fig. 12 shows this drill mounted on a tripod. The makers recommend this drill for conditions of low air pressures and soft rock. The severe duty imposed upon the rocker of a tappet rock drill, and the necessity for continuous and exact performance of its functions, have made this part the subject of much study. STANDARD PISTON DRILL 19 FIG. 12. Sullivan tappet valve drill on tripod. 20 ROCK DRILLS STANDARD PISTON DRILL 21 The Sullivan rocker is perfect in its action, cannot be broken, and will wear for years. It is shaped like a gear segment, the projection at the top corresponding to a tooth of standard rack form. The curved ends of the rocker are so shaped as to present an ample rubbing surface to the piston, while the gear tooth projection, with its broad area, engaging the flat valve, is a note- worthy improvement over the axial pin and knob used for this purpose in some drills. The rocker is of tool steel, accurately formed and tempered to the proper hardness. The cylinder and valve seat form a housing, allowing the rocker free motion, without side or vertical play. The sloping surfaces of the piston are hardened, by an improved process, to reduce wear. The valve is of close-grained iron, finished to a perfect bearing upon the valve seat. The latter is removable, and scraped to fit the cylinder and chest cover without the use of gaskets. The cover is flat, occupying the least possible space. Taylor Horsfield's Drill The New Type " National" is a tappet drill of somewhat novel design. The pin 20, Fig. 13, of the flat circular valve 19, engages with a sleeve 21 on the piston, and moves in a peculiar shaped groove shown which causes the valve to partially rotate around the pin 20, alternately opening and closing the exhaust and admission ports. The valve has a "bell topper" device which is a cap to reduce air pressure on the back of the valve. The pin 20' keeps the sleeve from revolving with the piston so that it merely reciprocates with it. This device works with little friction or jar as the valve is nearly bal- anced and is only rotated around a center and not moved bodily. The air ports run along the side of cylinder instead of along the top, and the exhaust is on the top of cylinder. The section Fig. 13 and illustration Fig. 14 give a good idea of this drill. Mr. Taylor Horsfield, of Bendigo, lately manufactured for Messrs. C. R. McKenzie and Company, Government Contract- ors, of New South Wales, a drill of this type of exceptionally large proportions, which is to be used in drilling holes of 18 in. diameter in rock about 30 ft. or 40 ft. under water. The drill, which weighs one and a quarter ton, has a cylinder with a diameter of 8 in. with 12-in. stroke. This is said to be the largest of its kind ever manufactured. It is made on the same pattern as Horsfield's "National" drills, which are in common 22 ROCK DRILLS FIG. 14. Taylor Horsfield's rock drills. STANDARD PISTON DRILL 23 use in mines throughout Australia. The holes that are to be drilled by it are in connection with the erection of wharves, etc. The drilling rods weigh 12 cwt. The Holman Tappet Drill. The sectional illustration of this drill in Fig. 15 clearly shows its construction, and the action requires but little explanation. The valve is of the ordinary D type as used in most small steam engines, the tappet taking the FIG. 15. Holman tappet valve drill. place of the valve-spill or rod, and the piston ball doing the work of the eccentric. The working fluid passes alternately from each end of the valve into the ports, exhausting around the tappet into the cylinder between the pistons and thence to the atmos- phere. The length of stroke can be varied at will by turning the handle and feeding the cylinder towards the rock. The same manufacturers turn out a tappet quarry drill, which has special FIG. 16. Climax tappet valve machine. advantages for deep boring. A large diameter is given to the front cylinder for lifting the bit, and by this means holes are commonly bored to a depth of from 30 to 40 ft. For working tappet drills by steam, a blow-through cock is generally fitted to the machine to get rid of excessive moisture in the pipe line. Stephens Climax Tappet Valve Drill. In this type of drill the tappet and valve are combined. Fig. 16 is one of the later types of this drill. 24 ROCK DRILLS Air Valve Drills Examples of air valve machines include the new Ingersoll Eclipse drills; the Rand Slugger and Konomax drills; the Sullivan differential valve drill; the Stephens Climax Imperial; the Wood, McKeeinan, Little Hercules, Hardy, and others. In these machines the disadvantages connected with the use of a D slide valve are avoided; the valve being of the "piston" or " spool" type. As in some designs of the Slugger, and in the Climax Imperial the valve can be adjusted to use air expansively. It can also be set to strike a free blow by not closing exhaust port until the stroke is finished. Such machines can be made to drill very fast in certain rock when the air does not contain too much moisture. Trouble with these types of machines is liable to arise from FIG. 17. Ingersoll "Eclipse" drill. wear in the cylinder piston. When, despite the rings, leakage of air develops from one end of the cylinder to the other, the valve becomes irregular in its action; cut-off is late, while both valve and piston " cushion." The valve " nutters" or moves on short stroke and the machine becomes inefficient until the cylinder is relined or bored out to fit a new piston. It is claimed for the Slugger drill that owing to the valve being moved by the closing of exhaust ports, wear and leakage tend only to lengthen the stroke. In the Climax drill made by Stephens this difficulty is met by placing two circular conical leather valve seats in the top of the cylinder below the valve chest. These, though called auxiliary valves, do not move at all and might perhaps better be called "rubbing contacts," as their use is always to make a close rubbing contact with the piston, whatever the wear, thus preventing any leakage of air at the wrong moment into their ports to reverse the valve. Thus the valve motion is kept regu- STANDARD PISTON DRILL 25 lar. This object is satisfactorily attained in practice by this device. Wear on the leathers is taken up by pressing them down with washers put in on the top, face down, by tightening the nuts on the bolts holding on the valve chest. Leakage past the valve itself does not render its action irregular. Ingersoll Eclipse Drill. In this drill the valve is thrown over by live air leaking past the ends, and by means of the recess in the piston, the ends of the valve are alternately opened to exhaust through the space between piston and cylinder, and through two holes, A and B, Fig. 17, bored through the cylinder walls, to the outside. "Little Hardy" Rock Drill The sectional illustration, Fig. 18, shows the general arrangement of the " Little Hardy" drill. FIG. 18. Section of "Little Hardy" rock drill. According to the makers the salient feature of the construction is the circular distributing valve which is thrown over by live air, fed to the end valve pistons by special ports in constant communication with the main inlet. There are no tappets, guide-bolts, or other mechanical connections between the valve and the drill piston. Consequently there is nothing to lessen the force of the blow or to cause battering and breakage to any part of the valve motion. The makers claim the following advantages in this system: "The valve is automatically locked in its position by the full air pressure acting upon the whole surface of one of the end valve pistons, the opposite one being open to complete exhaust. Variable valve speed, due to wear or fluttering of the valve in other systems, is impossible in 'Little Hardy' drills. The valve is unique in speed of travel, being thrown at full pressure." 26 ROCK DRILLS STANDARD PISTON DRILL 27 Taylor Horsfield's New Type Ingersoll Drill. This drill, Fig. 19, is of Australian manufacture, and of the air-moved type, with a valve motion similar to the Ingersoll Eclipse drill, only the e valve is placed across the cylinder and not longitudinal with it. The rotation device is similar to that in use on the Sullivan drills. Taper chucks are used exclusively. The Sullivan Differential Valve Rock Drill. The especial feature of the Sullivan differential valve drill, Figs. 20 and 21, 28 ROCK DRILLS FIG. 21. Sullivan differential valve rock drill on adjustable tripod. STANDARD PISTON DRILL 29 according to the makers, is the spool pattern of the valve, Fig. 22, with its surfaces so proportioned as to secure a differential effect original in this machine. Its action is instantaneous, exact, and uniform; it permits the length of the stroke and the force of the blow to be regulated to the best advantage, depending upon the local conditions. Thus, in starting a hole, or in seamy ground, the drill may be cranked down to give a short stroke and a light blow; while in hard, solid rock, the full stroke secures a blow of great strength. Full steam or air pressure on the return stroke, or recover, causes proper mudding of the hole under all circum- stances. The valve itself is simple, strong, and rarely breaks. Its action is not affected by wear in other parts of the drill; and it works equally well with steam or air. FIG. 22. Sullivan differential spool valve. The Rand "Slugger" Rock Drill The "Slugger" rock drill is a machine designed especially for heavy work and rapid drilling in mine and tunnel headings. It can be successfully operated only with compressed air. The " Slugger" has an " air-thrown" piston or spool valve, Fig. 23, traveling in a reamed valve chest with a maximum move- ment of not more than three-quarters of an inch. Buffers at the ends of the valve chest receive the impact of the valve at the end of its travel. The valve, being perfectly balanced, is subject to no tendency to wear unevenly and has a free, easy movement. It is of hardened steel, carefully ground to a working fit in the valve chest bore. The valve mechanism of the "Slugger" is such that it strikes 30 ROCK DRILLS an uncushioned blow, due to retarding the reversal of the valve until the blow is struck; the lower exhaust port is thus held full open during the complete down stroke. At the same time the action of the valve permits of the usual variation in length of stroke that is necessary in rock drills. The "33 type" is a late model of this machine. In this type, the upper as well as the lower exhaust port is controlled by the piston valve and the necessary cushion is afforded by live air pressure, the exhaust remaining full open to the end of the stroke. The result is a dead, uncushioned blow. A distinctive feature of this type of drill is the device whereby the throw of the main valve is caused by the closing instead of by the opening of an auxiliary port. The result is that the wear of piston, cylinder, etc., tends to lengthen, instead of shorten, the stroke. FIG. 23. Rand "Slugger." The "Slugger" drill is a rapid driller and a reliable machine, striking a dead, powerful blow while still retaining a quick return, and especially adapted for work in hard, solid rock where the cushion effect on the down stroke is not required and where air pressures are high. Corliss Valve Drills Torpedo Drill. The only example of this style of drill used in practical work that I know of was one designed by Mr. D. A. Foote of California. It was named the " Torpedo" drill, Fig. 24; I believe it was abandoned owing to the enormous wear on the tappets, connecting rods, and pins. Remarkable results were, however, attained with new drills, and for certain work I believe a drill of this type with Corliss valves worked by air pressure from auxiliary valves might give excellent results. STANDARD PISTON DRILL 31 Auxiliary Valve Drills Two examples of this type are the Ingersoll-Sergeant machine, which was the pioneer, and the Holman machine. Ingersoll Sergeant Drill. "The auxiliary valve is a successful combination of the independent air- thrown valve of the piston or spool type"; or in the case of the Holman machine of a D-slide valve having a concave seat with piston ends and an improved modification of the tappet action. It retains certain advan- tages while avoiding defects of both valve movements. This valve movement is one in which the strains, shocks, and jars to which the tappet is subjected are transferred from the main valve Avith its vital and delicate functions to small, light auxiliary valve, or valves, which "are designed to withstand this service to the best advantage and which are cheaply replaced when worn." FIG. 24. Foote torpedo drill. The movements of such valves are quite free and short, thus "the auxiliary valve is simply a trigger that releases the main valve." These drills can be run on a very short stroke rendering the starting of a hole easy, enabling the drill bit to be driven past heads and slips in the rock which would deflect the hole were they attacked with long glancing blows. They are designed to strike a free uncushioned blow on the rock, and do so when wear is not excessive, as the exhaust port at the front end is kept open until after the blow has been struck. All makes of drill are designed to cushion on the return stroke; when, with any design of spool or piston valve, the piston begins to knock on the back stroke, it is a sign that leakage is taking place between valve and valve chest. The auxiliary valve drill has the capacity of working with 32 ROCK DRILLS very small number of bits, which is also advantageous where the supply of drill bits is lim- ited and it is hard to get one of just convenient length to insert, or where a bit so long that the machine must work at first on a very short stroke. One great advantage with this machine lies in the fact that piston and cylinder wear do not interfere with the valve action owing to any leakage between them. The steel balls on the Holman drill have almost no wear, while wear on the arc valve of the Sergeant drill is compensated by renew- ing liners, placed between the air chest and the cylinder, which lowers the auxiliary valve into fuller contact with the piston. The piston B of the Ser- geant drill, Fig. 25, has in it a recess forming two shoulders. These engage the ends of the auxiliary valve A and throw it over as one end always pro- jects into the cylinder. This arc-shaped valve has a recess R cut in it. In the seat in which the valve moves are three ports; the two end ones P and P' lead to the spaces at the ends of the main valve. The other leads to the exhaust port E. In the figure the port P' is in communication with the exhaust. The piston has just finished its return stroke and the main valve has the port, leading to the back of the cylinder, STANDARD PISTON DRILL 33 open to exhaust. It will now be thrown over admitting live air to the rear of the piston, and open the exhaust port leading to the front of the piston. Pressure to throw the valve over is gained by allowing live air to leak past the ends of the main valve to act on the end surfaces. It will be seen that the action of the valve in the Holman machine is practically the same. This type of valve has several important advantages over the other types with the exception, perhaps, of air-valve drills having some compensating device for cylinder wear. These, theoretically, having fewer wearing parts should work with less friction and be rapid drillers. It is wise in examining the merits of various valve devices always to investigate closely what effect wear and leakage will have upon them. It will then be noticed that many advantages claimed would not be realized in practice. Where the travel of the piston regulates the point of cut-off in drills using air expansively, leakage between piston and cylinder will generally make the cut-off later. Comparing the valve action of the Holman with the Ingersoll machine it will be noted that the Ingersoll valve works with less friction and requires less frequent lubrication, while the Holman valve, being really a Z)-slide valve with cylindrical seat, retains its seat and freedom from leakage for a much longer period, thus requiring a smaller sum spent for repairs. Spool valves are now fitted if required in Holman machines. A spool valve, properly hardened and ground to fit, should, under good conditions, run nearly six months before requiring replacement by a larger size and the chamber to be bored out. With bad usage, in the presence of grit, this may have to be attended to oftener. The Holman Auxiliary Ball-Valve Drill. The construction of this drill is shown in Fig. 26. When the piston a is at the rear end of the cylinder, it will have raised the ball valve c and allowed d to drop on the valve seat. The result is, that the air in the end of the valve chest e has been exhausted, and passing through a small groove in the bottom of the valve chest at the opposite end, it forces the valve forward. This places the fluid in communication with the main ports. The pressure then passes through the port g and drives the piston forward, whilst the previous admission at the opposite end exhausts through h into the exhaust port j. The process is reversed for the return stroke. As the piston moves inwards the ball valve c drops on its seat, and the air passes STANDARD PISTON DRILL 35 through the groove filling the space at e; as the valve chest at / has been exhausted, the valve moves in the opposite direction. The ball valve and buffer valve require no adjustment and resist wearing. The main valve is of the ordinary D type, and consequently the live fluid cannot pass over into the exhaust. In order to eliminate the friction and maintain the speed neces- sary, the valve chest is a steel casting hardened and ground; the valve is also hardened. No adjustment of the air-locking device is required, consequently the drill will work with slacker piston than is possible with most drills. The balls controlling the valve exhaust are made of the hardest crucible steel. The movement of the piston in its backward and forward stroke, and the twist motion, tend to keep the ball revolving, thus presenting a large wearing surface. These balls are practically indestructible. ROTATION SYSTEMS ON PISTON ROCK DRILLS Slip Rotation. Many makers have copied the Sergeant sys- tem of slip rotation, Fig. 27, which is described by the makers as follows: "The Sergeant slip rotation is one of the most valuable fea- tures of these drills, permitting the machine to free itself in a binding, caving material without injury to steels or piston. It is applied on all but the 'Eclipse' type of drill. The ratchet is held by friction between the washer and the back head, under pres- ft a . 27. Sergeant slip rotation, sure of the cushion spring. It is thus free to slip when the steel l glances ' or twists backward, freeing the bar from twisting strains; and by changing the spring tension, the friction effect may be varied to meet dif- ferent service requirements. The ratchet and pawls are case- hardened, and the device is one of great durability and strength." In this type the pawls are pressed out by cylin- drical coil springs. In the Stephens drills the slip rotation is employed; in this as well as in the Little Hardy drills, springs can be replaced through stud holes. Generally speaking, in all standard types of drills, 36 ROCK DRILLS rotation gives little trouble except that occasionally a badly tem- pered lot of springs may be met with. Modified Slip Rotation. In the Sullivan drills the rotation FIG. 28. Sullivan rotating device. device is modified, and is described by the makers as follows: "The drill steel is given the necessary rotation, to preserve the cylindrical shape of the hole, by a rifle bar, extending into the top of the piston, Fig. 28, and terminating at its upper extremity FIG. 29. Holman ratchet and pawls in a ratchet head. Rotation occurs on the up stroke. The fric- tion between the top head and the ratchet ring and collar is such as to permit the ring to slip in case the drill steel becomes wedged in the hole, thus precluding damage to the mechanism. STANDARD PISTON DRILL 37 The whole device is unusually effective and durable, and will outwear four of any other pattern. The ratchet head and rifle bar are milled out of a solid piece of tool steel and hardened in oil. Rounded surfaces and hardened steel pins or rollers provide the ratchet movement, instead of the thin teeth and pawls sometimes employed." Pawl-and-Ratchet Rotation. - The makers of the Holman drills employ the non-slipping FIG. 30. Rand rotation, showing upper head removed, rotative bar and pawls in place. type as shown in Fig. 29. The Rand " Little Giant" has a similar system, Fig. 30, and the makers describe it as follows : "Two pawls, Fig. 31, engage at once, thus distributing the strain 2637 FIG. 31. Pawls. between two pawls and two ratchet teeth. The inserted pawl requires no studs, but fits in a bored recess in the ratchet box with a very large bearing sur- face. Wear is thus reduced and a long life assured. There is no pin to break or wear. The pawl is a solid drop forg- FIG. 32. Rotating bar, "Little Giant" in g of selected steel, properly drill. hardened. The bearing por- tion is of large diameter. A flat spring holds the pawls to their seat. The rotating bar, Fig. 32, is of high-carbon steel and works in a bronze rotating nut. It is carried through the ratchet, giving a 38 ROCK DRILLS back bearing of large diameter in the ratchet box. The ratchet is of hardened steel, pressed and keyed on the rotating bar. The upper head and ratchet box cover the entire rotation, excluding dust and dirt." DESIGN OF FRONT OR LOWER HEADS For use with air, nearly all machines use the type of head, first introduced by the Rand Drill Company. " In this style the split malleable head, Fig. 33, is bored to receive a split bush- ing of cast iron, accurately fit- ting the chuck rod. A cup leather held in the rear be- tween bushing and head fur- nishes the packing necessary. All strain on the head proper is taken up by the taper fit of the steel ring over the head FIG. 3.-C&H ring lower head-parts under the tension of the side assembled and separate. rods and buffer. The bushings may be renewed and replaced when worn. Some machines, and especially those in which steam is used still, employ front heads similar to those shown in Type "15," Fig. 34, of the Rand Drill Com- pany, which is described as follows: "A selected metal is used for the front and lower heads. The joints between head and cylinder are ground no gasket or packing is used. This front head is made in two types: one, for steam, has a gland and proper stuffing-box; the other, for air, has a cup leather. The steam head may be used for air, but steam must never be used with the air head. Both patterns are long and reamed to perfect trueness, giving an ample piston guide. Powerful through-bolts hold them in place and transfer all stresses directly to the cushion springs in the rear.' FIG. 34. The" 15 "type front head, steam and air patterns. STANDARD PISTON DRILL 39 DRILL MOUNTINGS AND FITTINGS The following views of arms, bars, and saddles or clamps as made by two leading makers show the construction of three parts clearly. The following description is taken from a paper by Arthur H. Smith, " Machine Drills for Hard Rock." It con- cisely describes the various mountings used in mines. "Drill Clamp. The cylinder of a rock drill slides in a guide or cradle, Fig. 35, which in turn is mounted on a stretcher bar, tunnel column or tripod, etc., according to the work to be done. The actual attachment consists of a powerful jaw chuck or cone clamp which holds the bottom of the cradle and is in turn saddled round the bar or column and secured to it by a cap and bolts. The adjustments of the drill and saddle are independent of each other, and the drill can revolve on its seating for setting in any direction. "This fact is taken advan- tage of in coal mines and dimen- sion stone quarries, where a lever handle is sometimes attached to the machine for conveniently im- parting a swinging action to it, the clamp nut of the mounting being given just sufficient tension to hold the' machine firmly without impeding the lateral movement. Thus, by gradually swinging the machine across the face during work, the cutting bit strikes each blow in close proximity to the previous one, the outcome being a straight cut or nick right across the face. Generally each cut from one fixing is from 10 to 12 ft. in length by from 4 to 6 ft. deep and from 2| in. to 3 in. across according to the size of the cutting bits employed. Some makers employ a worm gearing operated by handle to produce this swinging movement. The cutting bits used in connection with these machines in coal measures are usually provided with several radially disposed teeth, an odd number being employed to prevent sticking. FIG. 35. Sullivan guide or cradle. 40 ROCK DRILLS " Stretcher Bar. For drifts of small dimensions, for winze work and for sloping, the rock drill is generally clamped to a single screw column, Figs. 36 and 38, or stretcher bar. The usual length is 6 ft. with jack screw in, the latter increasing the Single jack bar. Double jack bar. FIG. 36. Ingersoll-Sergeant rock drill column. length about 10 in. The diameter of the bar is from 3 to 5 in. according to the machine employed. "Double Screw Tunnel Column. For larger drifts and tun- nels double jack screw columns, Figs. 36 and 37, are employed, these being of sufficient strength to support two machines. The drill is saddled on a steel cross arm, which in turn is clamped to the column. By means of a safety clamp, or collar, which is placed immediately below the arm clamp, the arm may be loosened STANDARD PISTON DRILL 41 FIG. 37. Sullivan drill on double screw, a jack, mining column. FIG. 38. Sullivan drill on single-screw mining column, or shaft on stopping bar. 42 ROCK DRILLS and the drill swung out of the way, and swung back without losing alignment when drilling is to be resumed. For holes on a lower level, the safety clamp is first lowered to the desired point, after which the arm is loosened, and the arm with the machine attached is slid to the place without unnecessary labor. The double screw column is usually 4J in. diameter by 7 ft. long, with 10-in. FIG. 39. Tripod for mounting drills in open air or large stopes. jack screws drawn in. Wood blocking is used above and below the columns to secure a firm hold. " Tripod. For general outdoor work and for operations in mines where drifting columns have no application, the rock drill is clamped to a tripod stand, Fig. 39. A universal joint permits the legs of the stand to be adjusted to any desired angle or posi- tion. Moreover, the legs are telescopic and may be lengthened or shortened at will. The machine can thus be quickly set up no matter how irregular the ground, or how awkwardly situated the surface to be drilled. Detachable weights are hung to the STANDARD PISTON DRILL 43 legs to steady the machine during operation, these weights vary- ing from 150 Ib. to 400 Ib. per set of three, according to the size of the machine. "A variation of the standard tripod is found in the Lewis type, which is employed where three or four holes are required to be put down close together and parallel to each other. The general arrangement of this stand only differs from that of the last described by the addition of a planed and slotted front bar which gives the drill a lateral movement of from 6 to 9 inches. Several holes can thus be bored parallel, and the standing rock between the holes can be cut out by a special flat broaching bit without change of position. "Rock Drill Carriages. Various forms of drill carriages to mount either two or four machines have been used for tunneling. One type consists of a vertical externally screwed column carried on a small trolley. Two horizontal arms are mounted on the column, and upon these arms are saddled the drills. The trolley is run up to the face, the column jacked tight against the roof, the arms set to the required positions and jacked to the walls. The raising and lowering of the arms on the secured column is effected by means of worm gear and handle. Another type of carriage is a steel girder framework mounted on wheels and carry- ing two vertical stretcher bars, each supporting one or two drills. The frame and stretcher bars are so disposed that a truck can be run through and up to the face to facilitate the removal of debris. "Rock drill carriages have, however, been almost entirely superseded by tunnel columns, as in the case of the former either the whole, or a considerable part, of the debris from the previous blast must of necessity be removed to clear the track, and to enable the laying of fresh lengths of rail before the carriage can again run up to the face, whilst with the latter only the small space necessary to set up the column need be cleared and boring recommenced almost simultaneously with the removal of debris. "Shaft Sinking Frame. Heavy expenditure must always accompany the sinking of main shafts, the diameter of which the present tendency is to increase, and it follows that those in charge of the work are anxious to increase the speed of boring as much as is mechanically possible. In large main shafts stretcher bars cannot be employed for mounting the machine drills, and under 44 ROCK DRILLS certain conditions tripods are somewhat impracticable owing to the time lost in lowering and adjusting plant, and raising it to FIG. 40. Shaft-sinking frames. surface preparatory to blasting operations. Shaft-sinking frames, Fig. 40, have, under these conditions, been found of considerable service. A useful type of shaft frame by Howarth and Larmuth may be described as a steel wheel-shaped center piece with flanged STANDARD PISTON DRILL 45 rim, on which a ring made in halves is bolted and can revolve, being supported between the rim flanges. In the center piece are three bosses through which adjustable legs are passed to support the frame on the shaft floor. Three or more stretcher bars are hinged to the ring, provision being made to fasten these bars securely to it. The rock drills are clamped to the stretcher bars, which are provided with screws for jacking to the walls. On the center piece, where eye bolts are arranged for hoisting and dropping the frame, is a manifold tail for an air pipe, with as many branches, cocks, and unions as there are drills employed. The plant is put together at surface, lowered into position by means of a winch, and raised again after completion of boring the floor, thus abolishing the slower methods of clearing gear from the shaft bottom." DRILL CHUCKS In the chapter on repair and maintenance of drills the impor- tant part played by the chuck in drilling economy has been pointed out. The ordinary chuck with its cylindrical liners, U-bolt, nuts and pad or key is illustrated in several drills. Its disadvantages are: that it takes some time to insert and take out drill bits; that the removal of the chuck bushing when worn is troublesome. The earlier forms of chuck were the one-bolt chuck, which broke too readily in large drills, and the taper chuck. This chuck is still used entirely in drills of Australian manufac- ture. The chuck is bored out with a taper recess, having a slot cut through the body of chuck for the insertion of a wedge to be hammered to loosen the drill when finished. The shank end of drill bit is made with a corresponding taper. This type of chuck has some important advantages. It always keeps the drill bit centered true despite wear, and is simple. A machine fitted with this chuck will always out drill one fitted with U-bolt chuck. Its disadvantages are that the drill sticks sometimes, causing vexatious delays., It is also difficult to harden the taper end of the shank sufficiently without making it too % brittle. The Ingersoll-Sergeant Company introduced a taper chuck with an arrangement of liners; but afterwards withdrew it though it gave satisfaction to users. Most manufacturers are now supply- ing a half-bush chuck, a chuck in which half the bushing opposite the pad or key is removable by hand and reversible. 46 ROCK DRILLS FIG. 41. Maynard chuck. The Maynard chuck, Fig. 41, illustrates one device of this type; the liner is not, however, reversible, and wear between the wedge 17 and 13 can only be taken up by placing liners under 14. It is described as follows: "The chuck has two jaws, 7, 22, with rounded projections at their front ends to facilitate in- QlUjf^^ sertion of the drill. The jaws 17 \ \ o/ f7 are mounted in the head 1 and "- r-^mnl' 6 - are prevented from falling out of, or too far into, the chuck, the jaw, 22, by means of a pin- held projection, 23, passing through a hole in the head, and the jaw, 7, having longitudinal lugs 8 adapted to engage the edges of the slot, 6, through which the jaw slides. The provision of a forward end, 10, of the jaw, 7, prevents tilting, and the rear end, 11, is beveled to facilitate in- sertion. The jaws are closed by a wedge, 17, with a hole, 19, and split-pin to prevent displacement; the wedge engages a U-piece, 13, passing through slots, 12, in the head and formed with a wider base, 14. A cylindrical recess may be formed in the bottom of the axial hole to receive the end of the drill." The Warren-Tregoning chuck, Fig. 42, appears to have fea- tures of great merit, but has not been largely used. The end of the piston-rod, A, of the drilling machine is enlarged and a dovetail hole made in it. Two keys, B, #, with taper corresponding to that of the dovetail, will just slip into the hole; but when the drill is inserted between them, they are prevented from falling out. When the drill is put in place, the keys, B, B, are drawn out by a pinch-bar, or any other convenient tool, work- ing against their heads. Then, as soon as the machine is started, the shock of the drill on the rock tends to force the keys outwards, and they thus grip very firmly. To release the drill, it is only neces- sary to strike one of the keys sharply on the head with a hammer. It will be noticed that the chuck can easily be adapted to different sections of drill shank by means of separate sets of keys. FIG. 42. Warren- Tregoning rock drill chuck. STANDARD PISTON DRILL 47 The chuck just used on the Chersen light stoping drill is shown in Fig. 43. Wear between wedge pad and ring must also be taken up by inserting liners on the opposite side of ring. FIG. 43. Chersen 2|-inch diameter, 6-inch strike ball valve drill, weight 113 pounds. Shows chuck which is self-tightening. Holman Chuck. The Holman chuck is shown in Fig. 44, and described as follows: It comprises a slotted piston-rod end, a, holding a half-round bushing, c, between which and a pad, d, FIG. 44. J. H. Holman chuck. the drill is clamped. The pad has lateral lugs, e, provided with holes, /, through which passes a U-bolt, h, holding nuts, i, and fixed by a wedge, j. The slot for the pad and also the pad and separate half-bushing extend to the end of the shank. 48 ROCK DRILLS The Ingersoll-Rand Company has introduced a somewhat similar chuck. The Stephens Chuck is one of the simplest and is also shown in Fig. 147. These chucks are a distinct advance on the old style. They allow a more rapid changing of drills; can be renewed more easily, and looked after better; hence, there is not the excuse for trying to bore holes with the end of drill bits showing an eccentric move- ment of a quarter of an inch in every direction. These half bushings wear irregularly and should be turned end for end every week. In some designs, liners may be inserted behind them to make up for wear. The ordinary U-bolt chuck can be modified by inserting a wedge between the back of the pad and the U-bolt, which, in some cases, makes manipulation quicker. All makers supply flat- backed pads for this purpose if required. MATERIALS USED IN PISTON ROCK DRILLS The cylinder shell and valve chest are usually made of a special mixture of cast iron. The cradle is cast steel. The ratchet box and cover are special rough steel. The piston-rod is solid open-hearth steel. The valve is case-hardened iron or cast steel. The tappet, ratchet, pawl, and twist bar are tool steel. The rotation nut is bronze. All bolts, studs, feed-screw, handle, nut and tool-holder are made of best mild steel. Some- times malleable cast iron is employed in certain parts. Pistons and other parts are oil-hardened, and some manufacturers, espe- cially in the case of hammer drills, use special alloys, such as of nickel- or vanadium-steel for parts subject to great vibration. Ill HAMMER DRILLS THE use of hammer drills in mining is quite a recent develop- ment, though the idea is an old one. Instead of striking the drill with a hammer swung by hand the drill is struck by a piston-hammer reciprocating in a cylinder. Such tDols were first designed by the mechanical engineer to help him in his work in calking, chipping, and riveting; for this work they proved a great success. The Franke drill was, I believe, the first attempt to employ this method underground. It was intro- duced into the Mansfield copper mines, Germany. That it did not prove a success is readily understood when its complicated mechanism, is seen. 1 It had a bewildering number of working parts and was designed to strike 8000 blows per minute. It weighs 16 Ib. The development of the hammer drill is closely associated with the name of George Leyner, though the chief development has not taken place quite along the lines he started. His first drill was put on the market 1898. CLASSIFICATION OF HAMMER DRILLS Hammer drills may be classed under several heads, as fol- lows: (1) Those mounted on a cradle like a piston drill and fed forward by a screw; (2) those used and held in the hand; and (3) those used and mounted on an air-fed arrangement. The last two classes are often interchangeable. Mr. Leyner, though now making drills of the latter classes, was the pioneer of the large 3-inch diameter piston machine to be worked in competition with large piston drills. The smaller Leyner Rock Terrier drill was brought out for stoping and driving; it could not, apparently, compete with machines of other classes. Divided thus we have : 1. Cradle drills Leyner, Leyner Rock Terrier, Stephens Imperial hammer drills and the Kimber. 1 C. Le Neve Forster's Text Book of Ore and Stone Mining, p. 192. 49 50 ROCK DRILLS 2. Drills used only with air feed Gordon drill and the large sizes of the Murphy, Little Wonder, and others. 3. Drills used held in hand or with air feed Murphy, Flottman, Cleveland, Little Wonder, Shaw, Hardy Nipper, Sinclair, Sullivan, Little Jap, Little Imp, Traylor, and others. Again, they may be divided into those that are valveless, with the differential piston or hammer itself acting as a valve. The Murphy, Sinclair, Little Wonder, Shaw, Little Imp, Leyner Rock Terrier, and Kimber drills belong to this class. The large Leyner drill is worked by a spool valve resembling that of the Slugger drill, Fig. 22; the Flottman by a ball valve; the Little Jap, by an axial valve; the Gordon drill, by a spool valve set at one end of cylin- der at right angles to it; the Waugh and Sullivan drills, by spool valves set in the same axial line as cylinder; the Hardy Nipper, and the Stephens Imperial hammer drills by an air-moved slide- valve set midway on the side of cylinder; the Cleveland by a spool valve set towards rear of cylinder. They may again be divided into those drills in which the piston hammer delivers its blow on the end of the steel itself. A collar is placed on the drill to prevent it entering the cylinder. The other class has an anvil block or striking pin. This anvil block fits into the end of cylinder between piston and steel. It receives and transmits the blow, also prevents the drill end entering cylinder. Rotation. Different systems are also employed to produce rotation of drill steel. In the large Leyner machine, Model VI, this is done automatically by a simple arrangement of expanding ring and rifle bar. In the Flottman, Hardy " Nipper," and Kimber, it is automatic by various devices. In the Leyner Rock Terrier it is positive and geared to a feed screw. In the Gordon and Climax Imperial drill it is by hand, by means of a spindle provided with a ratchet or handle at the rear of the machine. In almost all the other types it is either oscillatory, the machine being pivoted on a central spindle, or, as in the Hardscogg Wonder, the whole cylinder is completely rotated. ADVANTAGES AND DISADVANTAGES OF DIFFERENT TYPES I give drawings and descriptions or illustrations of most of these machines to compare the advantages and disadvantages of the various types for various branches of mining work. HAMMER DRILLS 51 Water Leyner Hammer Drill. A sectional drawing of Model No. VI, the latest design, is shown in Figs. 45 and 46. The general design is clear from the cross-section shown. It will be seen that an arrangement of buffers is provided to take up the energy of the blow struck by hammer should the head of the drill not be in position. Rotation is effected by means of three strong, simple parts a rifle bar, 18; a rotating brake, 47; and a rotating ring, 48. It is entirely unlike any other method and entirely eliminates all small, frail, complicated parts, such as pawls, pawl springs, plungers, rollers, etc. There is no toothed ratchet, in the machine. Some of the principal parts are shown in Fig 47. The rotating brake fits over the head of the rifle bar inside of the rotating ring, the rotating ring being held firmly by ten- sion against the back head. Turning the rifle bar to the left contracts the brake and allows both brake and rifle bar to slip freely. Turning to the right expands the brake against the rotating ring and holds both brake and rifle bar firm. The rifle bar fits into the hammer, 13, and the hammer into the chuck, 7, which in turn loosely accommodates the lugs of the shank of the drill steel. The Leyner release rotation prevents accidents to the machine in case, for any reason, rotation in the proper direction is impeded. As explained above, the rotating ring, 48, is held against the back head, 28, by tension, which is so adjusted that the entire rotating mechanism rifle bar, rotating brake, and rotating ring (and, necessarily, hammer, 52 ROCK DRILLS HAMMER DRILLS 53 Rotating plate. Back head. Back cindering. Rifle bar, it rotates hammer. Pawl spring. Pawl spring plunger. Shanks on drill steel. One of four oblong pawls. Hammer. Chuck rotated by hammers. FIG. 47. 54 ROCK DRILLS chuck, and drill steel), will turn in the wrong direction in case of some excessive strain and before anything breaks or the drill stops running. The steels employed are steel tubes welded to a specially hard head having two lugs on the shank, with a hollow high-grade steel-cutting portion welded on the other end. The two lugs engage with the chuck and cause the drill to rotate with it and the piston. The arrangement enabling a spray of air and water to be passed down the hollow steel to the cutting edge is a vital one, and is the main cause, I believe, in the efficiency of the machine. No dust is formed which will affect the health of the miners. For a discussion regarding the merits and defects of this type of drill see Chapter VII on the " Philosophy of the Process of Drilling Rock." The makers claim that it will drill faster than any piston drill of equal cylinder diameter and use 20 per cent, less air. It requires 80 to 100 cu. ft. of air per minute at 100 Ib. pressure. It needs high pressures to operate to advantage. It is working in numerous mining fields in America; but owing to various causes, some of which have little to do with the drill itself, it has not so far proved successful in hard rock like the Rand, Rhodesia and Kalgoorlie. The claim that drills can be changed in a very much shorter time than those employed with piston drills does not hold to any great extent against the latest styles of chucks now used in piston drills. An automatic lubricator is now provided for use with this machine. There can be no doubt that the Leyner drill (particularly in the last model "No. 9 heavy," having side rods and spring buffers to take up blows of hammer) has established its position as a formidable competitor to the piston drill in tunnel driving. It now holds the records in the Elizabeth Lake and Roosevelt tun- nels. The conditions under which it does its best work are those evidently in which speed is of far greater importance than main- tenance cost, and where pure water is available for use in the drill. Leyner Rock Terrier. The smaller drill shown in section, Fig. 48, was recently introduced on the Rand as a stoping drill for small stopes. It is no more powerful than the air-feed types of drill; is not nearly so easily handled and so cannot compete with them except in special work for which they are most used. HAMMER DRILLS 55 Kimber Air-Hammer Drill. The Kimber drill, Fig. 49, and the Gordon drill, Fig. 50, were designed to meet certain special conditions largely peculiar to the district of the Witwatersrand in South Africa. The Kimber drill is merely in its experimental stages, so I merely give a drawing and brief description. The Kimber drill with a cylinder diameter of 3| in., length of stroke 3 in., length of feed 1 in., weighs 100 Ib. The hammer or striker is actuated without a valve on the differential piston prin- ciple, striking 800 to 1000 blows per minute. The weight of the hammer is 12 Ib. The rotation of the drill steel is effected by a small cylinder cast on the front end of the main cylinder and at right angles to it. To the piston of this cylinder is attached a pawl, which FIG. 48. Leyner rock terrier drill. engages with a ratchet wheel. This ratchet wheel has a square hole through the center to receive the chuck on which the blow is struck. The square part of this chuck is made a sliding fit and is allowed to move longitudinally as the blows are struck, while the ratchet wheel gives the turning movement. The small piston is driven forward by means of air, admitted to one end and governed by ports communicating with the main piston, and is driven backward by a spring. The arrangement is such that for each blow the drill steel makes -fa of a revolution. The cradle is cylindrical in shape, with a slot at the top, which fits a lug cast on the cylinder and forms a slide. The feed is obtained by means of a screw and nut, with a crank handle attached in the ordinary way. These drills are built to put in 45-in. holes in narrow, flat stopes in hard quart zite where most of the holes dip 10 to 45 deg. 56 ROCK DRILLS HAMMER DRILLS 57 8 58 ROCK DRILLS from the horizontal and where it is necessary to mount the machine on a bar and arm. Gordon Air-Hammer Drill. The Kimber machine and the Gordon machine, Fig. 50, are also designed to work with air pressures as low as 50 lb., which explains the fact that the Kimber machine uses a 12-lb. hammer with 3-in. stroke to drive much smaller and shorter bits than those used in the Leyner machine. This also explains the great length of stroke adopted in the Gordon machine. Both machines are also built with the idea of being one-man machines, i.e., being easily handled and rapidly operated by one man. The weight of the Gordon drill has been cut down to about 72 lb. The hammer of the Gordon drill weighs about 1J lb. and has a diameter of 1A in. So far, despite its apparently simple construction, this machine has given poor results in actual work owing to the various difficulties involved in its construction. It was a mistake to employ a light hammer with such a high velocity due to long stroke. It is a most rapid driller with moderate sized bits in holes about 42 inches deep. It uses much less air than a piston drill. It is designed to strike about 600 blows per minute with air at 50 lb. pressure. As with the Leyner machine, this high drilling efficiency is aided greatly by water issuing from hollow steel at the cutting edge, removing rock particles as broken. The water is introduced in the front head through the anvil block or striking piece. HAND HAMMER DRILLS The hammer drill was used first as a hand drill for cutting small holes for hitches or pop holes in large rocks. These drills weigh 18 to 25 lb. "Hardy Simplex. The Hardy simplex hammer drill weighs 28 lb., and can drill holes 6 to 7 ft. deep. The arrangement of piston and valve can be gathered from Figs. 52 and 53. It con- sists essentially of a cylinder in which is caused to reciprocate by compressed air a hardened steel hammer or piston which strikes on the drilling tool 1500 to 2000 times a minute; moreover, the borer is turned automatically. Cleveland Hammer Drills. The makers of Cleveland drills claim the following advantages for the valve hammer drills : They are all of the valve type, the valve being the same in design as is at present in use in over 25,000 Cleveland riveters and chippers. HAMMER DRILLS 59 They contend there is no question about the superiority of the valve over the valveless type of drills in innumerable ways. FIGS. 51 and 52. Details of the Hardy-Simplex hammer drill. And they also state that with the valve drill assured of equal distribution of air, which minimizes the wear of both piston and Haw FIG. 53. The patent Hardy-Simplex hammer drill. cylinder, a heavier blow is delivered since the piston is driven forward against atmospheric pressure only, the initial air pres- 60 ROCK DRILLS sure behind it being maintained throughout the stroke. The pis- ton is solid tool steel and practically unbreakable. Less than 70 per cent, of the air is required to do the same amount of work, FIG. 54. Cleveland hammer drill. which means quite a saving of money in a year's time; there is less vibration to the machine, and it is, therefore, much easier to hold when operating by hand, and the parts have less tendency to crystallize. Variations in air pressure have little or no effect FIG. 55. Sullivan hand hammer drill, D 15. on their operation, while a valveless drill must have constant high pressure. Weight 20 Ib. The drill is shown in section in Fig. 54. Sullivan Hammer Drill. The "D 15" is also used for holes HAMMER DRILLS 61 up to 30 inches in depth, and together with the "D 19" machine, which has a capacity of from 1 to 4 ft., for drilling pop or block holes, for splitting up large boulders or pieces of stone in lime rock, cement rock, and trap rock quarries, and in open-cut contract work, to render these blocks small enough to be handled by the excavator. For this work hollow steel is ordinarily em- ployed, the entire drill being rotated by means of a handle. See Fig. 55 for sectional view. TABLE OF SIZES AND WEIGHTS OF SULLIVAN Am HAMMER DRILLS Class of Drill D15 D 19 D 21 Diameter of cylinder (inches) Depth to which holes may be drilled (inches) Maximum diameter of holes (inches) . Hf 6 to 30 H U 12 to 48 If 2 96 2 Size of hose recjiiired (inches) T ? (5 i i Air consumption at 100 Ib. pressure cu. ft. per min . Weight of drill in pounds . 15 18 25 30 35 70 Sinclair Valveless Hand Drill. This machine, Fig. 56, is particularly adapted to shaft and wing work, cutting hitches, taking up bottoms of drifts, underhand stoping and block-holing. The construction is such that the handle can be removed and the feed bar attached when desired. One 10 X 12-inch compressor will operate five or six drills. Murphy Standard Drill. The accom- panying cut, Fig. 57, represents the No. 1 or standard machine with handle, and Fig. 58 shows a section of the machine and parts. This machine weighs 17J Ibs. It can be used to good advantage as a hand machine in all kinds cf work. There is only one moving part, to wit, the hammer. The drill steel is hollow and part of the exhaust air passes through it and blows back the cuttings from in front of the bit. The drill is operated by one hand grasping the handle and the other the throttle valve. The drill is rotated back and forth FIG. 56. Sullivan valve hand drill. 62 ROCK DRILLS one-fourth the way around, with the hand grasping the throttle valve. The machine strikes 2000 blows a minute, and requires 30 cu. ft. of air per minute. Hardscogg Little Wonder. The " Little Won- der" trigger valve drill, Fig. 59, is especially adapted for block-holes, hitch cutting and in all work where it is necessary to start and stop the drill, at frequent intervals. The air is admitted to the drill by a valve operated and controlled by the finger, and so constructed that it will remain open when desired, but can be instantly closed. Weight 19 Ib. It HOLLOW DRILL STEEL was, however, only when the air-feed stoping bar was introduced that the present heavier types of hammer drills were developed. This development was also helped by the use of hollow steel. Hollow steel of good quality at a reasonable price has been produced the last few with handle, sinking or in drifting, a portion of the exhaust Carnahan Mfg. a j r an( j some }j v e air is passed through the hollow steel to the bottom of the hole and thus removes the broken rock chips. It must be remembered that for drilling down-holes with hammer drills, hollow steel with air, air and water, or water alone, under pressure, must be used to remove FIG. 59. Hardscogg's No. 2, wonder drill with trigger valve. the drillings, as there is not the splash and spitting action caused by the stroke of piston drills. HAMMER DRILLS 63 64 ROCK DRILLS The Leyner people claim that drilling is more rapid with only air passing down the steel, than with air and water. This is due to the fact that the particles of cut rock are more mobile with an air blast than when in a state of mud, and so are more rapidly driven out of the way of the cutting edges. The water, though, preserves the temper of the bit and allays the dust trouble. HAMMER DRILL USED ON STOPING BAR The hammer drill of to-day, with air feed, as a practical ma- chine, is employed mainly for holes having a high elevation out of which the cuttings fall by gravity. Solid steel is used. In most places where the practice is not prohibited by law the miners have to put up with the dust produced. In the St. John del Rey mine, Minas Geraes, Brazil, the management has provided masks for their workmen. This type of hammer drill was developed in the Cripple Creek mines of America. The conditions that called it into being were fairly hard ground; expensive labor, narrow, steeply inclined stopes carrying rich ore, that, owing to high transportation and treatment charges, must be mined with the minimum of waste rock. It was impossible to use large machines, although 2J-in. piston drills were formerly employed to put in 5-ft. holes. These drills, weighing up to 134 lb., were heavy handling for one man, and required to be firmly set up on a bar. The clamp bolts had to be loosened whenever a change of steel was made or a new hole started. The hammer drill with stoping bar changed all this. Sloping Bar. The bar 'consists of a piston which forms the extension of the machine proper, instead of a handle. This piston works in a long pipe-like cylinder with packing rings to prevent air leakage. At the base of the cylinder is a cock for the admission of compressed air, and also a spike to fix against the rock or a plank. The machines are rotated or oscillated by hand. With hose and stoping bar they are light and easily carried by one man. They are taken into the stope. The spike of the stoping bar is fixed on a board on the broken rock or on a timber; a short drill is fitted into the chuck and placed where the hole is required. The air is turned on and the piston of the stope-bar automatically clamps everything in position and drilling begins. When the first drill is run out the air is turned off behind the stope-bar piston; the machine is run back, a new drill inserted, HAMMER DRILLS 65 the air turned on again and drilling proceeds. Thus very little time is lost as one man can actually drill from 80 to 90 per cent, of his total working time, against perhaps 50 per cent, with a piston drill. Wolcott says "a 2-in. hammer-drill drills 40 ft. in 8 hours against 25 ft. for a 2|-in. piston-drill, in Cripple Creek granite." In drilling, these machines are generally mounted on a 2J-in. column with arm and bar. Hollow steel is used with air or air and water; this manipulation thus takes more time. The length of hole put in by 2-in. hammer drills is from 4 to 6 ft., the hole being usually 1 in. in diameter at bottom. Hammer Drills in Europe. In Europe, especially, hammer drills are coming into extended use for coal mining, working splendidly in coal and the soft formations of sandstone, limestone, slate, etc., associated with it. In mining metalliferous ores and in quarries the smaller sizes save much time in " popping," " bull- dozing," and " block holing," to break up large boulders of ores displaced by heavy changes of explosives. TYPES OF HAMMER DRILLS Most hammer drills are made to operate with compressed air at 80 to 100 Ib. pressure. The following are illustrations and short descriptions of the principal makes: Stephens Imperial hammer drills, Sinclair air-feed drill, Murphy drill, Sullivan air- hammer sloping drill, Hardscogg Wonder air-hammer drill, Cleve- land stope drill, and the Waugh drifting and sinking drills. The Stephens Climax Imperial Hammer Drill. An English firm, R. Stephens & Son, of Cornwall, has designed a hammer drill built as largely as possible on the lines of a piston drill and having every part readily accessible for inspection; this is the latest type of hammer drill, especially designed to meet the con- ditions on the Rand. In designing this drill, it was determined to construct a machine of the maximum power possible within the limiting weight of 100 Ib. laid down as the maximum weight allowed for machines competing for the 4000 prize on the stope- drill contest. In this drill air consumption has not 'been con- sidered an important item. The consumption is given as being about three-fifths that of a 3j-in. drill. It would therefore be about equal to that of a 2f-in. drill or from 70 to 80 cu. ft. per minute with air at a pressure of 80 Ib. per square inch. The complete machine weighs 95 Ib., 20 Ib. more than the 66 ROCK DRILLS Gordon drill. With an air pres- sure of 75 Ib. per square inch, the number of strokes per minute is said to be about 700. The length of stroke is 5 in. ; the diameter of cylinder is If in., and the weight of the hammer is 6f Ib. It will be seen that this drill is more powerful than any American stoping drill except the Leyner, model 6 machine. The general construction of the ma- chine which includes some novel features can be seen from the accompanying sketch sections. Fig. 60, part 1, is a longitudinal section; part 2 is a transverse section. Fig. 61 shows the ma- chine set up for work and also two drill bits. In Fig. 60 A is the anvil block. It is about 9 in. long by If in. diameter; it weighs 8 to 10 Ib. The anvil block and pinion wheel G are made in. one piece and from special steel. This pinion wheel prevents the anvil block's being forced back into the cylinder. It will be noted that it is pro- vided with a taper recess for a taper chuck C, having a water- feed channel WFC through it. This channel communicates with a brass water-feed ring W, which is surrounded by buffer rings made water-tight by packing PK. Water is fed from the two-way throttle valve, shown in the half- tone illustration, through the channel WFC, along the side of cylinder and front head to the brass water ring W. HAMMER DRILLS 67 The amount of water used is regulated by means of two cocks one on the hose; the other, a brass screw-head, on the machine itself. No air passes down the hollow steel with the water. Any water leaking past the ring toward the cylinder drains away through holes ES W. The pinion wheel S gears with the spur wheel G] this is ro- tated by crank handles to which it is connected by a telescopic rod. The rotation is thus geared and positive, being operated by hand similarly to the way that rotation is effected in the Leyner "Rock Terrier" drill, which this machine resembles some- what. FF is the main cylinder casting and slides in the flat FIG. 61. Stephens Climax Imperial hammer drill. cradle. It is bored out for two cylinders; AFC is the air-feed cylinder, AFP is the air-feed piston attached to- the cradle. The air admitted to the machine enters the air-feed cylinder and feeds the machine forward before it enters the main cylinder; as soon as the air is turned off, AFC is opened so as to exhaust. The drill must be slid back by hand, but as the drill is light and the holes seldom vertical this can be easily done. Another for- ward feed is gained (see Fig. 61) by sliding the cradle forward in the clamp. One side of the cradle has teeth on it; when the clamp bolt is loosened the cradle slides easily forward and is then securely fastened again by the toothed clamp, when it is tightened. With these two feeds, a total advance of 28 inches is gained; 68 ROCK DRILLS this is ample in the hard ground here, where hammer-drill bits are generally blunted after boring 12 or 15 inches. The main cylinder is If in. in diameter. The piston P is of shape shown. PO and PO' are the air ports; VB is the valve chest; V is a piston valve, and AV and AV are two auxiliary leather valves which control the exhaust from the valve ends. They are pushed down so as to always make an air-tight sliding fit with the piston P, no matter how worn the cylinder may be. Thus the valve movement is kept regular. The valve action can be seen from Fig. 60. The air is allowed to leak past each end of the valve from the live-air chamber in the center of the air chest in sufficient quantity to throw the valve over when the other end is open to exhaust. The movements of the piston P place each end of the valve chest alternately in connection with the atmosphere through AV and AV, the recess in piston and the two exhaust ports EX and EX' in the walls of the cylin- der. In Fig. 60 the piston P has finished its stroke, and A V is open to exhaust, so the valve will be thrown over for the return stroke. The valve could be set to cut off and use air expansively on either front or return stroke. This is done in the large piston drill made by the same company. It will be noted that the valve motion is simple and that the valve can be easily inspected. The machine is held together by side rods SR. The packing in the front head can be readily taken out and changed if it becomes worn. The novel points about the design are: First, the compact air feed which allows the machine's being kept short and so made similar in shape to a piston drill, and yet without a feed-screw; second, the great weight of the anvil block this would seem at first to be a mistake in design owing to its great weight and inertia; third, the adoption of the taper chuck attachment. This makes the anvil block simply a part of the drill bit as it fastens immediately to the drill shank. This construction seems to me to reduce vibration greatly and to be the reason why the makers say that they have had no trouble with breakages of this part, in spite of the fact that it has holes bored in it and of the difficulty that every maker finds in tempering anvil blocks with holes in them. The anvil block is always "up to its work," and there is never any lost motion between it and the drill owing to rebound. Of course, a somewhat harder blow has to be struck HAMMER DRILLS 69 to make up for the greater inertia of the combined boring tool, but the advantage gained seems to outweigh this. The machine does not seem to be very economical in air, for the cylinder volume on the return stroke is large, owing to the fact that there is no piston rod to take up this space. The length of the machine over all is 2 ft. 10 in. I witnessed a trial of this machine on a block of granite similar to that used in the South African mines stope-drill competition. The hole drilled was horizontal, the water pressure about 10 lb v and the air pressure 80 Ib. per square inch. The machine bored about 12 in. with a IJ-in. double-chisel bit, 13 in. with a IJ-in. chisel bit, and 14 in. with a 1-in. chisel bit; or a total of 39 in., in a total of 9 min. 22 sec., or an actual drilling time of 8 min. 48 sec. The average speed was 4.23 in. per minute. In another trial 36| in. was bored in 12 min. 15 sec.; the bits were chipped and well blunted. It will be noted that the width of the bits used was less than that of those used in the South African mines trials; had the drilling been done with 1J-, 1J-, and If-in. bits, the rate of drilling would be slower. In the Gov- ernment trials in 1909 the finishing gage of the holes at a depth of 48 in. was If in. This meant that holes would have to be started with If- or IJ-in. bits. I have already shown what effect this has on boring speed. This machine, I should say, has a speed of boring equal to that of 2|-in. piston drill having a 6-in. stroke and boring with bits of the same size; but the Stephens is, of course, lighter, smaller and more easily handled than the piston drill, while with a double-pointed wedge key the drill bits are changed very rapidly indeed. The shape of drill bits used is shown in Fig. 61. The shank ring is necessary for taking out the bits by means of the key. Sinclair Hammer Drill. The advantages claimed for this drill, Fig. 62, are: 1. It has been the endeavor of its inventors, by employing machine and tool steel in the place of cast iron, to build a machine which is practically indestructible. It is constructed of machine and tool steel throughout, except the throttle valve, which is of polished brass. 2. It is simple and substantial. An endeavor has been to make the machine so simple and strong in every particular that there is little or no chance for leakage. 70 ROCK DRILLS 3. It is protected against crystallization by buffers and buffer plates. One of the faults noticed in hammer drills is the tendency toward crystallization of the steel in the cylinders. This is caused by the piston striking the chuck, or collar protecting the chuck, when the steel is not far enough into the machine to allow the piston to ^strike the end. In the Sinclair drill this defect is entirely obviated by f-in. rubber buffers and steel buffer plates. 4. Steel used is either hollow or solid, with no bulldozed shanks to break and cause trouble. A bulldozed shank is not required as the shoulder necessary to keep the steel from going far into the chuck is made by turning off the shank end of the drill steel. In making shanks in a bulldozer, the hole through the steel is made considerably smaller at the point where the shoulder is FIG. 62. Sinclair air-feed drill. raised, and four times out of five a weak place is made where wreakage will occur. Murphy Drill. The makers thus describe the No. 2 drill, Fig. 63, with water attachment and air feed, as follows: In up-raises and stopes, where up-holes only are required, solid steel is generally used with the Murphy drills. In shaft sinking and all down-hole work, hollow steel is used and water added in the usual manner, but in drifting, or in any work in a vertical face, it is necessary to put in up-holes, down-holes, and horizontal holes, and in such work hollow steel is required, and it is not convenient to add water in the usual manner. In such work the Murphy No. 2 machine, with feeder mounted on column, is usually used, and this is provided with the water attachment as shown in the illustration. The tank is light, is provided with handles, and is easily moved about. Compressed air is admitted above the water in the tank. A 50-ft. length of f-in. hose is con- nected to the water in the tank and to the side of the Murphy HAMMER DRILLS 71 FIG. 63. Murphy No. 2 drill wit] iment. ROCK DRILLS FIG. 64. Sullivan D-21 air hammer drill. HAMMER DRILLS drill. Water is forced through the hollow steel. A needle valve is on the water line, so that it may be regulated just as required. A small amount of water only is needed. A tank full should last a shift. A small piece of sponge is put in the hose connection, so that it is necessary for the water to strain through this sponge before reaching the needle valve. This is done to prevent any solid particles getting to the needle valve and clogging it. If the sponge clogs it can be quickly removed, washed out, and replaced. The Sullivzn Air-Hammer Drill. The Sul- livan Class "D 21," Fig. 64, mining drill is de- signed for driving stopes and raises. It is mounted on a feed cylinder and piston, the rear end of which rests upon the floor or back wall of the working. As the drill bit advances the feed piston is also advanced by compressed air, thus automatically keeping the drill up to its work. The machine, complete, weighs 70 Ib. and employs solid steel. As the holes are all uppers they are kept free of the cuttings by gravity. The drill is rotated by hand and will put in holes up to 6 ft. in depth. It uses only a small quantity of air as compared with the standard piston drill, and owing to its light weight and absence of separate mounting may be carried readily and quickly into any working where a man may go, and may be set up and removed more rapidly than a machine mounted on a tripod or column. Hardscogg Wonder Air-Feed Water Drill - In some formations where the rock is exceed- ingly dry and free cutting, the dust from a drill giving an air-cleaned hole is objectionable. To overcome this a special machine, Fig. 65, has been built, with a water device, with which water is used rather than air to expel the drill cuttings. The water is taken into the drill 74 ROCK DRILLS HAMMER DRILLS 75 and passes into the end of the drill bit. This arrangement also obviates the necessity of using a special water socket or water joint. Water may be taken from a water pipe or column, or from a special water tank, as desired. The drill is simple in construction and there are no complicated or expensive parts liable to break or get out of repair. With this device the drill and bit are completely rotated, which assures a perfectly round, smooth hole and prevents the drill bit from sticking. It is recommended and guaranteed to drill a 4-ft. hole, and its weight complete, with 6-ft. column and arm, is 100 Ib. Cleveland Slope Drill. The drawing, Fig. 66, shows the design of the Cleveland stope drill. The valve chest being on the outside, renders the valve easily removed without disturbing any other part of the machine, in case it sticks, because of dirt in FIG. 67. Cleveland hammer drill and air feed the air line; and inasmuch as the chuck, back head, and cylinder are held together by side rods the whole machine can be pulled apart in a few minutes, should this operation be necessary. This drill can be entirely taken apart and assembled again in the mine, without using a vise, and without taking the drill on top. The operation of the machine is simple, and as follows : After the machine, Fig. 67, is set in place and the air line con- nected, the throttle handle being in line with the machine, a turn to the first notch opens the air feed enough to slowly raise the drill to the rock; the next notch starts the hammer running slowly, and the last starts the hammer at full speed. It is then only necessary to keep the drill rotating back and forth through 180 until the air is shut off, in order to keep the holes round and in shape to receive the next steel. Closing the throttle opens a small relief hole, allowing the air feed to telescope. To get the greatest possible amount of drilling out of the machine, the air 76 ROCK DRILLS * pressure at the drill should be between 80 and 100 Ib. The air consumption at this pressure is about 35 cu. ft. per minute. If the machine is idle a long time, a good supply of oil poured in the oilers, and the machine run for a few minutes, will clean it out thoroughly, after which lubricating oil should be added. Good oil which will not gum must be used. It is advisable to pour a small quantity of oil, about four times per shift, into the oiler the action of the machine will distribute it to every working part. This drill uses 1-in. cruciform solid steel and is designed to put in up-holes only. Waugh Drifting and Sloping Drill. The Denver Rock and Machine Company says that a special feature of the No. 8-D and 3-D sinking and drifting drills, Fig. 68, is the automatic tappet, which regulates the pressure in the air-feed cylinder, so that the drill will always rotate easily. The duty of the air-feed cylinder is to keep the drill steel always up against the bottom of the hole, and owing to constant pressure expands as the depth of the hole is increased. An air-feed cylinder with sufficient area to keep the drill and steel up against the bottom of the hole when drilling a hole above the horizontal would be found altogether too powerful on a down-hole, when in addition to the pressure in the air-feed cylinder is added the weight of the machine and drill steel. A brief explanation of the working of this automatic tappet or regulator is this : There are two annular grooves one inch apart around the small end of the tappet. These grooves register with ports in the wall of the barrel which connect with the air supply in the air-feed cylinder, and automatically regulate the pressure in the air-feed cylinder according to the hardness of the rock being drilled. This alternating pressure is obtained by the shift- ing of the tappet, which change in position is caused by the recoil of the piston hammer. In drilling in hard rock this recoil is more accentuated than when drilling in softer rock, and the position of the tappet is governed accordingly. Waugh drifting and sinking drills use hexagon hollow steel. The No. 8-D uses 1-in. hexagon hollow steel, and the No. 3-D uses |-in. hexagon hollow steel. There are no prepared shanks necessary further than to smooth off the ends and harden them slightly. To get results from the operation of the Waugh hammer drill HAMMER DRILLS 77 in putting in down angle holes it is necessary to keep the bottom of the hole free from cuttings. This is done by a very simple three-way valve device, which is connected to the drifting and sinking drills. The three-way valve seat is screwed into the side of the head, and the three-way valve is operated by the sleeve handle, which fits over the rotating handle, and as the operator rotates the drill he can very easily, with a simple turn of the wrist, change the position of the three-way, valve and force either live air or water through the drill steel. FIG. 68. The Waugh drill. There is a hexagon leather gasket in the chuck end of the drilll which by pressure from behind makes a tight joint around the drill steel and keeps the water and air from escaping out of the chuck end, and causes them to be forced through the hollow drill steel to the bottom of the holes. This gasket can be quickly replaced when worn out, and in putting in a new gasket it is neces- sary to be sure that the hexagon sides of the gasket are in line with the hexagon side of the chuck. Nothing but a light oil should be used for oiling this drill ; lard oil is recommended. In addition to pouring some oil in the short 78 ROCK DRILLS hose air connection, it is well to pour some oil down the chuck end, in order to keep the tappet chamber lubricated. The No. 8-D weighs 75 Ib. and uses 40 cu. ft. of air per minute; the No. 3-D weighs 60 Ib. and uses 35 cu. ft. of air per minute. At a recent trial in black syenite in No. 6 shaft Vindicator Mine, Colorado, the Waugh machine, 8 C, drilled 49 ft. in I? hours, and the Shaw machine, 10 A, drilled 35 ft. in 1J hours. "ANVIL-BLOCK" MACHINES COMPARED WITH THOSE' STRIKING THE STEEL DIRECT The anvil-block striking pin, or tappet, is a short cylinder of specially hardened steel fitting in the end of the cylinder and kept from entering it by an annular projection. It sometimes takes the form of a false chuck seen in Fig. 69. When this is em- ployed there is no need to forge or turn any collar in front of the shank on the drill steel. It also tends to prevent leak- age of air from the front end of drill, though if it be used with hollow steel a hole must be bored in it to allow air to pass down the drill. The anvil block also helps to keep grit out of the cylinder. When boring up-holes with a machine not using this device grit is very liable to enter through the front head around the shank of the drill. In practice, the disadvan- tages of this device are that its elasticity and inertia must be overcome by the blow of the hammer. If it is not pressed very tightly against the drill shank the force FIG. 69. False chuck of the blow will be greatly reduced. Under Machine O^ ^^ the Prolonged hammering if the anvil block is not tempered to a nicety it will either break or burr up, sometimes wedging itself in its place. A recent writer in the Engineering and Mining Journal states that the benefit of a vanadium alloy is that it allows a solid anvil block being tempered properly all the way through. The form of the solid anvil block is shown in Fig. 70. In the Gordon drill it is weakened by having holes bored in it to transmit water to the HAMMER DRILLS 79 end of the hollow drill shank. This liability to rupture becomes much increased. The piston can be made very solid and strong. It will be noted that the valve machines usually have an anvil FIG. 70. Average type of hammer in which vanadium steel is employed. block, which is necessary in order to reduce air leakage on return stroke, while the valveless drills strike the steel direct. Valveless Drills. The operation of valveless drills is plainly seen in the drawing and description of the action of the Kimber, Fig. 49, and Hardscogg Little Wonder machine, Fig. 59. It is evident that in machines of this type, when live air is ad- mitted to drive the piston hammer back, considerable leakage must occur around the shank and through the hollow of the steel. With most of these machines the forward stroke is made by air under expansion, the air supply being cut off before the piston has completed its travel and struck its blow. The action is similar to that of the Adelaide piston drill. With many of the valve ma- chines full, air is kept on the piston until the end of stroke. The blow is not cush- ioned and is harder. The piston hammer of the valveless machine has passages and holes bored in it, thus being more liable to break. Fig. 71 shows the principle upon which the valveless machines work. As shown, the hammer H is on the forward stroke and the air entering at / passes through the ports P in the hammer and exerts a forward pressure FIG. over the entire rear portion. At the same time the exhaust E has allowed the escape of the compressed air from the previous stroke, and the inner ring R, which is a part of the barrel B, prevents the air from the inlet from going to the front of the hammer. The effective air 71. Section of 80 ROCK DRILLS pressure then is the pressure on the rear portion of the hammer minus a backward pressure upon the shoulder S. As the hammer moves forward the ports P are closed by the ring R, until the ring is passed, when they open to the exhaust E; the air pressure then is upon the shoulder S and moves the hammer back. Collars have to be placed in the drill steel to allow the front head to press against it and thus prevent the shank of drill steel entering the cylinder too far, preventing the proper stroke. These collars are either turned off the steel or swaged up on it. If turned off, the area struck by the hammer is reduced too much and the shank will be liable to burr up or break while swaying a collar, or appears to weaken the drill, as they often break at this place. These drawbacks can be reduced by using the largest possible section of steel. This section is determined by the minimum diameter necessary at the bottom of the hole bored. In all these discussions of advantages and disadvantages of vari- ous machines and various types of the same machine the question of the class of labor available for supervision must always be taken into consideration. On the Continent skilled labor with technical knowledge is able to get very fair results from electrical drills. Hammer drills, with attachment for water feed, with hollow steel require careful and skilful operators. On a mining field like the Witwatersrand, where the labor is mainly unskilled and where many white supervisors are both careless and untrained, many devices that might be a success elsewhere fail altogether. As a general rule the miner hates complications of any kind. He would in some cases refuse to make a success of a machine because its use involved coupling up a few extra hose and a tank before he started work. Unfortunately, it is no real excuse for the failure of a device or machine to say that if it had had care- ful treatment it would have been all right; because any machine for underground work must put up with careless treatment and neglect. Herein lies the cause of the failure of several machines of the hammer type. DESIGN OF HAMMER DRILLS The design of a good hammer drill should include provision for taking up the blow of the hammer on the front head without seriously damaging the machine. It will be noted in some de- signs that this is well done by means of springs and side rods HAMMER DRILLS 81 as in a piston machine. In others it is provided for by rubber buffer plates. If the machine is of the valve type, the valve being very rapid in motion should, if possible, take up its own wear or allow of having its seat bored out and a new valve fitted easily. It should have some arrangement to prevent grit enter- ing. Above all, the valve should be easily accessible for examina- tion as is the valve of a piston machine. The water service should be arranged so that the water cannot corrode any vital internal part of the machine, or enter the cylinder or valve chest. Leakage due to wear must be easily taken up. The weight of hammer and length of stroke should be suitable to the pressure of air under which the machine will work, giving a blow hard enough to cut the rock with long steel, yet not power- ful enough to smash anvil blocks or steel. If anvil blocks are used, they should, if possible, be kept solid and not weakened by holes bored in them. Rotation or oscillation for up-holes is best performed by hand in those types for use with air-feed stoping bar with solid steel. Mechanical rotation is, however, perhaps preferable for those machines used on bars and arms. A secondary hand rotation should be available also. The design of hammer drills is in an evolutionary stage. Special material is being called into use for their construction. Vanadium steel is found most suitable for anvil blocks. They produced a demand for hollow steel and for a hard, acid- water resisting alloy. To define the limits of the economical use of hammer drills at this time, as against piston drills, is difficult. For very large, deep holes the piston drill has, at present, nearly the whole field. The Leyner drill challenges its position for holes of moderate size and length, such as are usually employed in development work in mining. A drill like the Leyner, however, is hampered by requiring the use of water under pressure, valuable as such an auxiliary is from a health standpoint. THE ADVANTAGES OF THE HAMMER DRILL 1 "The hammer drill is extremely simple, having only one, or at the most two, moving parts. This means a steady reliability and ease of up-keep with low repair costs. "Requiring but a moment to change steels or start a new 1 Ingersoll-Sergeant Catalogue. 82 ROCK DRILLS hole, probably 70 to 90 per cent, of the work paid for is applied in actual drilling, while with an ordinary piston drill usually not more than two-thirds and often less than half the time is actual drilling time. This is a most important point in work where a large number of small, shallow, and carefully placed holes are required. "The great number of light blows of the hammer drill is less destructive of steels than the heavier blow of the piston drill. The loss of gage of the bits is not so rapid. The breaking or dulling of steels for a given footage of holes is much less than in hand drilling and usually not more than half with the hammer drill what it is with the piston drill. "The hammer drill can be used in extremely close quarters places where no piston drill with a fixed mounting could be used, or even a hand hammer swung. Wherever a man can go he can take a hammer drill with him. It is truly a 'handy' machine, easily carried anywhere under all conditions. "The air consumption of hammer drills is about one-half that of the smallest piston drill, meaning that a given compressor plant will run twice as many hammer drills, doing probably twice the work and often more, in certain conditions. Or, the initial power and plant investment for a hammer drill outfit to do a given work, as in prospecting or development, need be much less than that required for an equipment of piston drills. "No special skill is required to operate a hammer drill and herein lies one of its greatest advantages. Only a skilled machine man can overcome a 'fitchered' hole, start a difficult hole, or determine the proper feed and stroke, thus getting maximum results with the piston drill. But a half day's work will familiarize any intelligent laborer with a hammer drill. One skilled miner can direct or 'point' the holes for half a dozen or more hammer drills a most important item where good men are hard to get. "It is no exaggeration to say that 95 per cent, of the stoping work in the mines of. the world is still being done by hand. It is also a fact that one hammer drill will average an equivalent of six to fifteen hand drillers. Good labor is every year more scarce. If 10 hammer drills will do the work of 100 miners, they are cer- tainly a good investment. With a limited force provided with these drills, ten times the drilling can be done, and the prcduc- HAMMER DRILLS 83 tion correspondingly increased, thus getting cheap machine re- sults in one year which would otherwise take much longer. "This advantage goes still farther. Much of the economy of mining depends on the holes being properly and skilfully placed to bring out the maximum quantity of ore with the minimum powder charge, and with the minimum amount of undesirable waste rock. It is certainly true that the average skill of 10 selected hammer-drill men will be higher than that of a gang of 100 hand drillers. The importance of this point in its bearing on low mining costs and improved operating conditions will be appreciated by every mine manager. "The hammer drill enables the miner to follow a vein in a stope only wide enough for his body, bringing out the ore with maximum values and with the minimum of waste rock to be sorted or treated. One instance may be noted. A 2j-in. piston drill stoping in a 14 to 18 in. vein gave ore values of $30 to $35 per ton. The substitution of a hammer drill brought out one- third more ore from the stope 18 in. wide than the piston drill brought out from a 3|-ft. stope; and values at once ran up from $80 to $90 per ton. Hoisting, sorting, and powder costs were cut in two; timbering costs were reduced two-thirds; and the total ore tonnage was increased. Power cost per shift for one drill was reduced from $3 to $1. In this case the user figured that the smaller machine was worth $1000 per month to him. "The experience of the most careful users has shown that the hammer-drill brings about a most important reduction in the cost of explosives. The average powder man will load a hole to the limit, regardless of whether so much powder is needed or not. The small hole made by the hammer drill reduces the likelihood of over-charged holes or over-shooting and the objec- tionable pulverizing of rich ore. "But as the diameter and depth of hole best suited to move a given amount of rock diminishes, a point is reached where the economical field of the standard drill merges into one best covered by the hammer drill. The dividing line is reached (this does not apply to machines of the Leyner type), in mining work, for in- stance, where narrow stopes are encountered, where raises have to be driven : as in the caving system, in underhand stoping, where a thin vein must be worked with a breaking of waste rock, or wherever small, comparatively shallow holes (usually up-holes) 84 ROCK DRILLS require easy placing of the machine used and economical drill- ing through reduced 'dead time' become determining factors. This means that as large a proportion of the time as possible shall be spent in actual drilling rather than in setting up and moving. From the line here denned the field of the hammer drill extends down to the drilling of the smallest holes for trim- ming pop shots and similar work." IV ELECTRIC DRILLS THE comparatively high power consumption and low efficiency per unit of power employed by standard rock drills have always encouraged inventors to seek some machine in which better results could be obtained. Electricity appeared to be just the force required. It could be transmitted by wires instead of by cum- bersome pipes. Machines for performing almost every other kind of work had been successfully run by means of electricity, with a high mechanical efficiency. The designers of electric drills found, however, that they were entering a new field of work with many unforeseen difficulties. Electricity is a force particularly adapted for producing rotation, and could rotary drills or augurs have been used for boring hard rock, the design of a simple effective machine adapted for working underground might have been easy. Such rotary drills are work- ing in soft rock and coal; some are employed in the Cleveland Ironstone district in England. The diamond drill bores hard rock by this means, but is too heavy, complicated, and expensive, and does not work rapidly enough to compete with air machines. The principle of the electric solenoid was first taken advan- tage of to produce percussive action, similar to that of a piston machine. Siemens-Halske built the first percussion electric drill about 1879. In the Marvin Sandy croft drill the soft steel piston, of which the chuck is an extension, works in a cylinder surrounded by two coils of wire. The coils are made to alter- nately attract the piston backwards and forwards. The piston and tool are rotated by the usual rifle bar, ratchet wheel, and pawls. There is a cushion spring to check or cushion the back stroke. The energy thus stored is given out to assist the forward blow. The current is brought by a three- wire cable, the center wire being common to both circuits. A special make of two- phase alternator, with separate exciter, sends the current alter- nately every half revolution to back and front coils. The dynamo 85 86 ROCK DRILLS runs about 400 revolutions per minute. The drill strikes a cor- responding number of blows. The copper wire in the coils is of square section, insulated by mica. They are solidly wound on a steel tube, enclosed in the casing, and thus shifting, a wear of insulation is guarded against. Losses of power are said to amount to 6| h.p. for 1J h.p. exerted in actually cutting rock. The chief electrical loss is found in the heating of the solenoids. The drill heats rapidly, owing to the reversals of current. This drill is heavy in comparison with its power; but has found a limited field for useful employment in quarries and other open-air work. It cannot, I think, compete with the standard rock drill in speed of drilling, handiness, and reliability in underground work. The Edison drill is of same class; also the Van Depoele; voltage, 110- 220; weight, 400-450 lb.; stroke, 300-600. The second class of electric drills includes the Durkee, Dietz, and the Siemens-Halske. These place the motor in a separate case, and it is connected with the drill by a flexible shaft. The third class has the motor mounted on or near the drill itself or rigidly connected with it. This includes the Adams and the Gardner, which is a hammer drill. The Siemens-Halske, Gardner, Adams, Durkee, and Dietz drills use a crank-shaft. In all these drills rotary motion has to be converted into reciprocatory motion, involving the use of springs, cams, journals, and bearings. If the motor is on the machine, the jar caused by its working and by the drill sticking sometimes tends to destroy the insulation; short-circuiting may occur and the armature become burnt out. The plan of effecting this transmission, as in the Siemens-Halske machine, is to have the flexible shaft drive the crank-shaft by closed gearing. The crank-shaft carries a heavy fly-wheel on one end, and the other a pin, cam, or draw bar, or a crank disc, having a throw of about 3 inches. This pin engages and moves a sliding cylinder holding two powerful springs. As the travel of the draw bar is limited, and the cam must have certain definite limits of motion, the connection between it and the piston must be made flexible to allow the draw bar to continue its motion when the drill steel gets stack; otherwise the motor would be stalled, or some con- nection broken. These springs must be strong enough to strike a powerful blow of 100-foot lb. or more. The momentum of the moving piston throws it out' at the end of each stroke, and the ELECTRIC DRILLS 87 piston actually travels twice the length of the crank. The fly- wheel is fitted to absorb any irregular stresses and to prevent shock to the gearing, crank-pin, shaft, and bearings when the drill has to pull back; also when the crank passes back of center position; at the beginning of forward stroke, and when the drill strikes. It is thus obvious that the electric drill cannot be of as simple construction as the standard rock drill of piston or ham- mer type worked by air. Siemens-Schuckert Drill. A crank impact drill has been ii FIG. 72 Deitz drill. designed recently by the Siemens-Schuckert works. It is operated by a 1 h.p. motor, fitted directly to the drill, and is said to be far more efficient than the usual design of rock drill with flexible shaft and motor box. The electro-motor is placed in a saddle in the back of the drill and is readily removable. Like the drill itself, it is enclosed in a dust and water-proof casing. According as the drill is working on the right or left side of the supporting column, the motor is placed above or below the drill. This differ- ence in the position of the motor, however, exerts no influence ROCK DRILLS on the working of the drill ; it may be used as well on a horizontal column or transportable supports provided it is fitted with a special feeding slide. Gardner Electric Drill. In the Gardner drill, the power is trans- mitted, similar to the Siemens drill, to a crank-shaft, the crank of which works in a special shaped slot in a crosshead so that a quarter revo- lution strikes a blow. The next withdraws the drill, rotating it partially, and during the last quarter the drill remains station- ary. On the opposite end of the crank-shaft is a fly-wheel which absorbs energy during the last quarter of the stroke, and gives it out during the first, thus overcom- ing any tendency, of the quick for- ward and slow return reciprocation of the crosshead, to impart irregu- larity to the rotation of the gear- ing. Buffer springs connect the crosshead to piston and drill. The largest Gardner drill uses 2 h.p. and strikes 550 blows per minute. The drill and motor together weigh, it is claimed, less than that of an air drill of similar power. Deitz Drill. Referring to Figs. 72 and 73, the drill operates as follows: As the yoke A moves for- ward, the piston B compresses the air in the chamber C; this forces the cylindrical air hammer D against the tappet E, which strikes the head of the drill steel at F. The reverse stroke of yoke A then moves back the piston ELECTRIC DRILLS 89 B, which compresses the air in chamber G, which brings back the cylindrical air hammer D, the momentum of which compresses again the air in chamber C, at the time that the piston B reverses for the return stroke forward. Thus the speed of the hammer D, forward, is almost twice the speed as the piston B, for the reason that the hammer D does not start forward until the piston B has about finished half of its stroke forward. This delivers a tremendous blow upon the drill steel, and at the same time transmits no perceptible jar to the mechanism of the drill, for the reason that the piston is cushioned on air, both at the forward and backward strike; the cylindrical hammer merely floating on the air cushions. In the large size Model D drill, the hammer weighs 12 lb., and strikes 600 blows per minute. In the smaller size Model E drill, the hammer weighs six lb., and strikes 1,000 blows per minute. Locke Drill. In the Locke drill, an attempt is made to mount the motor on the drill. The crank axle is driven direct by means of gearing, and is connected to the piston by a helical spring. The speed of the motor is so adjusted that the drill strikes the blow on the backward stroke of the crank. This could be done while the spring retained the exact elasticity required and the drill the proper speed. Locke contends that the insulation difficulty can be overcome by having the axis of the motor parallel to that of the drill, so the vibration will not throw the brushes off the commutator, thus causing sparking. The motor is firmly attached to the cradle of drill, and a telescopic shaft is used to transmit the power as the drill is fed forward. He states that his drill has been in use 15 months in Colorado without any injury to the insulation. He contends that springs will stand if not over-compressed to more than J of their length. Springs have been in use for six months on a drill, striking 420 blows per minute. He thinks that the advantages due to initial low cost for installing electric gener- ators, and the less cost of wires compared with air pipes and their maintenance, together with power costs at only 10 per cent, that of air drills, make the development of the electric drill certain. The following is the result of a test carried out in Germany between the Siemens-Halske electric drill and a standard air drill. 90 ROCK DRILLS Work done in Bore Hole Air Drill Electric Drill Cubic inches per min 2.75 3.00 Ft Ibs per min 11.664 12.960 Consumption of power in generator and motor, ) 10 H. P. 1.7 H. P. the power being transmitted 2000 yds. . . . ) 324,000 ft. 1 bs., min. 54,000 Total efficiency, per cent 3.6 24 Electric Drill Results. Gliickauf, of June 4, 1904, publishes some very interesting details regarding the working of an electric rock-drill installation at the iron ore mines at Peine, Hanover, Germany. "The installation referred to comprises 10 electric percus- sion Siemens-Halske rock drills, driven by 2 15- volt three-phase motors. The primary plant consists of a 10 kw. three-phase generator driven by a gas engine using blast-furnace gas. The current is generated at 1,000 volts, and is transformed to 217 volts in the mine. "It has been found essential for the efficient working of these electric drills to give them frequent and careful inspection, in order to make certain of even the smallest part being in good working condition. "Apart from this the drills seem to have given good results, and the repairs necessary have by no means been heavy. The most troublesome part appears to have been the crank-pin, but it is now the practice to replace it after 50 hours' work. Another weak spot is the spring used, and it was found that the average life of a spring is from 30 to 33 shifts. "The consumption of energy per drill amounts to 5.5 amp. at 220 volts, or about 1.7 b.h.p., so that the 10 kw. generator, stationed over a mile from the mine, is large enough for six drills. "The cost of one drill complete with wall box, flexible shaft, motor, cable, column, and 125 bits amounted to about 233, and as two drills were used in one shaft, the total cost was 466, plus 16 for a tool case, or 482. "The working expenses for the year June 1, 1901, to May 31, 1902, were as follows, there being two drills constantly in use: "Cost of energy, 11 10s.; spare parts, 64 10s.; wages of fitters, 40 10s.; materials, 23 10s.; blacksmiths' wages, 36 ELECTRIC DRILLS 91 10s.; new drills and drill sharpening, 39 10s.; interest on capital and depreciation on six drills, including portion of switchboard, water supply, etc., 125 Os.; total, 341 10s. "The work done during the year amounted to 1,652 drill shifts, or a cost per drill per shift of 4.134 shillings. From June 1 to November 30, 1902, seven drills were in use, and the cost per drill per shift amounted to 3.68 shillings, including all the items previously mentioned, along with lubricating oil, waste, etc. The following are some particulars of the performances of FIG. 74. Adams electrically driven rock drill. electric drills in actual work. Gillette gives the following data regarding the work of four Gardner electric drills in an hydraulic mine, Bullion, B. C. Three 2-h.p. drills, and one l|-h.p. drill were in use two years; each of the larger machines has drilled 13 holes 8 ft. deep in augite-diorite and porphyrite in a 10-hour shift; the cost per shift, for 3 drills, $31.55, for 312 ft. drilled. Thirty-six Box electric drills were installed in the D. L. & W. R. R. Tunnel at Hoboken, New Jersey, August, 1906, but replaced by standard piston air drills, January, 1907. Adams Electric Drill. Figs. 74 and 75 will show the various 92 ROCK DRILLS parts of the drill assembled. The motor is suspended in a fork which is booted to the guide shell, and can be placed in four different positions, viz.: on either side, front or back, as con- ditions may require. Connection is made from the motor to the controller by means of a flexible armored cable with contact box having spring contacts and a rubber protector, which on being placed in position makes a perfectly waterproof connection. The FIG. 75. Adams drill on column with internal mechanism removed. power is transmitted to the drill by means of a loose square steel rod running through the armature shaft in the motor, and a set of bevel gears on the drill, which impart motion to the crank- shaft, thence to the draw bar, which, in turn, reciprocates the piston. The piston is cushioned by two gangs of helical springs, which add to the force of the blow and render sticking of the steel in a hole a rare occurrence. Each spring is provided with a rubber auxiliary cushion, which prevents excessive breakage. This arrangement also permits the drill to be operated at full ELECTRIC DRILLS 93 speed without hitting the rock, and with no damage to the machine, and in addition makes a perfect reamer. The rotation of the piston is secured by a double set of ratchets, one working in a straight and the other in a spiral groove in the piston. The spiral groove is milled so as to cause the piston to turn on the backward stroke, the straight ratchet preventing it from turning on the forward stroke. The rotation after each blow is about ^V of a complete revolution, and when operated at full speed will make thirty turns per minute. The piston and ratchets are case-hardened to provide against wear. Each wheel has six pawls with phos- phor bronze springs. The pis- ton is guided by a head which* works in the draw bar and body, and a long bushing in front of the ratchets, this head being- held to the piston by means of a removable key. The crank-pin has a hardened box, divided in halves, operating in the draw bar. In order to protect the ma- chine and springs when feeding too close to the rock, or in deep holes, a rubber nose buffing col- lar is placed in front of the nose bushing, directly behind the FlG - 76. - Adam^s ^ectrically driven chuck. Side doors are provided in the body for removing and inspecting the springs without taking the machine apart. The entire internal mechanism can be removed by taking off one nut at the back of the draw bar, and removing the spanner sleeve in front. The internal mechan- ism can then be drawn out in front. To remove the parts from the piston, all that is required is to drive out a key in the pis- ton head. The draw bar, spring spacer, and ratchets may then be lifted off the piston. The steel is held by the usual form of U-bolt chuck common to air drills, and is simple, durable, and 94 ROCK DRILLS effective. All bearings, as well as other moving parts, are case- hardened, ground, and lapped, giving a hard surface and a soft, strong interior. Provision is made at all points possible for taking up wear or lost motion, either by taking out a shim or adjusting the taper bearings. The reader's attention is called to cuts, illustrating how this may be accomplished. This enables the operator to have a smoothly running machine at all times, as well as insuring a low cost of maintenance. The drill strikes 600 blows per minute when running at full speed, the motor running at 1800 r.p.m., the gears making a three to one reduction. The weight of the drill complete, Fig. 76, is approximately 295 lb., the D. C. motor 150 lb., the A. C. motor 125 lb. Edward Stoiber, of Colorado, states that he tried the Siemens drills, but they failed to stand the rough usage of mining condi- tions in hard ground. The following is given in the Engineering and Mining Journal, as comparative results of 2f-in. air piston drills and 2-in. Adams electric drills, air pressure 80 lb. Air Drill Adams' Electric Drill Actual time drilling, hrs. . 317 100 Ft. drilled 1279 253 Ft. drilled per hour . 4 2.53 Time lost for repairs . 17 Boring was in black diabase, 10-hour shifts being worked. The electric drills did good work in driving the Raibl adit in Corinthia, Europe. Rotary Electric Drills. Mr. H. W. Appleby states that in the Cleveland iron ore mine, Cleveland, Yorkshire, England, one air compressor was working six 3i-in. diameter air drills. Indi- cator diagrams showed an average of 111.06 h.p. developed, or 18.5 h.p. per drill. This engine was replaced by an electric generator, a smaller engine and six electric rotary rock drills. When these drills were working (and it is stated breaking as much rock as before), the new engine showed only 24.52 i.h.p., being a reduction of 77.91 per cent, in power used. Costs in pence per ton are as follows: ELECTRIC DRILLS 95 Air Drill Electric Drill Oil, stores and labor Coal 0.297 0.242 0.253 0.108 Repairs, making, sharpening drills, and maintain- ing pipes or cable 0.340 170 Total ... 0.879 0.531 In the Engineering and Mining Journal, W. H. Yeandle, Jr., gives the results obtained from working three Box drills for ten months at El Banco mine, Oaxaca, Mexico. Two drills were new. one being kept as an extra. Drills were run 12-hour shifts, except Sundays, and were operated, repaired, and cleaned by Mexican labor. The drills worked in metamorphosed, calcareous slate, pyroxene, andesite, and quartz vein matter, all being hard rock. The drills worked under hard conditions, as the mine was wet, hot, and foggy. Each drill put in one round of 16 five-foot holes in 24 to 28 hours. The extra parts used during 12 months included one rheostat or controller; 2 sets brush holders; 4 sets graphite motor bearings; 36 brushes; 6 sets chuck gears and shaft; 1 crank- shaft and bevel gears; 3 full sets of bearings; 2 chuck blocks and gears; 1 air cylinder shell, hammer, wire, and insulation. Those parts transmitting turning motion to the chuck blocks and steel were worst, as the water injection system failed and the bits jammed in holes. Fitchering was uncommon. Vibration caused the use of the large number of brushes, etc., and each commutator had to be turned down. The drills could not be run at full speed or current owing to motor heating, and excessive vibration; drill runners operated with one-half or three-fourths power, thus burn- ing out the rheostats. Short-circuiting was common. The drills, though far less efficient than air drills, did better and cheaper work than the hand labor available. The makers now claim to have greatly improved the water injection system, rendering the drill more efficient. ELECTRIC AIR DRILL The Temple-Ingersoll electric air drill, Fig. 77, is a compara- tively new machine, and I take the following description from ROCK DRILLS the Bi-monthly Bulletin (November, 1907) of the American Insti- tute of Mining Engineers: Many features of electrical transmission are undoubtedly con- venient and economical; but the direct application of the electric current in rock drilling has long been a baffling problem; of which, in my judgment, the machine here described has furnished the first, and thus far the only satisfactory solution, by combining the ac- knowledged advantages of air-driven percussion with the acknowledged advantages of electric power trans- mission, while avoiding the ac- knowledged disadvantages of both systems. This drill is correctly desig- nated; it is not an electric drill, but more completely an air drill than any other in existence, because it can be driven only by air and not, like other air drills, by steam also. Yet, while it is thus distinctly air- operated, the power transmission is electric, and the sole connection of the drill with the power-house is made by the electric wire, air com- pressors and pipe lines being entirely superseded. Very near the drill, and con- nected to it by two short lengths of hose, is a small air compressor, or, more properly, a pulsator, mounted upon a little truck. This constitutes the entire apparatus of a single drill. Each drill is accompanied by its individual pulsator, and each pulsator is con- nected to the line of wire from the power-house. The usual drill shell is employed, and may be mounted upon tripod, bar, or column, according to the work. The drill cylinder, fitted to slide in the shell, is moved forward or backward by the feed-screw. The cylinder is as simple as can be imagined: a ELECTRIC DRILLS 97 straight bore, having at each end a large opening. The piston also is plain, much shortened in the body, with a large piston- rod, which has a long bearing in a sleeve-elongation of the cylinder. Upon a truck is mounted an electric motor, geared to a hori- zontal shaft, with cranks on each end, which drive two single- acting trunk pistons making alternate strokes in vertical air cylinders. One of these air cylinders is connected by the hose to one end of the drill cylinder and the other end of the drill cylinder is connected by the other hose to the other air cylinder. The air, therefore, in either cylinder, in its hose and in the end of the drill cylinder to which it is connected, remains there con- stantly, playing back and forth through the hose according to the movements of the parts, being never discharged, and only replenished from time to time to make up for leakage. The propriety of calling the apparatus a pulsator instead of a com- pressor is evident. Details of Operation. The essential details of the cycle of operation will be easily understood. We may assume, to begin with, that the entire system is filled with air at a pressure of 30 or 35 Ib. This pressure being alike upon both sides of the drill piston, it will have no tendency to move in either direction. If, now, the motor, instead of being at rest, is assumed to be in motion, one pulsator piston will be rising in its cylinder and the other piston will be descending in its cylinder; and, as a conse- quence, the pressure upon one side of the drill piston will be increased and the pressure upon the other side will be proportion- ately reduced, this difference of pressure causing the drill piston to move and make its stroke. Just before the end of this stroke, the movement of the pulsator pistons is reversed, and the pre- ponderance of pressure is transferred to the other side of the piston, causing a stroke in the other direction and so on con- tinuously. The drill thus makes a double stroke, or at least receives a double impulse, for each revolution of the pulsator crank-shaft. The drill cylinder, while generally similar to that of the air -or steam drill, is in many respects quite different; and especially is it remarkable for its simplicity. The usual operating valve- chest; the valve and the complicated means for operating it; the main air ports and the intricate little passages in and connected with the chest are all absent, and nothing takes their place. 98 ROCK DRILLS The cylinder heads are both solid and both fastened securely in place. The split front head, the yielding fastenings for both heads, the buffers, the springs, the side-rods, etc., of other drills, have all been banished. The cylinder is absolutely plain, with direct openings into the interior, and a boss at each end to which the hose is attached. The piston also has been simplified. The device for securing rotation is necessarily retained; but the enlargement at the end of the piston-rod, which constituted the chuck and necessitated the split front head, has been discarded. The piston-rod is much enlarged throughout, and a simple but effective self-tightening chuck is slipped upon the end of it. The compressor or pulsator cylinders are likewise simple. There are no valves for either inlet or discharge, and there is neither jacketing nor the slightest need of it. The heating of the air by the compression stroke is compensated by the cooling which attends the re-expansion of the same air, so that it does not become increasingly hot and heat the parts of the machine with which it comes in contact. Air Pressure. In the foregoing description of the principle of operation I assumed a mean air pressure of about 30 Ib. in the apparatus. It may be asked how this pressure is secured and maintained. When the pulsator is in operation, the air pressure in the cylinders alternately rises above and falls considerably below the mean. At a certain point, indeed, it is below that of the atmosphere; and at this point a little valve is provided, which admits more or less air, until a sufficiency has been provided. At the beginning of operation the influx of air is rapid, so that no time is lost in getting sufficient pressure to begin with. The admission of air and also the apportionment of relative volumes thereof to the two ends of the drill cylinder are easily adjusted by the operator. The electric-air drill is not troubled by the freezing up or choking of the exhaust, because there is no exhaust. Moreover, the air does not accumulate moisture, and the temperature does not fall to the freezing-point. Again, air becomes and remains a constant vehicle for the conveyance and distribution of the lubricant. A certain amount of oil being contributed to the system at regular intervals, it would be more difficult to prevent than to insure its reaching every working part. ELECTRIC DRILLS 99 The length of hose employed seems to be limited to about 8 ft. on each side. The hose may be attached to either side of the drill, but each always to its own end of the cylinder. This length of hose gives all necessary liberty for the location of the pulsator truck near the drill. The truck (of steel, with flanged wheels) is usually made for the standard 18-in. mine track, but may be made for any other gage. Special care in leveling is not necessary, since the pulsator will work at any angle at which the truck can stand. Electric Current. Either a direct or an alternating current motor may be employed, the latter being preferred because it is a smaller, lighter, mechanically simpler, hardier machine, and more nearly " fool-proof." Four different speeds may be obtained with the direct-current, and two with the alternating-current motor in the latter case, full speed for steady running and a considerably lower speed for starting a hole or working through bad ground, with immediate transition from the one speed to the other, as required. The controller is on the top of the motor and the operator at the drill can start, speed, or stop the motor by simply pulling a cord, this being the only connection. The electrical connection ends at the motor; both the hose and the cord insulate the drill; and the operator is never exposed to the current. Sizes. The 5-C electric air drill may be regarded as the full equivalent of the 3.25-in standard air drill of any make; of its comparative efficiency something will be said later. The power requirement for this drill is from 18 to 20 amperes at 220 volts, or from 9 to 10 amperes at 440 volts the electrical equiva- lent of about 5 h.p. The system being a closed circuit, this is independent of conditions of altitude, which make so much difference with the work of the air compressor which supplies the ordinary air drill. The 4-C electric-air drill uses a 3-h.p. motor, and is a much lighter drill throughout, equivalent to a 2.75-in. standard air drill. The accompanying table on page 100 gives particulars of size, weight, etc., of both of these drills. The electric-air drill strikes a blow, normally so much harder than that of the air drill of the same capacity that it has been found advisable in many cases in " dressing" the steel bits to make them blunter or thicker, in order to avoid breakage. The 100 ROCK DRILLS DIMENSIONS, ETC., OF TEMPLE-!NGERSOLL ELECTRIC-AIR DRILLS 5-C 4-C~ Diameter of drill cylinder 5f in. 4.75 in. Length of stroke Length of drill end of crank to end of piston Depth of hole drilled without change of bit 8 in. 45 in. 24 in. 7 in. 42 in. 20 in. Depth of vertical holes machine will drill easily . 16 ft. 8 ft. Diameter of holes drilled from 1.75 to 2.75 in Strokes per minute Horse-power (at motor) . 425 5 1 to 1.5 in. 460 3 practical force of the drill had not been computed beforehand, but was demonstrated in extensive practice and experiment, and the clear and sufficient explanation came later. Piston. The drill piston, when running at full speed, and making a stroke for each rotation of the pulsator crank-shaft, does not strike either head. The hole by which the air enters the cylinder from the hose is located, not at the extreme end, nor close to the head of the cylinder, but a certain distance away, so that when the piston approaches the head a portion of enclosed air acts as a cushion, which first checks the piston and then shoots it back. The piston thus starts upon its working stroke impelled by a certain amount of force which, we may say, has been saved over from the preceding stroke to be utilized for this. The piston after being thus started is driven forward by an air pressure which increases as it advances, the pulsator piston being in the attitude of chasing and gaining upon the drill piston for a considerable portion of the stroke, while in the case of the ordinary drill piston, driven by a constant flow of air from which it runs away, the pressure must constantly diminish as the piston-speed is acceler- ated. In the same way, by the action of the other pulsator piston the opposing pressure upon the advancing, side of the drill piston is a diminishing pressure instead of the constant atmospheric resist- ance, and these combined cause a greater unbalanced difference of pressures upon the opposite sides of the drill, a more rapid accel- eration of the piston movement, and a consequent higher velocity and force at the moment of impact of the steel upon the rock. 1 Size 3-C is equal, in capacity, to a 2-iri. standard air drill; 4-C is equal to a 2|-in., and 5-C is equal to a 3|-in. ELECTRIC DRILLS 101 Advantages. Perhaps the most gratifying, and also surpris- ing, revelation of all in connection with the electric-air drill is the now indisputable fact that it takes only from one-third to one-fourth of the power, at the power-house, to drive it to do the same work. This is accounted for by the fact that the same air is used over and over, and that all of its elastic force is utilized in both directions instead of exhausting the charge for each stroke at full pressure. There are also no large clearance spaces to fill anew at each stroke, as these spaces are never emptied. A valuable feature of the electric- air drill is the ability to yank the bit free if stuck in a hole and immediately continue its work. When the bit of the electric-air drill sticks, the motor and the pulsator pistons do not stop. If the drill piston is mak- ing, say 400 strokes a minute, as soon as the bit becomes stuck the piston will receive per minute 400 alternate thrusts and pulls with full force, and nothing could be more effective for freeing the bit than these alternate thrusts and pulls. When the electric-air drill is operated without its own gener- ating plant, the current being taken from a large power company, some very low figures are already on record. At Idaho Springs, Colo., a mine shaft was put down 67 ft. in 24 shifts and the total power cost was $24 for the entire work. Results Obtained. This drill has been before the public five years, and several hundred are in use. Some of the work done to date includes 2200 ft. of 8 X 9 ft. tunnel at Salida, Colorado. At Georgetown, Colorado, as much as 62 to 65 ft. of holes have- been put in in 7| hours. At Ouray, Colorado, 1329 ft. of 7 X 7J ft. tunnel were completed in 11 months at a cost of $13 per ft. At Idaho Springs, Colorado, 8 ft. of 5 X 7 ft. heading per day are common. This drill will do similar and equal work to the standard air drill, and, as shown, power consumption is only from one-half to one-quarter as great. The makers state: " Where electric power is available at a less price than air or steam power, due to high fuel cost; where high altitudes impair the efficiency of the ordi- nary air compressor; where pipe lines would be objectionable in an ordinary air-drill plant; where electric distribution of power and its attendant uses and advantages are a controlling factor, these are the places where the electric-air drill offers the best combination of maximum work output with minimum cost." 102 ROCK DRILLS Disadvantages. There are several other factors that limit the sphere of usefulness of this drill in underground mining. Theoret- ical engineers profess small regard for the benefits derived from the ventilation caused by the exhaust of standard air drills, and state that this work can be better and more cheaply done by installing special machinery. This is not true in most cases in metalliferous mines. This machine would not, in most mines, be used in ill-ventilated ends or in hot workings where the ice- cold exhaust air of the ordinary drill is a stimulant and alone makes working conditions bearable in many cases. Where, as in South Africa, it pays to work two or three machines in one face of only 7 X 6 ft., this drill with its compressor would be in the way and would retard moving broken rock. In steep stopes it could not be used, but in flat stopes there should be a field for the operation of the smaller sizes. Where, however, headings are advanced with one drill, or where they are large enough to allow of two such drills being worked together and where arti- ficial ventilation is available as in some tunnel or adit work, then this drill should prove most efficient. Am DRILLS vs. ELECTRIC DRILLS In attempting to compare electric with air drills one can only say that, for mining purposes, there does not seem to be a large field open for them in competition with air drills under ordinary conditions. Their use might be recommended in places where power costs are very high and where high altitudes reduce the efficiency of compressor per unit of air-cylinder area; where con- ditions are such that separate artificial ventilation, or efficient natural ventilation, would have to be provided, regardless of the type of drilling machine employed; where labor, as in Germany, for instance, is cheap and efficient; where maximum output from any face is not the chief consideration; where the rock is not too hard and where the shorter stroke of the electric piston drill does not handicap boring speed by slow ejection of the broken particles. For instance, an electric piston drill would be handi- capped putting down long vertical holes. Electric drills must be constructed with quick running shafts, fly-wheels, and gears. On the surface, electrical machines are carefully kept from dust, dirt, and water. In actual mining they must work constantly exposed to these drawbacks, despite care- ELECTRIC DRILLS 103 fully contrived covers. Dynamos and their insulation are on the surface guarded from jar or undue stresses of any kind, and from working in a dusty atmosphere. In mining, they are mounted on a machine whose function is to produce jar and concussion. On the surface such machines are placed in the hands of skilled certificated mechanics. Underground they must be left to the tender mercies of the man whose chief tools are the hammer and the drill. The development of the air-hammer drill has, I think, prac- tically cut off the chance of any large use of electric drills. They are able to bore more rapidly, are simpler and lighter than any electric drill ; while their consumption of power is smaller than that of a piston drill, for the same work, in certain cases, the ratio of power developed at generator to power exerted on the bottom of the hole will almost bear comparison with that of electric drills. The Temple electric-air drill should also limit the sphere of usefulness of any purely electric drill. Air drills have one great advantage over electric drills in that they provide ventilation and cool the working place. The impor- tance of this in modern mining is not always realized. Professor Henry Louis writes: "I may add that the argument, occasionally put forward in favor of the pneumatic drill, that it helps to ventilate a close end, has in my opinion very little weight, because it is obviously easy to produce any desired amount of ventilation by means of small electrically driven fans, which will give a continuous air current, whereas the drill does not supply any air at the times when this is most needed, that is to say, after shots have been fired, and whilst the men are doing their hardest manual work namely, setting up the drill." It is true that the drill does not supply air after shots are fired; but it is no less true that rapid development work on the Rand, for instance, would be impossible if the same air hose that worked the drill were not there to blow out the smoke after blasting. Any one who knows anything of the difficulty of pro- tecting from damage by blasting, etc., our system of small pipes to carry air under high pressure in mines would hesitate before thinking of trying to put in large pipes to carry air from small electric fans. In the Rand mines the air pipes get blasted often enough as it is. 104 ROCK DRILLS Scott Gasolene Rock Drill. A rock drill operated entirely by gasolene has been designed by L. L. Scott, Joplin, Missouri. In gene'ral appearance it resembles an ordinary air drill. The machine operates on the two-cycle principle and the mixed air and gas is drawn in at the upper and lower ends of the drill, through ports on the top of the cylinder. A spark plug and timing device explode the charges alternately and these act on the inner faces of the pistons; an explosion occurs on each up- stroke -and on, each down stroke. The pistons are solid steel castings, the upper ends being connected to the crank-shaft through the connecting rod; the lower ends are connected by a swivel to the drill rod. The cushions are in the interior of the lower piston and the rotating mechanism is in the lower receiving chamber. In this drill the explosion chambers are so arranged that the heat will not affect the rotating device or drill rod. The rotation of the drill rod is independent of the piston. The steel is held by the usual form of a U-bolt chuck and the drill is fed by an ordinary feed screw. In the oiling system, the oil is mixed with the gasolene and the mixture is sucked in with each charge, thoroughly oiling every moving part of the machine. OPERATING DRILLS ON THE SURFACE AND UNDER- GROUND THE first consideration of both supervisor and miner must be to insure a plentiful supply of tools suitable for boring the rock. In many cases anything in the way of machines, fittings, tools, and bits is deemed good enough to use. UNDERGROUND DRILLING The miner should be furnished with a rock drill adapted to the work he has to do ; to the hardness of the ground; to the length of hole required; also with a bar or bars of such lengths as to adapt themselves to the width or height of the excavation made. These should be from one to two feet shorter than the hight of working place. A saddle, a clamp, and arm should also be pro- vided. Wedges and Blocks. Wedges and blocks for securing these bars in position should be also at hand. It is a good plan to make the blocks, Fig. 78, of large size, say 14 in. X 3 in. to 7 in. X 24 in. for, the foot block of a double jack bar, and 12 in. X 3 in. to 7 in. X 7 in. for the top block. These blocks are best made of hardwood and are secured against splitting by bolting two T\-in. iron plates on their opposite sides by two bolts across the grain of the wood. FIG. 78. Foot block with steel plate. These are for use in driving levels and in large stopes; other smaller blocks are also to be supplied for making up, and for use in narrower, steeper places. It is a wise plan to make a fixed issue to both day laborers and contractors of these blocks and wedges, and to charge for any excess used over a certain number; only in this way is waste checked. Lockers and Tools. The miner should be given, also, a box in which to keep his explosives if they are not issued to him at 105 106 ROCK DRILLS every firing; also a small box for detonators and a large box to keep fuse, certain spare parts of his machine, his oil can or oiler, chuck and clamp spanner, Stilson wrench, " shifting" spanner and a few hose connections. He will also require a sufficient number of drill bits of various sizes, sharpened to the gage and tempered suitably for boring the rock attacked. Pipe Lines and Hose. Water must be provided, preferably under pressure in a pipe line, following the air line, with a hose and nozzle so that a jet of water may be fed into the hole bored or to an attachment on the machine. An air hose of the right diameter should be supplied for the size of machine used, IJ-in. hose being the minimum size for a 3i-in machine. Care should be taken that the hose is not so punctured that most of the air escapes before reaching the rock drill, or so old that the rubber lining has perished or curled up, stopping the passage of the air at a right pressure through it. With it there must be a supply of proper fittings and gaskets to make air-tight connections between hose and pipe line, and hose and machine. Pieces of mining fuse cut to the proper length make an efficient packing. These are always available so there is no excuse for leaky connections. Setting Up. The miner who is the happy possessor of all these requisites for efficient work now proceeds to erect his bar in front of the rock face to be bored. Here at once his intelli- gence and experience are called into play. The first requisite for successful work is a firm base from which the rock drill may de- liver its blows on the rock. If the tripod, bar, clamp, and arm do not furnish a rigid support, every rebound from the blow delivered tends to throw the machine out of line; this causes the drill bit on the next blow struck to extend its force diagonally on the sides of the hole instead of on the bottom. In other words, a glancing blow is struck on the side of the hole instead of a true, fair, and direct blow on the bottom (Fig. 79). The hole will be bored rifled; the bit blunted; the machine strained and the drill bit bent or broken; finally the bar itself may become loosened and will fall. The roof and floor of the drive, the foot and hanging wall of stope, or the sides of shaft are now examined for two surfaces as nearly parallel as possible to "rig," or "set up," the bar between them. (See Fig. 80 for good and bad "set-up.") This is not the only consideration. In driving, sinking, or stoping, the bar must OPERATING ROCK DRILLS 107 be placed at the right distance from the face so that when the machine is erected on an arm, set parallel to the face, or on the bar itself, the first or starting bit will be about touching the rock when the piston is drawn out and the machine itself run back in its cradle. This will insure the holes being as far as possible bored the maximum length allowed by the length of the longest FIG. 79. Dotted line shows the effect of excessive vibration of arm and bar. bit, and that the minimum amount of boring will be done with the cylinder run far out of its cradle where it has more play, with less guidance given to the blow. It is very hard to start or pitch a hole with the machine run out, especially if the guides be worn. On the other hand, the machine may be set so close to the face that drill bits are hard to take out of the hole past the chuck and front end of machine; the jig bolt of the machine Wedge* FIG. 80. The left bar cannot slip out. The position at the right is bad a slight jar will tend to make the bar slip out. may have to be loosened every time and the machine swung aside to give enough room. Thus time would be lost. The rock driller has yet perhaps the most important matter to consider before he places his bar in position. He must set it up so that he can bore the maximum number of holes, so placed as to act with the greatest efficiency in breaking the rock from the one rigging up. In this matter experience alone can enable the workman to apply theoretical principles to actual work. 108 ROCK DRILLS Planning Work. A skilled workman studies the whole face. He must use an imagination based on practical knowledge to judge what ground a certain hole will break and how much it will leave for another. Unseen heads and slips in the rock may make his calculation more or less wrong; but can never render it useless. It is the possession of this faculty that makes all the difference between a good and bad workman, especially in hard, tight ground. When a workman is seen time after time, as is only too common in certain fields, putting in his second hole in such a position that the explosion of the first hole breaks all the burden from it, while he always gives it the same allowance of explosive, he is worse than useless as a miner. It must also be remembered that a large piston machine will be at work actually boring only about half its working time. The rest of the time will be taken up setting up machines, moving the machine to a new position on bar or arm, or changing drill bits, etc. Hence the miner plans his work to make the time lost in setting up bear as small a ratio as possible to the total working time. The whole face will be studied and every hole planned out beforehand. The place where each hole will be started or " pitched" is decided upon; its direc- tion and depth considered, and the relative position of the machine, bar and arm, to bore the required holes, is planned out. The bar is then set up in the best situation in regard to the matters mentioned. This right placing of the bar is especially important in stoping narrow reefs in hard and tight ground. In the case of a flat or inclined stope, as shown in Fig. 81, the direction of the holes should be parallel to the free face and placed in the way shown. Here there is only one right position for the bar in order that the holes may be bored against the bar and at the extremity of the arm, alternately. A careless set-up means a spoilt bench; while on a narrower bench, where only two or three holes can be bored to advantage, the bar now would be best set as shown in Fig. 82, so that all holes will be bored from one side of the bar, saving time in turning the arm and machine round the bar. FIG. 81. Showing correct position of the arm for drilling holes parallel to the free face. OPERATING ROCK DRILLS 109 In a winze, raise, or drive, the position of the bar will be about the center of the face unless holes are to be drilled towards some wall or seam. Each case calls for separate consideration, and when a tripod is used the same prin- ciples apply. The object must always be to bore as many holes as possible from one "rig up," to break the ground with the fewest possible number of holes, and to FIG. 82. Position of bar and arm avoid taking up more of the ac- when ^^ a narrow bench - tual working time in rigging up and moving machine than is necessary. Bars. Either single- or double-jack bars are used. Double- jack bars, as before explained, have two tightening screws at one end. These are generally used in flat stopes, raises, and in driving. In some cases the double jack is made separate from the bar itself, two screws being fixed to a block of wood, and a bar used without any screw on it at all. Generally, however, the screws are set in a steel frame fixed to the bar. The double-jack bar is always set so that the line of the jacks and the blocks used are in the direction of boring, otherwise they interfere with the arm and machine when holes are being bored low down. The bar is then placed between the blocks; wedges are driven between blocks and the rock until the bar is slightly wedged. The blocks at each end have their faces kept parallel to the faces of the ends of the bar as far as possible. Where a double-jack bar is used the ends of the double screws are placed in cast-iron feet which distribute the pressure over the face of the blocks. It is a good plan to get these feet bored out and secured together by a piece of chain about 18 in. long before they are sent down the mine. They are thus not so easily lost. The bar is now extended by means of its screw or the screws of the jack. This is done gently at first until its ends grip the block firmly. Then a jack bar, which is a piece of steel of 1J in. or IJ-in diameter, with suitable ends to go into the capstan heads of the screws, is inserted; the screws are pulled and ham- mered round until the bar forms a rigid column between the rock walls or between the timbers of a square set which have been pioperly braced to take the pressure. Miners must be pro- 110 ROCK DRILLS vided with special jack bars for this work, otherwise the shanks of drill bits will be used, thus bending and breaking them. Setting the Machine. Even after the bar has been tightened to its apparent limit, it will require further attention shortly after the machine has started working, and even if locked by the set screw will repay attention during work. The screws on the double jack are locked in position by driving f-in. bars through the capstan heads and against the bar itself, one on either side. Serious accidents have happened owing to operators starting their machine at full power before satisfying themselves that the bar is firm. Where an arm is employed, as it sometimes is in a steep stope, fixed to a horizontal bar, the extra leverage given to the weight and rebound of machine is most severe on the bar. When a vertical bar is used with arms a small collar is now fixed on the bar to support the arm at the hight suitable for boring the first hole. The arm is then placed on the bar and tightened up. The "clamp," "saddle," or "seat" for the machine is then placed in the proper position on the arm and fixed there not too tightly. It now remains to get the machine, which may weigh 300 lb., into its seat in the clamp. To lift this weight to a hight of 3 or 5 ft. and to place it in the clamp would require a great expenditure of brute strength. There are several tricks to avoid this. Where there is head room, as in shaft sinking, a starter drill bit is first placed in the machine and the machine up-ended on its bit until it stands nearly vertically against the bar or arm, which has the clamp fixed with its seat vertical (Fig. 83). The feed-screw of the machine is then run out until the neck and seat of the cradle is raised opposite the seat of the clamp, which has its jig FIG. 83.-AUaching drill to bolt slackened off. It then slips in without effort; the jig-bolt clamp is secured, and using the arm and clamp as a fulcrum, the machine can easily be swung into a horizontal or other position and every- thing tightened up. In other situations a tackle slung from the timber may be used, or in an inclined stope the machine, always with a starter to make handling more easy, is slid from higher up the slope on to the bar (Fig. 84). Oiling. The miner having his machine in the clamp, with OPERATING ROCK DRILLS 111 jig or clamp bolt sufficiently tightened to hold it, will now oil his machine, remembering that a teaspoonful of the best oil put in before every hole is bored, or oftener, is the only proper way to keep the machine working freely, if oil is not supplied auto- matically. The idea of most miners seems to be to give the largest possible doses with the longest possible interval between them. Oil should not be poured down rubber hose. Hose Connections. The hose is first attached to the pipe line, and the cock on the end of pipe turned on a moment to throw any grit out that may have entered since the hose was last in use. The air cock of the machine is then turned off and the hose attached to the spud on the machine. If rubber rings are not available for packing joints, fuse is always at hand and makes a satisfactory packing. No leaks should be allowed at any joint. Starting the Machine. The .clamp and jig bolts are then loosened sufficiently to allow the machine to be placed in position to start the first hole. Before starting holes all bolts are care- fully tightened and the starter secured in the clutch by the bolts or wedges used. With the old-fashioned taper chuck, now rapidly going out of use, no tightening was necessary as the bit tight- ened itself on striking the rock. The piston is pulled out to its full extension, if possible, and the machine fed forward by turn- ing the feed-screw until the bit touches the rock; air is then turned on very gently until the piston reciprocates and the bit begins to strike the rock. The stroke is then shortened by feeding the machine forward and more air turned on. In starting a hole in hard rock full stroke and full air are not used until the hole reaches a depth equal to the stroke of the ma- chine. In soft ground full speed and full stroke can often be used as soon as the operator is certain everything is tight and firm. If the surface to be bored is not at right angles to the drill bit, a true surface may in some cases be cut out with a short gad or pointed chisel or formed by chipping; but in really hard rock it may be necessary to start a hole with the position of the machine differ- ent from that used when boring in the direction required. Sup- pose we have a face like the one shown in plan, Fig. 85, with a hole required at A to go in the direction shown. The bar has 112 ROCK DRILLS to be in position B to bore the rest of holes to best advantage. If an attempt be made to start with machine or the arm against B, to bore the hole in hard ground, the bit will at every stroke glance away in the direc- tion shown, laying severe bending stresses on the piston guides, clamp, and seat of the machine; tending to break the drill bit at the shank and probably merely grooving the rock in a direction along its face away from the machine. Time is thus lost; drill bits are blunted, and the machine stressed for no re- FIG. 85. Starting a suit. Sometimes it is not at once apparent face ^ ^ bUqUe to the be S mner and others, not even those who are supposed to be skilled, that this action is being set up; but the intense vibration set up should at once be noticed and its cause sought. If the machine be placed first in position D, the drill bit will strike the rock squarely and a hole about 4 in. deep can be rapidly bored. The machine is then undamped, moved back to position B; the drill bit has a ledge to start cutting on and the hole can be bored in the direction required. Old Holes. The operator must, before starting any hole, satisfy himself that it is not in the vicinity of any old hole. If it is, the ground will generally be found so broken near it that the new hole will "run away" into the old hole. He must not bore in any old hole unless he has been able to make himself quite certain that there is no possibility of any explosive being in its vicinity. To do this he must be able to see the bottom of the hole and remove all shattered rock. Cases have occurred where an old hole has been apparently free from any portions of unex- ploded powder, yet in drilling in them an explosion has occurred, due to portions being driven into a crack or crevice, or owing to nitroglycerine having leaked out into the broken rock around the hole. Some cases have occurred on the Rand where a white supervisor has first drilled a little in an old hole, and then, satis- fied that there was no danger, has set a native to drill, when, some time later, an explosion has occurred. Drilling in the sockets of old holes is in many countries forbidden by law; but every practical miner knows that cases occur where it is impos- sible to avoid doing this. Any one who drills in an old hole, OPERATING ROCK DRILLS 113 the bottom of which he cannot properly examine, takes his life and the lives of others in his hand. The miner must also be care- ful to see that his hole does not run into any old hole in depth. In some stopes there might be 3 ft. or more of an old hole which had failed to explode with the previous blast; and accidents due to boring into these are only too frequent. Drilling in Hard Ground. Starting and drilling a hole in hard and soft ground are very different matters. I have seen miners from soft rock mines completely at a loss when asked to drill in really hard rock. To drill in such ground requires the closest attention on the part of the miner. In starting the hole constant watch has to be kept that the corners are not worn off the starter bit to such an extent that the hole is of too small a diameter for the next drill to follow; also that none of the fol- lowing sizes become worn away or broken with a like inconvenience. Excessive blunting of the bit has another bad result, as it causes breakage and bending of steel and jars the machine. A drill bit, no matter how hard the ground and how high the air pres- sure, will rarely bend or break as long as it keeps a cutting edge; but as soon as it begins to thump the rock, trouble ensues. An experienced operator boring in hard rock places his hand on the steel while the drill is working, and can tell by the sound and feel if it be excessively blunted or not. For boring hard ground, the steel supplied must be of short following lengths, as a bit cannot be expected to drill more than 12 or 15 in., often much less than that. As soon as the hole is started, if it be in a downward direction, water is splashed into it and enough always kept in it to allow the drill to "spit" or eject the broken fragments in splashes of dilute mud. In soft rock, in both dry and wet holes, the drill may cut faster than it can eject the cuttings. In such cases the stroke should be kept at its longest and part of the air turned off. If the drill steel is not running freely or turning properly, three things may be wrong: The drill may be bent, especially at the shank, thus causing the bit to strike and rub against the sides of the hole. The hole may have run away on some hard or soft head in the rock, causing the steel to bind against one side of the hole. To remedy this the jig and clamp bolt are loosened and the machine moved to one side; if necessary, the arm is also raised or lowered. Ill , ROCK DRILLS In ground with hard heads, or streaks, on which the bit tends to glance off or bind on the bottom of hole, it is sometimes help- ful to place pieces of hard rock or even small pieces of iron in the hole and run the drill with a short stroke for a time; thus the bit gets a chance to establish a landing on the hard ledge and to enter it. When drilling a dry hole with a small elevation, the broken rock tends to accumulate on the bottom of the hole and to force the boring tool upward. In such case it is frequently necessary to lower the arm. The third trouble may be that the ratchet and turning arrange- ments of the drill itself are out of order. This can be ascer- tained generally by turning the chuck by hand. The machine may need only oiling in some cases. With wet holes too much water is as bad as too little, as the splash is thereby reduced too much. In dry holes a constant stream of cuttings should run from the hole. When boring with solid steel the hole should be scraped out fairly often. The air should be turned off until the drill just reciprocates and the machine runs right back on its feed-screw; this helps the travel of the cuttings towards the mouth of hole. Changing Drill Bits. As soon as one drill is run out to its full length, or when it is judged to be blunted, the air is turned off. While the machine is being screwed back the bolts of the chuck are loosened by one of the operators so as to lose as little drilling time as possible. The drill is then withdrawn past the front head and chuck of the machine. When a long drill is being used and the machine is set up close to the face, difficulty may occur in doing this and in inserting a larger one in the hole. To render this easier, the jig bolt of the machine is loosened and the machine swung on one side. With a machine using solid steel, the drilling of holes in a true horizontal direction or a few degrees above must, if possible, be avoided, as it is a tedious and heart- breaking work. Special steel such as that shown in Fig. 107 should be used. Blasting. The tendency of the average miner is to drill too few holes for the work required in breaking the face in develop- ment. This causes bad work, loss of time, and disappointment. It is only the expert who understands something of the theory of blasting who can begin to economize in drilling and in the use of powder. The beginner does well to put in an extra hole in all doubtful cases. All the factors to be considered in the OPERATING ROCK DRILLS 115 work of breaking ground can be best learned by one who has to start with some knowledge of the theory of the subject: but this knowledge must be supplemented by plenty of actual practical experience. When all necessary holes have been drilled, the machine, arm, and bar are taken down and placed in a place of safety. In doing this, care must be exercised. The detonation of modern high explosives releases an immense volume of gas, and the blast from a heavily charged hole, or holes forming a cut, is most powerful and does damage only to be believed by those who have seen the effects wrought. Often a machine or gear may be moved by the blast of a shot going off first, or have its covering of rocks or planks removed and then be damaged by rocks from a second shot. After removing machine and gear, the holes are cleared of mud and water. This may be done by a blow pipe, which in min- ing consists of a suitable length of f-in. or 1-in. pipe, having a right-angle bend about 18 in. long, on one end, to serve as a handle. The end of the pipe on this bend is provided with a spud to attach it to the air hose. Holes may also be cleaned out in the manner described in the section on the use of machines in shaft sinking, or by the use of a pipe having a ball valve at the bottom, or even by a proper sized wooden rammer. With high explosives, a little water or loose mud in a hole is rather an advantage, as it displaces any air between the cartridges and acts as tamping. Starting a Steam Drill. When working with steam instead of compressed air several precautions have to be taken into con- sideration. A little steam must be admitted and then shut off; the piston worked by hand a few times to insure that all the parts of machine are evenly heated and expanded. The side rods are first loosened, and only tightened up when the machine is warmed. These rods should never be made too tight as they are liable to break at any time if too much stress is put upon them. It is generally necessary to screw a special pipe into the exhaust to take the exhaust stream far enough away so that it will not impede the workmen. The drill is not oiled until the condensed steam in pipes and passages has been blown out. Working a Drill with a Tripod. A drill is worked on a tripod where there are no side walls or roof available to set up a bar. It is often useful underground in cutting large chambers, sinking 116 ROCK DRILLS shafts, and in underhand stopes . It is, however, chiefly employed in quarries and railway cuttings. Before erecting the tripod, all loose earth and broken rock must be removed. If there is much of this work to do it will pay to employ a special gang to prepare the blasting spots. The place having been chosen for the proposed hole, the tripod is set up. Small holes or hitches are cut in the rock to prevent the legs spreading. Where the ground is of such a character that the legs gradually settle through it, wooden blocks may be employed, having washers or iron plates with holes punched in them to form a holding or socket for the point of the leg. When the legs are fixed, the saddle is placed as nearly horizontal as possible, tightened up and the weights put in position. The machine is put in the clamp or saddle, fastened, and is ready for work. The running of the machine, i.e., the feeding of it forward to give the correct length of stroke, can be learned only by practice. If the handle is not turned quickly enough to feed the cylinder forward, as the drill bits cut the rock, the piston strikes on the cylinder end, and if allowed to do this often, or too violently, a side rod will be broken. The short stroke is used when meeting with a head or when the bit shows tendency to stick, and in start- ing a hole. The beginner must not be distressed if the drill sticks occasionally; it is only repeated sticking and refusal to rotate which indicate that something is wrong. Most makes of drills will stick occasionally. A blow from a hammer, delivered on the drill, near the hole, will in such cases start the drill .off again. Hints for the Operator. The operator should make himself acquainted with the design and construction of each part of the machine used by him; only in this way can he intelligently work it and, if necessary, save time by doing small repairs and replace- ments himself, on the spot. This knowledge may be gained partly from books, but it can always be acquired by a few hours spent in the company of the mechanic who has charge of the repairs to machines on any mine or undertaking. A little care in oiling frequently, and in stopping both air chest and exhaust openings with a piece of cloth or waste as soon as work is finished, will amply repay themselves, especially if work is being performed on contract. If the valve sticks, do OPERATING ROCK DRILLS 117 not strike the valve chest, but spend a few minutes in taking it off carefully and examine it for grit or other things in the air chest, air ports, or auxiliary valve or valves. Above everything the operator should himself take an intelli- gent interest in the condition of his machine. Even the best system of inspection, which is usually absent, will not take the place of a man who takes a pride in keeping his tools and machine in good order. Watch, above all, for worn bushing in your chuck, and for bent jumpers, as they mean doing your work twice over. If the piston starts knocking the back plate, see that the fitter re-bores the valve chest. If you work on contract, tip the rock-drill fitter and the blacksmith; they will then see that you get your machines repaired; that you get the drills you need, and the lengths you require. Remember also that it is as much against your interest as the company's to work with a leaking air hose or connections. An inch hose does not, at best, supply the air it should to a 3j-in. machine. Every cubic foot of air loss in leakage means so many less blows struck per minute. Old miners, when boring in hard ground, having lost the gage of their hole and cannot get another bit to follow, will some- times swing the machine out of position and explode a small charge of gelatine in the hole to enlarge it. The operator can do this if he likes, but he must remember that the risk is far too great, and in the long run such practices are paid for by men's lives. The miner must take risks; but this is not a fair one. Many accidents have occurred through trying to force dynamite or blasting gelatine into a hole slightly too small, owing to excess- ive wear on the bits used. The miner is anxious not to lose the result of his shift's work and he uses more and more force until one day an explosion occurs. In such a case, if mod- erate pressure on the end of a wooden tamping rod will not dislodge the cartridge, put in about half a cupful of water, allowing it to stand for a few minutes. In nine cases out of ten it will be found that it has soaked the paper enclosing the cart- ridge and lubricated the sides of the hole so that the paper tears and gives; the cartridge will then go home easily. If it will not go right in the water soaking past, the water forms a tamping instead of the air, and the force of the blast is not lost to such a great extent. 118 ROCK DRILLS LUBRICATING DEVICES FOR ROCK DRILLS There is great need for a thoroughly satisfactory automatic lubricator for piston rock drills. In the Sergeant drills there is, in the valve chest, a spring loaded ball valve through which the machine may be oiled when the air is turned off. On other ma- chines there are holes in valve chest and in ratchet box, closed by studs. What is required is a lubricator that is part of the ma- chine itself, yet not taking up too much room, and at the same time strong enough so that it might not be damaged. Such a lubricator must feed oil in small charges over regular intervals while the machine is at work. On the Chicago Giant drill there FIG. 86. Lubricator for air drill. is a device shown (Fig. 9) attached to valve chest; but with what success it has met I do not know. The same company also manu- facture the oiler shown in Fig. 86, for attachment to air hose. The Chicago Pneumatic Tool Company, Chicago, Illinois, is supplying an independent rock-drill oiler which may be attached to the hose connections by using a standard nipple and tee joint. The upper part of the oiler body is made to form a reservoir for the oil, and is of sufficient capacity to hold from 50 to 60 oilings, which are measured out to the drill by turning a star wheel. One filling of the reservoir chamber will last a day's run. The device is constructed so that at each quarter turn of the star wheel a definite quantity of oil is delivered and passes into the drill with the operating fluid. OPERATING ROCK DRILLS 119 The positions of the arms on the star wheel and the measur- ing pockets in oiler coincide, and provision is made for automati- cally latching at each quarter turn of the star wheel. A strainer in the mouth of the filling chamber prevents dust- and grit from being introduced with the oil. This strainer is easily removed for cleaning . The addition of one teaspoonful of flake graphite to each pint of oil will be found to be very beneficial. The graphite and oil should be mixed as thoroughly as possible before placing in the oiler. George Leyner had a similar device also for hammer drills. The objections to them are that oil is not good for the rubber linings of the hose; that, with unskilled or careless labor, the ap- paratus may be left on the pipe line and blasted, or be damaged by trucks or shovelers. George Leyner claims, now, to have developed an efficient oiler for his large hammer drill. The automatic oiler for the Gordon drill may also be noted. In Stephens Climax drill lubrication has been attempted by means of a stiff lubricant and a lubricator like Staffaeur's. Claude T. Rice 1 thus describes the Western lubricating valve, Fig. 87: "There is great need for an efficient lubricator, continuous or intermittent, attached to the drill or, better still, incorporated in its design. As the speed of movement and number of strokes increases as the use of hammer drills increases, the need of a con- tinuous lubricator or oiler also becomes greater. It seems to me that this is the direction for immediate advance in drilling practice rather than ultra-refinements in interior design of the valves, ports, and cylinders. It appears that in view of this need a useful adjunct to the machine drill will be found in the Western lubricating valve, which I do not hesitate to describe, although I have never seen it in operation. I am informed that this valve has been used by the Granite Gold Mining Company, at Victor, Colorado, for more than six months, and D. L. McCarthy, the superintendent, says that it has proved satisfactory in every respect; that the drill is kept lubricated under all conditions; and that, while the drill is running, the valve remains in whatever position that it is turned by the machineman, which is a strong recommendation for the use of this valve on one-man machines. "It is an internal-pressure valve, conical in shape, which fits 1 Eng. and Min. Journ., April 11, 1908. 120 ROCK DRILLS into a barrel that is surrounded by the oil reservoir. The valve plug and the barrel have ports which register when the valve is closed, and air is then admitted to the top of the oil reservoir. FIG. 87. Western lubricating valve mounted on a small piston drill. Also section of same. Another duct leads from the bottom to a groove in the valve plug. This groove in the plug, when the valve is opened, connects with the main air-way of the valve at both its ends, so that the oil is forced out into the air-way, and is then carried by the air into the drill. The opening of the valve clqses the connection of the main air-way and the groove with the oil reservoir. The OPERATING ROCK DRILLS 121 valve thus becomes an intermittent lubricator, which oils the machine every time that the air is turned on and off. As the air is shut off frequently in drilling in order to change drills, to clean out the hole, etc., lubrication is frequent enough to be effi- cient. "This valve has also other merits, for it has two swivel joints, one where the hose is connected, and one where the valve is con- nected to the drill." I have tried this valve in South Africa, but find, for work in a drift where two machines are in use on one bar, with unskilled labor, that it projects too much from the machine. Besides this, all drills in use here lead the hose directly from the rear of the valve chest, as seen in the Holman drill, and not from the side. The Seargent air chest is also of a later type than any shown in catalogues. I believe, however, this valve has been modified to suit these conditions, and it appears to be in many ways an ideal device, also applicable to hammer drills. VI PISTON DRILLS DESIGNED TO USE AIR EXPANSIVELY IT has been shown, mechanically, that the piston drill is a most uneconomical machine. The air is exhausted into the atmosphere at full pressure, and where 15 to 30 h.p. may be em- ployed at the steam cylinders of an air compressor, only about 1.7 h.p. is usefully employed cutting rock. Thus the cost of generating compressed air to work one rock drill may be an impor- tant item of cost. On the Rand it varies from 6s. to 12s. per 10-hour shift. It is obvious that a reduction of 50 per cent, in air consumption would be an important saving. It has already been emphasized that this item is a comparatively small one in the total daily expenses of running the drill. In considering schemes for economizing air, the following questions present themselves for answer: Will the drilling speed be adversely affected? Will moisture in the air on its expansion choke the valve ports with ice, causing "freeze-ups" and stop the drill's working? In practice is the economy of air a real one, or will it soon disappear due to increased leakage, wear, and tear affecting the valve motion? Will extra cost of supervision and repairs amount, in the long run, to a sum equal to the alleged saving of air? Let us take two cases to illustrate what different conditions may mean. Mine No. 1 is worked by expensive labor. Compressed air is generated by water power, and is consequently cheap. The vein is narrow and rich in hard ground. Owing to various cir- cumstances a large treatment plant requiring a maximum output to supply it is not installed. The number of development faces on which rock drills can be employed is limited, and the present rock drills are working at the highest economic air pressure. Will it pay in this instance to install a rock drill consuming 25 per cent, less air, but having a drilling speed 10 per cent, less? It is obvious that in such a case it would not be good policy to make any change, as what would be saved in money spent in 122 PISTON DRILLS TO USE AIR EXPANSIVELY 123 generating compressed air would be more than that lost in other directions. At mine No. 2 a compressor is driven by steam generated at a high cost from expensive fuel. This plant is being worked above its real capacity, and the air pressure has fallen below the economic limit. The prospects of the mine do not allow of further-outlay in compressor plant; improvements have greatly raised the capacity of the treatment plant; labor is scarce and numerous faces are available for machines; running costs and labor are not high. The effect of installing machines having a 25 per cent, lower air consumption with a 10 per cent, less drilling speed would be that either 25 per cent, more machines could be put to work, or that the air pressure could be raised all over the mine, enabling these machines to attain an equal or greater drilling speed than those formerly employed. With 25 per cent, more machines the treat- ment plant could be kept fully supplied with rock and costs be thus lowered. The following are examples of drills constructed to work using air expansively. Optimus Compound Rock Drill. 1 This machine does not drill as rapidly as ordinary machines. Owing to the long exhaust ports it is liable to freeze up. The Optimus compound rock drill is manufactured by Schram, Harker & Company of London, and is shown in Fig. 88. The cylinder, a, has a wider portion, a', and correspondingly the pis- ton, c, has an enlargement, g. The air enters through the port, 6, into cylinder a, whilst cylinder a' is in communication with the air ports m and h. As the piston moves forward past the port 6, air enters the valve cylinder r, acts there on a larger area than at I, and moves the valve piston, c, forward, thereby cutting off communication with a, and making communication between a and a'. The air now acts on the larger area of g, and thereby moves the piston back, past the port 6, when the cylinder, r, is placed in communication with the atmosphere through ports b and h, and the valve, /, is moved back. The Slugger drill and the Stephens Climax Imperial drill have been already described. The Imperial drill working on the Witwatersrand gold fields cuts off air at half stroke forward. 1 Drawing and description, taken from pp. 79 and 80, Handbook of Blasting, Oscar Gutteman. 124 ROCK DRILLS I 8 \ PISTON DRILLS TO USE AIR EXPANSIVELY 125 Konomax Drill. A recent and novel design of drill is the Konomax, Fig. 89. The piston of the Konomax drill consists of two portions, AI and A 2 , working in a corresponding cylinder. The effective area of the face A 3 being double that of the face A 4 . The effective area of A^ is much greater than that of other piston drills of similar diameter, as passages are made past the rifle bar, so that the air pressure acts effectively on the face A 4 . This cannot be done with ordinary types, hence this machine has a somewhat more powerful blow for the same piston diameter. The air space of the smaller cylinder, B', is in constant communication with the air supply in the hose pipe through the inlet D. The supply of air to the forepart of the large cylinder air space B 2 is taken from FIG. 89. Konomax drill. B f , and is controlled by a piston-spool valve P, worked by air pressure to effect the following cycles. The piston being in the position shown, live air is admitted from B' to the front of the piston, and acting on the face A s (the area of which is double that of A 4 ) starts to drive this piston back against the less pressure on the face A 4 . At a predetermined point in the back stroke, the valve cuts this supply off, and the air is allowed to expand. This point is generally at half stroke, giving an expansion of 1:2. As expansion occurs, the pressure on the face A 3 is diminished until it is only equal to that on A. This pressure on A 4 is then able to overcome the momentum of the piston and bring it to rest. At this instant the air is exhausted from the front end of the piston by the movement of the valve, and the piston is driven forward and makes a free stroke. Air is again supplied to A s and the cycle repeated. 126 ROCK DRILLS Atmospheric pressure is maintained between the piston rings by means of an aperture A in the cylinder walls. This is in connection with the arrangement for moving the valve. The machine thus exhausts air once in the cycle, and that upon the backward stroke, instead of twice, as in the ordinary machine. The air is transferred from B' to drive the cylinder back. The pressure is always maintained behind the rear end. This allows the valve P to be placed right over the front end of the cylinder, thus making the exhaust port short and straight. There is thus no air lost in clearance spaces. The cold, exhausted, and expanded air having a direct exhaust, freezing up (which would otherwise occur) is obviated. Advantages and Disadvantages. With the ordinary 3-in. piston drill, piston area 7 sq. in., assuming a stroke of 6 in., the air consumption on the front stroke amounts to 42 cu. in. But on the back stroke the piston area is diminished by the area of the 1-2-in. piston-rod and so is only 5J sq. in. Therefore the air consumed on the back stroke amounts to 31.5 cu. in. The area of the valve ports and clearance is 18 X 1 X i in., or 9 cu. in. Therefore th the distance from the center of the hole increases the amount of rock to be cut increases as the square of the radius, hence the out- side portions of the cutting edges have most to do. For piston rock drills the cutting faces of the chisel should, for FIG. hard ground, make an angle of about 90 101. Chisel-bit of grooved steel. 1 y\~ FIG. 102. Drill bits. with each other. The edge should be straight, not convex, but if anything a lit- tle concave. The shoulders should be well brought up with plenty of metal behind them, and the gage should be most carefully kept. E. K. Judd in the Engineering and Mining Journal, Dec. 18, '09, discusses the question wheth- er drill bits should be given a concave or convex shape. FIG. 103. Types of drills forged by the Ward drill sharpening machine. FIGS. 104 and 105. Holman Brothers drill bits. 168 ROCK DRILLS He argues that as the ends of the bits have most rock to exca- vate that the center of the bit should be advanced giving a convex shape. Chisel bits, he argues, often strike on a corner owing to the drill being not "true" in the hole, which is another reason they should be given a convex shape. The bit shown in Fig. 101 is bad, as the notch in center weakens the cutting edge and the rounded shoulders are not an ad- vantage. The shape of the Anderson detachable bit, as shown in Fig. 108 and described, was based on a number of experiments and is worthy of study. Special Steel for Drilling Dry Up-Holes. In drilling dry holes at an angle of less than 25 from the horizontal, difficulty is encountered in getting broken rock fragments away from the face and out of the hole. A thin wire scraper is put in sometimes and worked while the bit is drilling, but this does not get the stuff away from the face of hole, consequently the bit does much work twice over. The Eureka Drill Steel Company have in- troduced the steel shown in Fig. 106, having lugs between the ribs which pull out the broken cuttings. I have recently introduced twisted drill steel (Fig. 107) to act as a spiral conveyor for the same purpose. In octagonal steel a special groove is rolled into the steel. These devices, which are patented, are simple, inexpensive, and reduce the time of boring flat-holes or up-holes not steeply inclined. DETACHABLE BITS The troubles incidental with moving the large quantity of drill steel in and out of the mine to be sharpened, and the losses in efficiency due to bits having wings of unequal length, or being bent, has led to inventors seeking to perfect some form of detachable bit. A bit is needed that can be made to exact size and shape, which can be attached to a permanent shank and taken off when blunted. These devices DRILL STEEL AND DRILL BITS 169 have failed in the past owing to the difficulty of obtaining a con- nection between shank and head that did not detach itself at the wrong time at the bottom of the hole. The detachable bits proved expensive and were frequently left in the ore, causing trouble in the reduction works. Major Derby had a detachable bit with a FIG. 107. Twisted drill steel for removing broken rock. system of water injection working on the Hell's Gate works, New York, for six months with great success. The rock drill manu- facturers who bought the patent never brought it before the public. The Anderson Detachable Drill. The Anderson bit is shown in Fig. 108. A is the hollow shaft or shank, B is detachable bit; C is front view of bit, showing the hole for the insertion of the wire, and three cutting edges, set at angles of about 90, 130, and 170 ROCK DRILLS 140 with each other; D is a piano wire with f-in. left-handed screw and bolt. The end of the wire is countersunk in the bit; G is guide faces, or shoulders cut in the form of a circle; they are f in. deep, and have no taper toward the back. When using this bit with the ordinary type of chuck in stand- ard machines, the chuck bushing was removed and a recess cut back for the projecting bolt at the end of the shank. The shank was thus supported by a circular rim. One effect of increasing the diameter of the shank was at once noticed. It was much more easily tightened up than the ordinary sized shank and did not work loose easily. Wear on the chuck was so reduced that one was used for several weeks without sign of wear. For the use of this device a special chuck would be necessary. When the bit is blunted another longer length is put in machine, the rod un- screwed, the old bit taken off, and replaced by a new one. Owing -2 '-6*- A according to Length FIG. 108. Anderson detachable bit. to the central hole these bits can be strung on a string or wire for carrying about. The worn bits can be also threaded up, so the danger of them getting mixed with the ore will be diminished. Mr. Anderson states that on the May Consolidated, 13 holes 5J ft. deep were drilled in 7 hr. 40 min., using 52 bits or 4 to a hole, against 5 or 6 with ordinary bits. Regarding his bit as a means of increasing speed of drilling, Mr. Anderson states that increased efficiency is due to the following factors: (a) No waiting for drill steel. (6) Never using a bit twice. (c) Drills always being of standard lengths. (d) The gage or diameters being accurate. (e) All bits being interchangeable (that is, the starting bit could be fixed to the finishing shank or vice versa). ({) The cutting edges being so arranged that they always form a round hole. (g) The end faces of the cutting edges form segments of the same circle and are of such a size that they wear evenly and without friction. DRILL STEEL AND DRILL BITS 171 (h) Ample clearance is allowed. (i) The permanent drill shanks are made much heavier than the present steel, and are capable of properly delivering the blow without loss of energy due to bending. (j) The combination of an improved arrangement of cutting edges with the increased strength of shank enable holes to be collared at angles which the present steel cannot attempt. (k) Due to the precise gaging of the bits, holes can be drilled starting with a less diameter of bit and finishing larger than with the present steel. The effect of the strong shank is to deliver a heavier blow, as the minimum of energy is lost in the give of the shank. This condition naturally causes more wear on the cutting edges. Mr. Anderson lays more importance on the arrangement of the cutting edges, and especially on the fact of the bit forming a round hole and having correct guiding faces which work without friction in that hole and keep the bit concentric with the axis of the piston- rod, than on the degree of sharpness retained by the chisel edges. In fact, the drill that has been binding on the side of the hole keeps its edge better than one which has worked freely. He also remarks that the usual form of starter in practice was 2J in. to 2f in. across the cutting edges, while the side or guiding faces of the drill were about 1J to 1| in., the cutting edges being forged either by hand or machine. These systems of dressing the bit are not accurate, the principal fault being that each blade is different in length. If there is only a difference of jV in., one guiding face is sure to be out of action. It is evident he says, that the bit or cutting head should be exact to T&TF part of an inch, and that on striking the bottom of the hole each edge should carry its equal share of the shock and each guiding face its share of side pressure. The present drill steel is tapered down to If in. where attached to the chuck, and the piston-rod, as a rule, is 2 in.; but he has noticed a good many much smaller in diam- eter than If in. The proportion between If in. and If in. is entirely wrong to transmit the heavy blow necessary for cutting hard rocks. In watching rock drills at work any one with a mechanical ear will suffer from the harsh sound which is the result of the wrong design of drill steel. The continual jar and shake due to the want of equilibrium cause fractures of the piston- rod and the drill steel. 172 ROCK DRILLS It is left to the care of the blacksmith to gage the reduction in diameter of the drills, and that is the principal reason why they start the hole 2f in. and finish up If in. As the rate of drilling is proportional to the volume excavated there would be much saving if you could start the hole with less diameter. With the Anderson detachable bit, the drill steel is made If in., where FIG. 109. Leyner patent starter. attached to the chuck. It is hardened and tapered down to the cutting head. There is just enough guiding face on the drill bit to keep the whole true, and the guiding face wears away without any binding against the side of the hole. The bit is never tight in the hole. The guiding faces are also segments of the same circle, the bit being made in dies, and, therefore, being perfectly accurate. The bit is also exactly true with the piston- FIG. 110. Correct drill bits (Leyner). rod, and it is impossible for the bit to work out of line without pulling the piston-rod with it. There is no scoring in starting a hole, and the shock that is delivered through the piston-rod is transmitted to the face of the bit and is not absorbed in friction on the side faces or in the loss of energy due to want of equilib- rium on the cutting edges. This bit is not yet at work on a large scale. Experiments DRILL STEEL AND DRILL BITS 173 100 ob- at several mines showed an increased boring rate of from 30 to per cent. A certain amount of trouble was experienced in taining bits of the exact temper and hardness required, as in the cases noted of anvil blocks for hammer drills. Some bits blunt very rapidly and in hard ground the shaft, near the bit, has a tremendous stress laid upon it by the rigidity of the shank. It is liable to bend or break. It is stated that no trouble has been occasioned by the breaking of the piano wire, and that no bits become detached. The problem has its financial side. The weight of steel discarded is very large and it cannot often be sold as waste metal to advantage. It has, however, been proved that there is much progress to be made in correctly designing and sharpening bits for pis- ton drills. Already marked economics have been shown by increasing the diameter of the shanks of ordinary steels from 1J to 1-J- in. The benefits to be derived from accurate machine sharpening are here again emphasized. BITS FOR HAMMER DRILLS Leyner Drill. Figs. 109 and 110 show the bits recommended for Leyner drills. The shanks have lugs on them for turning the drill. Murphy Drill. Fig. Ill shows bits used in the Murphy drill. A col- lar is forged on the shank as shown to prevent the drill entering the cylinder of machine. Hardscogg Drill. Fig. 112 shows bits used in the Hardscogg Wonder machine: (1) Hexagon hol- low; (5) hexagon solid; (13) special for soft rock; (14) hexagon 174 ROCK DRILLS hollow 8-point; (15) special round hollow for plug holes. Bits for all Wonder drills except No. 18 and No. 19 are made from f-in. hexagon material, while for the No. 18 and No. 19 drills the lengths up to 3 ft. are made from the 1-in. hexagon material. They are all fitted with the 6-point cutting surface, which in ordinary ground gives better satisfaction than any other shape. There are some cases, however, where the rock is very soft, that the 8-point or the No. 13 style bit will give better service, but the 6-point is supplied in every case where the other shapes are not specially ordered. No. 1. NO. 0. No. 13. No. 14. No. 15. FIG. 112. Hardscogg wonder drills. Waugh Drill. The type of bit used on this drill is shown in Fig. 113, and the makers recommend the following: "Sets of steel ordered from us are bitted and the shank ends ground off smooth and hardened. When customers wish to make up their own steel, we desire to emphazise the importance of having the shank ends ground off smooth and hardened. This will present a smooth surface for the tappet to strike against and the life of this part will be very materially prolonged. The shank ends should be hardened so that they will not upset or batter, and stick in the chuck. They should not be tempered, however, as they will have a tendency to sliver on the edges and leave only a small surface for the tappet to strike. DRILL STEEL AND DRILL BITS 175 ''Hexagon hollow steel for the drifters and sinkers should be prepared in the same way as the four-groove steel for the stopers, as far as the shank ends are concerned. The bits on hexa- gon steel should be 4-point, and when forming the bit the hole in the center can be allowed to come together, and instead of keeping the hole in the drill steel open the entire length, a hole should be punched between two lips of the bit about f in. back from the face, so as to connect with the hole in the center of the steel'. Experience has shown us that the hole for the air and water to come out will be less likely to become clogged if kept back from the face of the bit, and for the purpose of keeping the cut- tings back from the bottom of the hole will be equally as efficient." FIG. 113. Waugh drills. Latest Cripple Creek Practice. C. E. Wolcott says that: "At present there are three main types of bit used with these machines in the Cripple Creek district. These are illustrated in Nos. 1, 2, and 3, Fig. 114. The first is commonly called the bull bit and is made either as illustrated or with the sides slightly drawn in below the points bb in the side view. In either case it should be so made that the distance aa is greater than the dis- tance bb (plan view). The same point should be observed in making the cross-bit, No. 2. By observing this condition the edges ab and be act as reamers to cut away the outer circumference of the hole. If these edges become rounded, it becomes difficult to turn the bit in the hole. This difficulty is overcome, in the third style of bit illustrated, by rounding off the cutting edges as 176 ROCK DRILLS shown. The degree of curvature may vary appreciably, but is usually not very great. This bit has been in use a comparatively short time but has given great satisfaction wherever used. This bit not only cuts rapidly but it also gives less trouble in turning than either of the others illustrated, and will cross slips more readily. It is possible to use this bit in a hole that has become reamed when drilling with a square bit, and with but little diffi- FIG. 114. Various shapes of bits used with air hammer drills. culty to cut out the reams and start the drill to turning again. This is also true regarding a hole reamed by a bull bit." Stephens Drill. The latest hammer drill manufactured by this Cornwall company employs tapered and collared shanks, with double chisel bits, shown in Fig. 115. Sharpening Machines for Hammer Drills. Several manufacturers, as Leyner, Fair- banks-Morse, Hardscogg, Ingersoll-Sergeant Company, supply light sharpening machines worked by pneumatic hammers for use with hammer-drill steel. Hollow Steel. Good quality hollow steel is of recent manu- facture only. At first short pieces of solid steel were bored out and welded on to iron tubular shanks, but welds are always a source of weakness. The No. 9 Leyner still uses welded bits owing to the special shape of shank required. Hollow steel is FIG. 115. Stephens double chisel drill. DRILL STEEL AND DRILL BITS 177 now made by drawing out hollow billets and is mostly rolled. Most of the hollow steel is of high carbon, 0.45 per cent, or over. Some contains manganese. It requires careful tempering. T V per cent Vanadium in steel has a remarkable effect in strengthening and toughening drill steel. Hollow steel can be welded to pre- serve the central hollow core by greatly enlarging the core-before the weld is hammered. EXPLOSIVES AND THEIR USE THIS is not a handbook of explosives so I shall give only a few particulars regarding the types of powder in most common use in mining, with notes on their employment and on the theory of blasting. The chief explosives in use in metalliferous mines are (1) Low explosives, as ordinary gunpowder and compressed gunpowder; (2) High explosives, as dynamite, gelignite, gelatine dynamite, blasting gelatine, tonite or cotton powder, Atlas pow- der, Hercules powder, giant powder, forcite, rack a rock, Judson powder and jovite. Gunpowder. The composition varies from 65 to 75 per cent, niter, 10 to 15 per cent, sulphur, and 15 to 20 per cent, charcoal. It is sometimes used in very soft or loose ground, where a heaving or rending effect is required and where the rock is so full of cracks that the gases of a high explosive, being more rapidly evolved, would escape before doing their work. It is sometimes used in large blasts, mixed with high explosives for the same reason. HIGH EXPLOSIVES Dynamite. A mixture of various proportions of nitroglycer- ine with some porous and more or less inert substance that will absorb the liquid. Keiselguhr or infusorial earth was first em- ployed by Nobel, the inventor. Most of the powders used in America are dynamites with a low percentage of nitroglycerine, having absorbents calculated to increase the force of the explosion of the powder. In America 40 per cent, dynamite is commonly used in mining fairly hard ground. It consists of 40 per cent, nitroglycerine, 47.25 per cent, sodium nitrate, 11.75 per cent, wood pulp, and 1 per cent, calcium carbonate. The composition of these explosives is given because the rock driller, to use them safely and economically, must know something of their con- stituents and properties. Gelignite. This consists of nitroglycerine and nitrocellulose 178 EXPLOSIVES AND THEIR USE 179 with a certain proportion of nitrate of potash and wood meal. It is more plastic than dynamite and 12 per cent, more powerful. Gelatine Dynamite. This explosive consists of 80 per cent, nitrocellulose or blasting gelatine, with a certain proportion of nitrate of potash. It is considered 25 per cent, stronger than No. 1 dynamite. Blasting Gelatine. It is composed of 93 per cent, nitroglycer- ine, solidified by means of collodion. It is a solid plastic jelly. It is the explosive par-excellence for mining work in the hardest and strongest rocks. It explodes if heated to 400 F. It freezes at 35 to 40 F., and is very sensitive to shock when frozen. Water is not absorbed, nor does it leak nitroglycerine; hence can be used safely under water. For cite. This is really a thin blasting gelatine mixed with nitrate of soda, and coated with molten sulphur and wood tar. It contains 1 per cent, wood pulp. Nitroglycerine will leak out. Atlas Powder. The composition is, nitroglycerine 75 per cent., wood fiber 21 per cent., nitrate of soda 2 per cent., and 2 to 3 per cent, carbonate of manganese. It is made in grades containing from 20 to 75 per cent nitroglycerine. Hercules Powder. The highest grade contains 75 per cent, nitroglycerine, 20 per cent carbonate of manganese, 2.1 per cent, nitrate of soda, 1.05 per cent, chlorate of potash, and 1 per cent, white sugar. The carbonate of manganese is the absorbent. Judson Powder. The composition varies in some cases 5 to 15 per cent. Nitroglycerine is added to a mixture of 15 parts sulphur, 3 parts resin, 2 parts asphalt, 70 parts nitrate of soda, 10 parts anthracite coal. In all these explosives nitroglycerine is the important constituent. Tonite. This is a nitrated guncotton. Barium nitrate is generally used. Tonite is not plastic and is of equal strength to dynamite No. 1. It contains no nitroglycerine. Rack-a-Rock. It consists of 79 parts chlorate of potash and 21 parts of mono-nitrobenzine, which are mixed just before use. Nitroglycerine is not a constituent in this powder. Nitroglycerine. This is a very high power explosive made by the action of concentrated nitric acid on glycerine. It is a clear oily liquid with a specific gravity of 1.6. When applied to the skin it produces headache and sickness; some people being more susceptible than others. Hence dynamite and like explosives 180 ROCK DRILLS should not be handled too much with bare fingers. Over 10 grains acts as a fatal poison if swallowed. It may be heated to 100 C. without explosion, but is then very sensitive to shock. At 257 C. it detonates. One volume of nitroglycerine produces 1200 to 1500 volumes of gas, which is expanded eight times by the heat of combustion. A sudden blow will evolve enough heat to detonate it; but only that portion struck. If frozen, however, the detonation is distributed over all the mass. The direct rays of the sun decompose nitroglycerine into an unstable, easily exploded substance. The burning of nitroglycerine or its incom- plete detonation set free gases that are poisonous to the human system. The most important of these are carbon monoxide and nitrous acid. The gases produce symptoms and effects known among miners as "gasing." American miners call blasts that produce a large proportion of such gases, 'stinkers.' 1 Nitro- glycerine will, under water, exude from dynamites, but not from blasting gelatine. Many of the various nitrates are deliquescent; i.e., absorb moisture from the air and are soluble in water. Explosives con- taining these should be stored in dry places and not used if they show on the surface a frosted appearance, which shows that this action has begun. Nitroglycerine and the explosives containing it freezes at 42 to 46 F. When frozen, dynamite cannot be exploded by the ordinary detonators. Blasting gelatine is not properly detonated while frozen. Thawing Explosives. Numerous accidents occur through doing this improperly. Nitroglycerine, especially in the higher grades of dynamite, tends to exude from its "dope," or absolvent, when subject to heat in the presence of water. Frozen dynamite and blasting gelatine are also sensitive to friction. Cutting or breaking a cartridge while frozen is dangerous. On the other hand, should nitroglycerine exude under heat it is most sensitive to shock and even a drop falling will often explode. Leaking dynamite is shown by the oily appearance of the wrapper, or by drops forming. If the wrapper is discolored by greenish stains it shows that the nitroglycerine has begun to decompose and it should be at once destroyed. Frosted dynamite will almost cer- tainly leak and should be carefully removed and destroyed by burning in a safe place. It is best to lay the sticks touching one another in a row and light the end one. Since both cold and hot EXPLOSIVES AND THEIR USE 181 water tend to displace the nitroglycerine in dynamite, cartridges should never be softened by the use of steam or hot water. Nor should they be subjected to a dry heat that can possibly rise above 212 F. For this reason, thawing by placing near a fire, boiler, stove, or other such place is unsafe. Dynamite may be thawed by being placed in a room or box heated by hot water pipes. Small amounts might be thawed by being placed in a room or box with a can of hot water placed in with them at a safe distance. The safest way of thawing is, perhaps, to place a box, containing the dynamite, in the center of a heap of green manure, where an FIG. 116. Dynamite stone house. even heat is maintained. Since the contraction and expansion of freezing and thawing itself tends to displace nitroglycerine all cartridges thawed should be examined before use. Where elec- tric power is available, suitable thawing boxes heated by the elec- tric current and having the heat under complete control can be easily constructed by any electrician. Dynamite is sold in sticks or cartridges. A No. 1 dynamite stick is 1} in. in diameter. 8 in. long, and weighs^0.5 to 0.6 Ib. Dynamite Storehouse. In a recent bulletin of the Societe de PIndustrie Minerale, Gaston Beuret describes a rather elaborate structure, Fig. 116, for the storage of explosives that was built in connection with shaft development at Sancy. Its design was 182 ROCK DRILLS fully approved by the administration of mines. It is 150 m. from the nearest building. The chamber was built of the best ashlar masonry, after the plan shown in the accompanying drawing, and was then covered at least 4 m. deep with screened earth, with all the small stones re- moved. Opposite the entrance was built a smaller pile of earth with a masonry niche designed to catch and render harmless any ma- terials thrown out of the entrance passage in case of an explosion. A chimney extends from the level of the chamber floor to a height of 2 m. above the top of the dirt pile. The flue connecting the interior of the chamber with this chimney slopes downward so as to prevent the admission of any burning or inflammable substance into the chamber. The top of the chimney is further protected by a grating. The outer entrance is closed by a firmly locked iron door, and the inner entrance to the storage chamber is closed by a locked wooden door. A barbed wire and picket fence surrounds the magazine at a distance of 50 m. The doors are connected elec- trically with an alarm in the mine office, in such manner that the opening of either door, or the cutting of the electric wire, will give a signal. The storage chamber was designed to hold 200 kg. of dynamite, which obviated too frequent handling in the winter. The Transvaal government has issued strict regulations dealing with the storage of explosives. BLASTING Charging with Gunpowder. The hole must be properly dried by inserting a rod having cotton waste, cloth, straw, etc., fastened to one end. In small holes a long tin funnel is employed for charging. The stem is inserted nearly to the bottom of the hole, thus there is no chance of any of the powder sticking to the sides. With flat holes, or "up" holes the powder is best made up into paper cartridges. The experiments of Sir J. F. Burgoyne have shown that in holes of one inch diameter, 7 in. of clay tamping are sufficient; holes 2 in. in diameter, 18 in., and in holes 3 in. in diameter, 20 in. Generally, it may be said that tamping is most important; the better it is done the better will the results be. The charge should fill the chamber or hole; there should be no space left between it and the tamping as the presence of any air acts as a cushion to the force of the blast. EXPLOSIVES AND THEIR USE 183 Ignition of a Powder Charge. This is now performed by means of safety fuse which consists of a core of special gunpowder surrounded by tape or tape and gutta-percha. One end is inserted in the powder before placing the tamping in the hole. The rate of burning of this fuse per yard is known and a sufficient length cut to allow ample time for the operator to retire in safety. _ Where numerous holes are fired simultaneously low-power electric exploders are employed. DETONATION OF HIGH EXPLOSIVES The difference between this operation and that of firing low explosives is that the first are exploded by simple ignition. Explo- sives containing nitroglycerine can be thoroughly exploded only by detonation. The following extracts from a paper by Roland L. Oliver present the facts regarding high explosives, their detona- tion, and the precautions to be observed in their use in a practical manner. It is easily understood by any one, so I reproduce them. Maximum Strength of Powder How Produced. Detonators or blasting caps are made in several different grades of strength, because some powders require not only a greater but a different initial detonation than others to convey their maximum energy through a whole charge, and the detonating qualities of each powder vary by changes in its physical condition whether it be warm or cold, rigid, plastic, homogeneous or otherwise. The full significance of "detonation," as applied to high explo- sives, will become apparent in the course of this paper, but briefly it may be stated that detonation is a very much higher degree of explosion than that produced by fire alone or by a blow. While either of these will explode powder under certain conditions, neither of them will cause it to produce its greatest effect. An explosion is merely the rapid transformation of powder from its solid or liquid state into gases which struggle to occupy a space hundreds of times greater than that occupied by the original substance; but in order that these gases may produce their greatest rupturing force on the surrounding material, they, too, must be expanded suddenly to their greatest possible volume. This requires a practically instantaneous decomposition and oxidation at maximum temperature into their simplest elements, the result being the highest degree of explosion, which is called " detonation," and which can only be produced by a peculiar combination of 184 ROCK DRILLS intense heat and concussion, such as is supplied through the agency of detonators, or blasting caps, as they are commonly called. Hence, a thorough detonation of powder is controlled by the cap, the nature and strength of which is as essential to successful results as is the powder itself. The susceptibility of powder to detonation depends more upon the nature of its ingredients and on the physical conditions previously mentioned than on the amount of nitroglycerine or high explosive which it may contain. For instance, ordinary dynamite, with 40 per cent, nitroglycerine, is easier to detonate thoroughly than a gelatine dynamite containing even as much as 80 per cent, nitroglycerine, because in the first the liquid nitro- glycerine is merely absorbed mechanically in a dope, whereas in the latter it is chemically transformed with guncotton into a gelatinized mass, which is harder to detonate and harder to make transmit its detonation through a whole charge of it than ordinary dynamite; that is, a comparatively weak cap will detonate a larger charge of straight dynamite than of gelatine dynamite, yet gela- tine dynamite, when detonated with a suitable cap, is somewhat stronger than ordinary dynamite containing the same amount of nitroglycerine and possesses greater shattering effect. A spark will detonate fulminate of mercury; 2 grains of ful- minate will detonate nitroglycerine; but it requires at least 10 grains of fulminate to detonate guncotton. That there is some- thing more, however, than the actual force and quickness of these 10 grains of fulminate is shown by the fact that, although the mechanical force of nitroglycerine is more than that of fulminate of mercury, or ten times more than nitroglycerine, 100 grains, will not detonate guncotton; it will only scatter it, yet a small quantity of dry guncotton, which is slower than nitroglycerine, will easily detonate nitroglycerine and even wet guncotton, which are the two extremes, nitroglycerine being one of the most sensitive and wet guncotton one of the most inert forms of high explosives. Therefore the equilibrium of the different chemical molecules of these powders is susceptible to explosion not merely by the force of the shock, but by different kinds of impulses or vibrations. Another example of the disruptive effect of a particular wave motion without especial mechanical force are the glass globes, frequently exhibited in physical laboratories, which withstand a strong blow, but are shattered by the mere vibration of a par- EXPLOSIVES AND THEIR USE 185 ticular musical note, whereas a note of different tone will not affect them. The different degrees of facility with which some explosives will detonate others, and their susceptibility to one kind of detona- tion more than to another, must now be apparent. Let us next consider the action of the same explosive under different influences. It appears to many that when a charge of powder explodes at all, it explodes with maximum force throughout, but such is not the case. For instance, a large number of sticks suspended in the air close enough to explode one another (12 to 36 in. apart, accord- ing to the kind of powder and size of cartridges used) will explode down the line for a certain distance if a detonator be used to start the first stick, but a point will eventually be reached where one will not set off the stick next to it, showing conclusively that each successive stick of powder has lost some of its detonating force. That its explosive force also becomes weakened as it proceeds down the line may be illustrated by placing under each stick a thin plate of soft steel over the end of a piece of 4- or 6-in. iron pipe. The force of each explosion striking these plates of steel will cup them into the hollow of the pipe and the size of the cups will diminish as the explosion gets farther away from the initial detonation. It has also been demonstrated that when the first stick is fired with a weak cap the sympathetic detonation will not extend far down the line; per contra, a very strong cap, or one of some other composition to which the powder is more susceptible, will carry the detonation much farther. Difference between Combustion, Explosion, and Detonation. The effect of merely lighting a piece of unconfined dynamite with a squib or piece of fuse without any cap attached is that the dyna- mite will burn quickly without exploding, and make a dense smoke which has a disagreeable smell and produces violent headaches and if breathed in large quantities prdduce death. This is simple combustion. Confine another piece of dynamite, and light it in the same way and it will explode, but it will belch forth similar fumes. A very weak cap, like the old single-force cap, fired in dynamite will explode it with considerable energy, but there will still be some of the objectionable smoke. Repeat the experiment with a triple-force cap and the dynamite will be detonated with great violence even when unconfined, developing 186 ROCK DRILLS great explosive force and very little smoke. This illustrates the difference between combustion, explosion, and detonation, show- ing that the same powder may be made to transmit its energy by different means and with different degrees of intensity from a rapid burning to a violent detonation. The relative strengths of three well-known explosive com- pounds have been compared when exploded by fire simply and then by detonation. Considering the explosion from simple inflammation of gunpowder as unity, guncotton when exploded simply by fire is three times stronger than gunpowder, and when detonated by a cap it is six and one half-times stronger. Nitro- glycerine is five times stronger than gunpowder when exploded by fire and ten times stronger when detonated. Hence, these figures explain the enormous force which is given by detonation as compared with that by simple explosion. Conditions Influencing Different Powders. Gelatine powders do not transmit their explosive energy through themselves as readily or as far as regular dynamites, hence they require a stronger detonator, larger cartridges and more confinement to completely detonate a whole charge. A 3X cap gets nearly all the energy out of No. 1 and No. 2 dynamite, but gelatine dynamites, nitro- gelatine and other inert powders require at least a 5X cap to develop their energy, and a 6X or stronger cap will do it still better, especially if the charge be a long one. This relation between the length of charge, the diameter of the stick, and the strength of caps is another noteworthy fact, more marked with the inert powders than with ordinary dynamite. Thin sticks require a stronger cap than sticks of larger diameter, and a long charge, especially of slender sticks, requires a stronger cap to convey sufficient impulse through the whole charge; otherwise all the powder in the hole will not be detonated. The so-called "fumeless powders," meaning that their gases are not visible or noxious, are only fumeless in that sense of the word when well detonated. If the fuse burns them, or the cap is too weak, they, too, make " stinkers" and produce headaches. A poor detonation of gelatine and other inert powders, which does not go all through the charge, will disintegrate some of the other sticks without exploding them, leaving the hole unbot- tomed and scattering the unexploded powder about the mine, which is dangerous. This sometimes happens when the cap has EXPLOSIVES AND THEIR USE 187 been buried under several sticks of powder and there is no tamp- ing on top of the charge. The matter of tamping high explosives is much debated amongst miners, many asserting that it is unnecessary. As a matter of fact, tamping is not so essential with high explosives as with black blasting powder, because in the one case the expan- sion of gases is so sudden that just a small proportion gets a chance to escape, while in the case of slower powders the expansion is gradual; but in any explosive the better the confinement of the gases the greater will the effect be. The fact is, however, that most blasters use an excess of powder so as to make doubly sure of breaking the ground, and this excess also makes up for the loss of power by the escape of untamped gases. Close confinement, by ramming the powder well into a hole so as to fill up any spaces around the charge, is also important, as much of its effectiveness may otherwise be lost. For example, a quarter of an ounce of No. 2 dynamite will throw a ball of cer- tain weight from a mortar 300 ft. Leave f-in. air space between the ball and the powder and the same quantity of dynamite will throw the same ball only 210 ft., lessening the distance 90 ft. in 300, which is a loss of 30 per cent, of its efficiency. Several years ago a mining superintendent in Arizona noticed irregularities in the progress of different shifts. Some of the miners complained of unbottomed holes and bad air. He was supplying them with 40-per cent, gelatine dynamite, |-in. sticks and 5X caps, shift and shift alike, but with no more powder than his foreman considered was sufficient to do the work. Upon inves- tigation it was found that one shift always rammed the charges with a wooden bar and put tamping on top, but the other shift was not tamping. All hands have been using tamping ever since, and work has proceeded satisfactorily with the same powder and caps. Another consideration in handling any powder is the diameter of the sticks used. Seven-eighths-inch sticks require more con- finement and greater initial impulse than IJ-in. sticks to carry the detonation through the charge, because the more powder there is in the immediate vicinity of the cap, the .greater will be the initial explosive energy established, and this is particularly essential with gelatine dynamites and other inert powders. When powder becomes chilled, it is difficult to detonate it properly with the usual detonator, hence the advisability of using 188 ROCK DRILLS a very strong cap in cold weather. Many of the holes are fre- quently loaded for some time before firing, and even if the powder is soft and normal while charging, it afterward becomes somewhat chilled in the cold ground. As said before, a 3X cap, or even a double-force cap, will detonate ordinary dynamite if it be soft and plastic. But on the other hand, if it be hard, or if it should present a mottled appearance, even a 5X cap may fail to detonate it completely. Selection of Detonators. It is the nature of the initial detona- tion of the powder around the cap which governs the greater or less effect of the explosion of the whole charge. The cap com- municates to the first particles of powder a disruptive impulse, which according to the nature and strength of the cap more or less completely overthrows their equilibrium and decomposes the powder with great energy, setting up sympathetic vibrations which explode the next particles of powder and so on by the violent disturbances or friction between them in a regular succession of impulses and decompositions, which, if started with sufficient energy, are of such intense heat and velocity that the rupturing force of the explosive is developed practically instantaneously. This detonation has already been shown to be not only the result of mechanical force, but a combination of extremely sudden chemical and dynamical or impulsive reactions which set up vibrations to which different powders are more or less susceptible. These explosive reactions will be propagated through the mass of the powder according to the intensity of the vibrations and the resistance with which their motion is opposed by the nature and consistency of the powder, whether it be difficult or easy to oxidize, soft and plastic like dynamite, or hard. If the initial detonation of the powder surrounding the cap is of the highest degree, the vibrations will be most intense and will be propa- gated farther through the mass than by a poorer detonation. Hence the different degrees of detonation. Unless the first par- ticles of powder are so thoroughly decomposed by a detonation of high order, or first degree, as to convey the necessary heat and energy to detenate the whole charge, the greatest force of the powder will not be developed. There will frequently be unbot- tomed holes or pieces of unexploded powder scattered about, or both, and the air in the mine will be contaminated with some obnoxious gases which have not been completely oxidized. EXPLOSIVES AND THEIR USE 189 The accompanying illustrations are from cross-sections of explosions in solid lead cylinders, and represent graphically the difference in force developed. Fig. 117 is a good detonation from a strong cap. Fig. 118 is a poor detonation from a weak cap in the same quantity of powder. Some powders may lose as much as 20 per cent, of their effectiveness, unless fired with a suitable cap. No. 1 dynamite poorly detonated is less effective and more obnoxious than No. 2 dynamite thoroughly well detonated. A good rule is to use a cap of a grade too strong rather than FIGS. 117 and 118. Results obtained from use of strong and weak detonators. too weak. The strongest cap is always best adapted to the longest hole, and is therefore the most economical. It is customary to speak of caps as being of different degrees of strength. This is correct, but it means more than the mere mechanical force attained by different quantities of any particular detonating substance. It is the power or ability of that deto- nating substance by its peculiar dynamical and chemical nature to transform instantly an explosive into a state of great energy, and it has been shown in 'the early part of this paper that equal parts of some detonating substances possess this power immensely more than others. Different brands of blasting caps contain different detonating mixtures, but they are supposed to be numbered or graded accord- 190 ROCK DRILLS ing to their detonating power, regardless of the weight of explosive which they contain. It was the custom in early days of dynamite to grade caps according to the weight of straight fulminate of mercury which they contained, because Nobel, the discoverer, found that a gun or rifle cap, which contained only half a grain of fulminate, would partially explode straight nitroglycerine, and that its explosive force was increased in proportion to the increased weight of fulminate up to 5 grains, which seemed to get the maxi- mum energy out of this particular explosive. But other explo- sives required still more fulminate, some up to 30 grains or more, according to the length of charge to be detonated. Whenever fulminate of mercury is used, it must be incorporated with other ingredients to make the cap safe to handle. Some of these ingre- dients lessen its detonating effect, others intensify it, so the effects from given weights of fulminate have always been referred to as standards for different grades. It is well to emphasize the fact that as their cost is small compared with the cost of drilling and preparing holes, none but the very strongest and best detonators should be employed. Consider first the powder and conditions under which it is to be used, then select a detonator which will develop the greatest energy out of that particular powder under those conditions. Properly made detonators, if not tampered with, should be safe to handle regardless of their strength. Electrical fuses or exploders are for firing blasts by electricity. Electrical fuses are built into the blasting caps and form a part of them, Fig. 119. They are sealed up air tight, and are as FIG. 119. Electric fuse. , e u ,, . nearly waterproof as such things can be made without expensive rubber insulation; but when handled with ordinary care may be used freely under water, except when very deep, in which case they require special insu- lation and reinforced cartridges. Misfires and how to Avoid Them. No-blasting cap, unless it be a wet one, will fail to explode if fire reaches it, and there is no reason why the fire should not reach it if the fuse is good and has been properly handled. Nevertheless cap manufacturers, like other manufacturers, are blamed for failures in blasting and are called upon to investigate complaints, but, as a rule, the difficulties are traced to improper handling by the operator, EXPLOSIVES AND THEIR USE 191 generally unintentionally, sometimes through lack of proper instructions. Caps have failed to explode, although the fuse had apparently burned all right. Upon investigation it has invariably been found that the fuse had not been put all the way into the cap, and it had been crimped hard near the end with some objection- able tool which had made a groove around the shell and had choked the fire in the fuse so that it could not spit into the cap, Fig. 120. Upon removing the old fuse and putting a fresh i piece into the same caps which ^ IG - 12 - had failed before, but crimping them with a broad-face tool, every one has exploded. Hence, to avoid choking the fire in the fuse, always see that the fuse is pushed down into the cap as far as the composition and secured to the cap with a broad tool, making a flat compression around the shell, Fig. 121. Avoid thin crimpers, which make a groove around the shell, Fig. 122. FIG. 121. FIG. 122. FIGS. 120-122. Good and bad forms of inserting fuse in caps. Good Crimping Desirable. Why does a tool which makes a groove around the shell frequently choke the fire in the fuse, or cause the fire instead of spitting into the cap to break out through the fuse just above the cap, Fig. 122? The familiar Chinese firecracker will serve as an illustration. It is a core of meal powder rolled up in many layers of paper and choked at the bottom. The burning powder reaches this choke and can get no farther, so it takes the line of least resistance, bursts through the side of the paper and makes the FIG. 123. Type of crimper. ., . ... desired report. So it is with fuse; the choke weakens or stops the fire, according to how hard it is crimped and how near the choke is to the extreme end of the fuse. A broad crimper, Fig. 123, cannot choke the fire 192 ROCK DRILLS because it acts similarly to a vise, and any good fuse will burn through a pressure of 300 Ibs. in a vise. There are a great many more tools on the market which have the thin crimping part than have the broad. The thin ones, Fig. 124, have been cheaper to get up, hence find a market, but invariably wherever replaced by a broad tool the most frequent source of misfiring has ceased. FIG. 124^- Type of crimper. Miners should be cautioned also about some combination crimpers and fuse cutters, because although many have the broad crimper, in some it is placed behind the cutting part. This is not a good arrangement be- cause the cutter comes in the most convenient place to nip the cap with when in a hurry and, being sharp, not only makes a groove part way around the shell but also breaks the shell and lets water into the cap. Bad results have been traced to this very thing; hence operators desiring combination tools should be particular to use only those which have the cutter behind the crimping part, Fig. 125. When the use of a crimper is suggested to some miners, or when they hear of misfiring FIG. 125. - Type of crimper, being caused by poor crimpers, they smile and tell how they get along by merely biting the cap to the fuse with their teeth. This is a crude method, but a positive admission of the necessity of fastening caps some way, or else these fellows would not take such a risk of putting dangerous things in their mouths. They also admit of occasional misfires due to caps slipping away from the fuse when they didn't bite hard enough, perhaps, and all are familiar with " miners' headaches," taking them as a matter of course, even after losing time waiting for noxious gases to clear after firing; hence these blasters have all this time unconsciously not been getting the best results out of caps and powder, because good crimping not only secures the position of the cap and keeps dampness out, but also serves as additional confinement to the fulminate, thereby developing greater power from the cap, which, as has already been shown, produced a correspondingly increased result from the powder. EXPLOSIVES AND THEIR USE 193 Proper Care of Fuse. Other instances of complaint have been noted where the end of the fuse inserted in the cap had become damp. It had burned apparently down to the cap, but in so doing had forced the hot moisture into the cap, thereby not only moistening the fulminate but weakening the spit of the fire from the fuse. Damp fuse has been observed to burn a few feet and then slow down or hang fire and sometimes to go out. Cut- ting off the burned part immediately and relighting, the remainder burned a few inches and again went out, and so on through the whole length, showing conclusively that the heated dampness steamed the powder enough to weaken and at times to put out the fire. The remedy is as follows: Fuse should not be left lying around in a damp place; but if it has had to be for a short while, cut off a few inches and throw the piece away, or, having cut off the desired length for the whole, always put the freshly cut end into the cap. Of course, caps must be kept dry also. The question has been asked, "Why should fuse so well pro- tected with waterproof covering dampen so readily?" Because the meal powder in the fuse is very hygroscopic, drawing moisture from the atmosphere. Also, the yarn core along which the pow- der is strung is very dry and spongy, so that both the powder and yarn will draw moisture a long way into the fuse. That this moisture is driven ahead of the fire in the fuse, steaming and weakening it, has been demonstrated in still another way by placing one end of the damp fuse in a cold glass tube and observing the large amount of water vapor condensed in the cold tube. Dry fuse will spit fire several inches into the tube and the glass will be comparatively free from water, but damp fuse will only spit very weak fire, if any at all, and the cold glass tube will be wet with drops of condensed steam from the fuse, the amount of moisture increasing with the length of fuse burned. In other instances blasters have smeared double-tape fuse with vaseline, others with axle grease or crude oil, when working in wet ground, intending to make it waterproof, and these oils being solvents of tar had penetrated the tar into the core of powder in the fuse and spoiled it. The quantity of volatile tar products from the burning fuse may also be observed in the glass tube mentioned above by a brown stain which their condensation will make. Soap, clay, or tallow will protect the fuse for a short time, but these occasionally get chafed off when 194 ROCK DRILLS pushed into the hole or during tamping. Candle grease is often used and is efficient, but care must be taken not to apply it too hot. The safer and better way in such cases is to use triple-tape or other waterproof fuse in wet ground, and secure the cap with a broad crimper, or wrap about four inches of electricians' adhesive tape over the junction .of cap and fuse, Fig. 126. In very wet ^und it is often expedient to use electrical exploders, Fig. 119. Procuring a Complete Detonation. Unbottomed holes, " stink- ers" and premature blasts are sometimes complained of. These have been found to be cases either of (1) using too low a grade of cap for a particular kind of powder, (2) spoiled powder, (3) care- less loading, or (4) hole cut off by a previous shot. The proper choice of detonator will remedy the first cause: 3X or 4X caps are recommended for straight dynamites when not frozen; 5X, 6X, or Lions for gelatine dynamites, chlorate mixtures, and all other inert powders. In cold weather, nitroglycerine powders become less sensitive; the shortest cap is then especially recom- mended as it will get most work and least fumes out of any powder, even under favorable condi- tions. The second cause requires more careful stor- age of powder. Nitroglycerine evaporates percep- tibly at a temperature of 110 F., so that the powder will become weakened and somewhat inert. It freezes at about 42 F., becoming hard, inert, and dangerous. In a damp place it will absorb moisture, which displaces the nitroglycer- ine, and if stored there for any length of time will spoil. Hence dynamite should be soft and dry, stored in a dry and cool place, with the cases placed so that the sticks of powder lie flat not on end. As for the third cause, premature blasts, smoky blasts, and weak shots frequently result when the cap is buried far down in the mass of the charge, because the fuse in burning down, and before reaching the cap, may prematurely ignite the powder by side spitting or even by its own heat, and burn up part t///'/\ FIG. 127. Fuse placed too deep in pow- der, causing powder to burn before exploding. EXPLOSIVES AND THEIR USE 195 of it before the rest explodes (Fig. 127). Even in preparing a short piece of cartridge as a primer it is bad practice to push any of the fuse into the powder, especially if it is cotton covered, as this absorbs nitroglycerine rapidly, which, if injected into the cap, greatly weakens its explosive force, and sometimes causes misfire. Side spitting is not always the fault of the fuse. In rough handling it may have become kinked and the tape cracked or j^ weakened at that place, so that it blows out of the side of the fuse. Hence, never bury a cap and fuse beneath several sticks of powder. The cap must, however, be in actual contact with the powder, hence the advisability of always tying the cap and fuse into the last stick of powder placed in the hole, Fig. 128, so that the powder cannot slip away from the cap, in which event there would either be tamping or an air space between the cap and charge, both of which cause mis-shots or bad fumes in the mine, be- $ cause when the cap gets separated from the powder it cannot possibly exercise its full deto- nating effect. Suggestions to Insure Best Results in Blasting. FIG. 128. Cor- j n v j ew o f the importance of the facts which rect way to place cap and have been brought forward, a summary is offered, fuse< not with the desire to dictate hard and fast rules to those who are breaking ground nearly every day of their lives, but in the form of brief and specific suggestions to insure more thorough detonations of powder and best results. First Select the right fuse for the kind of work, and proper caps for the kind of powder in use, and see that both are thor- oughly dry. Second Powder must not get shaken out from end of fuse, nor sawdust or other obstruction get in between fuse and cap composition. Cutting fuse slanting not only allows a little of the powder to shake off, but .^.^^^ ^ often makes an obstruction to the fire because the slender end , ' ^ lntol * rabl FIG. 129. Wrong way to cut fuse, may fold under Fig. 129. Also a sharp-pointed piece of fuse is not a desirable thing to thrust into any cap. 196 ROCK DRILLS Third Cut the fuse straight across, not slanting, and push it into the cap half an inch or more, all the way down to the pow- der, Fig. 121. If the fuse be ragged at the end or too large to enter the cap easily, never peel off any of the tape or yarn, but swage the end of the fuse to the proper size. This may be easily and quickly done by twisting and squeezing the large part with the crimper, Fig. 130, if it be a broad one. Having in- serted the fuse, squeeze the shell tightly to it with a broad FIG. 130. -Swaging end of fuse. crimper placed around the shell so that one side just overlaps on to the fuse. This will make a compression about a quarter of an inch wide around the ex- treme upper end of the shell. Fourth The blasting powder should not be cold, much less frozen, and holes should be carefully charged, squeezing each cartridge separately with a wooden rammer so as to fill the hole completely to the desired hight. Fifth Having crimped the cap securely to the fuse, insert all of the cap but none of the fuse into a stick of powder and tie together, Fig. 131; then .^ * -?w-> put this priming stick upon the \ rest of the powder in the hole, Fig. 128, and do not ram it un- FIG. 131. Proper placing of cap in til some loose sand or other powder. tamping has been put in. Use tamping without any sharp rocks in it so as not to damage the fuse. Sixth Wherever a whole blast may be fired at once, and for all work in very wet places, electrical fuses will be found of advan- tage. Caps or Detonators. These, as shown in Figs. 119 to 122, consist of copper vessels about 1J in. long and 22 caliber. They contain in the end a mixture of mercury fulminate and potassium nitrate or chlorate; when used for electric blasting the remainder of the capsule is filled with sulphur, through which pass the two wires. If for use with a fuse the composition in the end is covered with shellac, collodion, or paper. In America, X caps contain 3 gr. fulminate of mercury; XX, 6 gr.; XXX, 9 gr.; XXXX, 12 gr.; XXXXX, 15 gr. EXPLOSIVES AND THEIR USE 197 In England, by law, detonators are numbered in accordance with the charge of fulminate. Nos. 1, 2, 3, 4, 5, 6, 7, and 8 con- tain respectively 4.6, 6.2, 8.3, 10, 12.3, 15.4, 23.1, and 30.9 gr. of fulminate. Dampness reduces the strength of the cap enor- mously. The filling is to a certain extent hygroscopic and absorbs moisture. The rock driller should make it a rule always to keep detonators in a dry place, and never to use detonators that have been kept open to the air for any time underground or where the air is damp. Electric Detonators are made in two styles, high tension and low tension. In this connection I take the liberty of reprinting the follow- ing article on "Group Shot Firing," 1 by Sydney F. Walker. GROUP ELECTRIC SHOT FIRING Group shot firing with electrical fuses is somewhat uncertain, and as explained in the Engineering and Mining Journal, Feb- ruary 29, 1908, the uncertainty is due to differences in the fuses themselves, and in the action of the current when passing through them. There are two forms of fuses, and in both, the fuse cap contains a small quantity of a detonating substance, fulminate of mercury, or some similar ingredient. In one form, fine platinum wire is embedded in the detonating matter, and in the other, two small copper wires, whose ends are separated by a small space, are also embedded in it. With the platinum wire form, which is known as the low-tension type, the neces- sary heat to produce detonation is produced by a current of electricity passing through the wire, and heating it to red- ness. With the other form the heat is produced by a spark passing between the ends of the two copper wires, this form being known as the high-tension fuse. The low-tension fuse requires a comparatively large current; according to some measurements I made some time ago, about 0.3 amp. per fuse, but the pressure required is small, only a few volts. The high-tension fuse requires but a small current, in fact I do not know of its having been actually measured, for it would be difficult to do so as it possesses the oscillating properties of the spark, but requires a compara- tively high tension. Much of the trouble with fuses that occurred some years ago was due to the fact that the high-tension fuses 1 Eng. and Min. Journ. June 20, 1908. 198 ROCK DRILLS were not made to gage. The tension required to throw a spark across the gap between the wires is as a rule fairly high, but it will necessarily vary with the distance between the ends, and it may also vary with the nature of the substance in which the wires are embedded, and with the manrier in which the substance is packed. In the tests which I made it was found that occasion- ally a fuse could be exploded with as low a pressure as two volts, while on the other hand, some require as much as 100 volts to explode them. Modern fuses have followed the course of the general improvement in engineering work, and are now made more nearly alike, and therefore there is considerably less difference between the individual high-tension fuses than formerly. The Necessity of Considering All Details. A little considera- tion, however, will show how small differences, either in the lengths of the platinum wires of the low-tension fuses, or in the gage of the wire, or in its attachment to the ends of the copper leading wires, will cause a considerable difference between the circuits that are open to the current; similarly, small differences in the distances between the wires of the high-tension fuses, and between the packing of the detonating substance, will also lead to considerable differences in the paths offered by them. If fuses are arranged in series, the danger is, with the low-tension fuses, that one of them will go before the others have had time to receive sufficient current to cause detonation, and then the fuses which have not ignited their charges cannot do so. With fuses connected in parallel, that is to say, where the current from the exploder divides between the different fuses of the group, the same difficulty may arise in another form. If one of the fuses is of a much lower resistance than the others, it may take so much current from the firing battery, that the pressure of the current delivered to the others is not sufficient to drive the neces- sary heating current through them, and hence they cannot ignite their charges. With the high-tension fuses, when connected in series, there is not the danger of the circuit being broken by one fuse going before the others explode, unless the explosion also breaks the connecting wires, which is possible. The danger in this case is, that one or more of the fuses may be of such resistance that a large portion of the pressure is absorbed, and only one or two of the group may be able to have a sufficient pressure to. EXPLOSIVES AND THEIR USE 199 throw the necessary sparks across. When high-tension fuses are arranged in parallel, there is not this danger, but there is still the possibility that some of the fuses may be of too high a resist- ance to allow a spark to pass, and therefore cannot fire. The trouble is often accentuated, as is stated in the " colliery notes," by the magnetism of the firing battery having been reduced. This is one of the troubles encountered in the" con- struction of the magneto-electric machines, that are now so uni- versally employed for firing batteries; but on the other hand, the improvements which have taken place in the manufacture of special magnet steel should have practically neutralized this difficulty. Within the last ten or fifteen years the demand for a steel that will accept a large amount of magnetism, and what is more important, that will hold it at practically the same limit of saturation, for electrical measuring instruments, has been followed by the usual result, and manufacturers are now able to produce a thoroughly satisfactory steel for the purpose. Steel made for this purpose, the writer understands, is alloyed with tungsten, and thoroughly satisfactory material has been obtained. There is another source of trouble which I believe is the cause of some of the failures of group firing. When two or three pieces of electrical apparatus are connected in series, it often happens that a leak connection is made to earth, of a greater or less resist- ance, and the wires connecting the different pieces of apparatus. It is found, for instance, where incandescent lamps are run in series, that sometimes the positive lamp of the series will burn more brightly than the remainder, and will consequently have a shorter life, the explanation being that there is a partial ground beyond the first lamp, and consequently the current passing to the second and subsequent lamps is less than that passing to the first lamp. The same thing may happen in the matter of fuses. Coal is not a good conductor, but if some of the connecting wires touch it, it may make a sufficiently good connection to carry off a certain portion of the current, and to practically reproduce the conditions mentioned above, in connection with incandescent lamps. The Importance of Care and Measurement. The remedy for all the troubles that have been described, in the " colliery notes" referred to, and in this article, lies in care and measurement. One of the great advantages that electricity possesses is the 200 ROCK DRILLS ability to take measurements with comparative ease. It is always a simple matter to insert a measuring apparatus to show whether a current is passing, and if sufficient money is spent, the actual strength of the current, or the actual amount of the pressure. One of the precautions that could be taken is to fix a small cur- rent indicator upon the case of the firing battery, which might be graduated to show approximately when the current passes for one, two, or more fuses, when connected in parallel, and it might also be arranged to show the pressure available from the battery, before the connection was made to the wires leading to the fuses. The objection to the addition of such an apparatus is two- fold: it increases the expense, and it makes something additional to get out of order; the expense, however, will be well incurred if it enables the shot-firer to have a more complete command of his shots than he has at present. The additional cost of a current and pressure indicator would not be very great; and if each shot- firer always had the same battery, he could become so familiar with the apparatus as to be able to read with considerable accuracy what has taken place in the shot holes. Possible Improvements. Another point where improvements might be made is in the size and quality of the wire employed for connecting the firing battery to the wires leading into the fuses, and the wires attached to the fuses themselves. The idea has prevailed that small wires and poor insulation is sufficient for the purpose, and the view is correct up to a certain point. If only one fuse is to be fired, the problems involved in the size of the wire and its insulation do not come in appreciably; but when low-tension fuses are to be fired in parallel, the size of the wire may have an important bearing upon the pressure available for the fuses; if, in addition, there is a partial ground taking place between the fuses, the defect already mentioned, the cutting off of a portion of the current from the second and following fuses may easily be brought about. The insulation of the wire connecting the battery to the fuses, and of the wires in the shot hole leading to the fuses themselves would also be much better if the insula- tion was higher than is usual, for the reasons given above. The problem involved in the insulation of these wires is somewhat similar to that of the insulation of wires for electric signals in mines, and for the electric bells in houses. In both cases, small wires and light insulation would answer perfectly if nothing had EXPLOSIVES AND THEIR USE 201 to be considered but keeping the wires clear of each other, off dry wood, and if the wires were not subject to damp, rough hand- ling. But experience has shown that for continuous work a large wire answers best in both cases, and a comparatively high amount of insulation; the same reasoning applies to the wires employed for shot-firing. If the wires lying on the ground leading from the battery to the shot holes are well insulated there will be less chance of the wires in the shot-holes making a leak, in case they touch the coal. Another precaution is to see that the fuses and shot-firing batteries are tested, both before going down the pit and, as far as possible, up to the moment of firing the charge. The indicator suggested above will answer for testing the battery; immediately the latter shows an appreciable loss of pressure it should be sent in to be overhauled. The question of testing the fuses is a some- what more difficult one, but by no means insuperable, with the knowledge of electrical apparatus that has been acquired by min- ing men during the last 20 years. The low-tension fuses can be tested with the same indicator mentioned above, and a single dry cell. The test is a simple one, and easily carried out. A circuit is made of the dry cell, the indicator, and the fuse, and the deflection of the needle of the indicator should be noted. It is not quite sufficient to be sure that the circuit is complete within the fuse. The shot-firer should also make sure that the circuit within the fuse is as it should be, and the indicator will show this. As explained above, when the shot-firer gets to know the indicator, it will tell him all about every fuse that passes through his hands, and he will know quickly, by connecting up in this way, whether or not the fuse is good. Method of Testing Fuses. '- It is a simple matter to test all fuses when they arrive. The batch of fuses that are taken into the pit should be tested before going underground, and they should be examined the last thing before fixing them in the shot hole. The small platinum wires are exceedingly delicate, and apt to be detached from the copper wires to which they are con- nected. The jolting of the cage, or the motions of the man who carries them as he walks, may cause one of the fuses to becom3 disconnected. For high-tension fuses, the test is more difficult, but can easily be arranged. The test the writer suggests is a resistance test 202 ROCK DRILLS made with a Wheatstone's bridge. The Wheatstone's bridge is the apparatus employed by electrical engineers, in various forms, for testing resistances. It may be a delicate and formidable apparatus, and is so when arranged for delicate laboratory tests. But on the other hand, portable, knock-about forms are made, arranged so that tests of the kind suggested can easily and quickly be carried out, and with sufficient accuracy for the pur- pose. A somewhat similar series of tests are carried out in copper-smelting works in the United Kingdom for the purpose of determining the purity of each batch of copper produced. A small sample of the copper is taken and drawn into a wire of definite length and of prescribed sectional area, and this is con- nected to two terminals of a Wheatstone's bridge, kept in the manager's office; in this way, the standard of the copper is quickly obtained. Each of the filaments of the millions of incan- descent electric lamps that are turned out are tested for resist- ance by a similar apparatus. Instrument makers will have no difficulty whatever in pro- ducing a portable apparatus that will answer the purpose described, and shot-firers, once they are instructed, will have no difficulty in testing their fuses, before taking them down the pit. There are two dangers in connection with the high-tension fuse that a resist- ance would show. The copper wires may be too far apart for the available spark to jump the space, and on the other hand, the wires may be so misplaced that there is no space to jump. The shot-firer would quickly learn to diagnose both these troubles. I believe that if the above is followed a great many, if not all the troubles that have attended group firing, will gradually disappear. Cautions Regarding Battery Blasting. The following points need careful attention according to A. and Z. Daw in The Blasting of Rocks. I. That the battery wire and detonators are suitable to each other. II. That the battery is of sufficient power. III. That the electric fuses, especially high-tension ones, are stored in a dry place and that all gear is kept dry and clean. IV. That the joints are made with wire that is bright, and that no short-circuiting takes place. V. That the wires do not kink or twist so as to cut the insula- tion during tamping. EXPLOSIVES AND THEIR USE 203 VI. That the operator's hand or any other conductor does not unite the terminals of the battery during firing. VII. That the battery is not connected to the cables until everything is ready and all persons out of the way. ELECTRIC FIRING vs. FUSE FIRING Simultaneous explosions of holes placed in such a manner as to take advantage of it are beneficial in certain cases. Such cases occur generally in quarrying by the bench system. In coal mining electric firing avoids the dangers of explosions due to the ignition of fuses. In underground mining with hard rock headings, the cut holes are fired together by concussion from the first charge going off. The other holes are fired separately. Robert N. Bell gives the following account of a selective electrical fuse-spitting device which seems to offer many advantages and to be worthy of adoption in many instances. "The device, Fig. 132, described in the following paragraphs was perfected at the Hecla mine in the Coeur d'Alene district, Idaho, for selective firing of holes from a distance by means of electric current. 11 One Miss in a Thousand Shots. The first device used was not satisfactory, but by rebuilding it and using a higher voltage, P. C. Schools, electrician at the mine, has succeeded in bringing the machine to such a state of perfection that the misses amount to only 1 in 1000. "The perfected system consists of a firing board, where the operator tests his circuits and l spits ' his holes in the order desired ; a reel, on which is wound the cable carrying the wire used in spitting; and firing blocks attached to the end of the cable. The holes are charged and primed in the usual way, and the spitting wire shown in the accompanying illustration is inserted in a slit cut in the fuse near its end. The fuse is wrapped tightly with electrician's tape, and thoroughly coated with axle grease, so that the juncture is practically waterproof and the spitting can be done successfully under water. "The spitting ends are all prepared before going into the shaft and the fuses are all cut the same length, as the operator gives the time interval between holes when he inserts the plug at the firing board. Each fuse has two leads of a spitting wire projecting from its end. The cable containing the wires with 204 ROCK DRILLS Firing Board Cable down Shaft (25 Wires) FIG. 132. Device for selective shot-firing by electricity. EXPLOSIVES AND THEIR USE 205 the attached firing blocks, which is kept on a reel in the station on the next level above the shaft bottom, is now lowered to the bottom, and the two No. 16 annunciator wires projecting from the fuse of the first hole to be fired are securely wrapped around the two heavy copper leads of block No. 1. This gives hole No. 1 direct connection with the firing board on the level above. Holes Nos. 2, 3, 4, etc., are then attached to the numbered blocks in the order in which they are desired to explode. "The system shown in the accompanying illustration is designed for a 24-hole round, which, of course, can be used for fewer holes, if desired ; the number of holes can easily be increased, but that rarely would be necessary. " Tests Insure Ignition of the Fuse. When all the holes are ready to be fired, the men are hoisted to the firing station, and the circuits are tested out. To test the circuits, the main-line switch is closed and care taken that the single-pole firing switch is open, for it is impossible to spit a fuse- unless the firing switch is closed. This firing switch is kept in a box Bunder lock and key, and only one man on each shift has a key to open it. The flexible cable and plug is then inserted into each of the holes in the firing board numbered to correspond to the holes below to be fired. If the circuits are closed, and ready to be fired, the lamps at the top of the board will light. If the lamps should not light, then there is something the matter with the circuit that must be remedied. If all the circuits test closed, then the shots are ready to be fired. "To fire the shots, the main-line switch is closed, the firing- switch box is unlocked, and plug inserted into No. 1, the lamp lights, the firing switch is closed. This short-circuits the lighted lamps, causing them to go out, and at the same time applies 440 volts directly across the No. 26 tinned iron wire in the fuse at the bottom of the shaft. This wire melts with a blinding flash, spits the fuse, and burns itself free. The firing switch is then opened immediately, so that if an arc is maintained at the fuse it will be smothered by the cutting in of the lamp resistance. With the plug still in No. 1, and the firing switch open, failure of the lamps to light indicates that the spitting wire at the bottom did its work and the fuse is now burned, but if the lamps again light up brightly, it indicates that the fuse did not spit and that the firing switch must again be closed. It is seldom, if ever, that the firing switch has to be reclosed. 206 ROCK DRILLS "Little Additional Time Required. The operator then allows his time interval a few seconds between holes which in most cases is simply time enough to change his plug to the next hole. He then proceeds with the second hole as above described, retest- ing the circuit-firing resistance to see if the operation was success- ful, and continuing until all the holes are spit. The melting of the fuse wire leading to each hole disconnects the firing blocks so that the lower end of the cable is free; the upper end is then detached from the firing board, the cable wound on the reel, and set aside until the next round. The fuses are all ignited and the shots go in the order desired without any attendant danger. "While seemingly complicated in description, this device can be cheaply installed where the current is available. In making this device, nothing is required besides the ordinary material and apparatus kept at a mine where electric current is used for power. "This device is as simple to operate as a telephone switch board, while the attaching of the firing blocks to the fuse takes little more time than would be required in spitting a fuse with a torch, and is quicker than spitting with a hot iron, but of course it is not speed that is important, but safety." Generally speaking, the simultaneous explosion of numerous holes heavily charged with high explosives would have an unpleas- ant, not to say disastrous, effect on the miners, and would damage timbering very badly. In sinking one of the large vertical tim- bered shafts on the Rand, all the charges were fired simul- taneously by electricity. The effect on the timbering was so disastrous that the experiment was not repeated. In wet workings the danger of short-circuiting is very great. When shaft sinking in hard ground, using heavy charges in long holes, even when firing in rotation with fuses, the accidental simultaneous discharge of several shots always resulted in damage to timbers. Where ground is liable to give trouble, the concentrated shock of one explosion of numerous charges might have most serious consequences. GASES RESULTING FROM THE USE OF NITROGLYCERINE EXPLOSIVES W. Cullen states l that the complete detonation of blasting gelatine should yield only carbonic acid, vapor of water, and nitro- gen; but in practice large quantities of carbon monoxide are 1 Journal of the Chemical, Metallurgical Society of South Africa. EXPLOSIVES AND THEIR USE 207 always formed even under the best conditions. This gas acts as a slow poison on the human system even if inhaled in small quantities over a long period and if it exceeds a proportion of more than 0.1 per cent, in the atmosphere it may cause death. If nitroglycerine compounds are ignited, nitrogen peroxide, which is also poisonous, is also given off in large quantities as a red vapor. Small quantities of this gas are frequently present after an ordinary explosion. The burning of blasting gelatine wrapped round a stick to form a torch should not be allowed. In ordinary blasting gelatine the ratio of CO to CO 2 present in the air after blasting was 1:6 to 1:8; gelegnites varied from 1:4.9 to 1:11.2. Samples of air were taken 40 ft. from the face immediately after blasting in an unventilated drive and showed percentages of CO varying from 0.467 per cent, to 0.88 per cent, and of CO 2 ranging from 7.44 per cent, to 4 per cent. CO 2 is an inert gas, but the proportion of CO caused by the explosion of about 50 Ibs. of blasting gelatine is highly dangerous. Mr. Cullen has since introduced a blasting gelatine in which the ratio of CO to CO 2 has been reduced under actual working conditions to 1 : 16.7. It has been proved that the paper covers of cartridges help to produce CO and that CO is also given off by the burning of ordinary safety fuses. GASSING The following rules for procedure in cases of gassing are copies of those posted on mines of the Transvaal prepared by Drs. Irvine and Macaulay. Warning. In cases of gassing, cold water must be avoided, as its application will further increase shock and lower the body temperature. (Application of warm clothing.) The immediate administration of whisky or brandy is also deprecated, as alcohol increases surgical shock, and the physiology of shock being the same whatever the cause, it is certain that it will do the same in shock from gassing. Rules to be Observed in Cases of Gassing. (1) In every case of gassing, the matter should be at once reported to the shift boss, and by him to the manager. (2) All cases must be kept under observation. This and the preceding rule should not be relaxed in any case, no matter how trivial the case or apparently slight the initial symptoms. 208 ROCK DRILLS (3) Steps must be immediately taken to bring the sufferer to fresh air, and at the same time the medical officer must be sent for. (4) Pending the arrival of the doctor, or when medical ser- vices are unprocurable, the immediate steps to be taken in cases of gassing are as follows: (a) In every case where the act of voluntary swallowing is possible, an emetic should be at once administered, and for this purpose a solution of sulphate of zinc containing thirty grains to the ounce is kept at the hospital. This is to be administered in ounce doses every ten minutes until vomiting is produced. (6) Also, a supply of sal volatile (aromatic spirits of ammonia) is kept, and a dose of two drams (two teaspoonfuls in water) are given to every patient who can swallow, immediately after the completion of the preceding maneuver. (c) For severe cases of gassing, there is kept at the hospital a cylinder of oxygen with mask. This should be administered in every severe case, and where artificial respiration is required, this should be performed in an unoxygenated atmosphere. (d) In case of gassing which is so profound as to cause coma and arrest of the respiration, artificial respiration must be started immediately, and persevered with so long as there are indications of life. Artificial Respiration. This is best performed by Sylves- tor's method, which is as follows: The patient is to be placed flat upon his back in the open air with his chest and arms bare. A pad such as a coat rolled up is to be placed under the shoulders. The tongue must be brought forward so that it does not fall backward and close the passage to the windpipe. The operator, standing at the head and looking at the patient, is then to take the arms of the patient by the wrist, one in each hand, and pull them straight out beyond the patient's head, so as to expand the chest as much as possible. By now doubling the arms of the patient so that the elbows press against the chest, the operator must bring the patient's arms back so as to expel the air from the lungs. He makes one complete motion while counting one, two, three, and the operation is then repeated about fifteen times per minute. CHOICE OF EXPLOSIVES The miner is called upon to decide as to the most suitable and economical explosive to employ. Often only one grade of EXPLOSIVES AND THEIR USE 209 powder is employed in any one mine, though the hardness and composition of the material to be broken may vary so much as to make it possible to effect economies by using cheaper varieties where the ground is softer. The following factors must be taken into consideration: (1) The cost of explosives relative to the cost of drilling holes; (2) cost of high-power explosives relative to cost of lower grades; and (3) the nature of the rock to be broken; whether it be full of open cracks or not, and whether it be hard or soft ; whether ore broken consists of brittle high-grade minerals such as argentiferous galena or copper ore, which shattering explo- sives would tend to powder, thus increasing mining, sorting, and concentrating losses; or whether it consists of hard, tough, low- grade material that must be broken to a certain size before leaving the mine. Generally speaking, if the ore or rock is hard it pays to use the highest grade explosive. Rock drilling becomes a great item of the cost of extraction, and with high explosives smaller holes per unit of rock broken can be bored. If the hard rock is being broken in comparatively narrow stopes, with two faces to break to, or in development ends, it will not pay to bull the holes, hence the diameter of the holes will have to be increased porportion- ately with lower grade explosives; the cost of drilling depends largely on the diameter of bit used. The specific gravity of the explosives employed must also be considered, since the power of explosives is compared on unit weights. For instance, blasting gelatine is 1.55 and its power is from 3.5 to 4 times that of black powder whose specific gravity is 1. Hence a chamber to contain an equally powerful charge of blasting gelatine would need to have only a cubic contents -^ that of one for gunpowder. l.oo X 3.5 Several powerful explosives are really useless for work in hard ground because they are light and take up too much space. If the rock is soft with numerous heads, boring is cheaper, and a less expensive low-grade explosive will be the one to use. The use of explosives under various circumstances, with different rocks and ores, is referred to in the chapter on "Rock Drill Prac- tice." The quarry man has other considerations to deal with in his choice of explosives which do not concern us here. XI THE THEORY OF BLASTING WITH HIGH EXPLOSIVES I HAVE been reading most of the works published on blasting to see if they could give me any data that would be useful in checking the work done in breaking rock in development faces and in both wide and narrow stopes in our mines. I think it will be found that these books have been written by engineers, who apparently have no great knowledge of underground con- ditions, and who deal with the subject mainly from a quarryman's or railway contractor's point of view. This is, I think, the ex- planation of the fact that we have rules laid down, based appar- ently on clearly proved mathematical deductions from known forces and resistance, which any right-thinking miner breaks every day of his life for obvious economic reasons. Students of this subject would do well to remember that whole discussions and theses in these books are set out with the object of showing how to break the rock with the smallest possible consumption of explosives. This is quite a secondary consideration with the miner, though in its way worthy of most careful consideration. The miner's object is to raise the rock to the surface and extract its contents with the minimum total costs per ton, and explosives are only one item of costs. So we need beware when we see theories laid down solemnly, ex cathedra, and without modifica- tion, for instance, in regard to the right length of hole to be bored in certain work; for no attention is given to a number of vital considerations relative to saving time, and therefore to total cost of the work to be done, nor to several obvious methods of evad- ing in practice the logical conclusions that can in theory be drawn from certain mathematically proved theorems. A general knowledge of the subject is necessary in order to see if these theories can be applied with useful results under local conditions, and if they point out any directions in which economy can be gained in the use of explosives. Journal of the Chemical, Metallurgical, and Mining Society of South Africa. 210 THEORY OF BLASTING 211 Another crying need of the industry is a printed sheet to be posted up on all mines, giving a simple and, as far as possible, non-technical resume of everything we know regarding the em- ployment of high explosives in boreholes to break rock, and point- ing out the mistakes miners so often make, and the reason why they are mistakes. Such a sheet of instructions would, I believe, pay for its cost of preparation and printing in a month, in increased efficiency. The subject was first studied practically and an endeavor made to evolve some general rules drawn from my own experi- ence. I have since found that the few laws guessed at regarding direction of holes and charges of explosives in relation to the burden, and of burden in relation to free face, were in the main correct. Readers of books on blasting will find several writers saying the theory of the others is wrong. Gillette, in his "Rock Excavation," makes some shrewd observations, but the "Blasting of Rock," by Daw, 1 if read in the light of practical experience, and by people ready to break every commandment laid down in this blasters' decalogue, to save time and money, is, I think, a valuable book. They deal with the following points. Conditions Influencing Blasting. Ten conditions are first laid down which influence the force and effect of a blast. They are, presuming that a hole has been bored, a charge inserted, the hole tamped and the charge detonated: (1) The size and number of the free faces presented by the rock mass. For instance, a drive has one free face only; a stope has two; a bench on an open cut, after the center hole of a row has gone, has three. (2) The tenacity or cohesive strength of the rock (available to resist rupture by shearing). (3) The structure of the rock, whether jointed, massive, laminated, stratified, or fissured. (4) The strength and nature of the explosive compound. (5) The character of the fuse and tamping. (6) The thermal conductivity of the rock, and, I might add, of the tamping. (7) Whether the blast acts alone, or simultaneously with others. 1 The Blasting of Rock in Mines, Quarries. Tunnels, etc., by A. W. Daw and Z. W. Daw. (E. and F. N. Spon, 153.) 212 ROCK DRILLS (8) Whether the rock falls when broken, or has to be lifted (by the force of the blast). (9) The specific gravity of the rock. (10) The size and form of the chamber. (11) One might also add that a blast is influenced by the length of the line of resistance, in proportion to that of the hight of the free face and of the length of the hole itself. Force Generated by Explosives. Daw proves without diffi- culty that the old time-honored formula L = CW 3 , where L repre- sents the weight of charge (quantity of explosive) necessary, and where W = the line of resistance or the shortest distance from the charge to the nearest free face of rock, and C = a coefficient found from experiment representing the relative resistance of the particular rock to rupture, leaves out of consideration most of these factors, and is useless when con- sidered by itself. The force generated by the detonation of explosives, to be successful, must overcome (a) the resistance due to the cohesion of the rock tending to resist rupture; (6) the resistance due to the mass or weight of the rock. This is not relatively important in stoping, and where the rock is shot down it even assists rupture; (c) the resistance due to the jambing or hanging of the rock pieces together and along the lines of frac- ture. The force must act at 90 to the free face for maximum results. The force exerted by a blast on the rock must be a shear- ing force and not a bending or stretching one, because the explo- sive is in a small chamber and its force is suddenly applied to an inelastic rock mass. The force required to produce rupture by shearing, according to the theory of mechanics, where P = force required to produce rupture and S denotes the periphery of the chamber in which the explosive is placed, W equals the line of resistance and KI = a factor that represents the comparative resistance of that rock to shearing as determined, say, in labora- tory in ft. Ib. per sq. in. = the modulus of shearing for the par- ticular rock. Then P = SWK^ Daw made experiments in ice, and proves that this formula holds good for gradual rupture, and he proves that suddenly applied forces produce similar results. The question that he seems to have neglected to investigate is, what effect varying the size and shape of the free faces has in regard to the other fac- tors? In his experiments the area of free face is varied within THEORY OF BLASTING 213 very narrow limits. He never defines a free face. This, as I will endeavor to show later, seems to me a serious omission, when we wish to apply this formula to actual mining. For instance, we have a hole of lj in. diameter bored in the face of a stope which is 6 ft. high. The hole is 6 ft. deep, bored parallel to the face of the bench. The burden on the hole, which is the line of resistance = W, is 3 ft. The charge occupies 2J ft. of the hole. P = SWKi = (1J in. + 30 in. + 1J in.) X 36 in. 'X modulus of rupture of quartzite to shear. The area of the free face at right angles to the line of resistance W is then 6 X 6 = 36 sq. ft. Take the same hole and the same charge in a stope only 3 ft. high; according to the formula, the effect should be the same. We know very well, however, that the first hole would break and the second one would never break. The area of free face being 6X3, or 18 sq. ft., in the second case. According to the authors, the rock should apparently shear in a plane parallel to W as readily as it does to form the usual frustum of a pyramid with fracture planes at 45 to W. With due deference to the authors, I would suggest that this formula is not true or satisfactory as thus stated. It is true only when the hight and length of the free face bear a certain ratio to W and to S, so that the limiting lines of fracture set off from the perimeter of the sides of the chamber at an angle of 45 fall within the area of the free face. I will return to this later on. The authors then point out that with two free faces available (as in st oping), two portions of the rock may be ruptured off by shearing. " Owing to the inelastic nature of rock and the sud- den force applied, equal tension is produced in the rock parallel to the line of resistance for any section that may be blasted/' and that the resistance to rupture of the cross-section parallel to the line of the hole may be equal to the resistance to shearing, and should be so to prevent " bull-ringed " holes. If F repre- sents the area of such a cross-section and K the modulus of rup- ture of rock, P = FK. .'.FK= SWKi. . Hence the authors argue that where there are two free faces, any hole should be given such a length in proportion to its bur- den, or W, that the rock lying between that portion sheared off directly in front of the charge and the free face at the mouth of the hole will also be ruptured off. The force tending to produce rupture in blasting is proportional to the periphery of the cham- 214 ROCK DRILLS her containing the explosive, such periphery taken at right angles to W, or line of resistance. "The section of rock that may be ruptured is proportional to the periphery of the chamber for a FIG. 133. Showing how this rock would break with high explosive. given line of resistance." It is owing to the condition that low explosives are employed to advantage in rocks of comparatively small cohesive strength, or where there are many lateral free faces and joints. These are used in large holes or "bulled," or "sprung" holes, and are more economical than high explosives in small holes. I r / i. 1 i , % % *- V* i --_ L ^_ l ^\ J FIG. 145. Section and plan No. 1 Shaft Rand Collieries, Ltd., showing posi- tion of drilling bars and arrangement of drill holes. average. G. A. Denny, the consulting engineer to this company, owing to the character of the ground disclosed, decided to use machines for sinking. Routine of Shaft Sinking with Machines. The routine of shaft sinking with machines, at the Rand Collieries, Ltd., Fig. 145, is as follows. Three white men work 8-hr, shifts and super- vise the cleaning out of the shaft and help during the drilling EXAMPLES OF ROCK DRILL PRACTICE 237 shift. These are paid 1 per shift. Three whites and a foreman and about 25 natives or Chinese comprise the drilling crew. There are three shifts of shovelers. These go down in rotation after a blast; their task is to send up 60 buckets of rock, or, when the bottom has to be scraped, only 50 buckets. There are about 25 natives or Chinese on each of these mucking shifts. The white men on the drilling crew get 25s., or $6, per day. They have to do the drilling and they also have to go down, when required, to assist in blowing out holes for second blasting and to help clean down the timbers and to lower hose ready for the drilling shift. Natives and Chinese get 2s. per shift with a 6d. or Is. bonus for work performed within a specified time. A bonus, depending on the equipment of the shaft and the class of ground passed through, is also given for feet sunk greater than a certain footage per month. As soon as the ends of the shaft are cleaned up, blocks, wedges, and bars are sent down and the end bars rigged up. Hose are lowered and any defective ones replaced; any stumps of holes are blown out and plugged. Then, when the center of the shaft is cleaned out, the drilling crew come down and work is started. Where the ground is shattered by joint planes or by previous blasts, but not broken sufficiently to remove, or where drilling has to go on under water so that there is a danger that rock frag- ments will wash into the holes, collar pipes are driven into the mouth of the hole. These are pieces of old pipe or boiler tube about 12 in. long, having a 3-in. to 3j-in. diameter inside. These help the drilling greatly, for the hole "muds" better than when drilling under water, for it can splash when these are used. After the hole is loaded, when it is possible, these pipes are drawn so as to be used again. When the ground is of such a character that the mud tends to settle in the bottom of the hole, the mud is pumped out, whenever a drill is changed. For this purpose, pipes, 3 to 12 ft. long and from f to 2 in. diameter, are used. They are moved rapidly up and down in the hole while the hand is used as a valve at the top of the pipe. The pipe is kept closed on the up stroke and the hand is taken away on the more rapid down stroke. This throws the mud and water out. In other places elaborate pumps, made with a plunger and a marble, or other valve at the bottom, are employed. Ordinary blow-pipes are also used here, but only when coarse grit or rocks in the holes render their use necessary. 238 ROCK DRILLS A single snatch-block is hung from the lowest set of timbers and a rope and hook are used to hoist the machines in and out of the buckets and to swing them into position in any part of the shaft. The machines are rigged on clamps directly off the bars, which are 8 ft. long and 4J in. diameter. There is no diffi- culty in making a secure set-up. Occasionally the bars have to support four machines at work, but generally two are placed on each bar except the one on the pump end which carries three. Machine Drilling in Hard Rock. The drilling of long holes in the shaft bottom, when the ground is full of joints and slips, requires considerable skill. In hard ground a close watch has to be kept, so that drills are not kept at work after they are too dull, otherwise the drills will either bend or break, or else it will be found impossible to get the next drill to follow. Realining a drill in a hole, that has "run away," is not so easy as it is when an arm is used on the bar, for no change in vertical elevation can be made. If a hole gives trouble the jig bolt is first slackened a little, then the clamp is removed along the bar, in whatever direction may appear best, and the bolts tightened again. If trouble is still apparent the clamp bolts are loosened a little, while the machine is running; then very often the machine will aline itself. The following trick, used when a bit is slightly too large for the hole, is certainly bad practice; but nevertheless, it is often useful. The chuck bolts are loosened and the machine is cranked back so that the chuck is used as a hammer to strike the shank of the drill; meanwhile the drill is turned by hand. The hole can thus often be reamed out and the drill made to follow. As we had no drill-sharpening machine at this mine, bits of star section could not be jumped up and formed from the steel. Consequently we had to follow what is the usual custom in this field of using, for all cross-bits, star-section steel welded upon octagon steel. There are in fact only a few mines on the Rand equipped with machines for sharpening and making machine drill bits. In this respect I believe American practice is far in advance of ours, when really hard ground has to be drilled. Welds, however well made, are always a source of weakness and trouble. The diabase in this shaft was of exceptionally hard and tough character. Therefore during the drilling shift, it was necessary to have a blacksmith always available to sharpen drills to any gage required owing to bits wearing abnormally or shattering. EXAMPLES OF ROCK DRILL PRACTICE 239 Star bits had to be employed up to a length of 7| ft., as chisel bits lost their gage too rapidly. At the Village Deep shaft, where the rock was favorable for drilling, only chisel bits were used, after the starter had " pitched" the hole. Recovering Broken-off Bits. Owing to the use of welded steel, breakage of drills was frequent and holes were repeatedly FIG. 145a. Arrangement of bell crank levers, used in signaling, Rand Collieries. FIG. 146. Clamps used to extract drills from fitchered holes. lost owing to this cause. Nothing is more annoying and dis- heartening to the operator than to have a 6-in. end break off in a 5-ft. hole that had required, as was frequently the case, three hours' drilling to reach that depth. I found it impossible to devise any really satisfactory tongs or other extractor for regaining these ends. When drills stuck in holes, owing to bending or other causes, I found a clamp extractor, Fig. 146, very useful. 240 ROCK DRILLS The air pressure that we used in hard rock was 80 Ib. per square inch; when, in the hardest rock, we found it better to reduce this to 70 Ib., for though the speed of drilling was much reduced, fewer drills were broken and fewer holes were lost on that account. But, when the shaft bottom was in quartzites of moderate hardness, 90-lb. pressure was employed and it resulted in much more rapid drilling. In such rock three 8 ft. vertical holes are easily drilled in two hours; at the producing mines in rock of the same hardness, with the low-air pressure there employed, 22 ft. of hole is the average amount drilled during an 8-hr, shift. Size of Steel Used. Only the best brands of chisel steel V u J FIG. 147. Simplex drill chuck. costing 11 to 12 cents per pound, would stand in this diabase without bending; but, for the longest drills, having chisel bits and 11 ft. long, 1-in. steel was found to stand satisfactorily with the 3J-in. machines. Next to the welds, the worst breakage of steel occurred at the shanks. The ends of the shanks were most carefully hardened to prevent burring up, but they broke badly just outside the chuck, where the diameter was reduced by swaging to form the shank. In the patent Simplex chuck, Fig. 147, manufactured by Stephens, of Camborne, England, steel of ordinary octagonal section can be used without shanking. As shown in the accom- panying cut, the side of the chuck is cut away and the long pad or key clamps the steel against a half-chuck bushing on the other EXAMPLES OF ROCK DRILL PRACTICE 241 side. Wear on this bushing can be cheaply taken up by liners. The key is easily tightened or loosened by a tap of a hammer. A great saving in bushings and in the cost of shanking results when this chuck is used. The machines in use here are 3-J-in. Ingersoll-Sergeant drills, equipped with an auxiliary valve, and the 3J-in. Holmarr air- valve drills. No great difference in the speed of drilling was noted. Eleven machines are used in the shaft bottom. At the Village Deep shaft 12 machines, rigged on four bars, were used. Here we sometimes find 11 machines sufficient, but often 12 were used. The hoisting buckets work in the two compartments, 5 ft. long, next the pump compartment. The pump compartment y t ^ _^ - r < <- L * "*~ *~ o o o o ( O O O O < 10 01 \ o 3 -3 6 a iz 6 15 /a 2/ 24 9 27 SO 33 < \3C ( -> $ ~& "o { s ^ o o*~ o ( r ) 19 tt 7 1 J T t( 25 2 J/ | 'C A / // ai w FIG. 148. Arrangement of four drill bars in bottom of shaft. is 8 ft. long. When the sump or cut is taken out under the two hoisting compartments there is a space of about 13 ft. at one end of the shaft and 10 ft. under the pump-compartment end. Five bars are rigged, two under the pump end and three under the two unused hoisting compartments. Five machines drill 15 holes on one side of the cut and six machines drill 18 holes on the other side of the cut. If any extra holes should be required, there is always a machine that has finished its holes, before the machines, drilling the center cut holes, are through, and it is available for the work. The distances between the bars and the arrangement of holes are shown in Fig. 148. METHOD OF HANDLING THE AIR HOSE The air is carried down the shaft in a 6-in. pipe, placed in the pump compartment. A double platform is put in over the pump compartment and the two unused hoisting compartments. 242 ROCK DRILLS LOG FOR SHAFT SINKING WITH MACHINES, RAND COLLIERIES, LTD. December, 1906 Buckets Hoisted Time of Shift Length Shift Time Lost Date Shift i 1 03 Timber Cleaning M .S-8 III | 1 ffl 5th Drilling 6 1:40 a.m. 4:10 a.m. Hr. M. 14 30 Hr. M. 1 25 Hr. M. Hr. M. Mucking 1st 60 5:35 a.m. 10:10 a.m. 4 35 1 35 6th 2d 50 11: 45 a.m. 3: 20 p.m. 3 35 3d 50 3: 20 p.m. 11:45 a.m. 5 55 1 30 7th 4th 20 12: 15 a.m. 3:45 a.m. 3 30 Total buckets! hoisted j 180 Total time j mucking j 17 35 1 25 1 35 1 30 Total time for round = 36 hr. 35 min. Footage sunk for week = 28 ft. For month = 103 ft. Ground sunk through, hard diabase. Number of machines drilling on shaft bottom, 11. A cross piece of 4-in. pipe, provided with cocks, is run across the shaft; five hose are coiled on hooks, hanging from the shaft timbers on one end and the other six on the other end. At first these hose were 100 ft. long and the stage kept from 60 to 100 ft. from the bottom, the 6-in. pipe being lengthened whenever a distance of 40 ft. was sunk. In really hard ground, however, the hose and platforms suffered too much from flying rock. Hose, 150 ft. long, were therefore used and the platforms kept further from the bottom. Six natives and a white man are sent up, just before the drilling of the round is completed, to haul up the hose. Two of the natives remain on the timber platform about 40 ft. from the shaft bottom; thus the hose, though heavy, are easily and quickly hauled up. In some cases all the hose are attached to one detachable pipe and are counterbalanced by a weight on a rope passing over a pulley up in the shaft. This pipe is taken off just before blast- ing and hoisted high enough so that the hose hang high enough in the shaft to be out of the way of flying rocks. This method has the disadvantage that excess length lowered must be taken up again and the hose secured with rope; besides, all the hose EXAMPLES OF ROCK DRILL PRACTICE 243 must be lowered, when only one is required at each end of the shaft for blowing out holes, etc.; the remainder are then in the way of timbering and shoveling. The platform method, though it is expensive and troublesome, is perhaps the most convenient. The costs of sinking these shafts during certain months, are shown in accompanying tables: COST OF SINKING No. 1 SHAFT August, 1907; 131 ft., sunk through hard quartzites s. d. Winding ropes and bell lines 11.183 Tramming 17 7.611 Sinking l 7 14 1.923 Cleaning up broken rock 4 0.672 Pumping 1 2 2.885 Hauling 1 13 11.527 Lighting : . _6^ 6.336 Total sinking costs per foot 15 15 6.137 Timbering 4 17 5.315 Ladders 2 5.413 Lagging 6 9.020 Air brattice 7 0.375 Total cost .... ^l ~0 10.0 General expenses on two-shaft basis 1 5 9.8 Total cost per foot 22 6 7.8 1 This includes the cost of breaking the ground and shoveling, of explo- sives and of maintenance of rock drills. COST OF SINKING No. 11 SHAFT December, 1906, 103 ft., sunk through hard diabase s. d. Winding ropes and bell lines 7 4.1 Surface tramming 1 2 4.5 Sinking l 14 9 8.0 Pumping 1 7 2.2 Hauling 2 7.2 Lighting 3 3.8 Total sinking costs 19 12 6.31 Timbering 4 19 7.31 Ladders 2 10.67 Air brattice wall 6 11.23 Lagging 19 7.29 Administration and general charges 2 1 2.40 Total cost per foot 28 2 9.21 1 This includes the cost of breaking the ground and shoveling, of explo- sives and of maintenance of rock drills. 244 ROCK DRILLS SUMP AND BENCH SYSTEM The Cinderella Deep shaft was sunk by this system; the advantage claimed for the method is economy in labor and explo- sives. Mr. G. Browne gives the following particulars in regard to sinking this shaft. The shaft was excavated 9 X 32 ft. "When sinking with four machines, three men are employed, one being responsible for placing the holes. Two bars are used, with two machines on each bar, so that each man has two machines. The leading hand relieves and helps throughout the shift; he also looks after the hand-drill labor. With this method a number of hand-drill boys (natives), not exceeding ten, are put to work drilling holes for shaping the shaft and easing sockets which had not broken to the bottom on the previous blast. Two boys are allowed to each machine. "The scheme of drilling calls for the taking up of the sump on the one shift and the benches during the next. The time taken to drill over, from the tirrie the men leave the bank until blasting- takes place, averages 8J hours. The sump is usually blasted with 16 to 18 holes. The lifting sump holes are finished off with a special long chisel jumper 10 ft. in length. The back holes (ver- tical) are drilled to a depth of 8 ft. Great care is taken that jumpers are not allowed to wear short. " Mucking. Immediately after blasting the cleaner goes down, spending on an average If hours in cleaning down the bot- tom two sets of timbers, and in an examination of the sides of the shaft from the last set of timbers (usually kept between 50 and 60 ft. from the bottom). Following upon this, 25 to 30 cleaning boys are sent down, arid the first bucket of rock is up within two hours from the time of blasting. The average number of buckets of rock obtained from a sump blast is 110, and the average time to clean out the shaft bottom is 18 hours. After the first 65 buckets are sent up, the shift of cleaners is changed, the second shift finishing the work. The total time from the commencement of drilling until the blast is cleaned out averages 28 J hours. Of the 110 tons hoisted only 10 per cent, is water. In estimating the tonnage 260 cu. ft. are reckoned per foot sunk, except where the conditions are such as to increase the average cross-sectional area of the shaft. "Following the sump shift, as just described, the rock drill EXAMPLES OF ROCK DRILL PRACTICE 245 men proceed with the benches one bar being rigged on each bench which are generally dislodged with eight holes each. Care is taken to give the end holes the full length of drill, so that the ends of the shaft will be left low and the sump high. It should be mentioned that hand labor is also put to work on the sump, shaping the shaft and easing the sockets, which are reblasted when benches are fired. The bench blast generally gives 110 to 115 buckets, and the footage made for the two blasts during the month of thirty-one days under review averages 7.62 ft., making a total for the month of 99.18 ft. CONDITIONS FAVORING RAPID SINKING WITH AIR DRILLS I must now pass on to a discussion of what I believe to be the conditions most favorable for rapid sinking with machines. Such conditions are: (1) The maximum quantity of rock should be broken at each blast. In this way time will be saved because there will be fewer delays in loading and firing holes, setting up and tearing down machines, taking out tools and workmen, cleaning down timbers, and examining the walls of the shaft after blasting. (2) By rightly judging the charge of explosive necessary, the rock should be broken to . the best size for rapid loading into buckets or skips. However, the size to which the rock breaks, depends largely on the character of the rock. Rock broken into pieces weighing from 20 to 200 Ib. is most rapidly placed by hand in buckets, while very fine rock must be shoveled, which takes longer. Where water is present in moderate quantities, by having a large quantity of broken rock on the shaft bottom several hours of dry shoveling can be obtained. The amount of time lost in dealing with even a moderate amount of water is very notice- able. When the sandstones and quartzites of the Witwatersrand, as is often the case, contain a considerable proportion of talcose and micaceous material, water converts the mass into a pudding- like aggregate that must be dealt with in the right manner or it is very difficult to shovel. In my own experience I found that such ground would settle and pack just as badly after a round of hand-drilled holes had been blasted as it would after a round of machine-drilled holes has been fired. Where rock of this character is met with, the best way to 246 ROCK DRILLS deal with it is by lowering a hose at each end of the shaft and attaching to each hose a short blow-pipe. The blow-pipe is stabbed about 4 in. into the loose rock and the whole mass worked over thus. It is important also to excavate a good sump, the water in which is either pumped or bailed out frequently, so that the level of the water stays below that of the broken rock, thus keeping it partially drained. By these means even the worst setting rock, that is almost hopeless to attack with pick and shovel while water-logged, may be shoveled fairly rapidly. (3) It will then be obvious that the most rapid cleaning out can be done when there is a maximum quantity of broken rock on the bottom, which is easily available for loosening with picks and raising into the bucket by hand or shovel. It is always the last 10 or 15 tons of rock spread all over the shaft bottom, or partially loosened by the blast, that takes the major portion of the time to clean up and which reduces the average tonnage hoisted per hour. It is obvious, therefore, that if a shaft can be sunk by blasting a " round" every 5 ft., it will be sunk quicker than when a round is blasted every 4 ft., for the more easily and more quickly removed rock will, in the first case, bear a greater ratio to that portion of the rock hard and slow to remove. Besides, less time will be lost in setting up and blasting. CONDITIONS THAT INFLUENCE THE LENGTH OF HOLE TO BE USED The question as to what is the most economical length of hole to drill in sinking a five-compartment shaft must be con- sidered in the light of these and other considerations. We must remember first that, where two buckets are available for hoist- ing, most of the actual time of the drilling shift is occupied by setting up, taking down, and sending up machine steel and such gear as bars, block, wedges, etc. It must also be remembered that, other things being equal, it is economical to drill long holes instead of short ones. Less time on the average is lost setting up; besides, the first few feet of the hole occupy the greater part of the time in drilling, because the hole has to be carefully "pitched," sometimes a long and tedious operation requiring patience and skill; then the hole must be started with a slow-drilling star- bit of large gage. It takes only a few minutes of drilling to lengthen a hole from 6 ft. to 8 ft. It would appear, therefore, that the most economical length of hole must be found by trial. EXAMPLES OF ROCK DRILL PRACTICE 247 Theoretically the length would be such that it will break clear to the bottom with one loading and firing. Other factors have, however, to be considered. The longer the holes drilled in the sump, and these are drilled at an angle of 45 to 35 from the vertical, the greater the width of shaft bottom that can be abridged, and the less the number of holes required behind the sump holes to give a fair burden between the cut holes and those for blasting out the ends of the shaft. If the space under both hoisting compartments can be left avail- able for the use of both buckets, gear can be more rapidly sent up and down. The most fatal objection, however, to relying on this method for making the best progress is the fact that, where deep holes are blasted in rock, broken by many jointings, the blasts, explod- ing first, lift large slabs of rock even from the ground behind them, and so are very apt to cut off or tear out fuses from other holes, thus causing misfires. But in most cases misfires can be traced either to defective fuse or to old fuse in which the rubber has rotted so that it cracks when thrust into the holes. Fuse lighted out of proper rotation, and water entering detonators, also cause misfires. At the Hercules mine the danger of drilling into missed holes is guarded against by making a rough sketch of the shaft bottom before each firing showing the position and direction of holes; this is handed to the foreman on the following shift. THE MOST ECONOMICAL LENGTH OF HOLE TO USE A certain percentage of misfires thus occurs frequently. This means that in many cases a second blast must be made; and in any case, it is impossible to be sure that some stumps of holes will not be left. Of course it may happen several times in succession that all the holes "go" and also break well, but this cannot be depended on in practical work. In these large shafts it has bever been found practical to employ electric blasting. Reliance is placed on fuses, the very best quality, costing in South Africa 11 cents per coil of 24 ft., being generally used here. Fuses, 12 ft. long, are used; double fuses are placed in the leading holes, and all are well greased at the detonators. If a second blast has to be made, there is, of course, a loss of time involved in finding, blowing out, and recharging the old holes. Hence in practice 248 ROCK DRILLS the best length of hole to be employed in shaft sinking will be the longest that can be conveniently drilled. In five-compartment shafts, about 34 X 9 ft. between rock, the most convenient length of hole is bout 10 ft. for the sump holes and about 8 ft. for other holes. In seven-compartment shafts steel 14 ft. long is used in drilling the cut holes; these lengths of holes mean that the bottom of the shaft is cleaned up once for every 3J to 4 ft. sunk. It often happens in favorable ground that no second blast is required, but in very tough ground, or when many misfires have occurred, a third blast may some- times be necessary. The practical objection to using cut holes, as long as 12 ft., and followed by the breaking out holes, 10 ft. deep, is that in hard ground the starters would have to be given a greater gage than 3i in. and the total weight of steel used would have to be much increased. The gages used at its gold mines by the Rand Collieries, Ltd., are 3J, 2f, 2|, 2J, 2, If, and 1J in. Besides, the very long steel used would be awkward to handle and to send up and down, while the first charge would be too far down to lift the top half of the burden on the holes. For comparison I give the costs of breaking and shoveling rock in sinking the following shafts. The No. 1 shaft at the Rand Collieries and the Kleinfontein Reef shaft were sunk with machines, the others were sunk by hand. No. 1 shaft, Rand Collieries, average for four months, shaft about 34 X 9ft. ; ground, quartzites and amygdaloidal diabase. The average footage sunk per month was 120; cost per ton 10s. 9d. In very hard diabase, 103 ft. were sunk; cost per ton 12s. 0.2t/. In soft shales, 112 ft. were sunk; cost per ton 8s. 5.5d; Kleinfontein Reef shaft, 34 X 9 ft. in quartzites, 107 ft. sunk, cost per ton 11s. 7.286V/.; Brakpan mines shaft, 43 X 9 ft., quartzites, 124 ft. sunk, cost per ton 8s. 11. 2d. City Reef shaft, 46 X 9 ft., 125.6 ft. sunk, cost per ton 9s. 2d.; Hercules shaft, 47 X 9 ft., 119 ft. sunk, cost per ton 8s. 5d.; Wolhuter Reef shaft 46 X 9 ft., 95 ft. sunk, cost per ton 10s. 6d SINKING OF INCLINED SHAFTS The rate and cost of sinking inclined shafts varies consider- ably according to circumstances. The variations in the strati- fication, jointing and texture of the quartzites and conglomerates; EXAMPLES OF ROCK DRILL PRACTICE 249 the presence of dikes and faults; the angle the shaft makes with the strata; the presence or absence of water and the amount of timber required are important considerations. The angle of the shaft itself to the horizon is most important, the flatter the angle the more easily is the broken rock removed from the face and drilling again started. The East shaft of the New Klein- foiitein mine, 6 X 21 ft., was sunk 213.5 ft. in one month. The angle or dip of shaft was about 30. Timbering consisted of sills only. This was sunk in foot-wall slates. The incline on the Nigel Deep, 7 X 14 ft., was sunk in foot- wall slates which are fairly hard and tough, breaking badly. The angle of dip was 15. Two hundred and sixty feet were sunk in one month. At the bottom of a shaft 3100 ft. deep at the Brakpan mines in June, 1903, 223 ft. were sunk in one month in foot- wall shales with quartzite hanging wall. The ground was hard and tough, no timbering, except sills, being put in; a brattice, the lower half of galvanized iron and the top half of loosely hung canvas, which was the only construction that would stand the concus- sion from the blasts. The size of shaft was 7 X 19 ft.; dip 13. Thus the shaft more nearly approximated a large cross-cut. Six 3J-in. Holman drills working from 10 to 13 hours would put in 31 holes, the number required to break the face; a center cut, as in driving, was employed, as the ground was too tight to allow a V-cut being used. For 223 ft., 114 cases, 50 Ib. each, of IJ-in. gelatine, were employed. The longest chisel used was 9J ft. Generally 6 to 7 ft. were broken per round. The consumption of gelatine was 5.4 Ib. per ton of rock. In August, 1908, 261 ft. were sunk in the same shaft. Air pressure at the surface was 80 Ib. per square inch. About five hours were required to clear away the rock from the blast before drilling could be resumed. The contract price to six rock drill miners for breaking the ground, on the same terms as for driving quoted above, was 4 10s. per ft. Six or seven holes formed the cut, three holes being drilled to meet with a 4-in. short collar hole between them. The other holes were arranged in rows of three. The miners made high wages at this price. STOPING ON THE WITWATERSRAND The width of reefs worked varies from the inch-wide South reef on the West Rand, to the large quarry stopes on the Rose 250 ROCK DRILLS Deep, shown in Fig. 149. The angle of dip is 80 or over on the Randfontein mines to practically flat reefs on the East Rand. Perhaps the average dip would be about 30 and the majority of stopes are worked at from 45 to 25. The general system of work is underhand or breast stoping. Where overhand stgping is employed (except for some experimental work with air-fed hammer drills), it is used mainly in breaking down waste wall rock for EXAMPLES OF ROCK DRILL PRACTICE 251 FIG. 150. The little Holman 2-inch diam., 5-inch stroke working underground. FIG. 151. The Imperial drill boring with hollow steel. Note the arrange- ment of the feed screw to make a light cradle and the slag attachment. 252 ROCK DRILLS filling, and then shooting down the ore on to planks and stacks. Hand labor is usually employed for this work. Under usual conditions, stopes under about 48 in. in width are worked by hand drills or " single jacking" with natives; but when native labor is scarce machines are employed in smaller stopes. It is anticipated that a suitable machine will be evolved for work in narrow, flat stopes which will enable a large proportion of native labor to be dispensed with. The 3|-in. machine is usually employed for stoping in the larger stopes. It is mounted on an arm and saddle from a more or less vertical bar rigged between hanging and foot-wall of the stope; 2f in., 2J in., and 2 in. diameter piston drills have also been employed in increasing numbers in narrow stopes. See Figs. 150 and 151. Air Pressure. Air pressures vary at the various mines. In the newer mines air at 80 Ib. pressure is often available for develop- ment, but in the older mines 65 to 75-lb. pressure is maintained on the surface. Many machines are called upon to operate at as low as 40 to 50 Ib. Air pressures have, however, been improved recently. At the pressures available small piston drills have not been able to drill sufficient holes to enable them to compete in cheapness with hand labor, except in a few instances. Shape of Stope. Levels are driven from 150 to 300 ft. apart on the dip. The shapes which stopes assume vary greatly with the conditions of roof, hanging and foot-wall and pillars to be left. J. J. Wilkes (Jour. Chem. Met. and Min. Soc., October, 1905) gives the following figures showing shape of stopes. Fig. 152 ' "^7vvr FIG. 152. Overhead stoping on 15 to 45 reef. shows overhand stoping with pillars left along the drive in a reef dipping 15 to 45. Figs. 153 and 154 show a similar face with the benches carried at an angle to the drive. Fig. 155 shows a EXAMPLES OF ROCK DRILL PRACTICE 253 stope with a pillar being cut out by means of a drive underneath it. Fig. 156 shows a face working in, to come down and cut out a lower drive pillar. Fig. 157 shows a pillar being cut out by eating in under it. Fig. 158 shows a stope face from pillars with FIG. 153. FIG. 154. FIGS. 153 and 154. Similar to Fig. 152, except that benches are carried at angle to the drift. benches for machine holes to be drilled, and a box hole rise put up from the level below. Mr. Tom. Johnson (Jour. Chem. Met. and Min. Soc., March, 1908) gives the following: "As to the manner of carrying stopes, with a dip up to about 40, I like to see the faces of benches bearing away about 30 from the direction of full dip (Fig. 159), greater in flatter stopes. The benches should be broken from the bottom of the stope upwards, instead of downwards as most miners prefer to do; in working up- wards the next bench above is lengthened, which is an advan- tage as it gives room for the explosives to kick beyond the bottom of the holes; in steep stopes the angle of the faces from the direction of full dip would be less, Fig. 160. Stop- ing would become more underhand in mines, where it was not ad- visable to have a large amount of broken ore in the stopes, Fig. 160; but in a mine where the broken ore could be left so as to work on it, Fig. 161, then it would be cheaper to allow the stoping to FIG. 155. Stope with pillar being cut on lower side at drive. 254 ROCK DRILLS become more overhand as the dip became greater. As more ma- chines could be got to work comfortably, time would be saved in clearing away the gear, and there would be no danger of the workers slipping down the stope. Also the lower part of the stope FIG. 156. Face working in to cut pillar from above. being full of broken ore and the workers close up to the face, there would be less chance of accidents. Many accidents happen to natives in the bottom of steep stopes, when underhand stoping, from tools slipping or pieces of rock from the hanging or foot- E22& CS23 V~L\r& FIG. 157. Face working in to cut pillar from above. wall coming away. Care would be needed to regulate the quantity of rock taken out of the stope so as not to lower it too much, and to see that the rock blasted was broken small enough to pass the boxes freely without choking. EXAMPLES OF ROCK DRILL PRACTICE 255 "It might be asked, in what manner would it be best to start stoping overhand, whether from the back of drive or leave a rib in? This would depend a great deal on the circumstances of each place; it would certainly be cheaper to start at the corner of the raise and take the back of the drive out and stull. In this case I should take about 4 ft. out along the back of the drive well ahead of the stope, blasting the rock on to a temporary stage just high enough for the cars to go under, putting in the perma- nent stulling behind, taking care before blasting, either on to the temporary stage or permanent stulling, to get a cushion of rock on the stage Fig. 161." Ideal Arrangement of Stope. The ideal arrangement of a FIG. 158. Stope face with benches for drills. stope would be such that the number of machines breaking ore would always have available a bench or benches that would allow of the machine being set up, and boring the maximum number of holes possible during the shift, each hole being given the maxi- mum economic burden and also the maximum economic length. This ideal condition is never attained, though it might be added that the holes should be so placed as to blast out the rock in the direction in which the ore is to be loaded and to break it, neither too fine for subsequent sorting, nor so large as to require reboring, "popping," or "bull-dozing," to reduce it to a size convenient for handling. Faults and the necessity of cutting pillars often spoil the face; where a machine is given less than 5 ft. of face to work on it has often to be set up to drill a narrow or shallow bench at a loss of 256 ROCK DRILLS time. The following gives the cost of running four 2-in. machines, per shift, in stoping. Thirty-six 3-ft. holes are drilled per shift. FIG. 159. Part of stope-face showing run of benches 30 from the direction of full dip. Dip. 15 to 40. The machines are moved until the four benches are drilled, and then returned to No. 1 bench. Cost of Four " Little Won- der Drills" per Shift. Air (including compressor charges and depreciation): four machines at 3s. 3. Id. per shift 13 0.40 White labor: One skilled white miner ' 1 Native labor: Ten natives at 3s. per shift 1 10 Thirty-six hammer boys and one shift boy at 3s. per shift - Oil: Four machines at lAld. each 5.64 Hoses: Four machines at 3.51d. each 1 2.04 Maintenance, taken at 2 11s. 4d. per machine per month, and depreciation (cost of drill 28, and life estimate four years) . . 4 10.16 Totals 3 9 6.24 Miners' Wages. Miners are generally paid by the fathom, EXAMPLES OF ROCK DRILL PRACTICE 257 and the area of all pillars is measured up for them. Miners are charged for explosives, stores, , ,. riM. i Higher side r/b and natives. The price paid varies from 3 10s. to 2 10s. per fathom. In one instance 45s. per fathom was paid, gel- atine being charged at 58s. per 50-lb. case; natives at 2s. 9d. , other stores at cost ; fuse 3d. to 4:d. per coil; candles 11s. per box. Prior to the strike two machines and five natives would be under the charge of one miner. Now, according to Mr. _ Phillips, one man has to super- FlG 160 _ Part of under hand slope. intend three machines or more, and each machine must drill five holes per shift, if the con- tractor wishes to make any- thing on his contract. The general conditions remain the same, and these conditions are not such as to enable a miner to put in his five holes regularly, as they cause a large waste of time nearly every day. Given a good The top gets too far back to carry light machines as the broken rock would fall on the lower benches and need shoveling off before drilling could commence. FIG. 161. Part of overhand stope. f Benches car- ried at such an angle that all holes are wet, top or back of drive taken out and strelling put in. machine, and good air pressure, I find 1.75 in. per minute the average rate of drilling, although I have timed machines drilling at rates varying from 0.47 up to 2.4 in. per minute. Taking 258 ROCK DRILLS the average, the actual drilling time for a 6-ft. hole is 40 minutes; therefore, with eight hours at his disposal, assuming 9J hours for a full shift and allowing 1J hour for getting to his working face, charging up, etc., a contractor could put in 12 holes if there were no stoppages of any kind. Now, of course, it is obvious that a machine cannot be drilling con- stantly, but it is also obvious that there must be a considerable waste of time if it takes eight hours to do two hours and forty minutes' drilling. A fair time allowance for work, incidental to running a machine, is, I think, the following: three-quarters of an hour for rigging up and oiling the machine, five minutes for changing drills, and ten minutes for shifting the machine on the bar to start a new hole; this would give an average of a little over an hour per hole, excluding rigging up, or time for six holes per shift and two rigs. ROCK-DKILL PRACTICE IN AUSTRALIA The Ingersoll-Sergeant, Holman, Sullivan, and Taylor-Hors- field rock drills are generally employed. In Victoria generally one star bit followed by chisels only are used. Leyner hammer drills were for a time in use on the Star of East mine and the Long Tunnel mine. W. A. T. Davis gives the following notes on the arrangement of holes and blasting method in use in West Australia: "In driving, the 'triangle' cut is usually preferable to the 'V cut, Fig 162, as there are less dry holes to bore, than to the 'drag' cut, Figs 167-168, because a greater quantity of ground can be broken in a given time with less boring; nevertheless the drag cut is often used to advantage, especially where there is a wall or dig in the face to bore to. For sinking, in faces of large area, the V or center cut, Fig. 162, is usually preferable, more especially where there are electrical appliances for firing, and where there are no walls or natural fractures in the rock to bore to. Further, the 'cut opening' is the full width of the face, which is not the case with other cuts. The V is also preferable to the drag cut, because more ground is broken by one rigging of the bar or column. It is, never- theless, very destructive to timber in the locality. In sinking where no electric battery is in use and there is a quantity of water to contend with, the drag cut is often adopted and used EXAMPLES OF ROCK DRILL PRACTICE 259 to advantage, as the water is always confined to one end of the shaft. In rising, the triangle cut is usually adopted in preference to the drag cut, as there is not the difficulty in collaring the holes, the face being always at right angles to the machine drill. In stoping, the general stope or drag cut is used; the holes should be horizontally zigzag, vertically in line. In stoping hard^ground a considerable saving can often be effected where holes are all 'water holes/ by having the stope face a good hight and fol- lowing up the same line of holes after each firing until the stope has 'run out.' FIG. 162. Shaft sinking method, V cut. "In the general use of the triangle and V cuts, the center holes should always be fired first and cleaned up, thus giving the surrounding holes clearance and more freedom. In some cases a marked saving can be effected by boring the center holes, remov- ing the machines, firing and cleaning up same; better judgment can then be formed in boring out the remainder of the cut, a con- siderable amount of boring and explosives thus being saved. The loss of 20 or 30 minutes through the second rigging of the machine is more than compensated for by the above advantages." Firing. This should in most cases be carried out in two sec- tions. The system, though occupying a little more time, is wise, as a whole round may be destroyed by a misfire, throwing double 260 ROCK DRILLS burden upon the nearest holes, and thus ineffectively breaking the ground and spoiling the shape of the face for the next boring out, thus resulting in loss of time and costly work. ROCK-DRILL PRACTICE IN BROKEN HILL, NEW SOUTH WALES When I was on that field some years ago the practice was poor. Air pressures were low and pipes much too small, with numerous angles and bends in them. Holes were put in too short. I do not know where more recent figures have been made public. PRACTICE ON THE KALGOOHLIE FIELD E. Davenport Cleland writes in the monthly journal of the West Australian Chamber of Mines as follows: "By using the 'stope-cut/ Fig. 163, it is a simple matter to maintain one end of the shaft deeper than the other, and thus facilitate the bailing of water and the filling of buckets with broken rock. And when firing out the bottom, the rock is pro- jected against the end of the shaft and not so directly upwards as would be the case with center cuts, and therefore there is not so much risk of damaging the timber overhead. "The boring of the shaft is universally performed by means of machine-drills. These are 3f in. diameter, and are operated by compressed air at a pressure ranging from 80 Ib. to 90 Ib. per square inch. The diameter of steel used varies, according to the kind of rock to be bored, from Ij in. to 2j in. "Both cruciform and chisel-shaped bits are used, though on some mines the cruciform bit is not in favor. The first, or t pitch- ing' bits, bore to a diameter of If in., second bits to li in., third bits to Is in., and the finishing bit to lj in. "Slope-cut. In this method, as shown in Fig. 163, the stretcher-bar and machine are fixed at a distance of about 2 ft. from one end of the shaft. From this point the total number of holes required for the first cut are drilled. As a rule, 11 are necessary. The two holes marked A are bored so as to incline at a rather flat angle towards the center of the shaft. Rows B and C are bored to greater depths, and at steeper angles, respect- ively; and the row D, quite at the end of the shaft, is vertical, or with a slight inclination outwards, so as to keep the end of the shaft well open. The depth of this row of holes would be about 6 ft. The shaft is 14 by 5 ft. 9 in. EXAMPLES OF ROCK DRILL PRACTICE 261 "The two holes A constituting the cut are fired and the rock cleaned out. The firing of rows B, C, D, follows in rotation, a Effect of firing hoies A.B.G.Q Showing position cf cfri// ho/es FIG. 163. Stope cut as used on Kalgoorlie field. and they are cleaned up as fired. The excavation resulting from this operation is shown in Fig. 163. 262 ROCK DRILLS "In taking out the second cut, the machine is rigged at the opposite end of the shaft, and boring proceeds as in the first cut, but with the difference that now only three rows of holes, marked E, F, G, are required, and a total number of 9 as against 11 in the first cut. Rows E and F also are deeper and laid at a natter angle than those in the first cut. This is rendered possible because they are firing to a face, and the tearing of the rock is greatly facilitated by the removal of the first cut. "The total number of holes required is 20. The average depth to which the shaft is deepened on the completion of the second cut is 5 ft. in country that is recognized as being very hard." GOLDEN HORSESHOE MINE, WEST AUSTRALIA It will be noted in the accompanying table that the size of drill used is 3f-in. diameter piston, owing to the hard ground met with. It will be seen that even four drills were sharpened per hole, showing that the drillers had a fair supply of sharp steel. Yet the footage bored per eight-hour shift is lower than on the Rand. This is largely due, first, to shorter working hours; second, to some of the work being done in nearly vertical stopes which rendered erecting and moving drills more difficult. The average ground is as hard or harder than that on the Rand. Drilling and Blasting. The following figures, kindly supplied by Mr. Sutherland, manager of the Golden Horseshoe, are instruct- ive. The average width of the lode in this mine is about 12 ft. WORK OF NEW INGERSOLL, 3|, F. 9, ROCK DRILLS IN STOPES FROM JANUARY 1 TO JULY 31, 1906. (GOLDEN HORSESHOE MINE) Average number of machines in use 19.2 Number of shifts 541 Number of holes drilled 31,660 Number of feet drilled 217,280 Feet drilled per drill per shift 20.94 Average depth of holes 6.86 Tons of ore broken . 149,313 Average tonnage per drill per shift 14.39 Steel sharpened: Hand drills 79,151 Machine drills 130,094 Picks pointed 694 EXAMPLES OF ROCK DRILL PRACTICE 263 EXPLOSIVES USED IN THE GOLDEN HORSESHOE FROM JANUARY 1 TO JULY 31, 1906 Sloping Driving Cross- cutting Winzing and Raising Shaft Sinking Plat Cutting Tons of ore broken 149,313 -~_ . Footage Pounds of explosives used: Gelignite Gelatine dynamite 89,580 130 2,175 1,210 5,885 434 140 450 1,578| 995 260 103i 50 3,350 cu. ft. Blasting gelatine Detonators . . 890 52,525 21,975 10,100 5,125 2,200 9,195 6,875 1,750 700 200 Coils of fuse 11,575 2,320 552 1,401 203 33 Average pounds of explo- sives per ton of ore broken Pounds of explosives per foot progressed .61 13.37 13.17 6.62 17.39 4.375 RECORD SHAFT SINKING AT THE VICTORIA REEF QUARTZ MINING COMPANY/ AUSTRALIA The work of shaft sinking was commenced (from the 4024 plat) at 4048 ft. from the surface and was continued until the depth of 4300 ft. was reached in one lift of 252 ft. Two plats also were cut. Size of shaft within the timbers 10 ft. 7 in. X 4 ft., and divided into three compartments. From the time of start- ing (working only two shifts per day) twenty weeks were occupied, and at the end of that time the cages were running to the bottom. Putting in pent house, etc., was included in this time. Two Plats Shaft, Totals Cost Per Foot Wages 87 35 10 29 9 6 12 9 4 1 3 787 315 167 92 99 *2 3 12 1 10 2 5 5 2 3 1 2 5 13 7 7 6 3 4 11 874 17 9 749 5 9 Firewood Shaft timber . Explosives . Sundries Totals . 162 8 5 1461 9 2 5 10 1624 3 6 Taylor Horsfield's Catalogue. 264 ROCK DRILLS SINKING AN INCLINE SHAFT AT THE LONG TUNNEL MINE, WALHALLA 1 , AUSTRALIA The country rock consists of hard slates and sandstones (Silurian), with bars of "el van," and is regarded as bad drilling rock. The total depth, sunk at an angle of 49 from the hori- zontal, is 2886 ft., and the time occupied in this work, twenty months. The first 2300 ft. of the shaft was sunk in two sections at once, and the last 586 ft. sunk in one section. The work was carried forward by contractors working three shifts of eight hours each for six days per week. Six Victorian miners were employed in each shift to do all of the work of sinking, cleaning up, and fitting timbers as the shaft proceeded. Two 3J rock drills were used at one time in each section for the first 2000 ft., and three machines of the same sizes for the remaining distance. The machines were made by Taylor Hors- field, Bendigo. The pressure of air at the drills was 100 Ib. per square inch. Size of shaft inside of timbers 14 ft. by 5 ft.; size of timbers 8 in. by 8 in. in frame; sets 4 ft. 6 in. apart. The shaft is divided into three compartments, the total width of rock excavated being 16 ft. by 7 ft. The total cost of repairs to rock drills was 144, or about Is. per foot. The explosives used were 500 50-lb. cases of Nobel's Glasgow dynamite, costing 1500. Detonators to the number of 17,200 were used, costing 30 Is. 3d. Fuse cost per foot of shaft 10.75rf., and candles (Rangoon) cost the same amount for each foot of sink- ing, viz., 10.75d. Size of Octagon steel used, lj in. and 1J in., with chisel bits. Total cost of steel 50. Average depth of holes bored, 5 ft. 6 in., and diameters If in. Number of holes fired (per shift) 30 in three rounds of 10 each. Average rate of pay per shift for all wages men, 11s. SCOTLAND GRANITE QUARRYING IN ABERDEENSHIRE, SCOTLAND 2 The methods here employed are similar to the ones used in the United States. This example is introduced to show varia- tions in methods of breaking rock to suit different ends. 1 J. Findlayson, Taylor Horsfield's Catalogue. 2 BY WILLIAM SIMPSON, Eng. and Min. Journ. Aug. 31, 1907. EXAMPLES OF ROCK DRILL PRACTICE 265 Excavation. The rock is removed by boring and blasting, and for this purpose the working face is usually divided into two benches. The top bench is first worked back to meet a good \ Main Floor Level Elevation Section Feet 10 40 60 Feet FIG. 163a. Rubislaw quarry, showing working face. vertical joint, a distance generally of 20 to 30 ft. from the face, after which the bottom bench is excavated and the rock entirely removed down to the level of the floor of the dip, Fig. 163a. Ver- tical shot holes up to 21 ft. deep are used to blast out the upper parts of the benches, and breast holes to remove the basal parts Quarry Elevation mpZLJ^fo Section FIG. 1636. Method of drilling breast shot-holes. of the working face where there are no bed joints. These latter are placed at an inclination of about 10 to 15 to the horizontal, and are drilled up to 21 ft. long, as the nature of the rock may require, Fig. 1636, and are calculated to increase the efficiency 266 ROCK DRILLS of the blast and level up the quarry floor. As it is not convenient to use the ordinary rock-drill tripod for such holes, a special frame, Fig. 163c, made of timber is employed, on which the rock drill is mounted, the frame being loaded with stones to steady it, Fig. 1636. As the rock is blasted out the blocks are lifted from the working face by cranes and cableways, but the larger masses, beyond the power of the lifting appliances, are broken up. Rock Drilling. The drilling of shot holes is done by power drills worked either by steam or compressed air. Hand drilling is only resorted to where it is impossible or inconvenient to use Elevation Plan FIG. 163c. Drill frame for boring breast shot-holes. a machine drill, as in bringing down dangerous parts of the quarry wall. The machine drills are chiefly of the Ingersoll or Henderson types, and the usual motive power is steam. The drill bits used are the chisel, cross, and Y forms. The practice of the various quarries in the application of these bits to drill a hole differs considerably, some preferring to use almost exclusively the cross-bit throughout, but, more commonly, holes are started with cross or Y bits and finished, if deep, with chisel bits for about the latter half of the hole. The results, however, in the speed of drilling do not vary much, as a hole 21 ft. deep takes on an average about a working day of ten hours to com- plete under ordinary circumstances, the speed of drilling being higher than this average at the beginning, and less at the end. EXAMPLES OF ROCK DRILL PRACTICE 267 In drilling a shot hole a change of bit is made at every foot of depth drilled, and the successive diameters are gradually de- creased by yV in., owing to the conicity of the hole caused by the wear of the bit, so that a hole 21 ft. deep started with a 3j-in. diameter bit terminates with one 2-in. diameter. Water is removed from the shot holes by a small iron-closed bucket, from 9 to 18 in. long, made from a piece of tube 1? in. diameter, let down by a light chain, and the sludge by a sludge pump and sludge spoons of various lengths. The sludge pump consists of a piece of iron tube from 4 to 6 ft. long, and If -in. diameter, fitted with a plunger and long iron handle. The end is conical, with an inlet hole of | in. diameter. Blasting. In quarrying granite the main object is to obtain large blocks, and explosives must therefore be applied judiciously and in a sparing manner. Coarse gunpowder is used in the Aber- deenshire quarries for blasting purposes as higher grade explosives, such as dynamite and gelignite, shatter the rock too much, and are not used at all, except to blast away bad rock or in very wet places. No general formula can be given to determine precisely the amount of the charge for a blast, owing to the very irregular nature of the rock, but it is estimated that one pound of gun- powder should produce eight tons of rock under ordinary condi- tions of quarrying. In blasting out a long face, vertical holes are drilled down to the horizontal bed joint, and at a distance back from the working face generally equal to their depth, and small charges of gunpowder used, the object being to heave the mass on its bed without shattering it. If one end of a working face is bound, as is sometimes the case, a narrow trench is blasted forcibly out between the quarry wall and the working face to permit this method of blasting being carried out. The mass having thus been shaken and the joints developed, it can be blasted off into smaller blocks, and dragged from the face. For breast blasting, where there are no natural bed joints, the shot holes are usually placed in line close together with about 1J in. of clearance be- tween each at the top, but both the position and number are decided by the actual rock joints, and the quantity of material to be dislodged. Groups of three, five, and seven holes are com- mon, and these may be drilled parallel, radially, or in different planes. If dry, vertical shot holes are filled directly from the top with loose powder passed through a copper filler, but in the case 268 ROCK DRILLS of wet holes, both vertical and inclined, the powder is made up into a cartridge by filling it into thin waterproof tubing, and tying the ends securely. Dry breast holes are loaded from a piece of open -end copper tube, 1J in. in diameter, fixed on the end of a long wooden rod. The regular shot holes are fired electrically, and the detonator or electric fuse is placed about 9 in. from the surface of the charge in the loose holes, and is tied up with the cartridge in wet holes. At some quarries a time fuse is also inserted into the charge of each shot hole as a safeguard against electrical misfire. The charge is rammed home with a timber ramrod, and the holes are stemmed or tamped with granite dust. The electric wires of the shot holes are connected up in series, this method being preferred to the parallel system, and the charges are fired by a high-tension electric exploder. The firing is done either during meal hours, or when work has been stopped for the day, unless the nature of the blast is such that the men can readily find safe cover in the quarry. A steam-jet is used at some of the quarries for effectively washing out the tamping and charge of a misfire shot hole, instead of boring a new one alongside. XIII EXAMPLES OF ROCK DRILL PRACTICE AMERICA CALEDONIA MINE, NEW YORK Character of Rock. The mining of hematite ore is carried on quite extensively in New York. The ore is massive, hard, blue specular variety, interspersed with stringers of calcite, and is usually pockety. A portion of the ore is micaceous and almost as soft as clay. The hanging wall is Potsdam sandstone, and the foot-wall is crystalline limestone, with some serpentine. Robert B. Brinsmade gives the following account of the drill practice at this mine: 1 Drifting and Sloping. The method of ore extraction now used in the Caledonia mine, which was the first to apply it, is as follows: Every 40 or 50 ft. along the incline (when in ore) a drift wide enough to reach from the limestone foot to the serpen- tine hanging wall is started, and of sufficient hight to allow an arched roof, Fig. 164. When a drift has advanced far enough from the incline to leave a sufficient pillar, as at D, a raise is started and driven just under the hanging wall to the level above at C. When this raise has been holed through, one drill is started at the top and (with down-holes and underhand stoping) the ore is broken off clean down to the foot -wall, except a narrow bench left at the top, as at R. Simultaneously, another drift is cutting underhand benches at G to extend the stope to its full length. When a stope is cut as long in the strike as the roof will stand, it is squared down, as at J-K, preparatory to starting another drift and raise under a new pillar, as at L-M. This system conforms well to the pockety nature of the deposit. When the ore has pinched out, as at A 7 ", the drift is not continued beyond the end of the stope, but the advancing for the levels below is done at P, where there is still ore in the face. Each stope has, as far as possible, a pillar below it, as shown in Fig. 164. 1 Eng. and Min. Journ., Sept. 15 and 22, 1906. 269 270 ROCK DRILLS Drilling. In shaft sinking, the limestone foot-wall is followed, and a cross-section of 18 X 8 ft. is excavated. The center cut sys- tem is pursued and two drills, with two men on each, are set on vertical columns to drill during the day shift the four to six 8-ft. holes necessary for each side of the cut. The cut is blasted by electricity at 5.20 P.M. and the debris cleaned up by muckers on the night shift. On the next day shift, the five to six end holes to complete the round are drilled by each machine, blasted and mucked out the following night. This speed is for soft hema- tite; when the face is specular ore it may take five or six shifts to finish a round instead of four. These hindrances render it difficult to average an advance exceeding 12 ft. per week of 13 shifts, or 117J hours actual working time. Section on ABCDEF Longitudinal Section FIG. 164. Ore extraction system Caledonia mine. In drifting, the common method of four horizontal rows of three 6 to 8-ft. holes is used; one drill on a vertical column, set but once for a round, does the drilling. The second row from the bottom is pointed down about 45 for the cut and is fired first, followed by the bottom, third, and top rows in order. For soft ground nine holes are enough, the center hole of the second, third, and top rows being omitted. When the drift exceeds 8 ft. in hight, a heading is advanced above and the floor is cut up behind by lifters; or, in case of a thick floor bench, by vertical down- holes. The raises are at least 6 ft. high and 10 ft. wide to admit of easy breaking for one drill. No regular system of placing holes is in vogue; the bottom, side, or top cut being taken to best break the ground, with the drill column set vertically and usually but once a round. EXAMPLES OF ROCK DRILL PRACTICE 271 In the underhand sloping the holes are seldom quite vertical, or over 8 ft. long, as the irregularity and low dip in many places of the foot-wall make the regular vertical benches and deep holes of an open quarry impracticable. In this mine there are eight McKieran rock drills of 3-in. size; it being found that the 2J-in. size, though lighter to carry around the stopes, could not economically be made to strike a heavy enough blow in the hard specular ore. The rate of drill- ing varies with the ground. In the red ore, seven 6-ft. holes per shift are as easily put down as are two 6-ft. holes in the hardest specular; uppers, sufficiently steep to shed the dust, and down waterholes, drill faster than flat holes, as is usually the case. Before loading, the holes are freed from cuttings by a wooden swab; down-holes are blown out by a 1-in. pipe, attached to the compressed air hose. In sinking, drifting, and raising, the double screw with arm is in use, all new orders are made of 4-in. wrought-iron pipes, but to utilize the old 3-in. column arms and fittings (formerly employed on the discarded 2J-in. drills) extra heavy 3-in. pipe was ordered, and found to be steady enough for the large drill, even when in 8-ft. lengths. For drilling on the underhand benches, tripods are usually necessary; but the drillers prefer to stand on them to make them steady in operation, rather than to put on their legs the customary counterweights. The constant breaking of the set-screws in the extension legs of the tripods was almost entirely prevented by the substitution of soft-iron round bars for the old drill butts the drillers insisted on using for extension. Blasting. Electric caps are used only in shaft sinking; else- where the heavy shocks of simultaneous firing shake up the serpentine roof too much to be safe. " Silver medal" caps and single-tape fuse are in vogue, the fuse being cut in equal 4 to 6-ft. lengths and its split ends ignited in the order required by the round of holes. Double-tape fuse is kept for wet down-holes, as it saves the careful drying before loading essential for the single- tape variety. The drillers are erstwhile Austrian farmers, whose mining knowledge is limited to putting in and loading the machine holes; hence the placing of the holes and the quantity of powder to use must be directed by the American shift boss. Everything is blasted with 40 per cent, dynamite, except the shaft, drift, and 272 ROCK DRILLS raise cuts in specular ore, which are broken by 50 per cent., with 60 per cent, for the primer cartridges. Three half-pound sticks will usually break a 6-ft. hole, when firmly tamped with a small clay ball. Blasting (except for block holes) is done generally just before the end of the shift, each pair of drillers touching off their own holes on a signal from the shift boss. Misfires, arising from the failure of the cap to explode, are blasted at the beginning of the next shift by inserting a new fuse and primer cartridge after removing the clay tamping. Compressed Air. The air is kept at 60 lb., which will do the work and is more economical for single-stage compression than a higher pressure. Cooling water for the air cylinder jackets of both compressors is circulated from a cistern under the engine room by a 4|-in. Blake pump. The air goes down the incline through a 3j-in. wrought-iron pipe, from which the 2J-in. main leading into each working level can be shut off by a 2|-in. iron body gate valve. On the end of the level main, at a safe distance from the working face, is screwed a 2J-in. branch tee, with three IJ-in. and one 2|-in. openings, from which a 1-in. pipe goes off to each drill, shut off by a IJ-in. handle cock at the branch tee. The air hose, in 25 or 40-ft. lengths, is of unwrapped six-ply rubber; it is 1J in. diameter, the idea being to preserve from the level main a minimum section of 1 in. diameter through IJ-in. cock, IJ-in. hose (which is choked on mending to 1 in. inside by the insertion of a 1-in. nipple) and IJ-in. handle cock to the drill's valve chest. Tool Sharpening. The blacksmith shop has two forges, a drill press and a power hammer made from a 2J-in. air drill. On each shift are a tool sharpener and helper, with a repair black- smith and helper on day shift besides. Each rock drill uses from 10 to 15 bits per shift, which are in sets as follows: Name Length Width (Cutting Edge; Shape Starter 2d 2' 6" 4' 6" 2|" 2i" \l" star alone. ) H" star bit; 3d 6' 6* If" ( 1|" octagon shank. 1^" octagon shank. 4th 8' 6" If" lj" octagon shank. 5th 10' 6 V H" 1 j " octagon alone EXAMPLES OF ROCK DRILL PRACTICE 273 The starters are of Vulcan star steel swaged down at one end for the shank. The fifths are of Vulcan octagon steel. The seconds, thirds, and fourths have each a star steel bit, 18 in. long, split at one end for welding to the wedge-shaped end of the octagon steel shank. The bits are draw-tempered to a brown color with great care to withstand the hardness of the specular ore. WITHERBEE-SHERMAN IRON MINES, NEW YORK l About 35 Ingersoll-Sergeant drills are in use in the mines, operating on double shifts. These are of the 2|-in. size and put down from 43 to 45 ft. of holes per man-day (ten hours). They are arranged, on account of the character of the ore drilled, to operate at a higher speed and on a shorter stroke than is usual, and have put down 48 ft. per man-day (average of one month's run). Hand-hammer drills of the "Little Jap" pattern are used to some extent and are giving satisfactory results. They are operated on roof work and block-holing. The holes average about 8 ft. in depth; they are not drilled in any regular order and each hole is, to all intents and purposes, blown out by itself. They are all fired from fuses, for the reason that a series of holes fired by electricity is found to give pieces too large for convenience in handling; the large pieces have to be broken up and it is found more economical and less arduous to fire individual holes. Of course the firing is not so apt to pro- duce falls of roof when done singly as when a number of holes are fired at once, nor is the resulting smoke or fume nearly so great in quantity. The powder generally used is a 45 per cent, dynamite, except in cases where the ventilation is not so perfect; here a gelatine powder of the same strength is used. In most of the New York iron mines, an air pressure of 60 lb., at the surface, is used. THE DAVIS PYRITES MiNE, 2 MASSACHUSETTS Character of Ore. The deposit of hard pyrites is about 20 ft. thick and lies between a foot-wall of mica-schist and a hanging wall of quartzite. 1 Eng. and Min. Journ., June 2, 1905. 2 J. J. Rutledge, Eng. and Min. Journ., Oct. 13 and 20, 1906. 274 ROCK DRILLS The ore is very hard and the crystals are firmly bound together, so that there is only a small percentage of fines made in mining the ore. Sloping. The ore is mined by underhand stoping, Fig. 165. The rise is driven much faster than the winze, but as all holes (except when the water Leyner drill is used) are dry ones the work is done under considerable difficulty, on account of the fine dust filling the lungs of the drillers. The Cover respirator was used with good results while putting up a raise last summer. Such respirators are cheap and rather effective. FIG. 165. Underhand stoping system (Davis mine). After the winze and raise are connected the stope is opened up by taking a "bench" down. Usually a "12-hole" bench is started by drilling 12 holes on foot and hanging walls, about 2 ft. apart. The six holes nearest the winze are first fired and the bench split in that way; then this first bench is carried down one step in advance of the second bench. Usually when the ore is of average thickness it requires one month to take down a 12-ft. bench from top to bottom of the stope. Horizontal floors or jointing planes are found cutting the ore-body at distances vary- EXAMPLES OF ROCK DRILL PRACTICE 275 ing from 2 to 9 ft. apart measured vertically. Holes are always drilled nearly to these floors and the usual depth of hole is from 7 to 11 ft. Long holes give best results. The distance from collar of hole to edge of bench varies from 18 in. to 2 ft.; never more than 2 ft. A hole on each wall is always necessary. National dynamite of 40 to 50 per cent, strength is employed on the stopes, and as the ore to be merchantable must not be over powdered, great care is used in charging the holes. In some stopes three benches are carried down simultaneously, though this plan usually results in considerable mucking down of the ore left on the lower benches by shots from the upper ones. When this plan is followed, the benches are found to be from 4 to 6 ft. wide. Rand " Little Giant" No. 2 drills are used in stoping, one runner and one helper being employed on each drill. The helper carries his own steel to and from the shaft. Hitches. These are cut by hand hammers and "points," which latter are of J-in. steel, sharpened at one end, somewhat in the manner in which a lead pencil is sharpened. Usually two good men, one holding and the other striking the point, can cut an ordinary hitch in a shift, or at most a shift and a half. Some progress has been made in cutting hitches by means of the Little Wonder hand drill and special hitch-cutting tool in places where the foot-wall is not too hard. Where the wall is hard, nothing but the points will do the work. Back-Sloping vs. Underhand Stoping in Large Bodies of Iron Pyrites. Theoretically, in mining large bodies as uniform in nature as iron pyrites it would seem that the overhand or back- stoping method would be most economical, and yet in several large iron-pyrites mines it has been found by experience that the best method is that of underhand stoping, Fig. 165. A con- sideration of the conditions which have led to the adoption of the underhand method may not be out of place. Ordinarily, when back-stoping has been the method of mining employed, it has been necessary to drive the drift above the stope in order to open it up, and this has added to the cost of -the stoping as well as delaying the rapid opening out of the stope. The usual practice is to use stulls in mines in which the walls require support and the deposit dips at a high angle, and to allow the ore and rock to fall on the stulls at the bottom of the stope, chutes being used to load the ore into the cars in the level below. By this 276 ROCK DRILLS method gravity assists in the work of mining and less powder is necessary to break the ground than in underhand stoping. The ore is separated from the rock on the stulls and the rock left to support the walls, instead of being sent to the surface. The miners usually are close to their work and can examine the ground overhead at all times and pull down any loose pieces of ore or rock. If drills are placed on staging made usually of lagging poles, instead of being set upon the loose rock and ore in the stope, there is always vexatious delay in cutting hitches for the lagging poles, before the staging can be erected. The spring of the lag- ging, if long, bothers the driller and the staging often falls, endan- gering the lives of the driller and helper; there are often loose scales of pyrite, sometimes of considerable thickness, which must be dislodged before the staging is set up, or before any work whatever can be done in the stope> and this delay of necessity retards all other work; loose pieces of ore are found over the back of the drifts, as well as over the stopes, and become very dan- gerous, for they cannot easily be detected, as the ground may be solid one moment and the next a dangerous piece of ore or rock may become loosened from the backs. All holes drilled are necessarily dry holes and must be care- fully tamped and fired or there will be great danger from sulphur fumes. In addition to the foregoing the drillings fall down upon the drill and tend to shorten its life. Drillers and timbermen, especially those inexperienced, generally dislike to trim the breasts and walls of back-stopes, or to prepare for and erect the stagings, for the work is dangerous. If the stope is wet the men cannot as easily avoid the dropping water as they can in underhand work. Machine Drills. In the stopes the Rand " Little Giant" No. 2 is used for stoping. This drill is easily hoisted up and down the stopes by means of the cargo winch before mentioned. Rand drills are also used in the drifts and " Little Giant" No. 3 is used in the sinking. The only trouble I have found with these drills is the great cost for repairs, due to broken pistons, wornout feed-nuts, chuck bolts, etc. McKiernan drills have been used in the stopes and also in the drifts, and in shafts and winze work. They do not readily throw the mud out of a deep hole in shafts or on the stopes, prob- ably due to the fact that the moisture in the air freezes in them. EXAMPLES OF ROCK DRILL PRACTICE 277 In drifts, rises, and in all dry holes the McKiernan gave far better results than the Rand. A Leyner water drill has been used in drifting with good results when in the hands of a careful runner. On account of the difficulty in carrying water to the Leyner in the stopes, it did not give very satisfactory results. However, water could be brought from the shaft column pipe for use with drills (Davis mine water is extremely acid, and generally eats metal sur- faces very rapidly) and by using Leyners in stoping, one helper could be dispensed with ; as the two drills are usually side by side, two runners and one helper could easily operate two drills. Most of the helper's duty at present on the Leyner consists in carrying water to the tanks and assisting in jacking bar, setting tripod, or changing bits. Another good feature of this drill is that dry holes never result from its use. This drill creates no dust when used in rising or drifting and removes a very disagreeable accompani- ment of such work when performed with other drills. Among the disadvantages connected with the use of the water Leyner are the complicated nature of the machine, and the necessity for the employment of a competent, skilled runner, the greater skill necessary to sharpen the drills, the necessity for having a uni- formly high air pressure in order to obtain the best results, and frequent breakage of chucks. Little Wonder air hammer drills and Little Jap hammer drills are used for block holing and, where the foot- wall is soft enough, for hitch cutting. For the latter purpose a special hitch-cutting tool is employed. Both these drills give considerable annoyance at times, through the sticking of the hammer. The Little Wonder gave most satisfactory results. At one time the stopes were kept going two weeks by the use of the Little Wonder drills alone by drilling 4-ft. holes, while the Rand stope drills were being overhauled. Both the Little Winder and the Little Jap drill the pyrites easily and cheaply, but refuse to cut the hard foot or hanging. They do not work well in wet ground. Generally the greatest source of trouble connected with their use, aside from the sticking of the hammer, was the bending or breaking of the hollow bits at the point where the steel shank or point was welded or brazed to the stay-bolt iron constituting the body of the drill. This difficulty has been lessened through the employment of a solid bit of hexagonal steel, which has a f-in. hole drilled lengthwise through it. These bits will not bend, do 278 ROCK DRILLS not require tempering of shank or points, and can be sharpened like the steel used in the large drills, and do not require careful handling. Their use is a decided improvement over the soldered or brazed bits. Although the dust from the small air drills is annoying, their use results in such a great saving over hand drills that they are generally used for block holing and trimming ore on foot and hanging. A 1-in. air pipe is run along behind the muckers, and they can use the hand drills themselves whenever necessary. The hand drills cannot drill wet ground. Shaft Sinking. Rand "Little Giants" No. 3 are used in sinking. From 25 to 30 ft. of holes is a fair shift's work in drilling. Usually four cuts are taken out per month. These cuts vary in depth from 5 to 7 ft. The shaft is 9 X 18 ft. out- side the timbers. Experience has shown that the V cut gives the best results when placed as shown in the accompanying drawing, Fig. 165. Sometimes it is necessary only to drill four holes in a round, but usually five holes are required to pull the ground. A 60 per cent, powder is used to pull the V cut (No. 1 and No. 2 rounds), and 40 per cent, powder is used on No. 3 and No. 4, as it has been found that the shaft is more quickly mucked when lumps are made, rather than fine ore. No. 3 and No. 4 on one end are fired and entirely mucked before the No. 3 and No. 4 of the other end are fired; and if No. 1 and No. 2 break well, No. 3 and No. 4 on each end merely break like stope holes and yield large lumps with consequent easy mucking and rapid hoisting. An average rate of progress is about 20 to 30 ft. per month. Blasting. In the Davis pyrites mine it will be noted that blasting practice is regulated by the necessity of preparing the pyrites in lump size for the market. Holes are not loaded with the maximum charge, nor fired with the maximum burden. PORTLAND GOLD MINING COMPANY, CRIPPLE CREEK, COLO. A discussion of the relative merits of the large 3|-in. machine and the small 2J-in. machine by Frederick T. Williams, 1 gives the following particulars of costs and methods employed by the Portland Gold Mining Company. Large vs. Small Drilling-Machines. The headings here described w r ere driven through highly indurated, andesitic breccia, 1 Bull No. 8, Mar. 1906, Am. Inst. Min. Eng. UOAIIQ O O > I <* rr 1C CO < CN (N (N tN uox Jad euox pjox Q I-H O d Tt< CJ O GO 00 >C CO CO TjH CC ^ooj aad joq^q jo ^803 rH CO 1C tO W 1C 00 CO CO CO 00 CO 1-H 00 T-J O C IN uarajiaBJX pun adi j 1 I 1 b j a a islll ss,c32 o era nd 280 ROCK DRILLS having a hardness of from 5.2 to 7.2 and a sp. gr. of from 2.2 to 2.8. The action of the breccia under the drill was not materially different from that of ordinary red granite. The breccia was not as free-drilling as granite, and sludge accumulated very rapidly after a shallow depth of hole had been gained, but it broke better than granite. Aside from the usual work of setting up, drilling, and loading, the machine-men or helpers mucked back, cleaning the floor of muck 3 or 4 ft. back from the breast in order to position the column properly. If the "lifters" acted properly at the previous firing, the muck was fairly well thrown back from the breast; but if either missed fire or were exploded before the other holes, considerable muck was left at the breast which required much additional labor. The usual time needed to muck back was 1.25 hour, but this varied considerably. Flat steel 48 X 96 X f- in. sheets were used, from which to shovel the material. These were placed in position 3 or 4 ft. back from the breast by the trammer just before going off shift. The ground broke fine enough to require little or no sledging. A cubic foot of breccia in place will average 154 Ib. in weight as compared with 90 Ib. on the muck-pile, giving an average of 42 per cent, of void space. All the waste was trammed to the shaft 800 ft. distant, and hoisted to the surface. No timber was used in either heading. The following summary of the results obtained by using both large and small machines has been prepared from the data given in Tables 1 and 2. Labor is the largest individual item. The wages of machine-men were $4 per shift, and the addition of the items given under the several heads of Table I shows the total cost of labor performed in each heading. The cost of operating the machines per shift was $3.70 for the large machine and $1.85 for the small machine; these figures, which vary from month to month, include the cost of everything connected with the opera- tion of the machines : engineer's wages, blacksmith expense, new steel, repairs to the machines, cost and repair of air-lines, etc. The cost of labor, per foot driven, by the large machine was $3.45, and by small machine $2.56. The cost of explosives, a detailed report of which is given in Table II, shows that the 40-per cent, dynamite costs $0.127 per Ib., the fuse, $0.0035 per ft.; and the caps, $0.007 each. These figures, which include freight, unloading, wages of the EXAMPLES OF ROCK DRILL PRACTICE 281 TABLE II. EXPLOSIVES DETAILED REPORT OF THE PORTLAND GOLD MINING COMPANY FOR 20 DAYS, ENDING OCTOBER 16, 1903 Lb.of Powder Lb. of Powder per Foot Driven Feet of Fuse Feet of Fuse per Foot Driven Number of Caps Number of Caps per Foot Driven Large machine (3|"). Cross-cut (5.5' X 7.5'). 5-day run 491 1723 872 30 59 116 407 8-day run 7-day run . 669 544 14.39 15.32 1,179 804 25.35 2265 158 134 3.39 3 77 Averages and totals. . . 1,704 15.40 2,855 25.80 408 3.69 Small machine (2f"). Cross-cut (4.5' X 7'). 5-day run 264 11.00 672 2800 96 400 8-day run 7~day run 378 262 9.45 7.82 1,129 742 28.22 22.15 151 120 3.77 3.58 Averages and totals . . . 904 9.27 2,543 26.08 367 3.76 powder-man, and one third of the wages of the storekeeper, represent the entire cost of the material, as laid down at the station for the machine men. All fuse burned was in 7-ft. lengths. The number of feet of fuse burned and the number of caps used per foot are practically the same; but the cost of dynamite is $0.78 less per foot in the heading driven by the small machine than in that of the large machine. The best record for a shift's run, made by the large machine, was 4.08 ft., as compared with 2.96 ft. for the small machine. In drilling these rounds it was found that the large machine had made 3109.56 cu. in. of hole, and the small machine 971.10 cu. in. Comparing these figures with the cubic feet of ground pulled, 1 cu. in. of hole drilled by the large machine broke 0.053 cu. ft. of breast, while the small machine gave 0.097 cu. ft. This com- parison shows that too much work was done by the big machine on the breast for the amount of ground broken. Figs. 167 and 168 show the number of holes drilled, the degrees of pitch from the horizontal, the depth drilled by the starters, seconds and thirds, and the order of firing. The cost of coal before the boilers was $4.40 per ton. Ordinary cross or 282 ROCK DRILLS 4-50 "FRONT ELEVATION SIDE ELEVATION FIG. 167. Arrangement of holes for 2-inch drill, Portland G. M. Co. Cripple Creek. ^xvZ'&Z%$%%> fcSO- 1 - FBONT ELEVATION SIDE ELEVATION Fio. 168. Arrangement of holes for 3}-inch drill, Portland Gold Mining Co. EXAMPLES OF ROCK DRILL PRACTICE 283 square bits were used, and all the steel was sharpened by machine. At each sharpening the steel lost J to f in. in length. The general tramming cost includes repairs to tram-cars, tram-tracks and the greasing of the cars. The cost of pipe and track is figured at $0.41 per ft., the 2-in. pipe costing, with connections, $0.10 per ft., the track, together with the spikes, plates, and ties, costing $0.31 per ft. Lumber costs $20 per thousand feet. Hoisting cost $0.243 per ton, which includes all accounts that can be charged to the maintenance of the hoisting engines such as wages of the engineers, wipers, top-men and cagers, repairs, cost of steam, cables, and repairs to shaft. The hoist used is a 500-h.p. Webster, Camp & Lane, first-motion hoist, size 20 X 48 in., having a capacity for a maximum depth of 2500 ft., using 5 X | -in. rope to hoist an unbalanced load of 8000 Ib. at an aver- age speed of 1500 ft. per minute. To supplies is charged the cost of picks and shovels. To general expense is charged the wages of foremen and shift bosses, assaying and surveying, pumping, lighting, including candles, office expense, and general repairs on the surface. The air pres- sure at the receiver was 100 Ib. and at the drills 85 Ib. per square inch. The bore of the large machine cross-cut is 5.5 X 7.5 ft., that of the small machine is 4.5 X 7 ft.; it is held that the increase of 1 ft. in width and 0.5 ft. in hight of the large machine cross-cut over that of the small machine cross-cut does not facilitate mining operations. The merits of the work done by the two machines may be briefly stated thus: The use of the small machine saves 25 per cent, of the cost of labor necessary to operate a large machine foot per foot. The cost of operating a small machine is 50 per cent, less than that of operating a large machine, shift for shift. The general tramming cost of the large machine cross-cut is lessened 20 per cent, by using a small machine. The cost of explosives per foot driven by the large machine can be reduced 37.7 per cent, by the use of the small machine. The cost of hoisting and general expense of the large machine cross-cut is lessened nearly 20 per cent, by using the small machine. Greater speed, regardless of cost, can be obtained with the large machine, the small machine being from 10 to 20 per cent. 284 ROCK DRILLS slower. The cost of the large machine cross-cut was reduced 27 per cent, by using the small machine. We have here in Mr. Williams' discussion an example of the use of the drag cut instead of center cut, and of 40 per cent, dynamite instead of blasting gelatine used on the Rand. The cost and efficiency of the labor employed also governs the way in which the work is carried out. Extreme speed is not necessary and one man can be made to operate a 2J-in. machine as compared with one man, and five natives for two machines on the Rand. The ground breaks with fewer holes. Such an arrangement of holes as shown in Figs. 167 and 168 would not break a really tight face, but is most economical in boring and in the use of explosives in the case given. Air pressures at Cripple Creek are 85 Ib. at the machines. CENTER STAR MINE, ROSSLAND, B. C. Large Machines for Stoping. 1 There are 36 air drills employed in the mine, most of which are 3f in. Rand machines. Of these drills 10 to 16 are constantly employed on development work. In the stopes a pair of miners, with one machine, will drill from 30 to 40 ft. of holes in an 8-hour shift, 30 ft. being the rule. The holes are from 6 to 8 ft. deep, the longest steel in use being 10 ft. in length. Each drill in the stopes averages from 20 to 30 tons of broken ore in the two 8-hour shifts. From 1200 to 1600 ft. of development work are done each month. In a drift 6 X 9 ft. in the clear, the monthly advance is from 120 to 180 ft., the latter figure being the record. The round consists of 10 holes 5 to 6 ft. deep, which advances the drift from 4 2 to 5 ft. A round is usually drilled in two shifts. The Center Star group of mines employs about 425 men, who average a little better than li tons of ore broken per man. Two 8-hour shifts are worked, the first crew going underground at 7 a.m., and the second at 3 p.m. The change is made under- ground at the work. At 11 p.m. a crew of four blasters for each mine goes on, and these men load and blast all the holes drilled during the previous two shifts. Any missed holes are reported and listed on a blackboard in the shaft house. This system has greatly reduced the number of accidents, and also makes it pos- sible for the miners to work in good air; for there is ample time 1 Eng. and Min. Journ., Jan. 1, 1910. EXAMPLES OF ROCK DRILL PRACTICE 285 for the slopes and drifts to become cleared of powder smoke and gas before the day shift comes on. FINDLEY CONSOLIDATED GOLD MINING COMPANY, CRIPPLE CREEK, COLORADO Sloping. Hammer drills of the types already discussed Have largely displaced piston drills for stoping, and are also used for sinking, raising, and drifting. G. E. Wolcott 1 gives the following description of stoping as done by the Findley Consolidated Gold Mining Company. The machine used is surmounted with the air-feed attachment. The method of stoping is the ordinary filled stope system as represented in Fig. 169. The ore is drawn out from the stopes so as to leave a working space of from 6 to 8 ft. between the FIG. 169. Method of stoping in Findley Consolidated mine. broken rock and the roof. In starting to drill all that is neces- sary is to lay a short plank on top of the muck pile, place the point of the air-feed upon this and start the machine. In prac- tice it is easy to begin drilling in less than 15 minutes after enter- ing the stope, all that is necessary being to bring the machine to place and connect the hose. A plank to stand the air-feed upon is not even necessary, as when the broken rock lies rather close to the roof the end of the air-feed can be thrust into the muck pile and drilling carried on as well as with a plank to rest upon. HOT-TIME LATERAL OF THE NEWHOUSE TUNNEL, COLORADO The adit 2 was driven through granite, gneiss, and schist, very hard to drill and so tough and tenacious that it broke badly. There were no soft seams nor any defined walls to follow. The 1 Eng. and Min. Journ., July 20, 1907. 2 Eng. and Min. Journ., Oct. 17, 1908. 286 ROCK DRILLS fact that there was no timbering to be done; that the ground was not wet enough to require rubber coats; and that the size of the bore, 5 X 7? ft. in the clear above the rails, corresponded so closely with the usual size of mine workings made the problem, in all essential conditions, the counterpart of the problem hun- dreds of properties are working on every day. The machine-man and helper set up the drill without waiting for the dirt from the previous shots to be cleaned up. The set-up was on a cross-bar placed high enough in the drift and far enough away from the face to allow the upper row of holes to be started close to the back and to be drilled with very little rise in their depth of 6 ft. The usual round was 15 holes, each 6 ft. or more deep and having a diameter of li in. at the bottom. When the ground showed any peculiarities which indicated that another hole or two would be necessary in order to break the ground well these were drilled where needed. The ordinary round con- tained 90 ft. of drill holes, so that to make the set-ups, drill the round, tear down, load and shoot the holes required the full 8-hour shift. Each round broke from 4 to 4J ft. Mr. Knowles used the Model 6, Water-Ley ner drill. The use of hollow steel flushed with a stream of water made it possible to keep the bottom of the hole clear of cuttings, and the bit cool, so that each blow is struck full on the clean face of the rock. By using this drill the crew gained the time usually lost in scrap- ing the hole, and in changing the steel frequently. The saving of this lost time, which in the aggregate consumes a large part of the drilling period, is one of the most important features of this work, and one to which Mr. Knowles ascribes a large part of his success. OPHELIA TUNNEL, CRIPPLE CREEK, COLORADO W. P. J. Dinsmore in Mine and Quarry gives particulars of the work of driving the Ophelia Tunnel. The tunnel was driven straight 8500 ft., and was about 9X9 ft. in the clear. It pierced granite and breccia with dikes of phonolite, andesite, and nepha- line. The rate of advance was 350 to 375 ft. per month. In one month 395J ft. were driven. Two Sullivan UE-Z, 3J-in. drills were employed, three 8-hour shifts. The number of men per shift was seven, consisting of two machine drill men, two helpers, and three muckers or " clean-up men." Each shift was EXAMPLES OF ROCK DRILL PRACTICE 287 to drill, load, and shoot a round of from 18 to 22 holes, drilled 5| to 7 ft. deep, as well as to load broken rock from preceding blast and deliver it to the end of haulage line. The method pursued was essentially as follows: 1 11 As soon as the smoke resulting from the shooting done by the previous shift was cleared, the new shift of drill men, helpers, nand 'muckers' all went to work, and the broken rock from the face was thrown back sufficiently to allow the columns for mounting the drills to be put in place. The two drill men worked together, and the two helpers worked together in pairs, relieving each other at intervals; the 'muckers' going immediately to work, getting the 'muck' into the cars and on its way to the dump. When the helpers were working on the muck pile, the drill men were back of the work; looking up equipment; seeing that all the machine drills, steel, hose, tools, blocking, etc., that would be required for the shift's work were on hand, and, if anything was found missing, taking steps to secure it. When the drill men were working on the muck pile, the helpers were employed in bringing the required material up to the face, where it would be readily available. "Muck as Staging. In clearing away the muck, care was taken that it should not fall back toward the face until a sufficient space was provided in which to set the columns. After the col- umns were set the muck was allowed, and in fact encouraged to fall back, until it had filled the space in front of the face up to such a level that the tops of the jack screws of the columns could just be reached. By this method the back holes, or those nearest the top of the tunnel, were the first to be drilled, and the drill men and helpers worked from the top of the muck pile. This did away with any form of staging, and while the drill men worked toward the bottom of the tunnel, the helpers were removing the pile, Fig. 170, thus always giving the drill men standing ground of proper hight, or really a self-adjusting platform, much wider and more solid than any portable timber staging. It was, of course, necessary for the muckers to finish loading out the muck before the drill men reached the bottom holes or 'lifters,' but they did not stop work until the end of the shift was reached, as there was rail laying, and the placing of sheets, to occupy their attention until the holes were loaded and ready for shooting. 1 Mine and Quarry. 288 ROCK DRILLS "Arrangement of Drill Holes. The important matter of prop- erly placing and shooting drill holes was carried on as follows: In Fig. 171, holes Nos. 1 and 2 are cut holes. These were drilled from 6 to 7 ft. deep, looking down, and were so placed and directed FIG. 170. Drilling and mucking in face of Ophelia tunnel. that their inner ends nearly met. The fuse for these holes was so cut that they were fired first and nearly at the same moment. Holes Nos. 3 and 4 are cut holes, drilled looking up and about the same depth as Nos. 1 and 2. They were so directed that their inner ends did not meet, as in the case of Nos. 1 and 2. FIG. 171. Arrangement of holes for heading in hard ground, Ophelia tunnel. The fuse was so adjusted that these holes were fired just after Nos. 1 and 2. Holes Nos. 5 and 6 are the back cut holes. They were drilled looking up, and so directed that their inner ends did not meet, nor did they extend beyond the top of the tunnel. These holes were shot together and just after Nos. 3 and 4. Cut EXAMPLES OF ROCK DRILL PRACTICE 289 holes Nos. 7 and 8 look down, and were timed to shoot after Nos. 5 and 6. 'Holes Nos. 9 and 10, the cut lifters, look down and extend below the proposed bottom of the tunnel. Holes Nos. 11 and 12, the back rib holes, and holes Nos. 13 and 14, rib holes, look up. Holes Nos. 15 and 16, also Nos. 17 and 18, rib holes, and holes Nos. 19^ and 20, rib lifters, all look down "and all extend beyond the line of the side walls, and were all shot at nearly the same time. " Where stiff ground was encountered holes A and B were put in, and shot with holes Nos. 1 and 2 and Nos. 7 and 8 respectively. Where very difficult ground was found, holes C and D were added and shot with holes Nos. 5 and 6 and Nos. 3 and 4 respectively. By analyzing the above it will be found that holes Nos. 1 and 2 take out or loosen a wedge-shaped portion of the rock, thus reliev- ing the resistance to the action of the powder in holes Nos. 3 and 4 and holes Nos. 7 and 8. Holes Nos. 3 and 4 and Nos. 7 and 8 clear the way for holes Nos. 5 and 6 and Nos. 9 and 10. Holes Nos. 9 and 10 have a tendency to throw any broken rock above them out of the way of the remaining rib holes. Holes A, B, C, and D serve simply to increase the effect of the holes with which they are shot. By placing the holes in this way and shooting in this order, the break, with very few exceptions, always cleared the rock for the full width and depth of the tunnel, thus doing away with the necessity of following the heading with any work designed to break off projections. " Tamping material for use in the loading of the holes was always employed. It was found that by using this, the re- sults obtained were most satisfactory, and that less solder was consumed. "Handling the Muck. Two tracks were maintained close to the heading. Before the shots were fired, steel sheets were placed on the floor close to the face, extending back far enough to receive all the broken rock. It was found important to have these sheets weighted, and enough muck was kept on at the face to do this properly. The sheets formed a smooth floor from which to shovel the muck, but unless the sheets were weighted, it was found that the vacuum, created by heavy shot, was likely to lift them and mix them with the muck, thus not only defeating the purpose for which they were intended, but actually increasing the labor of mucking. The sheets behind the main portion of the 290 ROCK DRILLS muck pile served to receive part of the muck thrown from the face, and also to facilitate the handling of cars." It will be noticed, in the Ophelia tunnel, that the wide face open to attack by drill holes enables the center 3 or 4 hole cut to be avoided; several holes of a " breaking in" character form a " square center cut." The difference in the rate of drilling com- pared with that attained in South Africa is obvious. Two machines bore 18 to 20 holes in 5 or 6 hours; in South Africa three machines of larger diameter take about 8 hours to bore 15 holes. ROOSEVELT DRAINAGE TUNNEL, CRIPPLE CREEK, COLORADO l The country rock through which the Roosevelt drainage tun- nel in the Cripple Creek district has already been driven more than two miles is entirely of biotite-granite gneiss. The abun- dance of biotite (black mica) in the rock renders the granite elas- tic, and this elasticity interferes with the breaking of the rock. The method of overcoming this difficulty is to increase the per cent, of nitroglycerine in the blasting powder, and also to add gun cotton. Such an explosive shatters the rock much more effect- ively than the ordinary dynamite used in mining. A. S. Pearce, the superintendent, used powder composed of 92 per cent, nitro- glycerine and 8 per cent, gun cotton. This compound he found the most satisfactory explosive for gneissoid granite. This ex- plosive is used in the center cuts while lower-grade powder, some containing 40, some 50, and some 60 per cent, of nitroglycerine, is used for the balance of the ground. The tunnel is 10 ft. wide and 6 ft. high, with the roof and sides well squared up throughout. Leyner drills, No. 6, were used and found satisfactory; they drill rapidly and do not get out of order readily. The holes are 2J in. in diameter at the collar and 1J in. at the bottom; the depth is from 7 to 9 ft. Two men are required to run each large machine used in the heading, and three 8-hour shifts are employed. Twenty-six holes are drilled and these are so directed and fired that much of the waste is thrown to one side as it breaks, greatly facilitating its quick removal while the next shift is com- mencing operations. Mr. Pearce states that his average during 10 months was 1 Eng. and Min. Journ,, Nov. 27, 1909. EXAMPLES OF ROCK DRILL PRACTICE 291 361 ft., 4 in. per month. During the month of August he made 410 ft. This distance was drilled in spite of the fact that he lost 56 hours from the disabling of the electric plant, through wash- outs down the creek. In September, with a loss of 108 hours, he drove the heading 399 ft. ROCK DRILLS IN TUNNELS IN EUROPE AND AMERICA The following particulars have been taken from an article by R. L. Herrick in Miners and Minerals, April, 1909, and from later data collected by myself. Sullivan machines were used in the Ophelia and Gunnison tunnels; Leyner drills in Hot-Time Lateral and Elizabeth Lake tunnels. The Brandt rotary drill was employed in the Simplon tunnel, putting in holes 33 in. deep, 3? in. in diameter. The Ferioux percussion drill drove the Arlberg tunnel. The Ingersoll-Sergeant auxiliary valve drill (3f in. diam.), using from drills on a carriage, drove the Loetschberg tunnel, putting in 12 to 14 holes, 4 ft. deep, 2 in. diameter at the bottom, in 60 minutes. Generally the European practice has been to drill slant holes of large diameter and to blast often, while the American practice has been to drill longer holes and to blast seldom. The advance for one round in Europe would be 3 to 4 ft., and in America 4? to 7 ft. The chief criticism to be raised in regard to American min- ing and tunnel practice has been that until recently the economy gained by using the highest known explosives for such work in hard ground has not been realized. TABLE I. SHOWING SPEED ATTAINED IN TUNNEL DRIVING IN AMERICA Name of Tunnel Size of Heading Description Rock Highest Footage per Month Average over Six Months or More Elizabeth Lake Gunnison Gunnison 12 X 12 ft. 8 X 12 ft. 8 X 12 ft. Granite Soft shale Granite 466 & 476 842 449 625 Ophelia 9 X 9 ft. Granite, basalt, phonolite 395 Newhouse 6 X 9 ft. Granite, gneiss 290 Les Angelos Aqueduct Kellogg 101 X 81ft. 8 X 6 ft. Soft sandstone Hard rocks 1061 354 Roosevelt 6 X 10 ft. Hard granite 435 Hot-Time Lateral. . . 5 X 7Ht. Hard granite 263 238 292 ROCK DRILLS TABLE II. SHOWING SPEED ATTAINED IN TUNNEL HEADING DRIVING IN EUROPE. Name of Tunnel Size of Heading Description of Rock Highest Footage per Month Average over Six Months or More Simplon Arlberg 6i X 9^ ft. about same siz( Gneiss and schist Schist 755 641 426 ft. 400 ft Albula a ft Gneiss 607 550 ft. Loetschberg. . a it j Soft rock ( Hard schist 1013 574 342 ft. St. Gothard . . n (i Gneiss 563 Karawanker. . ii tt t*- (N p d O 00 iO cd S o id p GO >o CO O5 iO id OS t^ 00 o id o OS O 1> ^s. iq id OS o t^ 1 ^ 1 10 iO cd o CO iO o id iO cd O l^ <* iO d >o ** O GO ec p CO lO ^ O I> C rj5 p (N <*i 00 O (N O ^ t^ CO o iO Tj5 to IO CO o GO iO GO 1C o (N o GO O I OS *! o Tj5 o GO to GO eo iO CO iO GO IO CO (N o CO iO GO O GO - CO iO GO iO cd No. of Holes b/D . a Q Drift sloping bC d a 1 o 02 1 H ! ! 15* CO CO CO , "S o ** 1 ^ bfi S .S v -c s Q O EXAMPLES OF ROCK DRILL PRACTICE 297 in feet, of a complete round, by the time required to drill one foot of hole. (See Column 6, Table II.) The time thus obtained is 13 hours, 16 min., which, as the length of a shift is 10 hours, gives approximately 1J shifts. The advance made on shooting the round of holes is, as shown in Fig. 172, more than 4 ft., or about two thirds of the longest hole, probably a fair estimate. The advance made per month on a basis of 4 ft. per 1J shift would be 69.2 ft. The practice is not, however, to fill a complete round of holes before charging and firing, but rather to fill a few, charge and fire, then clean up, * . j* ---- 6 ---- | FIG. 172. Arrangement of holes in drifting as practised in Lake Superior district. and so on until the advance has been made. .It is then evident that much time is spent other than in drilling. The usual time taken for an advance is 2| to 3 shifts, and as only 1 shift is worked a day, from 2J to 3 days are required for an advance of 4 ft. In 26 working days (one month) there would then be 10.4 advances made, which, at 4 ft. to the advance, gives 41.6 ft. The rates of advance for a number of months' work in the drift in question range from 30 to 43 ft., averaging 40 ft. Drifting is paid for at the rate of $8 to $8.50 per linear foot. The cost of drifting itemized is as follows : Eight boxes of powder, $136; one box of candles, $8; 1100 ft. fuse, $11; three boxes caps, $6; three gallons of oil, 90c.; drill boy, $15; steel, $2. Total, 298 ROCK DRILLS of $178.90. An advance of 40 ft. at $8 gives $320, which, minus expenses, leaves $141.10, or $70.55 per man per month. Sloping. Drift stoping is the usual method of developing and work- ing a level, and consists in carrying a face 25 ft. wide practically the full hight of the lode the lower part includes the drift, and is run at the required grade of the level. A com- mon arrangement of holes for drift stoping is given in Fig. 173, although no exact rule can be given regarding the practice; conditions and character of rock govern. When possible, how- ever, the lower or drift portion is at- tacked first, thus forming a sump into which the remaining upper portion is broken. Length of holes, total depth of holes, and time of drilling are given in Table I, page 296. Stoping is paid for by the fathom, the exact amount varying with the particular stope and conditions pre- vailing therein; $6 to $9 per fathom is common, average probably $8. A fathom is 216 cu. ft. (6 X 6 X 6). The average hight of stope is 12 ft., or 2 fathoms, the miner being paid for that hight of stope, regard- less of whether the actual hight exceeds or falls below it. In drift stoping the width of drift is sub- tracted from the width of stope, that portion being paid for as drift- ing rather than stoping; $5.50 is the usual rate per foot. The miner then receives $8 a fathom for 19 ft. width of stope, 12 ft. high, and $5.50 per foot of drift, 6 ft. wide by 12 ft. high. Fia. 173. Arrangement holes in drift stoping. FIG. 175. Arrangement holes in raise stoping. EXAMPLES OF ROCK DRILL PRACTICE 299 The amount of rock mined in the stope shown in Fig. 173 is about 4J fathoms, steady drilling for two shifts; but owing to cleaning up and delays other than those attendant upon drilling, which have been considered, not more than one half of this amount can be broken down regularly, and 2J fathoms may be considered a fair estimate. As there are two regular shifts per day, the num- ber of fathoms per month would be 58|, which, at $8, gives $468 per month. Two drilling crews must divide this amount among themselves, each man receiving $117, from which the expenses FIG. 176. Raise stoping. Breaking through. must be deducted. A drill boy serves two crews, his wages being divided equally between them. In a similar manner the company charge of $4 for drill steel per drill per month is divided between the crews. Details of miners' expenses in stoping are as follows: Candles, 2 boxes, $16; powder, 7 boxes, $119; fuse, 800 ft., $8; caps, 200, $4; oil, 3 gal., 90 cents; drill boy, $15; steel, $2. Total, $164.90. Incident with this expense, 40 fathoms were broken down, which at $8 gives $320. Deducting expenses, there remains $155.10. 300 ROCK DRILLS The expense per fathom, average of a number of accounts, is $4.24. The cost of the 58J fathoms is then $248, which, deducted from the amount received, $468, leaves $220 profit for the 19 ft. of stoping. The expense of driving the drift por- tion of the stope a distance corresponding to the advance of the stope portion, 6J ft., at $4.44 per ft., amounts to $28.86, while there was received for that advance $35.75. The total expense and amount received for advancing the drift stope 6J ft. are FIG. 177. Longitudinal section of shaft, Wolverine mine. $276.86 and $503.75, leaving a profit of $226.89, which, divided among four men, gives $56.72 per month. SHAFT SINKING AT THE WOLVERINE MINE/ MICHIGAN Shaft sinking is carried on slowly and the arrangement shown by Dr. Crane is the one found most suited to the circumstances. "The work preliminary to shaft sinking consists in preparing the last station, at the foot of the shaft to be extended by flooring up to the level of the drift. A small sinking shaft, often the size 1 W. R. Crane, Eng. and Min. Journ., Oct. 20, 1906. EXAMPLES OF ROCK DRILL PRACTICE 301 of only 5-| X 5J ft., but usually 5J ft. wide by 9 ft. long, is begun in line with the manway portion of the finished shaft above. It is usually driven for a distance of 6 to 7 ft., after which it is abruptly enlarged to the full size of the main hoisting shaft and in exact alignment with it. The enlargement must then of necessity be all on one side, which is to the right of that of the initial opening. A block of undisturbed rock is thus left directly below the hoisting compartment of the shaft above, insuring ab- solute safety to the operations conducted below. The block of unmined ground is called a pentice, and is shown in Figs. 177 and 178. "The sinking of the shaft, after the full section has been attained by the enlargement PLAN OF FACE. LON& SECTION ROCK of the small opening to the pentice, is accom- FIG. 178. Arrange- plished by one drilling crew, as stated above, ment of holes m and there is, therefore, but one drill employed, ^^ *"* which is mounted upon a column. The holes are usually placed as shown in Fig. 179, i.e., they are arranged to take advantage of the shape and condition of the working face. A depression or re-entrant angle in the face indi- cates the point of attack; if at one end of the shaft section the holes are drilled as shown, but if at or near the middle the holes are drilled on both ends of the section, and slope toward the middle. The arrangement of holes is practically the center or draw-cut system, which is modified largely by character of rock and local conditions." -. .::v *---. - . -..--.*r.-- '-.v- ~ FIG. 179. Arrange- ment of holes in shaft sinking, Wol- verine mine. ROCK-DRILLING PRACTICE AT JOPLIN, MISSOURI We have here an example of working in ore that drills and breaks easily. Large faces are available and often free on three sides; hence long holes are drilled to advan- tage. They are first enlarged to hold large charges of low-grade powder. As in Lake Superior region, drifting and stoping are combined to give large faces of attack. 302 ROCK DRILLS The following description of the methods of breaking ore in sheet ground l at Joplin, Missouri, is given by Doss Brittain. " Raid Ground Sloping. Hard ground consists of massively bedded rock requiring heavy blasting to loosen it. Such ground is to be found throughout the district in the same localities as the soft ground, but more extensively. "All hard ground breaking is done with machine drills and powder. The type of drill in most common use is the Sullivan U C, and the Ingersoll C 24 for shaft sinking, and the Sullivan U F 2, and the Ingersoll C 24 for heavy stoping. A few lighter and a few heavier drills of the same make are in use, but are not common. Nearly all of the machine drills in use are air drills, though some steam drills find employment in the district. Hand steel cannot be said to find a use there in breaking hard ground; it was discarded when deeper mining began. In ordinary ground an average 8-hour shift's work, for a drill, is 45 ft. of holes. Steels have to be changed with a frequency varying with the hardness of the ground and the skill used in tempering. In most cases a change is required every two or three feet, while in others a bit can be used for twice this distance. The bit employed most commonly is known as the bull-head or chisel bit, with the cut- ting edge in a straight line. Some of the larger Webb City mines, however, employ the diamond-edge bit with cutting edge arranged in the form of a cross. In shaft sinking the holes are usually started with If-in. steel and finished with the 1-in. size. In stoping the holes are usually started with IJ-in. steel and finished with the If-in. size. If the holes are deeper than 10 ft. they are usually finished with smaller steel. "In order to break the greatest amount of ground at the least cost, it has been found advisable in most cases to 'squib/ 'bull,' or 'spring' the holes before putting in and firing the charge intended to accomplish the work of real ground-breaking. Squib- bing is the process of enlarging the drill holes with powder so that they will hold more powder than otherwise, thus enabling each blast to lift more ground than if the holes were charged without being enlarged. It is done with from one half to one stick of dynamite, and is repeated sometimes as many as three times in very hard ground. Two or three slight explosions so enlarge the hole that it will hold from 50 to 75 sticks of powder. 1 Eng. and Min. Journ., Dec. 14, 1907. EXAMPLES OF ROCK DRILL PRACTICE 303 The hole is then cleaned with a blow-pipe made for the purpose, and charged with the heavy charge. " In charging, the sticks are usually split down the side so that when tamped they will spread readily. Each stick is placed on the sharp end of a spoon and pressed to the bottom of the hole, where it is tamped with, a round wooden tamping stick of oak or hickory 8 to 12 ft. long. The last stick or part of stick passed in contains the cap, or primer, and fuse, electric firing being employed in the district only for sinking purposes. This last stick is called the starter and is prepared by making a round cavity in the end of the mass of powder with a sharp stick. The primer is slipped over the end of the fuse and tightly crimped with a pair of pincers or the teeth so as to prevent water from moistening the primer. The end of the fuse bearing the primer is then inserted into the hole in the starter and the paper covering is drawn up over the fuse above the primer and securely tied with a stout string. As additional precaution against moisture in very wet mines the tar melted from a piece of fuse is allowed to drop around the junction of the cap and fuse before intro- duction into the starter. The latter, after being prepared to suit local conditions, is inserted into the drill hole in intimate con- tact with the charge. The hole is then tamped full of clay and gravel to prevent ths charge from being wasted by blowing out through the hole, and the blast is ready for firing, which is the only thing now necessary to complete the utility of the drill and dynamite. About 1 Ib. of dynamite is required for every ton of ground broken in drifting, and 25 Ib. to the foot for sinking shafts of ordinary size. " Shaft Sinking. As a rule 12 holes are drilled in the bottom of the shaft and are arranged as indicated in Fig. 180. The four holes occupying the middle of the shaft, and known as sump holes, are inclined, or "look," inward toward the center of the shaft at an angle of about 30 from the vertical. They have a slant hight of about 5 ft. and pull vertically about 4 ft. Four other holes are driven about 1 ft. from the corners respec- tively and look slightly outward, so that the shaft will break to a uniform width as it progresses downward. Likewise the four holes near the middle of the sides look outward for the same purpose. Both the corner holes and those at the sides are sunk about 4 ft., so that they will pull vertically the same distance as 304 ROCK DRILLS the sump holes, which are fired first. These are followed by the side holes and these by the corner holes. The reason for the order is evident when the area blasted out by each series of shots, as indicated in Fig. 180, is considered. Figs. 181 and 182 indicate PLAN OF SHAFT o"' s o > ..---I FIG. 180. Showing arrangement of holes in shaft sinking at Joplin. other arrangements of holes for shaft sinking which are now rarely used except for shale or other soft formations. 11 Drifting. In the arrangement of holes, Fig. 183, the same principles obtain as to depth, inclination, and indicated order of firing as in the case of shaft sinking. EXAMPLES OF ROCK DRILL PRACTICE 305 \ ' PLAN OF SHAFT SECTION OF SHAFT FIG. 181. Showing arrangement of holes in shaft sinking, Joplin. V PLAN OF SHAFT SECTION OF SHAFT FIG. 182. Showing arrangement of holes in shaft sinking, Joplin. 306 ROCK DRILLS ''When the ore is reached, or if the drift started in ore, when it reaches a distance sufficient to keep the shaft from caving, it is widened to about 50 ft., or until the width of the ore deposit is embraced. This widened excavation, the heading of which is usually 8 ft. high, the hight of the drift, of which it is but a wide expansion, proceeds along the top of the orebody. If this be more than the hight of the heading in thickness, a step, or stope, is taken up. Should there still be ore in the drift, more stopes are taken up until the orebody is exhausted. Regularly two stopes are carried at once, giving -the wide drift a depth of 30 ft., including lO > il \ \ o x ' FIG. 183. Arrangement of drift holes, Joplin, Mo. 8 ft. for the heading and 11 ft. for each stope, which begins at the shaft, thus keeping the floor of the narrow drift always on a level with that of the wider drift so as to furnish a comparatively level surface for hauling the ore to the shaft. The heading and stopes are kept about 10 ft. ahead of the stope below. For carrying such a drift the holes for blasting are arranged as indicated in Fig. 184. "The first four holes at either end of the heading are drilled 5 ft deep, the other 7 ft. The next series of heading holes, after the first is fired, is arranged with the shallow holes at the reverse end of the heading, so that each series of shots breaks the face EXAMPLES OF ROCK DRILL PRACTICE 307 of the heading at a right angle with the direction of the drift, thus releasing or unbinding the rock to be blasted. The shallow holes are fired first, for the obvious purpose of making the deeper shots more effective. The holes drilled in the first stope are arranged, as also indicated in Fig. 184, in two rows of three holes each, one at each corner, and one near the middle of the top and the bottom of the stope. " Orebody. The average thickness of ore is 6 to 9 ft., though it is sometimes followed as thin as 2 ft., and has occurred 25 ft. /" 0000 J 1 1 '4 2 2 O I 1 1 2 2 2 f O 3 1 2 J o 4- 6 : e. 80-ft-r , o > 3 - ? 2 Faces of Stopes Section through Stopes. and Profile Section through A-A FIG. 184. Drift stoping, Joplin, Mo. thick. Two layers of mineral separated by a thin layer of rock are removed simultaneously with the dividing seam. Mineral rarely occurs here in layers so far apart as to prohibit working in this manner. When widely separated they are sometimes worked simultaneously, but more often the upper stratum is exhausted before the lower is touched, except for developing purposes. ' Breaking the Ore. The mineralized ground is composed of very hard flint, compactly bedded. A wide range of notions prevails as to methods of ground-breaking, but the conventional position of the holes and their number are represented in Fig. 185. Each set of four holes, considered a round, should break an aver- 308 ROCK DRILLS age of 30 tons of dirt, 9 to 10 ft. laterally and from the roof to the floor. The top hole, No. 2, on the vertical median line of the area to be broken and very near the roof, is so directed as to break the roof level. Holes No. 1 and No. 3, equidistant from the median line, are 3 ft. from each other and the roof. The stope hole, No. 4, as near the floor as the drill will allow, slants so the shot will lift clean to the floor. The lateral direc- tion of these holes varies with the individual taste of the machine man. All are uniformly 9 ft. deep, started with a IJ-m- bit, and finished with a If to 1-in. steel. " After squibbing to enlarge the bound end of the hole for FIG. 185. Arrangement of holes for breaking ore, Joplin, Mo. powder, the holes are loaded with 50 Ib. of powder, Nos. 1, 2, and 3 receiving half and No. 4 the remainder. The blasts are fired as numbered in the figure." ROCK-DRILLING PRACTICE IN UTAH The following data concerning the method of quarrying the soft porphyries of Bingham, Utah, 1 are given by W. R. Ingalls. " Loosening the Ground. The Boston company loosens the ground by sinking holes with churn drills and exploding large charges of dynamite in them. It has five Keystone drills for this work. These use a 5|-iri. bit, making a hole about 6J in. in diameter, which is sunk to a depth of 150 or 160 ft. The holes are put down 15 to 20 ft. below the level of the bench that is 1 Eng. and Min. Journ., Sept. 7, 1907. EXAMPLES OF ROCK DRILL PRACTICE 309 being broken, so as to insure loosening of the ground below the level on which the steam shovel is at work and prevent the exist- ence of unbroken knobs in the floor, which would be troublesome to the shovel. The holes are put down about 30 ft. apart and at such distance back from the face of the bench that the horizontal distance from the face at the bottom will be about 30 ft. From six to nine holes are shot at a time, with 1200 to 4700 Ib. of dyna- mite per hole. Dynamite with 40 and 60 per cent, of nitro- glycerine is used, the former grade being most commonly employed. This grade costs 11.5 c. per Ib. at Bingham. As much as 225,000 tons of rock have been dislodged by a blast of nine holes, the powder cost being about 1.5 c. per ton. " In the Utah mine the ground is loosened by means of 3j-in. Ingersoll air drills, which put down holes 20 ft. deep with IJ-in. steel star bits. These holes are put down 15 to 20 ft. apart, about 20 ft. back from the face. It is obviously a less efficient method of loosening the ground than that which has been adopted by the Boston company. The extensive character of the under- ground workings in the Utah mine is practically prohibitive as to the use of churn drills there." METHOD OF EXCAVATING ROCK IN LARGE MASSES 1 The following notes are taken from experience in heavy rock excavation on the line of the Grand Trunk Pacific Railroad in the region of the Lake of the Woods. The rocks of this locality consist of hard granites, traps, and diabase of the Laurentian and Huronian systems. Owing to the extreme hardness of the rocks the expense of drilling is very high, consequently deep holes and heavy blasts are used wherever permissible. " Hand and Machine Drilling. In the smaller cuts hand steel is used for putting down the blast holes, which are often drilled to a depth of 30 ft.; 1-in. steel is used, and the same gage, lf-in., is carried throughout. The holes are started with two hammers on a drill, and when down 5 or 6 ft. the drill turner also swings in with a hammer; the rapid blows jump the steel enough to bore a fairly round hole. The average depth drilled per day by three men is 16 to 29 ft., and 45 c. is the average price paid to foot drillers. " Steam drills are generally used in the big cuts, a 3-in. machine 1 By Geo. C. McFarland, Eng. and Min. Journ., Aug. 3, 1907. 310 ROCK DRILLS drilling to 25 ft. and a 3i to 3^-in. machine drilling the depths of 30 and 35 ft. In using steam the only change required for an air drill is a steam front head and thin paper gaskets in the outer joints. Flexible metal steam hose is used exclusively, the oiler being placed at the end of the steam pipe to lubricate the hose as well as the machine. When several drills are run from the same boiler, a sight feed lubricator can be placed on the main steam pipe. This saves the runner the bother of oiling and insures a regular and continuous lubrication of the hose and machines. "The life of the metal hose is about six months, as against two months for the best grades of rubber steam hose. When drilling over 20 ft. the steam pressure is run up to 115 Ib. or more. During the past winter drills were operated when the temper- ature was 45 below zero, some of the machines being 500 to 600 ft. from the boiler. "Drill Steel. For deep holes the drill steels are made up for 24-in. runs, the starters being gaged 3| in. and the gage being dropped f to -fg in. for each succeeding steel, so as to finish the hole about 1J in. The bits are forged with long, heavy shoulders and very little clearance to reinforce the corners of the cutting edge and prevent excessive wear in the gage. The last two or three drills of the set are usually fitted with blunt chisel bits. "The cheaper grades of drill steel are used almost exclusively; the high-grade brands of bar and cruciform steels require to be forged and dressed at low heat, and even when properly dressed and tempered wear as fast as the low-priced drills. The latter, while they can be forged at a much softer heat, will not stand excessive upsetting, and it is often good practice to weld on short lengths of heavy steel to form the bit. " In tempering, the bit should be toughened by heating to a bright red heat, then plunged into the water f to J in. and held there 15 to 20 seconds, soused a few times until the part out of the water is cooled sufficiently to show no color, and finally immersed in the tub until cold. If tempered in this manner a drill will show \ in. of cutting edge, with a fine gray temper backed by softer tough metal. "Method of Drilling. The usual practice is to drill the blast hole on the center line of the cut. A 15-ft. hole is set back 15 ft. and a 30-ft. hole 25 ft. from the face of the cut. Where the cut EXAMPLES OF ROCK DRILL PRACTICE 311 is much more than 30 ft., it is best to take it out in two benches. In granite the average footage drilled by a machine is 30 ft. per 10-hour shift, while in trap and diabase 20 to 25 ft. is considered a good shift's work. "After drilling, the bottom of the whole is chambered to the required size by springing with dynamite. In the bottom bench, where a heavy lift is required, no more than a foot of the hole is chambered; in the upper benches it is permissible to chamber 2 or 3 ft. of the bottom. In the first case each spring would be loaded until the dynamite raised 8 or 10 in. ; in the second, a 12- or 15-in. raise would be permissible. The first springs are held down by 5 or 6 ft. of water tamping and detonated by a cap-and- drop fuse. The fuse, usually 12 in. long, after being split is held under water for 5 or 6 seconds to kill any fire hanging in the taping, and then dropped into the hole. Unless the drop fuse were dipped in water, it might ignite dynamite adhering to the sides of the hole, causing a premature explosion. After each water spring, the hole is blown out with steam or pumped out with a sludge pump. Usually two or three water springs will be used; the succeeding springs are tamped up with sand and detonated with a battery. "Two exploders are always placed in a hole, as it would be exceedingly hazardous to draw the tamping in case of a misfire. Misfires with a battery are, however, extremely rare. Usually the spring will not throw the tamping if more than 6 or 7 ft. are used. "Blasting. Springing is continued until it is estimated that the pocket is large enough to hold the blasting charge. The charge is computed from the number of cubic yards the blaster estimates will be thrown out. The springing opens up the rock jointing and indicates very closely where the burden of the shot will cleave from the solid, and the successive springing charges indicate the ratio of enlargement of the pocket. At least 60 Ib. of black powder or 40 Ib. of dynamite should be loaded for each 100 cu. yd. of the shot. "The following are typical springing and blasting charges: (1) A 25-ft. hole, burdened 18 ft., in the bottom bench of a 45-ft. cut first spring, 2 sticks (60 per cent, dynamite); second spring, 4 sticks; third spring, 10 sticks; fourth spring, 25 sticks; fifth spring, 60 sticks; sixth spring, 100 sticks; seventh, 180 sticks; 312 ROCK DRILLS blast charge, 325 Ib. black powder. (2) A 25-ft. hole, burdened 12 ft., in the upper bench of a 45-ft. cut first spring, 6 sticks (60 per cent, dynamite); second spring, 20 sticks; third spring, 60 sticks; fourth spring, 125 sticks; blast charge, 325 sticks (150 Ib.) of 40 per cent, dynamite. " The effective force of the blast is a short powerful blow equiva- lent in length to about one-half the diameter of the powder charge. This blow is transmitted in all directions. In the immediate vicinity of the powder charge the compression is so great as to crush and pulverize the rock. As it expands toward the free faces its energy becomes absorbed by the elasticity of the rock, and the recoil from the compression throws the rock out, the propulsion being assisted by the backlash of the wave of com- pression from the solid behind the shot. The rock is heaved out not so much by direct propulsion from the seat of the explo- sion as by the momentum of the transmitted shock which is greatest near the free faces. The natural rock jointing materially influences the results of a heavy blast. "Conditions Affecting the Blast. The heavy springing opens up the jointing and the blocks shift irregularly on the bed planes, often completely closing off the drill hole. Here is one great advantage of machine-drilled holes, for owing to their greater diameter they permit of considerable shifting before the hole is cut off. The effect of floors and slips between the explosive and the free faces is to cause the rock to cut off at one of these floors while the rock around the explosive is merely crushed and shat- tered. These slips and floors deaden and deflect, or at least imperfectly transmit, the shock of the explosion. On the other hand, if the slips and floors are behind and under the blast charge, the momentum of the rock ahead of the shot would tear back to these slips and floors, giving a great deal more muck than would be expected. "The slips and floors put a practical limit to the size of the blast. I find that this limit is reached with 30-ft. holes, burdened 15 ft., and throwing out from 400 to 800 tons of muck. "The remark is often made that water is the best tamping for dynamite. As a matter of fact, I note that, in springing, water tamping is always blown even if the hole is full of water, whereas 7 or 8 ft. of sand tamping is seldom blown out unless the rock is very tough and the bottom of the hole dead on the solid. EXAMPLES OF ROCK DRILL PRACTICE 313 "Loading. The following precautions should be observed in loading blast holes. The loading stick should be a single straight- grained stick 1J in. in diameter at the middle, tapering to 1 in. at the ends. It is made by dressing down a long tamarack sapling. Before loading a hole, put in the loading stick for ten minutes and see that it is cold for its entire length as it is with- drawn, because a hole may be cold on the bottom and hot a few feet above. After a heavy spring the holes should be allowed to cool for hours ; sometimes the gases catch fire after an explosion, and burn quietly for an hour or more in the hole. Never load partially thawed dynamite, and in loading a ragged hole do not skin the cartridges. Simply slit the paper in two or three places. If loose dynamite is put in, it lodges in crevices along the sides of the hole and is liable to be exploded by the blow pipe or churn drill used to draw the tamping after firing the springs. Use exploders with lead wires as long as the hole. " Ragged holes are more easily loaded with black powder than with dynamite. I have loaded holes in which the springing had shifted the rock so that a loading stick could not be shoved down, by simply pouring in the powder, lowering the primer and lead wire and then pouring down dry sand. Of course this is taking big chances, for the hole is liable to plug up with the first keg. Black powder can be used only when the hole is dry. A wet hole can often be dried by firing a few sticks of dynamite in the pocket. Black powder requires more tamping than dyna- mite. Not only the hole itself but all crevices showing in the rock above the blast should be tamped with dry sand. ' ' I find that three kegs of black powder are equal to 50 Ib. of 40 per cent, dynamite. Neither dynamite nor black powder will throw a good shot if the rock has been shaken up too much by previous springing. With large burdens the heavy springing opens up the seams so much that excessive powder charges are required to make a shot; and the explosive is liable to kick back through a seam and leave a standing shot. The muck from a very heavy blast is usually coarse and requires much block-holing or bulldozing before it can be handled. The most economical shots are from holes 16 to 24 ft. deep and burdened from 12 to 15 ft. It is very seldom that a heavy blast throws the rock far, the bulk of the muck being heaved out 20 to 50 ft., and very rarely are any fragments thrown more than 150 ft. 314 ROCK DRILLS " Cost of Excavating. In the accompanying table is given the cost of excavating and moving a cubic yard (4400 Ib.) of red granite, steam drills being used for drilling and stone boats and pole tracks for hauling out the rock, the average hight of the cut being 46 ft. and the average haul 500 ft. The item of general expense covers the cost of hauling in the outfit and of building log camps for men, etc. Aside from this item the actual cost of breaking and hauling the rock is 87c. per cu. yd., or a little less than 40c. per ton." COST OF EXCAVATING RED GRANITE Per Cu. Yd. Breaking. Drilling blast holes $0.048 Labor, springing and loading holes 0.030 Dynamite 0.084 Black powder 0.024 Wire exploders 0.008 $0.194 Handling the Broken Rock. Block-holing and bulldozing $0.104 Loading 0.308 Haulage 0.165 $0.577 General expenses . 0.250 Total $1.021 XIV ROCK DRILL TESTS AND CONTESTS NOTES ON ROCK DRILL TESTS AND THE POSSIBLE LINES OF FUTURE DEVELOPMENT OF DRILLING MACHINES IT has been very truly said that the only test to which a rock drill can be subjected with any fairness is to put it to work under mining conditions for an extended period. I have already emphasized the importance of wear as bearing on rock drill efficiency, also the mining conditions and treatment as effecting their design. There are many types of machines that we know stand this test and do an average amount of boring. It might reasonably be urged that we wish to know other things about these drills, which, though secondary matters, are important in themselves. It is difficult to keep a record of actual footage bored in working time over such a period. We might wish to know as among any number of makes of rock drill what is the relative air and water consumption; the relative boring speed under similar conditions; the relative time of actual boring to the total working time; the relative efficiency in boring dry holes and wet down- holes; the relative efficiency with different air pressures; the relative percentage of energy supplied to the drill that is turned into actual work in boring rock; the reason for any difference, if found; the number of blows per minute, and what is the minimum difference in gage that can be employed in following sizes of steel. The relative cost of up-keep we can learn from mine account books. A test to give all this information has never yet been carried out. It would involve an immense amount of labor. Enough has been done to show how such information should be sought. The most thorough tests ever made of a rock drill were those conducted on the Torpedo baby "Corliss Valve Drill," by Hol- loran & Hamilton. Determining Number of Blows. To determine the number 315 316 ROCK DRILLS of blows struck per minute, a roll of stout Manila paper was mounted on a vertical spindle, and pulled rapidly in front of the bit so as to be punched by it. The paper was unwound for 15 seconds; the number of holes multiplied by four gave number of blows struck per minute. The machine was 2J-in. cylinder- diameter, with a stroke from 4 to If in. long. The number of blows struck per minute varied from 540 at 50 Ib. pressure to 896 at 99-lb. pressure; at 60 Ib. the number was 566; at 70 Ib., 626; and at 80 Ib., 660. Shortening the stroke to 2f in. greatly increased the number of blows per minute. At 60 Ib. the number was 829; at 70 Ib., 866; at 80 Ib., 935; and at 90 Ib., 993. Air Consumption. This was measured by connecting the exhaust to a 100-gal. tank as a receiver, and then carrying the air to two 300-light wet gas meters. In the measurement of the flow of gas the product of the absolute pressure, p, by volume, v, divided by absolute temperate, t, is a constant ; pv = constant. If P and T are kept constant the quantity discharged will vary as the volumes, and if P and T are known, the quantity can be computed. The gas meter is arranged with a series of chambers which are alter- nately filled and emptied of gas. Air consumption was 39 cu. ft. per minute at 70 Ib. pressure; 47 at 80 Ib.; 37 at 60 Ib.; and 33 at 50 Ib. These results were checked by measuring volumes in cylinder, taking temperature and number of blows per minute. Determination of Absolute Force of Blow with Varying Length of Stroke. The piston and drill were allowed to fall freely and indent a lead bar placed on an anvil. The hights of fall varied, and the indentation was measured. The indentation produced by the rock drill working at a certain pressure, with strokes of 4J in., 3J in., 2 in., and If in., was then compared with them, each being measured by a vernier micrometer. Trie foot-pounds of energy developed by a body of known weight falling a known distance can easily be calculated, V = \/2 gh. The foot-pounds per minute = 21 Ib. X hight X number of blows per minute. The If -in. stroke gave a vis viva for a single blow of 46.2 foot- pounds. The 4J-in. stroke gave 53.2 foot-pounds. With the If -in. stroke these was no cushioning effect, whereas there was some with the 4J-in. stroke. Yet in practice it would appear that the added force of blow gained by a long stroke does not make up for the loss of number of blows per minute. The authors say: "It has been found that a greater number of less powerful blows ROCK DRILL TESTS AND CONTESTS 317 does more work than a smaller number of greater blows." Yet it will be observed that most modern rock drills are designed on ex- actly the opposite principle the stroke being made long to kick mud from out the bottom of the hole. The force of a drill on rock cannot be exactly calculated as the force will be different for differ- ent substances, each having a different resistance to indentation. The writers say the consideration of the different rate at which the number of blows per minute increase with rise of air pressure " suggests the value of a careful investigation of the character of every rock drill and the condition under which it will do the best work." The assumption that an increased pres- sure means increased work is not always true. The best pres- sure indicated for this drill the authors consider to be 100 Ib. With hollow steel and water injection it might be run on a 2-in. stroke to greatest advantage. DRILL TESTS Mr. H. P. Griffiths 1 gives particulars regarding trials carried out in 1902. The machines tried were the Climax air and tappet valve, Rio Tinto drill, Holman drill, Champion Eclipse drill. The machines had to bore two holes on a faced rock. The quan- tity of air consumed was computed from dimensions of compressor, number of strokes, exact measurement of receiver, due correc- tions being made for temperature. The following were some of the conclusions arrived at as a result of the test: (1) Cross-bit bores further than chisel bit and bores a hole of larger capacity. (2) The wear is less on cross-bits than on chisel bits. (3) Air valves are more economical to work than tappet drills. (4) All drills, except the Eclipse, had exhaust ports of too small area. (5) Within reasonable limits the fewer the number of blows per minute the better the results. It is not stated how this conclusion was arrived at. (6) All valves leaked owing to negative lap. (7) Lightness of reciprocating part is necessary. (8) The effectiveness of blow depends more upon the velocity than upon the mass of the reciprocating part. These last two conclusions appear contrary to theory and practice. Theoretically the kinetic energy of the blow = MV 2 , where M = mass and V = velocity. Doubling the velocity increases the energy of blow four times, while M must be increased four times 1 Journal Mech. Eng. Assn. of South Africa. 318 ROCK DRILLS to accomplish the same result. The air consumption for an air pressure falling from 75 to 50 Ib. for these drills showed: 3^-in. drill, 178.9 Ib.; 3f-in. drill, 130.4 Ib.; and a 3-in. drill, 118.3 Ib. In 1903 a series of tests was carried out in Johannesburg by Messrs. Carper, Goffe, and Docharty. The results were recorded in the Journal of the Mechanical Engineers' Association of South Africa. All holes were drilled by 3-in. to 2-in. diameter star bits, ver- tically, into a block of granite 4i X 4i X 2 ft. Two air receivers had a capacity of 756.6 cu. ft. Machines were rigidly set up. Each run was conducted as follows: The compressor was worked until the gage on the receivers showed the required starting pressure (say 80 Ib.). The stop valve was then shut, closing con- nection with the compressor. The machine being in position on the bar and all ready was then started, and drilling continued until the terminal pressure of that stage (say 70 Ib.) was shown on the receiver. The machine was then stopped and the depth of the hole carefully measured and recorded. The times of starting and stopping were taken, and lengths of any stoppages during the run noted, the net time of the run being thus found. The machine was then restarted at 70 Ib. pressure and run to 60 Ib. and again measured, and so on for each stage down to 35 Ib. Before start- ing a hole the bit was carefully measured. On starting and stopping each stage of the run the pressure and temperature of the air passing through the machine was observed as well as the atmospheric pressure shown by barometer. It was intended originally to go through all the stages of pres- sure for each drill with one hole, but the stone was too thin and this scheme had to be modified; the plan was adopted of running the first two stages only, viz., 80 Ib. to 70 Ib., and 70 Ib. to 60 Ib., in one hole, then starting a new hole with a new drill bit and running three stages, viz., 60 Ib. to 50 Ib., 50 Ib. to 40 Ib., and 40 Ib. to 35 Ib. Calculation of Volume of Air. The following is the method adopted for calculating, from the observations taken, the quan- tity of air used by the drills: The standard of free air at 24.8 in. barometer with 70 F. tem- perature was adopted. Johannesburg is 6000 ft. above sea level. The pressure in pounds per square inch, due to pressure of atmosphere, was found by multiplying the barometric reading in inches by 0.4908. ROCK DRILL TESTS AND CONTESTS 319 The formula V l = V X t\ X 1 where V = Volume of 1 cu. ft. at standard pressure, and tem- perature = T Vi = Volume of 1 cu. ft. standard free air at new pres- sure and temperature P = Standard pressure (absolute) = 12.17184 Ib. p t = New pressure (absolute) T = Standard temperature (absolute) = 531 F. TI = New temperature (absolute) was used to find the volume of 1 cu. ft. of standard free air at any other pressure and temperature. Then taking the required observations for the stage 80 to 70 Ib., and working them out as an example, we have, at start of run: Gage pressure = 80 Ib. Barometer = 24.95 = 12.24546 Ib. Temperature = 100 F. Pi = 92.24546 Ti = 561 Therefore 12.17184 X 561 F ' = 92.24546 X 531 The cubic contents of the receiver, as stated, was 756.5 cu. ft. Evidently then the amount of standard free air contained will be 5426 - 8 cu - ft - > : ,. : Take next the conditions at finish of run Gage pressure = 70 Ib. Barometer = 24.95 = 12.24546 Temperature = 99 F. Pi = 82.24546 Ti = 560 Therefore, 12.17184 X 560 82.24546 X 531 = 0.15607 cu. ft. 320 ROCK DRILLS and the free air contained 756.5 = 4847.2 cu. ft. 0.15607 The amount of air consumed during the run will be the differ- ence between the contents at start and finish - 5426.8 - 4847.2 = 579.6 cu. ft. Air Consumption. The average of thirteen 3j-in. drills gave the following results as to quantity of air used at various pressures: Cubic Feet Mean Pressure Lb. per Sq. In. Ratio of Boring per Min. Inches 124 75 1.3 117 65 1.1 100 55 1.0 70 45 0.6 60 37^ 0.5 Rifling. These tests yielded much valuable information, but many of the results and the deductions drawn from them have to be accepted with caution. Most of the machines that in prac- tical work give no trouble were reported as rifling the hole badly and refusing to rotate. The drill bits used were not of uniform quality. Undoubtedly the chief mistake made was in starting holes with machines drilling at full speed. This was undoubtedly the cause of most of the rifling. No mine would think of start- ing a hole in hard rock in this way, as the vibration set up makes the bit strike the mouth and sides of holes. Table II shows particulars of runs carried out with 3J-in. drills of three types: Air valve machine Slugger; tappet valve Lit- tle Giant; auxiliary valve Ingersoll-Sergeant. For comparative purposes the run of the Ingersoll machine was spoiled by rifling. The figures from a similar run of a 3-in. Leyner hammer drill are shown by comparison. Why this drill did not show as high an efficiency as the piston drills is not known. These figures are interesting in showing the increase of drilling speed due to increased air pressures with corresponding increase of air con- sumption. It is interesting to note that at present few Slugger machines are working in this field and also comparatively few tappet machines. ROCK DRILL TESTS AND CONTESTS o . 321 a .2 x S3 ^ o *-< 1 2 S 02 5 a o * -g J 5 CG M o I o fC co cct- IN 10 t^. OiO OCOIN ^H d w K> csi e cJTfco ci ^ r-4 CD O CO t- O CO 00 O5 -* oit^cc d 10 O t^ Tft r-l codi>dd I-H O O -tfO v 03 3 5f H J -^ O * o O N I s 02 K TJ* (N 00 IM >O NrHt^.^. COOOO * ^kdidrHTiH t^idriH d O CO 00 ^ d COC4 d "5 S < O2 *Q S Na Size Cond : 2 ,_ 55 S P P H WWW 322 ROCK DRILLS TABLE II. ^ame Q drill INGERSOLL 3J Bore 3J in. Stroke 6} in. SLUGGER Bore 3J in.; gi ze Weight Condition 277 Ibs. New, from Robinson G. M. Co. 321 Ibs. New, from Reference No. of run 1 1 29 29 29 Totals 48 48 Air pressures (gage), Ib. per aq. in 80.70 70.60 60.50 50.40 40.35 80.35 80.70 70.60 45 Ibs. fall Size of bit, in. 3 3 3 3 3 3 3 3 Net time of run min 6.083 3.25 5.416 7.8 4.416 26.965 7.166 7.582 Depth drilled in. 7 1.15 5 1.54 6.875 1.26 5.625 0.72 5.75 0.62 27.25 1.01 10.625 1.48 8.375 1.10 Depth drilled per minute, in. Capacity of hole drilled, cu. in 49.48 35.34 48.59 39.76 19.44 192.61 75.10 59.20 Equivalent free air used at 70 Fah., 24.8 in. barom- eter, total cu. ft 642.7 611.4 620.3 610.3 301.8 2786.5 653.3 643.9 Equivalent free air used per in drilled cu. ft. 91.8 122.3 90.2 108.5 109.7 102.2 61.5 76.9 Equivalent free air used per min. run, cu. ft 105.6 188.1 114.5 78.2 68.3 103.3 91.1 84.9 Equivalent free air used per cu in of hole, cu. ft. 12.99 17.30 12.76 15.35 15.52 14.46 8.70 10.80 Notes on run M a c h i ne ran Rotation bad from start. Very satisfac- short stroke. Machine sluggish on t ory run. Rotating badly. return stroke. Drilled good Drill bent and round hole. hole rifled, caus- No stop from ing drill to drill sticking. bind and stick in hole. Consid- ered machine should be run again. A trial was also made with a 2J-in. Slugger machine (Table I) using different sized bits. The results are interesting as showing how, other things being equal, speed of drilling varies inversely as the area of hole excavated within certain limits. It shows the ROCK DRILL TESTS AND CONTESTS ROCK DRILL TESTS 323 Stroke 6J in. Agents (Fraser & Chalmers). 3t LEYNER WATER Bore 3 in. ; Stroke 3 in. 156 Iba. New, from Agents (Leyner & Co.). 27 27 27 Totals 19 19 20 20 Totals 60.50 50.40 40.35 80.35 80.70 70.60 80.70 70.60 80.60 45 Ibs. fall 20 Ibs. fall 3 3 3 3 2A 2 A 2| 21 2i' B 21 8.550 11.666 6.416 41.381 5.333 6.166 7.0 6.5 25.0 8.375 6.375 2.812 5 36.562 8.0 8.5 8.25 8.125 33.125 0.98 0.54 0.44 0.88 1.50 1.37 1.21 1.25 1.32 50.29 45.06 19.88 258.44 26.73 29.38 30.14 28.82 114.08 653.6 616.8 296.2 2863.8 614.6 621.7 608.8 609.9 2455.0 78.0 96.7 105.3 78.3 76.8 73.1 71.6 75.0 74.1 76.4 52.8 46.1 69.2 115.2 100.8 86.9 93.8 98.2 11.04 13.68 14.90 11.08 23.0 21.89 20.2 21.16 21.52 Machine run loose in Excessive vibra- Repeated same stage cradle. Hole slightly tion. Hole run with drill bar rifled. No stoppage b a d ly rifled. fast. Fair run, no from drill sticking. D r ill bar stoppages. slightly loose at start. importance of keeping the difference of following gages of bits as small as possible, and drilling the hole of the minimum size required to hold sufficient charge to break the rock. 324 ROCK DRILLS Gillette gives the following summary of the results of tests carried out at the Rose Deep mine, South Africa, by Major Seymour: Test of Air Consumption at the Rose Deep Mine. A six-hour run at the Rose Deep Mine, South Africa, showed the following results for 31 drills: The compressed air averaged 70 Ib. per square inch and each 3J-in drill consumed 81 cu. ft. of free air per minute, including all leakage of pipes (there was less leakage than is com- mon in mines). Each drill required 43 Ib. of coal per hour, to supply this compressed air; and each pound of coal developed 3.4 h.p. per hour, by the indicator on the steam engine, evaporat- ing 6.74 Ib. of water from 212 F. The average h.p. of the com- pressor engine was 12.7 i.h.p. per drill; but all the drillers were trying to make a record and accomplish in six hours an amount of drilling that ordinarily took eight hours. It was an efficient steam-power plant, as is seen by the fact that 3.4 h.p. were devel- oped with each pound of coal. The power plant was a vertical King-Reidler compound steam engine and double stage air compressor with two boilers of the horizontal return tubular type. The engine developed 393 i.h.p. and had a mechanical efficiency of 86 per cent. There were several sizes of machine drills used, but they were all reduced to the 3j-in. size as standard by the test of filling the cylinders, ports, etc., with water and ascertaining the volume of water for each drill cylinder. This showed the rating of the drills in air consumption to be as fol- lows: Relative Air Consumption 2j-in. drill 0.445 3^-in 1.000 3^-in 1.069 3f-in. . 1.123 The 31 drills averaged 4.5 ft. of hole drilled per hour for the 6-hour run; one 3J-in. drill making 52 ft. of hole in six hours; drill- ing four dry holes. Comparing the consumption of 81 cu. ft. of free air per minute, at 70 Ib., with the average of 120 cu. ft. (at average of 70 Ib.) given in the first two items in the table on page 321, gives a fair idea of the difference between a long test using a number of drills, and a short test of one drill. ROCK DRILL TESTS AND CONTESTS 325 Horse-Power Tests. M. K. Schweder in 1897 made experi- ments showing that the h.p. required at 65 Ib. air pressure was 17.8 per drill, but he assumed that all drills were running. Mr. C. E. Hut ton, in a paper read before the South African Association of Engineers, gives the accompanying Table III:_ TABLE III. ROCK DRILL TESTS Van Ryn Gold Mines Estate, Ltd. 1 *]t W M Name of Machines Average Time Worked per Machine Average Depth Drilled per Machine Average Depth Drilled per Machine per Min A 160.5 97.5 258 Minutes Inches Inches B 64.5 46.25 110.75 Ingersoll 99 1 f\ O 267 C 154 94.75 248.75 5 machines ~ir =19.8 o ~5~ = 53.4 2.69 D 162 91 253 E 157 89.75 246.75 Hercules, 115-6 288.5 7 machines _ = lb.5 7 2.49 F 153 89.75 242.75 G 155.5 100 255.5 Slugger, 175 414.5 H 167 92 259 8 machines = 21.87 ~8~~ 51 ' 8 2.37 I 111.5 67.25 178.75 J 165 98.5 263.5 Holman, 55.75 165 2 machines = 27.87 =82.5 2.96 K 90 54.5 144.5 L 165 97.5 262.5 Average i.h.p 223.9 Revs, of compressor during test for one hour. 2,639 revs. Volume of free air taken in at compressor . . . 100,492 cu. ft. Loss in air column and receivers in free air (see separate test) 16,905 cu. ft. 40.5 leakage loss Balance for use at drills 83,587 cu. ft. 83,587X85 Corrected to sea level Volume at 75 Ibs. pressure per sq. in 100 71,050X14.7 = 71,050 cu. ft. = 11,645 cu. ft. 75+14.7 Mr. Hutton also states that "the late Mr. L. I. Seymour, in his paper on the tests of a King-Riedler air compressor, read before 326 ROCK DRILLS this Association, showed that the average i.h.p. per drill was 12.72 and the total footage drilled in six hours 840; to get this footage of 840, the compressor had to exert continuously over the whole six hours 373 i.h.p., and making a comparison with the Van Ryn test of one hour, we get the following: Rose Deep, 373 i.h.p. exerted for one hour to drill 140 ft. Van Ryn, 227 i.h.p. exerted for one hour to drill 94.5 ft. or, again, Rose Deep 1, i.h.p. exerted for one hour to drill 0.3780 ft. Van Ryn 1, i.h.p. exerted for one hour to drill 0.4163 ft. Therefore, if the Van Ryn drills were working full strength one- third of their time and accomplished practically the same footage as the Rose Deep, one's natural conclusions would be that the Rose Deep drills ran only about one-third of the time. The enormous fluctuation of the air pressure shown by Mr. Seymour also goes to prove that the drills must have at times drawn from the air capacities to such an extent that although the compressor was running its hardest, the pressure could not be maintained; therefore, instead of a drill absorbing 12.72 i.h.p. for six hours, a drill with its proportion of pipe loss, etc., really absorbs some- thing like 37 i.h.p. for two hours. "Referring to test sheet, Table III, which gives details of i.h.p. and certain other particulars regarding work done by the rock drills and the air consumption by them, it will be seen that over a test of one hour made with 22 machines running, the i.h.p. of the air compressor averaged 227, although the actual running time of the machines only averaged 20.2 minutes out of the 60. It must be remembered that these results were obtained at a time when it was positively known that there were no leaks of any noticeable magnitude in the air mains either on surface or underground, and that the machines were in good condition; therefore it may be taken that the conditions were somewhat better than would be found in the average practice. "The short time actually run by the machines out of a pos- sible 60 minutes shows how large a percentage of the time the machines were off for changing drills, shifting positions of machines, etc., and when it is considered that notwithstanding all these stoppages and the short acutal running time of the machines, it was necessary to continuously exert an average of 227 i.h.p. ROCK DRILL TESTS AND CONTESTS 327 on the air-compressor steam cylinders, it can be realized what amount of power would have been required assuming that the whole of the machines had been run continuously through the trial hour. "This is, of course, to assume an impossible condition, but it is useful to realize that if the machines could be run continu- ously under the same conditions as in the test, that is, leaving the friction and leakage of the pipe lines, machines and compressor, with the same proportionate losses through drop of temperature, it would have been necessary to develop about 619 i.h.p. during the test to maintain a constant air pressure. On this basis the i.h.p. required on the compressor per rock drill run continuously in the mine would be 28, which figure therefore has been adopted at the Van Ryn as the prime basis for distribution of power to rock drills. It was, however, considered that the 4:est conditions might have been superior to the ordinary working conditions, and it was resolved to adopt a figure of 32 i.h.p. as representing the power developed in the steam cylinders of the compressor to run one drill in the mine; this figure, of course, to cover all the losses of the compressor, air mains, drop in air temperature, and machine inefficiencies." Losses in Compressed Air. It will be noted that Mr. Hutton found leakage losses to be 40.5 per cent. This large figure may be compared with a recent test at Meyer & Charlton mine when other losses were only 5 per cent., both being old mines. Regarding air consumption, E. C. Reybold makes the fol- lowing remarks: "This shows the amount of power thrown away by the fact that the drill exhausts air at full pressure. In order to secure as much power as possible from a given weight of drill, it is necessary to use the air non-expansively, and at the end of each stroke a volume of compressed air equivalent to the volume of the cylinder is discharged into the atmosphere. The energy thus wasted is measured by the power required to com- press to the given pressure a sufficient volume of free air to make a volume under pressure equal to the contents of the cylinder. This in cubic feet per minute for a 3i-in. drill of 6^-in. stroke, 350 strokes per minute, operating at 90-lb. pressure, the diameter of the piston rod being If in., is as follows: Area of cylinder, 8.29 sq. in.; area of piston rod, 2.07 sq. in.; volume of cylinder, forward stroke, 53.38 cu. in.; volume of cylinder, back stroke, 328 ROCK DRILLS 34.21 cu. in.; total displacement at 350 strokes, 30,831 cu. in., or 17.84 cu. ft. "The quantity of free air required to make 17.84 cu. ft. at 90-lb. pressure, together with the horse power required at vari- ous altitudes, assuming perfect cooling, with two-stage com- pression, is about as follows: Altitude Free Air Required Cu. Ft. H. P. Required to Compress 100 Cu. Ft. Total H. P. Required Sea level 5 000 ft. . 125 149 14.7 13.45 18.37 20.04 10,000 ft 179 12.33 22.07 "This gives the loss occasioned by exhausting at full pressure. The total theoretical horse-power that it is possible to transmit to the rock (forward stroke only) equals 8.29 sq. in. X 90 Ib. per square inch X 190 ft. per minute equals 141,729 foot-pounds per minute, or 4.29 horse power. "It will thus be seen that, when theoretically considered, it is possible to convey into actual work not more than 10 to 20 per cent, of the power used in compressing the air. When the losses from radiation from the air receiver and air pipe are considered, together with the friction of the air in passing through the pipes, as well as the friction in the air drill, loss of air from leaky valves, etc., it will be realized why so little of the power expended at the compressor is actually transmitted into work at the breast." Konomax vs. Ingersoll. In 1907 a test was conducted by J. A. McGeorge (the Journal of the Transvaal Institute of Mechanical Engineers) between a 3-in. Konomax drill and a 3i-in. Ingersoll-Sergeant drill. The test was carried out in the same manner as those by Messrs. Docharty and Goffe. It was open to the same objections, no holes being deeper than about 11 in. and the average about 6 in. Some of the results obtained are of interest in comparison with those already given. (See Table IV on opposite page.) It will be noted that the Konomax excavated one cubic inch of rock for expenditure of 8.4 cu. ft. of free air. For about the same pressures the Slugger drill in the 1903 tests used about 10 cu. ft. of air. It will be seen that the Ingersoll used 13.8 as against ROCK DRILL TESTS AND CONTESTS 329 TABLE IV. DRILL TEST, KONOMAX vs. INGERSOLL Name of Drill Size of Bit About Air Pressure per Sq. In. Average Drilling Inches per Min. Cu. Ft. Air (Free) Used per Linear Inch Drilled Free Air Cu. Ft. Used per Cu. In. Excavated Cu. Ft. Free Air Used per Minute Konomax . 2 80.7 1.62 41.7 8.2 66.2 Ingersoll Konomax Ingersoll . ... 2* 2 2 80.7 70.6 70.6 1.53 1.55 1.78 69.5 38.3 65.8 12.8 8.0 13.8 104.9 57.9 112.3 Konomax Ingersoll 2| 2| 60.5 60.5 1.26 1.67 36.8 58.2 9.2 14.5 45.5 93.2 14.46. Several obvious analogies show the results obtained to be not altogether reliable. For instance, the Ingersoll machine is shown to drill faster at 70 and 60 Ib. and to use more air at 70 than at 80 Ib. pressure. About the same time a test was made starting with holes 7 in. deep and drilling to a depth of 15 to 20 in. The air pressure was 50 Ib. and bits 2i-in. diameter. The result obtained was a drilling speed of 1.09 in. per minute for the Konomax drill and 1.7 in. per minute for the Ingersoll drill. Another test showed 1.21 in. per minute for Konomax drill at 50 Ib., and at 55 Ib. pressure, 1.48 in. per minute. In June, 1908, in the Journal of the South African Associa- tion of Engineers, Mr. E. J. Laschinger gives results of a com- parative working test lasting 15 days. The drills used were the new Konomax 3j-in. drills, new Ingersoll 3J-in. drill, and old Ingersoll 3J-in. drills, some of which had been at work for four years, but which had been recently thoroughly overhauled. This was designed as a practical test under working conditions. Many exact determinations were made. The accompanying Table V shows some of the data obtained. (See table on next page.) Some of the principal results are as follows : , (1) At 65.3 Ib. surface pressure, when drilling the same aver- age depth of hole (63 in.) and about the same percentage (average 8^) of dry hole, the Konomax drill used 24.4 per cent, less air per inch drilled than the new Ingersoll. During this test the Konomax drilled on the average 3.6 per cent, faster than the Ingersoll. (2) At 74.4 Ib. surface pressure, when drilling the same aver- age depth of hole (63 in.), and about the same percentage depth of dry hole (8.1 per cent.), the Konomax used about 5.1 per cent. 330 ROCK DRILLS TABLE V. ROCK DRILL TESTS MEYER AND CHARLTON MAY, 1908 PRINCIPAL DATA- AND RESULTS. AVERAGES PER DRILL SHIFT New Ingersolls A New Konomax B New Konomax C Old Ingersolls D Old Ingersolls E 1. Revs, of compressor chargeable 658.36 548.10 582.39 1021.29 1002.00 2. I. H. P. hours steam cylinders 41.924 34.879 39.428 72.261 65.991 3. I.H.P. hours air cylin- ders 38.769 32.204 36.898 66.268 60.595 4. Mechanical efficiency of compressor, per cent. . . . 92.47 92.33 93.58 91.71 91.8 5 Free air cubic ft. 19638.9 15360.0 17372.7 30465.1 20889.6 6. Inlet press, of air, bar. in. 24.780 24.828 24.722 24.666 24.660 7. Inlet press, of air, Ib. sq. in 12.17 12.19 12.14 12.11 12.11 8. Inlet temperature of air, deg Fah 83.96 85.58 76.60 80.40 81.51 9. Weight of air delivered, Ib. . 1187.2 987.3 1062.0 1845.2 1806.2 10. Press, at receiver, Ib. sq. in 65.30 65.30 74.39 73.16 64.20 11. Press, at llth Station, Ib. sq. in. 65.21 65.70 75.61 72.41 61.68 12. Temp, at llth station, deg. Fah 68.57 65.29 64.13 69.89 67.33 13. Depth drilled, in 301.87 332.47 335.95 . 286.48 287.15 14. No. of holes 4.7591 5.2042 5.3043 4.5417 4.6250 16. Average depth of hole, in 63.43 63.88 63.33 63.08 62.19 16. Ratio depth dry holes to total, per cent 8.16 9.04 7.12 12.36 11.23 17. Drilling time l hrs. and min. . 6 15 6 42 6 23 g 17 g 44 18. Revs, of compressor per inch drilled 2.1809 1.6486 1.7335 3.5650 3.4834 19. Steam H. P. hours per inch drilled 0.13888 0.10491 0.11736 0.25244 0.22942 20. Air H. P. hours per inch drilled 0.12843 0.09686 0.10983 0.23131 0.21066 21. Free air per inch drilled, cu. ft. 65.057 49.178 51.711 106.343 104 090 22. Lbs. air per inch drilled . 3.9329 2.9697 3.1612 6.4408 6.2901 23. Rate of drilling over total drilling time of shift, in. min. 0.8050 0.8270 0.8771 7599 7108 24. Relative rev. of com- pressor per inch drilled . . 100 75.59 79.49 163.46 159.72 25. Rel. steam power con- sumption of drills 100 75.53 84.50 181.62 165.47 26. Rel. air power consump- tion of drills 100 75.42 85.51 180.10 164.02 1 This refers to the time interval from commencement of first hole to finish of last hole. Average temperature of air in mine 68 F. ROCK DRILL TESTS AND CONTESTS 331 more air per inch drilled, while drilling about 6 per cent, faster than the same drills at 65.3 Ib. pressure. (3) The renovated old Ingersoll drills, at 64.2 Ib. surface pres- sure, used 59.7 per cent, more air per inch drilled than the new Ingersoll at 65.3 Ib. pressure, while the drilling speed dropped off. 11 per cent. (4) The renovated old Ingersolls, at 73.16 Ib. pressure, used 2.3 per cent, more air per inch drilled than when working at 64.2 Ib. pressure and drilled 6.8 per cent, faster. (5) From figures supplied by the manager of the Meyer & Charlton (Mr. Nitch), as to the revolutions of the compressor for five weeks previous to the test, when the old Ingersolls were working (before they were thoroughly overhauled in the shops), it appears that the old Ingersolls then consumed about 12 per cent, more air than after they were renovated. The footage drilled then was not measured, but was considerably less than during the test on the 27th May. Comparing this record with new Ingersoll gives the result that the old machines then used over 80 per cent, more air per inch drilled than new machines. (6) A dry hole took on the average 55.6 per cent, more time to drill than a wet hole, depth of holes 5 ft. (This is on the basis of total time from start to finish of holes, including change of bits.) (7) It is worthy of notice that, although the white men and natives drilling were unaccustomed to the use of the Konomax, they found no difficulty in handling it, and the work even on the first day was fully up to the standard. (8) It is also to be noted that the average depth of hole dur- ing these tests was only about 5 ft. 3 in. The deepest holes drilled were about 6 ft. These results would have been more interesting if old Konomax drills had also been available, and if it had been possible to get some idea of the number of .cubic inches drilled for a comparison with other tests regarding air consumption. The air consumption for linear inch drilled is naturally smaller than that shown in other tests, owing to the smaller average diameter of bits employed. STOPE DRILL TESTS In December, 1907, a series of trials of small stoping machines was carried out by the proprietor of the South African Mining 332 ROCK DRILLS Journal in Johannesburg. This was supervised by Professor J. Orr. A number of most exact determinations of boring speed in wet and dry holes with bits of various diameters were made. The accompanying Table VI shows the machines used: TABLE VI. THE MACHINES TESTED Name of Drill Type Diameter Cylinder and Valve Length Stroke Weight Hammer Hammer 31-in. Valveless 3" 12 Ibs. Little Wonder Piston 2-in. Tappet valve, hollow steel 5" Gordon Hammer 116-in. Spool valve, hollow steel 10" IJlb. Little Kid Piston 2-in. Little Giant, tappet valve 5" Baby Ingersoll Piston 2J-in. Arc valve, tappet 5" Flottman Hammer 2-in. Ball valve 3" 3 Ibs. Little Holman Piston 2-in. Auxiliary valve and spool valve 5" Chersen Piston 2f-m. Vale valve 6" This test was most carefully carried out, the machines boring for four hours on the surface and sixteen hours underground. The winning drill, however, proved an utter failure in actual practice. Drilling Speed and Air Practice. The increase of drilling speed in relation to air pressure is shown in accompanying Table VII. Relative air consumption and number of blows struck per minute were not exactly determined. The air consumption of the 2-in. Holman drill has since been determined at 60 Ib. pressure to be 30 cu. ft. of free air per minute. TABLE VII. SHOWING INCREASE OF DRILLING SPEED WITH INCREASE OF PRESSURE Name of Drill Depth Drilled at 50 Ibs. Air Pressure Depth Drilled at 60 Ibs. Air Pressure Percentage Increase in Depth Dr'lled at 60 Lbs. Pressure Kimber . . . 12' llf" 16' 7f" 28' 4f" 15' 9f* 25' 3" 18' 19f 14' 41' 26' 5f ' 16' 11" 19' llf" 36' 91' 22' 6i" 29' 6^" 25' 4| 17' or 33' 2" 30.6% 19.7% 29.5% 42.6% 17% 34.4% 18.6% 26.0% Little Wonder . . . Gordon . . Little Kid . . . Baby Ingersoll Flottmann Little Holman . . Chersen Mean percentage increase . 27.3% ROCK DRILL TESTS AND CONTESTS 333 The thorough manner in which results were recorded in the surface trials is shown in Table VIII on page 336. TRANSVAAL STOPE DRILL COMPETITION The accompanying table gives some results of the Transvaal stope-drill competition with simple averages of distances drilled and air consumption worked out. The pressures used were not uniform up to September, but during that month they were most closely regulated, varying from 69.1 Ib. per sq. in. on the Siskol to 60.1 on the Holman. CHERSEN Inches per Minute Elimination 4.110 June 17-22 3.27 July 26 3.74 August 19-31 2.16 September 21-29 3.523 Average 3.36 SISKOL Elimination 4.46 June 17-22 2.59 July 21 3.00 July 26 2.85 August 19-31 3.21 September 21-29 4.00 Average 3.35 HOLMAN 2|-iNCH Elimination 3.12 June 17-22 2.47 July 21-22 3.75 August 19-31 2.898 September 21-29 2.55 Average 2.957 CLIMAX IMPERIAL Elimination 3.52 June 17-22 3.03 July 21 2.55 July 26 3.04 August 19-31 , 2.44 September 21-29 2.52 Average 2.85 Free Air per Foot Drilled 239.9 310.4 252.0 256.6 281.9 268.1 202.4 362.5 321.2 397.4 317.66 216.2 302.89 385.14 646.3 346.0 325.6 445.4 429.688 329.74 334 ROCK DRILLS NEW CENTURY 00 Elimination 2.33 276.6 June 17-22 2 - 19 358.8 July21-26 2.13 351 ' 7 AugustKHil 2.77 253.3 September 21-29 2.70 330.6 Average 2.424 314.2 HOLMAN 2J-INCH Elimination 2.40 376.2 Junel7-22 1-85 452.5 July 21-26 2.38 397 ' 5 Augustl9-31 2.33 285.5 September 21-29 2.45 368.0 Average 2.282 375.94 The distance drilled is about the same for the Chersen and the Siskol, but the air consumption of the former was only 268 against 303. These are the only two drills which cut more than three inches per minute. MISCELLANEOUS DRILL TESTS Accounts of numerous so-called contests between drills have also been published as taking place in various mines and at exhibitions. Generally, no exact data have been furnished with these accounts, and as, especially with hammer drills, many types manufactured have since been improved, it is scarcely right to give comparative results which might be unfair to manufacturers and misleading to users. GENERAL REMARKS ON DRILL TESTS It will be seen from the foregoing records that the carrying out of a really authoritative comparative test of the relative air con- sumption, boring speed, and ease of manipulation of a number of machines would be a most formidable task. Both old and new machines would have to be tested. The test would have to be somewhat of a combination of Mr. Holloran's investigations, the use of Messrs. Goffe & Company's air consumption recording device, the accurate timing of Professor Orr in some surface trials, boring holes in various directions to some depth, and a comprehensive underground test such as Mr. Laschinger carried out on the Meyer & Charlton mine. Future Development of Rock Drills. It is difficult to suggest ROCK DRILL TESTS AND CONTESTS 335 with confidence the lines along which rock-drilling machines will be developed. Points to be aimed at have been shown to be: (a) The rapid removal of rock fragments from the end of the hole and from the front of the cutting bit; (6) Maximum out- put of energy per unit weight; (c) Strength, simplicity, and resistance to wear; (d) Easy replacement of worn parts; (e) Mechanical efficiency. The hammer drill, owing to its numerous advantages for certain work, seems to be encroaching on the sphere of the piston drill. It has already largely replaced small piston drills for most work, and new models are constantly appear- ing, claiming to eliminate drawbacks and defects. Though piston drills hold their own for long deep holes of large diameter, in hard ground, yet the Leyner hammer drill is in some places doing the same work. Conditions vary so greatly that nearly all the types of drills mentioned have their place and may do better work in that place than others. It seen.s to me that the ideal piston drill of the future might be constructed to work on a short stroke with water injection or air and water injection. The piston would be single headed, short, and wear on the cylinder would be provided for by liners easily replaced. Direct and rapid air admission and exhaust would be arranged for either on the Konomax principle or by two light Corliss valves like those used in the Baby Torpedo drill, but operated by air or auxiliary valves. Such a machine would tend to combine the advantage of both piston and hammer drills. The hammer drill evolved on the lines of the latest models, and with improved materials used in its construction, must increase its range of usefulness. With air pressure of 100 Ib. ordi- nary steel snaps off about 4 in. from the shank owing to some peculiar fatigue due to the blows and vibration. " At the present time the capacity (power) is limited by the ability of the drill steel to withstand the blows of the hammer." The electric-air drill has come to stay for certain work. The electric drill proper will find certain limited spheres of usefulness. An electric-rotary drill may be further developed to bore rock somewhat harder than it can attack at present. The manager will do well to allow some- body else to prove any new drill submitted to him no matter how attractive its general design may be. Minor troubles are sure to show themselves if greater ones do not, and it is not wise to dis- card old and tried friends until better ones have proved themselves. 336 ROCK DRILLS TABLE VIII. SOUTH AFRICAN GENERAL SUMMARY OF SUR Trials No. 1 at 50 Ib. and Trials No. 2 at 60 Kimber No. 1 Kimber No. 2 Little Wonder No. 1 Little Wonder No. 2 Gordon No. 1. Gordon No. 2 1st Hole Mean time to start drilling after sig- nal 8m. 4.7s. 5m. 25s. 5m. 27s. 7m. 40.7s. 1m. 31s. 1m. 43s. Mean diameter of first steel U" 11" 1!" if U" H" Mean depth drilled with first steel. . 6.4" 10" 8.9" 6.7" 6 9-16" 5 15-16" Mean time of drilling with first steel . 7m. 18.2s. 8m. 8s. 8m. 58s. 9m. 54s. 4m. 46fs. 3m. 3s. Mean time elapsing between stopping and re-starting in changing steels. 1m. 4.2s. 58s. 44.5s. 42.5s. 14.5s. 14.7s. Mean diameter of second steel 1|" If" n" H" H" 11" Mean depth drilled with second steel. 6.0" 5 3-16" 13.1" m* 81" 8 15-16" Mean time of drilling with second steel 5m. 36s. 4m. 12s. 12m. 2s. 6m. 14s. 4m. 30s. Mean time elapsing between stopping and re-starting in changing steels . 2m. 8.2s. 1m. 34s. 51.2s. 50.5s. 29 Js. 18.5s. Alean diameter of third steel If" If" U" U" U" U" Mean depth of drilling with third steel 5.7" 8|" 12.6" 9f" lOi" 10 5-16" Mean time of drilling with third steel 7m. 31.2s. 5m. 7s. 7m. 38.7s. 5m. 15s. 6m. 18fs. 4m. 24s. Mean time elapsing between stopping and re-starting in changing steels. 1m. 52.2s. 1m. 42s. 46.7s. 1m. 16s. 26 fs. 26.7s. Mean diameter of fourth steel n" H" U" H" H" U" Mean depth drilled with fourth steel . 6.4" 61" 8.4" 11.6" 14 f" 155" Mean time of drilling with fourth steel 5m. 52.7a. 2m. 58s. 5m. 2s. 3m. 51s. 7m. 32Js. 6m. 10.7s. Mean time elapsing between stopping and re-starting in changing steels. 2m. 43.5s. 2m. 52s. Mean diameter of fifth steel 1!" 1|* Mean depth drilled with fifth steel . . 7.1" lit* Mean time of drilling with fifth steel . 6m. 42s. 4m. 49s. Mean time elapsing between stopping and re-starting in changing steels. 2m. 42s. Mean diameter of sixth steel U* Mean depth drilled with sixth steel . . 5.3" Mean time of drilling with sixth steel 3m. 36s. Mean time elapsing between stopping and re-starting in changing steels . 2m. 18s. Mean diameter of seventh steel H" Mean depth drilled with seventh steel 5f" Mean time of drilling with seventh * steel 2m. 57s. ~ ~ ~ ~ ~ ROCK DRILL TESTS AND CONTESTS 337 MINES STOPE DRILL COMPETITION FACE TRIALS, BY PROF. J. ORR lb. Air Pressure per Square Inch, respectively Little Holman No. 1 Little Holman No. 2 Chersen No. 1 Chersen No. 2 Little Kid No. 1 Little Kid No. 2 Baby Inger- soll No. 1 Baby Inger- soll No. 2 Flott- mann No. 1 Flott- mann No. 2 4m. 44s. 3m. 9s. 3m. 45s. 2m. 56s. 4m. 18s. 3m. 51s. 4m. 2s. 3m. 28s. 3m.l3s. 4m. 59s. If If II* 1 21-32" II* H* 11* U" H" a* 91" 7 9-16" 10|" 5 11-16" 10f" 8|* 111" 8" 4 9-16" 4f* llm. 48s. 8m. 18s. 7m.38s. 4m. 8s. 13m. 38s. 6m. 23s. 8m. 24s. 4m. 42s. 6m. 16s. 4m. 47s. 42s. 27s. 30s. 27s. 39s. 57s. 40s. 33s. 17s. 12s. H* If" If 1 9-16" If" If" If" 1 1-76" 1 7-16" 7 9-16" 9" 101" 10" 10J" 8}" 9|" 8 5-16" 45-16" 6 3-16" 10m.43s. 8m. 58s. 7m. 35s. 4m. 20s. 9m. 46s. 6m. 17s. 6m. 54s. 3m. 44s. 2m.32s. 3m. 23s. 44s. 47s. 55s. 44s. 1m. 15s. 55s. 1m. 6s. 51s. 29s. 15s. 11* H" u U" n" n" U" If" If" 101" lot" 13 i" 10 5-16" 7 3-16" 10J" 8" 8" 51" 5 1-16" 12m. 11s 6m. 58s. 9m. 32s. 4m. 40s. 9m. 56s. 7m. 29s. 6m. 21s. 4m. 14s. 2m.52s. 4m. 8s. 56s. 39s. 49s. 45s. 2m. 9s. 1m. 1m. 20s. 1m. 26s. 1m. 2s. 1m. 57s. i|* U" 1 3-16" 11* 14* !i* H" H" iof" 10i" 8f" 10|" 12f" 113 16 10|* 101" 101" 13" 5m. 47s. 7m. 15s. 2m. 32s. 4m. S8s. 7m. Is. 7m. 45s. 6m. 25s. 8m. 58s. 5m.27s. 5m. 11s. 53s. 59s. 1m. 30s. 33s. 33s. 1 7-16" U" H" 4|" 7," 3" 51" 91-16" 10m.23s 10m. 23s. 6m. 37s. 4m.43s. 5m. 17s. 47s. 1m. 37s. U" 2" 5" 2m. 20s. 10m. 55s. XV DUST AND ITS PREVENTION IT was early recognized that one of the main essentials for rapid drilling was the immediate removal of the rock as broken from the bottom of the hole. This could best be done by direct- ing a jet of air or water into the bottom of the hole while drilling goes on. This can be done in two ways: either a hollow boring tool can be used and the air, water, or both can be passed through it to the cutting edge; or, a jet of water or air under pressure may be passed down between the sides of the hole and the drill shank. Air alone used in either manner is not perfectly satisfactory. It prevents water reaching the bottom of the hole; the drill bit is not kept sufficiently cool, and tends to lose its temper; dust is produced in large quantities. While an upper hole can be bored very much more rapidly with hollow steel and air, yet in most down-holes the difference in boring speed is not marked. Water Jets. These are effective means of clearing holes down to a certain depth; the limiting depth for up-holes being about 4 ft. Water may be supplied under natural or artificial pressure. For producing artificial pressure tanks such as that shown in the illustration of No. 3 Murphy drill may be employed, the pressure being given by the compressed air acting on the surface of the water, Fig. 186. The jet is employed by connecting 2 to 4 ft. of s-in. or f-in. pipe to the hose supplying water under pressure. The pipe is fitted with a tV or i-in. nozzle. With a large down-hole the pipe may be lowered into the hole as drilling proceeds. With other holes the jet must be directed as well as possible up the hole. For driving levels in the North of England coal mines, Professor Galloway designed a special carriage containing a tank with water under pressure. This served to supply water for jets and also for fixing a horizontal bar across the level by means of hydraulic rams. On the bar were mounted two rock drills. Holes were 338 DUST AND ITS PREVENTION 339 bored 4 ft. long and the drive was advanced very rapidly, the only delay being caused by firing and removing all broken rock before drilling could be resumed. Miners as a rule dislike jets and refuse to use them. They must be held in the hand and it is hard to keep them directed exactly into the hole or parallel with the hole; hence, there is much water sprayed about, rendering work uncomfortable. Mr. H. P. Stow quotes an experiment in which the use of jets increased the feet bored per shift by 11 per cent., using fewer drill bits. When an attempt is made to send a jet up an upper or dry hole more than 3 or 4 ft. deep, stiff mud is formed in the hole, the drill sticks and often cannot be withdrawn. However, Compressed <*t-r in Let Water outLet FIG. 186. Tank for Murphy drill. under certain circumstances, with miners who will take the trouble to use them, jets increase boring speed and prevent dust. Effect of Dust Produced in Rock Drilling. The particles of broken rock produced by drilling up-holes, without water, have a deadly effect on those constantly inhaling it. The particles are retained in the tissues of the lungs, gradually choking them up, which renders the tissue susceptible to phthisis and pneu- monia. This action, combined with the effect of gases due to imperfect combustion of explosives, renders rock drilling, espe- cially in some fields, one of the most dangerous occupations. It has been stated that the average life of a rock drill operator on the Witwatersrand is about five years. There is thus a humani- tarian reason, as well as an economic reason, for the prevention of the formation of dust in bore holes, or for allaying it after production. 340 ROCK DRILLS Respirators. Respirators can be used to prevent dust reach- ing the lungs, but they cannot be worn continuously, as it is impossible to do heavy muscular work while wearing them. In certain cases they are useful, especially where men use air- feed hammer drills in stoping and have merely to stand and reciprocate them while they are boring. Masks have been tried, supplied by a small hose with com- pressed air. These are much more pleasant to use; but com- pressed air contains sometimes poisonous carbon monoxide from FIG. 188. The Holman spray. the compressor lubrication; tubes hamper work and are in the way in confined spaces underground. Numerous dust collectors have been invented, but none of them are practical devices. Sprays. Several sprays using a mixture of compressed air and water are on the market. The Holman spray is shown in the accompanying section, Fig. 188. The Climax spray is shown in Fig. 189, attached to drill. It is of somewhat similar design. There are several other patterns and a device can easily be made at a mine for attachment to the valve chest of drill. With care- ful workmen, sprays are advantageous; they settle about 75 per cent, of the dust produced. Objections to Sprays. They are not favorites with most miners DUST AND ITS PREVENTION 341 and as a result they neglect to use them. With unskilled labor handling drills they are liable to damage. They produce a damp- ness which miners complain tends to rheumatism. Clean and wholesome water is not always procurable underground, and more damage to health might be done by inhaling a spray of disease- laden water than by inhaling the dust. Water often contains FIG. 189. Stephens patent " Climax" dust allayer in use. grit, which is liable to choke the small tubes and narrow parts of the spray. The miner is generally more concerned about making money than about his health, and unless compelled by law will generally use none of these devices because they are complicated. In a mine of which I was manager I provided water in pipes under moderate pressures to every working face, with sprays or jets. They were never used. I also provided a variation of James's 342 ROCK DRILLS water blast, Fig. 190, by using about 3 ft. of 1-in. pipe with T- piece with spuds fitted to one end. Just before blasting, the air- hose union was attached to the one on the end and the union on the water hose to the other. These were both turned on and /' Ptpe _ =* -* Spray FIG. 190. Variation of James's water blast. the pipe placed at a convenient distance back from the face, pointing in such a direction as to allow the cloud of spray formed to meet and absorb the gases from the explosion, cooling the air and rock. MACHINES AND DEVICES FOR USING HOLLOW-DRILL STEEL Piston Drills. One of the earliest devices for using water and hollow steel is shown in an old German patent, Fig. 191. It is practically the same as that shown in drawing of the Box hammer drill. Bolted to the body of drill D was a bracket carry- ing a hollow cylinder with a water space in the middle with packing glands at each end. A small transverse hole in drill connected Water space. ^])rLLL steel FIG. 191. An old German device for preventing dust. the hollow core to the water space, and the drill was supposed to revolve and reciprocate through the cylinder which fed water. This device applied to a piston drill was utterly impracticable. Packing could not be kept tight while allowing the machine a free stroke, and the drill was weakened by boring a lateral hole in it. The, Bornet System. "With this system there is an inter- mittent discharge of water at the point of the borer, the bit being hollow, as seen at Fig. 192. A supply of water is held in a DUST AND ITS PREVENTION 343 cistern and fed under pressure to the front head of a standard percussive air drill by means of flexible hose. Here the water passes through a valve into a water chamber arranged in the front cover piston bearings. The hollow borer bit is fastened in the drill chuck, which is provided with a stuffing-box to prevent leakage, and the piston for some distance back from the chuck is hollowed out longitudinally, and then diagonally. At each stroke of the piston this diagonal hole passes the water chamber, and in so doing takes a supply of pressure water which travels through the hollow piston and onwards through the borer, finally being ejected at the drill point. By the arrangement of the diagonal passage, and owing to the water chamber being con- siderably shorter than the stroke of the machine, the jet is only projected just before and after the cutting stroke. All dust is effectually killed, the drill point kept cool and the bottom of the FIG. 192. Bornet hollow drill bit for allaying dust. hole maintained clear of all chips which are forced from the hole by the pressure water. The jet being intermittent, only a small quantity of water is used, about 14 gallons sufficing for a shift." This appears at first sight to afford a satisfactory solution of the problem. Practical difficulties, however, at once present themselves. In the first place the end of the shank tends to burr up and close the hole in the bottom of the chuck. It is hard to keep a tight contact here also, as any packing tends to be dis- placed or ground up. Wear occurs on the piston and front head. The water leaks out of the front end, and works back- ward into the cylinder. Another trouble becomes apparent in practice. If the water is not turned on and issuing from the hole in the drill bit in sufficient quantity before cutting rock be- gins, a stiff mud is formed, which is forced into the central core and stops it up. This is a great trouble with any water-feed device that is not automatically turned on when the machine starts. 344 ROCK DRILLS Derby Tubular Bit. The Derby tubular bit was used for several months in drilling flood rock. H. P. Gillette writes: " Major Geo. McC. Derby invented a drill bit that was used in drilling on the flood rock work, and it proved so greatly su- perior to the cross-bits that I regard it as worthy of special description. Major Derby writes me that he patented the drill bit in 1885 and sold the patent rights to the Rand Drill Company, which, for reasons unknown to him, has never placed it upon the market. The drill steel was hollow, as was also the bit which was provided with six points or teeth. The bits were sharpened very much like the bits used in the plug drills made by the C. H. Shaw Pneumatic Tool Company, of Denver, Colorado. Each bit was only 2 to 6 in. long and fastened to the end of the hollow wrought- iron drill rod with a steel pin or expanding copper ring. This saved steel and saved transporting long, heavy drill rods to and from the blacksmith shop. This bit was used with the ordinary percussive air drill, and, in drilling, a small core was formed which broke up under a slight blow on the drill rod. The chips were washed out of the hole by a current of water that was forced down through the hollow drill rod. The water was introduced into the hollow drill rod, either through the rotating bar or through a sleeve surrounding the piston rod which was lengthened for this purpose; the first method being the best. Major Derby informs me that the coarse chips of rock broken off by the bit are washed out whole, instead of being reduced to dust, which saves power and time in drilling a hole of given depth. This fact is well shown by the following comparative records: Experiments were conducted for several months of actual work, during which time 39,119 ft. of hole were drilled with cross-bits and 39,200 ft. with the Derby tubular bit. The holes were about "9 ft. deep, and Rand 'Little Giant' drills were used. As a result of this competition it was found that the tubular bit drilled 51 i per cent, faster than the cross-bit, and that the diameter of the bottom of the hole was 25 per cent, greater than with the cross-bit, which in itself is a decided advantage. Using a starter cross-bit of 3J in., the bottom of a 10-ft. hole was 2 in. diameter; but with the tubular bit the bottom was 2? in. diameter. Moreover, the tubular bit made a perfectly round hole, which lessens the chances of a bit's stick- ing. It seems to me that the greater speed of drilling with the tubular bit was due to the use of a jet of water to wash out the DUST AND ITS PREVENTION 345 chips, which also accounts for the fact that the bit does not wear so rapidly. Whatever the reason, the record of excellence of the tubular bit is well worthy of serious consideration by all who are interested in economic drilling." Why this device which proved so favorable on trial was not put on the market is not stated. It may have been that experi- ence showed that wear caused too much leakage and that the detachable bit itself gave trouble. General Conclusions on Dust Prevention. During a long course of actual underground work with rock drills I came to the following conclusions regarding this problem: 1. That an apparatus was required that could be applied in such a way to any ordinary rock-drilling machine, without alter- ing it, as to be available when it was necessary to drill a dry hole, and allow the use of ordinary steel in downward holes. 2. That the difficulty of passing the water from the chuck to the jumper (drilling tool) must be avoided. 3. This could only be done by making some attachment to the drill stool outside the chuck of the machine. 4. This attachment must be quickly and readily removed and replaced to facilitate change of boring tools. 5. It must be attached in such a manner as to withstand the repeated and violent shocks caused by the drill tool striking the rock and must make a proper water-tight joint to prevent leakage. 6. It must be arranged in such a manner as to leave the drill tool clear to strike and it must not impede work in any way. 7. No projections must be made on the drill tool that would impede its being withdrawn past the chuck and front head of the machine when it is set up close to the rock. 8. The drill steel must not be weakened in any part, as a fracture would sooner or later develop. 9. The apparatus must be simple, having few parts, free from bolts and nuts liable to work loose, easily inspected and repaired, and adapted to the most trying conditions of underground work without a large expenditure for maintenance. 10. The rota- tion of the drill tool must not be impeded, as in that case rifled holes and poor results would destroy the advantage otherwise gained. The advantage that would be gained by the use of such a device would be as follows: 1. A greatly increased rate of boring upper or dry holes, in various cases from 25 to 100 per cent. 2. The total avoidance of the dust trouble. The life and comfort 346 ROCK DRILLS of miners would be increased and the disease known as "Sili- cosis" would be prevented entirely. In England, Australia, and the Transvaal, the use of some means of allaying dust is rendered compulsory by law. The drill steel is made in the shape shown, Fig. 193, near the shank. The tapered portion is swaged up and if necessary finished off on a lathe. Starters and seconds are of IJ-in. octagon steel with a star bit; thirds and fourths are of IJ-in. octagonal steel, which require to be slightly jumped up before the taper is formed. The taper is from If in. to 1| in. in 5 in., or from If in. to If in. in 3? in. for large drills. A transverse hole A, preferably of smaller diameter than the hollow core, is bored right through the drill tool as shown, or merely drilled to meet the hollow core. This weakens the steel and would, in practice, cause failure of the apparatus through constant breakages, were it not for the way in which the cylinder C makes a rigid joint on either side of it and makes it the strongest part of the drill. The cylinder C is of the shape shown and is bored out on a taper corresponding to that of the drill. The taper is so arranged that the cylinder is immediately tightened on and kept tight by the blows of the tool on the rock, but when it is necessary to detach the drill tool from the machine owing to its being blunted, the cylinder is easily and quickly detached by a rap with a hammer and slipped on another drill tool. This cylinder is bored out as shown to form a water space U (enclosed) between itself and the drill tool over the aperture of the transverse hole. It is also pierced by numerous radial holes connecting the water space U with the groove on its outside circumference. The packing is in this groove. A ring is hollowed out in the manner shown and sup- plied with water by a small hose clamped on to the tail piece B. As the drill tool and its rigidly attached cylinder rotate within this ring, the water under pressure, or air and water under pres- sure, is fed alternately in a continuous and intermittent stream through the radial holes, through the water space, the transverse hole in the drill, and the drill core to the cutting edge of the tool. It will be noticed that the edges of the bored-out space in the cylinder are recessed to prevent their being burred and that the packing being placed in the grooves cannot be dislodged. It is protected from injury while it is easily removed when worn. Two forms of the apparatus are shown, one in which the ring DUST AND ITS PREVENTION 347 B H* 5*. *i A "~r 1 r^ i. FIG. 193. Device for passing water through drill steel to allay dust. 348 ROCK DRILLS is in two parts, D (these parts are connected in such a manner by screws, split pins, and spring washers that they cannot be shaken apart by the vibration of the drilling), and the cylinder is turned out of a solid piece, E. This is the better arrangement. In the other, the cylinder is made in two pieces suitably connected and the ring is cast solid. Experiment has shown that with a water pressure more than sufficient to deliver the water at the end of a long upper hole the ring can be so tightly packed that leakage is practically nil and yet the rotation of the drill tool is not retarded. The water acts as a lubricant between the metal and the leather. The packing is in two parts, the inside ring being of soft rubber and the outside brass. The rotation of the ring itself is prevented merely by the weight of the hose attached to it, that it may be loosely held by the attendant or otherwise kept out of the way. The " flogging" of the hose is not nearly as severe as might be supposed and there is no great wear due to that cause. The apparatus is compact, light, simple, and sub- stantial. It is proposed to provide the miner, working in a drive, with enough hollow steel to bore the dry holes or " upper" holes, and he would employ them simply when necessary, boring the rest of the time with ordinary steel. Later experience showed that the apparatus in the form shown was not satisfactory; the hollow core was left open to the end of the shank and combined with the air-jet device used in Stephens Climax drill. Holman brought out a somewhat similar device combined with an arrangement to partially rotate the piston. With these devices, and water under very moderate pressure, holes may be put in rapidly, without any great loss of water or any formation of dust. Disadvantages. The drawbacks to their adoption are that they are complicated and must have intelligent handling; that it is practically impossible in a mine to have a regular, constant, and equal water pressure, available everywhere; where the pres- sure rises above about 20 Ib. to square inch it is impossible to avoid leakage; with many machines at work, the supply and pump- ing of this water is quite a serious matter. In practice the system of pressure tanks gives endless trouble with most miners, and water supplied under natural heads becomes choked with gravel or dirt. The wear on the hose connecting these attachments is severe, and hollow drill steel is expensive. In the case of the first DUST AND ITS PREVENTION 349 apparatus, forming the cone is an additional expense, and in the second place is weakened by the transverse hole. Hollow steel gives trouble in welding. It must be given very careful treat- ment as it is usually high-carbon steel and so does not weld well; in any case welding and sharpening cost more than with__solid steel. If left about the mine the core tends to rust and choke. I think that an air blast must always, as in the Leyner drill, be mixed with water to avoid the choking up and to economize water. If a detachable bit like the Anderson bit proved satis- factory after a long trial, the problem of water injection would prove somewhat easier. The large bedring at the end of the shank w^jald make a good water-tight joint more easily designed; the design of some readily adjustable packing for the front head would render the Bornet system practicable. Some of the chief rock-drill manufacturers have spent thousands of pounds experi- menting on this problem and have not given up hope of success. An efficient water drill may be on the market at any time. The small Konomax stoping drill is designed with a water feed. All the general objections and difficulties can be overcome by care and a -certain expense; but despite the terrible evils of pro- ducing dust in mines, miners and employees will refuse to employ any machine that gives more trouble than the present types, unless the benefit in more rapid boring is at once apparent. Ex- actly what the increased rate of boring down-holes is with water- feed drills cannot be stated. On the Witwatersrand it does not seem as if the increase is sufficient in boring down-holes with piston machines for stoping to warrant the adoption of hollow steel. In recent trials the Siskol drill drilled as fast with hollow steel and water injection. This is probably due to the fact that in down-holes in fairly hard rock the broken particles are kept suspended in the water, due to drill motion, and do not lie at the bottom of hole to deaden the effect of the flow. In softer rocks or in up-holes the difference would be marked, as a flat, dry up- hole takes from 50 to 100 per cent, longer time to drill than a down or wet hole. This discussion has been extended to show inventors the lines on which progress is possible and the real difficulties that must be met in facing the problem. It may be noted that the introduction of an effective water- feed device would allow of a great change being made in the design of piston drills. As will be seen in the chapter on "Rock Drill 350 ROCK DRILLS Tests," there is much evidence to show that if there was a means of at once ejecting the broken particles of rock from the face of the hole, a very much shorter stroke might be used with advan- tage; this would enable a shorter and lighter machine to be made with the same or greater capacity. A greater number of lighter blows would be struck per minute. The bit not being withdrawn so far every stroke would suffer less from frictional retardation in the hole, and from wear on its shoulders; the work of a piston drill could be made somewhat more like that of a hammer drill and a better efficiency obtained. Exhaust and inlet ports would be shorter, reducing clearance losses of air, and rendering reversal of stroke more rapid. The whole matter is an economic one, dependent on being shown in practice that the added advan- tage in health of workers, efficiency in design and operation of machines are worth the complications and expense caused. An apparatus such as that designed by myself could, with a machine designed to take advantage of its benefits, be worked to advantage only under certain circumstances. XVI COMPRESSED AIR NOTES ON THE USE OF COMPRESSED Am AND STEAM IN CONNEC- TION WITH ROCK DRILL WORK THE use of steam for rock drills is confined to small and tem- porary plants for quarries and surface excavations. The heat and vapor of the exhaust makes it unsuitable for use underground. For the physical properties of compressed air the reader is referred to the well-known text-books on the subject. As the problem affects the mining engineer it may be separated into three heads: (1) The generation of compressed air. (2) The transmission of compressed air with the minimum of loss to the place where it will be employed. (3) Its most economical use in rock drills, hoists, and pumps. When installing a compressor plant due regard should be paid to the probable life of the mine, which involves the question of amortization of capital and the value of the machinery when the mine is exhausted. Where steam power is employed, and where the expenditure is warranted, it is usual to install two-stage compressors driven by cross-compound engines having a con- denser. The air cylinders will be jacketed with water and should have thermometers attached. An inter-cooler will be provided with perhaps some arrangement for pre-cooling the air before compression and freeing it from dust. Ample facilities should be provided for freeing it from oil and water. At elevations above sea level, air is expanded and occupies more space for a given weight, and the capacity of an air cylinder is reduced. Hence the size and cost of an air compressor must be increased at high altitudes to secure the same output as would be maintained by the same machine at sea level. This reduction at 5700 ft. elevation is 17 per cent. The Cost of Compressed Air. The cost of steam-generated compressed air can be fairly accurately calculated when the fac- tors in any particular instance are known. A good compound condensing engine driving a compressor uses from 14 to 20 Ib. of steam per 1 h.p. per hour. Efficiency of the air compressor 351 352 ROCK DRILLS may be from 80 to 90 per cent. The cost of compressed air even when generated from cheap coal forms a considerable item of expense in running a drill. G. A. Denny stated that on the Rand one h.p. cost 20 per annum, and that only 6 per cent, efficiency was attained at the drill. E. Laschinger states that the cost of one steam h.p. is \d. per hour, and that the cost of one air-horse-power at the drill would be 2d. Other records of the horse-power actually neces- sary to run drills are given in the chapter on rock drill tests. It is influenced in any particular case by the type of drill employed, design of pipe line, losses in leakage; amount used for ventilation after blasting which in many cases is as necessary an expenditure as running the drill. Leakage in a pipe system can be kept under 5 per cent. Laschinger estimates that the efficiency of power transmission from steam one h.p. at the compressor to work done at the rock drill at 80 Ib. pressure is 15 to 35 per cent. Air Consumption of Rock Drills. This will vary with type of drill, and must not be compared with the efficiency of the drill, which is better compared by air comsumption per inch drilled with same diameter bit. Figures for this are given under drill tests. The Sullivan company furnishes tables for their machines. E. J. Lasch- inger in the Journal of the Trans. Inst. of Mech. Eng., presents what is perhaps the best modern practical discussion regarding the transmission of compressed air for rock drills and I have drawn largely from his articles (January and March, 1908, January, 1909). He estimates the average consumption of a 3J in. drill at 7 Ib. of air per minute at 75 Ib. pressure. This may be reduced to cubic feet per minute at any altitude by multiplying by the number of cubic feet of air weighing one pound. At sea level 13.091 cu. ft. air = 1 Ib. At 5700 ft. 15.094 cu. ft. air =1 Ib. Notes on Installation. In order to conduct drilling operations at the maximum efficiency the mining engineer must first decide on the probable number and type of rock drills to be employed and their probable air consumption. He must then install a compressor to provide this air with a liberal and sufficient margin for leakage, ventilation, and any pumps, hoists, or other machin- ery that may be operated by compressed air. He must then decide at what pressure he wishes to work his drills. This will depend on the hardness and character of the rock; cost of labor; cost of compressed air; the distance the air must be transmitted; COMPRESSED AIR 353 the cost of piping and other considerations. R. B. Brinsmade writes: "In a certain mine using 40 drills in hard fissured ground the rock broken was increased 40 per cent, by increasing the air pressure from 75 to 100 Ib. A low-pressure system requires larger pipes for the same power, and heavier pumps and hoist to do the work of a similar equipment working under high pressure." Compressed air is transmitted most economically at high pressures. The mining engineer may find it profitable to consider the question as to whether in any given case it might not be profitable to use the highest air pressures and to reduce the force of the blow, by ordering a special drill with short stroke, or to use a machine with a smaller piston diameter than the standard 3J in. size. Experience has proved that under most conditions drilling speed is of primary importance, and it must also be remem- bered that more rock has to be excavated and more work done in boring one hole of eight feet, than two holes of four feet, because the amount excavated will vary as the square of average diameter of holes. The average diameter of a long hole is much greater than that of two short ones. In most cases air should be supplied at the drill at from 75 to 85 Ib. pressure. Where speed of performance is the vital consideration, as in shaft sinking a tunnel driving work, drills should be run at the highest possible pressure, only regulated by the manner in which the drill bits and shanks behave. J. A. Vaughan, in Trans, of South African Soc. of Mech. Eng., states that to compress air to 60 Ib. requires 28 per cent, more work than to compress to 50 Ib. Used in a rock drill with 60 Ib. the number of strokes j^er minute increases as the square roots of the pressures or as \/60 to \/50 or 1.106 to 1.01, equal to 10 per cent, increase. Work done in drilling, or the Kinetic energy, de- veloped by the same mass, varies as square of velocity, and this varies directly as the pressure or as 60 to 50 = 1.2 to 1. The total work done in boring increases from 1 to 1.2 X 1.106 = 100 to 132 or 32 per cent, increase. This is borne out by actual trials. If, however, air is compressed to 80 Ib. and delivered to drill at 60 Ib. and at 50 Ib., the loss of efficiency from 60 to 50 Ib. is 13.4 per cent, and from 80 to 50 Ib. is much greater. Transmission of Air. The mining engineer must now make an estimate of the maximum distance air must be transmitted, and also the average distance. He will design his pipe line to make the loss of pressure in transmission as low as possible consistent with a reasonable expenditure on pipe service. Losses in transmission 351 ROCK DRILLS should roughly balance loss of interest and amortization in capital expended on his pipe lines; but the loss of pressure must be kept low. It must be remembered that when air is delivered at a lower elevation than that of the compressor its pressure increases. Laschinger gives the following table showing increase in pres- sure at varying depths at 80 F. If top pressure equals 1, at 500 ft. the pressure is 1.01755 800 ft. the pressure is 1.02823 1000 ft. the pressure is 1.03541 1500 ft. the pressure is 1.05358 2000 ft. the pressure is 1.07206 2500 ft. the pressure is 1.09090 3000 ft. the pressure is 1.11003 3500 ft. the pressure is 1.1295 4000 ft. the pressure is 1.14933 5000 ft. the pressure is 1.19003 At "3000 ft. 11 per cent, more drills can be run or the same number of drills at 11 per cent, higher pressure with same air as at the surface, assuming that an air-horse-power underground is worth 2d. per hour, and that the total cost of laying piping is according to the following table by Laschinger: TABLE I. COST PER FOOT FOR INSTALLING AIR-PIPE LINES ON THE RAND Nominal Size Pipe Inches Surface Underground 1 s. d. 9 s. 1 d. 11 1 1 4 t| 1 3 1 8 2 1 9* 2 5 2i 2 4 3 2 3 2 111 3 11 3* 3 7 4 10 4 4 3 5 8 4i 4 11 6 6 5 5 7 7 6 6 7 1 9 5 7 8 6 11 5 8 10 1 13 6 9 11 9 15 7 10 13 4 17 10 12 16 9 22 4 14 20 4 27 1 COMPRESSED AIR 355 Laschinger points out that higher velocities are allowable in larger pipes and that the velocities here shown are not excessive. TABLE II. SHOWING MOST ECONOMICAL NUMBER OF 3|-lNCH DRILLS SERVED BY STANDARD PIPES AND MEAN VELOCITY OF AIR Nominal Size Pipe Inches Internal Diameter Inches Surface Mains Shaft Mains Distributing Pipes Number of Drills Mean Velocity Feet per Second Number of Drills Mean Velocity Feet per Second Number of Drills Mean Velocity Feet per , Second 1 1.05 0.46 19.1 0.51 21.1 0.64 26.6 ii 1.38 0.85 20.5 0.94 22.6 1.18 28.4 It 1.61 1.21 21.3 1.33 23.5 1.67 29.6 2 2.07 2.12 22.7 2.34 25. 2.94 31.5 2t 2.47 3.16 23.7 3.48 26.1 4.37 32.9 3 3.07 5.15 25.0 5.17 27.6 7.14 34.7 3} 3.55 7.15 26.0 7.86 28.6 9.91 36. 4 4.03 9.5 26.8 10.5 29.5 13.2 37.2 41 4.51 12.2 27.5 13.5 30.3 17.0 38.2 5 5.05 15.8 28.4 17.4 31.2 21.9 39.4 6 6.07 23.8 29.7 26.3 32.7 33.1 41.4 7 7.02 33.1 30.8 36.5 33.9 45.9 42.7 8 7.98 44.2 31.8 48.6 35. 9 8.94 57.1 32.7 62.8 36.1 10 10.02 73.8 33.7 81.0 37.1 12 12. 111. 35.2 122. 38.8 14 14. 157. 36.6 172. 40.3 Laschinger gives in Table II, the most economical size of pipe to use, for any reasonable distance in mining work. The size of pipe given is that which under these costs makes the capital in pipe line equal the value of power lost, while, at same time, loss of pressure is within reasonable limits. He also points out that if the cost of installing pipes be doubled or halved the resulting diameter of pipe is only decreased or in- creased by about 11 per cent, and inversely for the same varia- tions in cost of power. This establishes tables of value where these costs can be esti- mated, and the results hold good for pressures from 40 to 80 Ib. gage per square inch. It must be remembered that pipe fittings increase resistance 356 ROCK DRILLS 72 to flow of air in pipes. When = velocity head, the equivalent length of pipe to which could be attributed the loss by friction of the energy of velocity head, would be, Length of pipe in feet = (value of constants below). Taking this equivalent length of pipe as 1, the resistance due to fittings Laschinger gives as follows: Air receiver, 2.5; entrance head, 1.5; sharp elbow, 2.0; round elbow, 1.0; easy bend, 0.2; tee, 2.0; globe valve, 4.0; angle valve, 2.5; gate valve, 0.2; cock, 0.5. It will be seen that sharp bends and globe valve should be avoided as much as possible, and gate valves or full-way valves used on pipes down to 3-in. size. Laschinger gives the following formulae which, when the weight of air required per second at the end of any pipe line is determined, will enable any particular case to be checked with the tables : When W= Ibs. weight of air delivered per second; d = internal diameter of pipe in inches; Pi= initial pressure in pounds per square inch absolute; p 2 = final pressure, absolute; absolute pressure equals gage pressure + atmospheric pressure. T = 'absolute temperature = (Deg. F. + 460.7) L = Length of pipe in feet. R = constant for air = 53.22. TT = 3.14159. 0.03 z = 0.005 + ~p- (Laschinger's formulae). v = mean velocity of flow in feet per second. Then, W = 0.17625 zLT 2.0024 v = 23.886 zL(pt V/ p 2 3 2 COMPRESSED AIR 357 MAINTAINANCE OF PIPE LINES AND AIR HOSES. Drainage pockets to collect condensed water should be in- stalled at suitable points having automatic discharge, or valves which must be opened at regular intervals. Pipes should be- laid so as not to be covered by mud and water. They should, in sizes above 3 in., be bent at the surface, to the curve required. They should be carefully bent while hot to avoid excessive con- traction of area. They should be of the best quality obtainable. Mr. Cullen found seamless piping to be most suitable for under- ground work along levels. Special cocks for attaching pressure gages at important points should be put in. When a pipe is broken and the usual connection is made, care must be taken that the rubber insertion for joint does not project into the pipe. Plug or cone valves should be used at hose connections. Large underground reservoirs are often a great help in regu- lating pressure, and assisting the compressor. Leakage in shaft mains are frequent, and are due often to the weight of pipe not being properly taken up. The alternate exhaustion and contraction of pipe for about 500 ft. down the shaft due to passage of hot air while the compressor is working and the cooling when compressor is stopped is liable to cause leaks. Soap solution poured into pipes before testing for leak- age shows up small leaks by blowing out bubbles. Oil and red lead should be used for screwed joints. Rock Drill Hose. A 3i-in. drill for pressure above 40 Ib. requires a hose of larger diameter than one inch. The loss of pressure is 6 Ib. to the square inch in 50 ft. of one inch hose when running a 3|-in. drill at 70 Ib. pressure. One and one- eight inch hose is now sold on the Rarid. Good hose is hard to obtain, as the filling used with the rubber is usually excessive in quantity. Beware of cheap hose, as it causes numerous losses owing to leakage; stoppage of air owing to the buckling up of the lining, and to its short life. Pay for the best article arid see that the quality is there. The inner lining of a good hose should be with- out a longitudinal joint. The rubber should be soft, pliable, and of a good color. The nature and quantity of filling used should be specified and checked by analysis where possible. All hoses in the mine should be examined and tested frequently 358 ROCK DRILLS to see that leakage is not excessive; that they are not seriously dented, or the area of air way otherwise contracted. Economy in expenditures here increases mining costs. Acid mine water attacks the wire armoring and rots the outside of the hose, while oil from the compressor softens the rubber lining. Hose for min- ing work may be either armored with well galvanized wire or completely unarmored. Marline wound hose is, I consider, unsuitable for mining work, as any injury causes the marline to ravel. Wire protects the hose; but retains dents, reducing the area of internal tube. It is well to try both kinds of hose and compare them under the special conditions of the case. CONCLUSION In conclusion, if I were to sum up the lessons forced on my attention during rny practical experience, with rock drills pipe lines, and hoses in one word, the word used would be maintenance. The engineer must employ expensive labor, surface equipment, and use expensive power to operate what is at its best an ineffi- cient machine to do the most important work of the mine. If he stints his expenditure in money, time, and constant personal supervision, and the whole system, from compressor to drill, is not maintained at the highest possible efficiency, the result of his neglect will most surely reveal itself in high mining costs. INDEX Aberdeenshire, granite quarrying, 264. Abrasion in rock drilling, 129. Adams electric drill, 91, 92, 93, 94. Adelaide drill, 11. Air, calculation of volume, 318. compressed, 137. Caledonia mine, 272. cost, 351. in rock drill work, 351. installation, 352. consumption, 316, 320, 327, 352. of hammer drills, 82. Rose deep mine, 324. drill, electric, 95. results, 94, 95. test, 90. versus electric drills, 102. economizing, 122. -fed drills, 49, 50. -hammer drill, 64, 65. feed, "Cleveland" hammer drill, 75. hose, handling, 241. maintenance, 357. losses, 327. mean velocity, 355, 356. practice, 332. pressure, 252. electric air drill, 98. tightness test, 146. transmission, 352. valve drills, 24. Ajax drill sharpener, 157. Allgemeine Electricitats Gesellschaft electric furnace, 152. America, rock drill practice, 269. Anderson detachable drill, 169, 170. Anvil Block Machine Co.'s false chuck, 78. Anvil-block machines, 78. "Arc Valve" tappet drill, 13. Arm, correct position, 108. maintenance, 146. Atlas powder, 179. Australia, rock drill practice, 258. Auxiliary valve drills, 31. Bar, bad arrangement, 107. double-jack, 109. drill, arrangement in bottom of shaft, 241. jack, 40. maintenance, 146. mounting drill on, in stope, 111. position, 108, 109. rifle, of hammer drill, 53. stoping, 64. Battery blasting, cautions, 202. Bench, hight compared with size of hole, 222. Bits, broken-off, recovering, 239. changing, 114. chisel, 163. sharpening, 156. of grooved steel, 166. correct drill (Leyner), 172. cross vs. chisel, 317. cruciform, sharpening, 157. detachable, 168. drill, 150, 151, 166. American system, 154. design and shape, 162. South African system, 155. for hammer drills, 173. forged by Word drill sharpener, 167. Holman Bros., 167. shaping, American practice, 163. star, 163, 166. 359 360 INDEX Bits used with air-hammer drills, 176. Blast, conditions affecting, 312. Blasting, 114, 182. Aberdeenshire, 267. Caledonia mine, 271. cautions regarding battery, 202. conditions influencing, 211. Davis mine, 278. Golden Horseshoe mine, 262. in heavy rock excavation, 311. suggestions, 195. with high explosives, 210. Blasts, premature, 194. smoky, 194. Blocks, 105. Blow, determining absolute force, 316. determining number, 315. electric air drill, 99. how delivered by hammer drill, 50. kinetic energy of, 138. nature of, in rock drilling, 129, 130. of hammer, taking up, 80. Boring rock, systems, 129, 130. speed, 332. Bornet hollow drill bit, 343. system for using hollow drill steel, 342. Box electric drills, 95. Broken Hill, rock drill practice, 260. Brunton's "Wind Hammer," 2. Caledonia mine, drill practice, 269. Caps, blasting, 184, 186, 188, 189, 194, 196. correctly placed, 195. proper placing of, 196. Carnahan Mfg. Co.'s Murphy Stand- ard drill, 61, 62, 63. Carriages, rock drill, 43. Center Star mine, rock-drilling prac- tice, 284. Charges, formula for calculating, 219. length, 225. Charlton and Meyer, rock drill tests, 330. Chersen ball valve drill, 47. Chersen chuck, 47. drill, 333. Chicago Giant rock drill, 16. Pneumatic Tool Co., rock drill oiler, 118. Chipping system of rock drilling, 129, 130. Chronology of rock drilling, 5. Chuck bushings, renewing, 145. false, of Anvil Block Machine Co., 78. drill, 45. hammer drill, 53. maintenance, 144. Churn drilling, 136. Clamp, drill, 39. maintenance, 146. to extract drills from fitchered holes, 239. Cleveland hammer drills, 58, 60, 74, 75. Climax Imperial drill, 333. spray, 340. tappet valve drill, 23. Colors of steel at different tempera- tures, 150, 153. Column, double screw tunnel, 40. Combustion differentiated from ex- plosion and detonation, 185. Conditions under which rock drills work, 133. Connections, machine, maintenance, 146. Construction of machine, 131. Contests, rock drill, 315. Corliss valve drills, 30. Costs, air, per rock drill per shift, 149. breaking and shoveling rock, 248. compressed air, 351. drifting, Lake Superior, 297. South Africa, 227. excavating, 314. explosives, 280. generating compressed air, 122. installation of air-pipe lines, 354. machine drilling, 280, 283. operating rock drill, 132. per foot for installing air-pipe lines, 218. INDEX 361 Costs, running machines in stoping, 256. shaft sinking with machines, South Africa, 237. sinking shafts, 243. stoping, 298, 299. with electric drill, 90. hammer drill, 83. Cradle, attaching drill to, 110. drills, 49. guides, wear on, 142. Sullivan, 39. Crimper, 191, 192. Crimping, 191. Cripple Creek practice' in use of bits, 175. Cross-bits versus chisel bits, 317. Cut, channeling, 233, 234. triangle and V, 258. Cylinder, valveless air-hammer drill, 79. boring out, 148. maintenance, 141. Cylindering, back, of hammer drill, 53. D 15 Sullivan hand hammer drill, 60. 19 Sullivan hand hammer drill, 61. Darlington drill, 10, 11. Davis pyrites mines, Mass., rock drill practice, 273. Deitz electric drill, 87, 88. Denver Rock and Machine Co., Waugh drill, 76, 77. Derby tubular bit, 344. Design of hammer drills, 80. Detonation, differentiated from ex- plosion and combustion, 185. of high explosives, 183. procuring complete, 194. Detonators, 183, 196. results obtained from strong and weak, 189. selection, 188. Development, 221. future, of rock drills, 334. report, Portland Gold Mining Co., 278. Drift stoping, Joplin, 307. Drift stoping, Wolverine mine, 292. Drifting, Caledonia mine, 269, 270. Joplin, 304. Lake Superior, 295. South Africa, 227. Driving, record, in Rand deep levels, 231. West Australia, 258. Dunstan's drill sharpener, 158. Durban Roodeport, driving results, 232. Dust, 338. preventers, disadvantages, 348. prevention, 338, 345. produced in rock drilling, effects, 339. Dynamite, 178, 179. storehouse, 181. East Rand Extension, driving results, 232. 'Eclipse" drill, 24, 25. Efficiency of drill, 131. Electric air drill, 95. air drill, advantages, 101. drill, disadvantages, 102. drill, results, 101. current for electric air drill, 99. drills, 85. results, 90, 91, 94, 95. rotary, 94. test, 89, 90. versus air drills, 102. firing versus fuse firing, 203. . shot firing, 197. Energy loss, 137, 138, 139. of blow, kinetic, 138. Eureka Steel Drill Co.'s drill, 168. Europe, hammer drills, 65. Excavation, Aberdeenshire, 265. of rock in large masses, 309. Explosion, causes, 112, 117. differentiated from combustion and detonation, 185. Explosives and their use, 178. choice of, 208. force generated by, 212. Golden Horseshoe mine, 263. 362 INDEX Explosives, high, 108, 210, 206. detonation, 183. effect, 214, 215. low, 178, 216. Portland Gold Mining Co., 281. thawing, 180. Face working in to cut pillar from above, 254. Feed-screws, maintenance, 146. Feeding forward of machine, 116. Findley Consolidated Gold Mining Co., rock-drilling practice, 285. Firing, electric versus fuse, 203. West Australia, 259. Fitter, 147. Fittings, drill, 39. Fluids, statics of, 216. Foot block with steel plate, 105. Foote, D. A., 30. torpedo drill, 31. Force generated by explosives, 212. Forcite, 179. Forges, 151. Fowle, J. W., 2. Frame, drill, for boring breast shot- holes, 266. shaft-sinking, 43, 44. Friction losses, 137. Furnaces, heating, 151. Fuse, correctly placed, 195. cut wrongly, 195. electric, 190. good and bad forms of inserting in caps, 191. igniting, 205. poorly placed, 194. proper care, 193. swaging end, 196. testing, 201. versus electric firing, 203. wrapped with adhesive tape, 194. Gardner electric drill, 88. Gases resulting from nitroglycerine explosives, 206. statics of, 216. Gasolene rock drill, 104. Gassing, 207. Gear, rotating; maintenance, 144. Gelatine, blasting, 179. dynamite, 179. Gelignite, 178. German device for preventing dust, 342. Golden Horseshoe mine, West Aus- tralia, 262. Gordon air-hammer drill, 55, 57, 58. Granite, excavation costs, 314. quarrying, Aberdeenshire, 264. Ground, hard, drilling, 113. Group electric shot firing, 197. Guide, Sullivan, 39. Gunpowder, 178. charging with, 182. Hammer drills, 49, 138. drills, advantages, 81. design, 80. Europe, 65. hand, 58. maintenance, 147. South Africa, 226. types, 65. used on stoping bar, 64. of hammer drill, 53. type in which vanadium steel is used, 79. versus piston drills, 136. Hand drilling, 309. drills, 49. hammer drills, 58. Hard ground, drilling in, 113. Hardscogg drill, 173. "Little Wonder" trigger valve drill, 62. "Wonder" air-hammer drill, 73. Wonder drills, 174. Hardy Simplex hammer drill, 58, 59. Heads, back, maintenance, 144. back of hammer drill, 53. front, maintenance, 144. Heat treatment of high-carbon steel, 153. Heating drills, 151. Hercules powder, 179. INDEX 363 Hints for operator, 116. History of rock drills, 1. Hitches, Davis mine, 275. Holes, arrangement, 282. arrangement for breaking ore, 308. in drift stoping, 298. in ordinary ground, 229. in raise stoping, 298. in removing pentice, 301. in shaft sinking, 301, 304, 305. Lake Superior, 297. Ophelia tunnel, 288. South Africa, 227, 228. Wolverine mine, 294. cut, arrangement, 233. cylindrical, 217. diameters, 217, 218. drift, arrangement, 306. in bottom of winze, 229. length, 221, 246, 247. long versus short, 223. numerical order of drilling with multiple arrangement of drills, 230. old, 112. proper depth, 214. ratio of depth to diameter, 218. size compared with height of bench, 222. starting, 111, 112. Holman auxiliary ball-valve drill, 33, 34. auxiliary valve drill, 31, 32, 33, 34. Brothers drill bits, 167. chuck, 47. ratchet and pawls, 36. spray, 340. tappet drill, 23. 2i-inch drill, 334. 2J-inch drill, 333. 2-inch diameter 5-inch stroke work- ing underground, 251. Horse-power tests, 325. Horsfield's "National" tappet drill, 20, 21, 22. new type of Ingersoll drill, 26, 27. Hose, 106. connections, 111. Hose, maintenance, 357. rock drill, 357. Hot- time lateral, Newhouse tunnel, rock-drilling practice, 285. Ignition of powder charge, 183. Imperial drill boring with hollow steel, 251. Indicator cards, 147. Ingersoll auxiliary valve drill, 31, 32, 33. drill, HorsfiekTs new type, 26, 27. " Eclipse" drill, 24, 25. -Rand chuck, 48. drill, 13. -Sergeant chuck, 45. drill, 31, 273. rock drill column, 40. versus Konomax drill, 328. Installation, compressed air, 352. Jack, maintenance, 146. stools, maintenance, 146. James's water blast, 342. Joints, maintenance, 146. Joplin, Mo., rock-drilling practice, 301. Judson powder, 179. Kalgoorlie field, rock drill practice, 260. Kid drill, 16. Kimber air-hammer drill, 55, 56, 58. t drill-sharpening machine, 160. Konomax drill, 125. versus Ingersoll drill, 328. Leakage in shaft mains, 357. of air hose, 117. Leyner correct drill bits, 172. drill, 136, 173. George, oiler, 119. hammer drill, water, 51, 52. patent starter, 172. Rock Terrier drill, 54, 55. water drill, Davis mine, 277. Little Giant rock drill, 13, 276. Hardy rock drill, 25. Jap hammer drills, 277. 364 INDEX Little Wonder air-hammer drills, 277. trigger valve drill, 62. Loading, 312. Locke electric drill, 89. Lockers, 105. Logging repairs, 146. Long Tunnel mine, sinking incline shaft, 264. Loosening ground, Utah, 308. Losses, air, 327. Lubricating devices for rock drills, 1 18. McKiernan drills, Davis mine, 276. drills, Caledonia mine, 271. Machine drilling, 309. drilling in hard rock, 238. sizes, 278. drills, Davis mine, 276. for using hollow drill steel, 342. Maintenance of hammer drills, 147. of pipe lines and air hose, 357. rock drills, 141. Marvin Sandy croft drill, 85. Masks, 340. Materials in piston rock drills, 48. Maynard chuck, 46. Meyer and Charlton, rock drill tests, 330. Michigan copper mines, details of drilling, 296. Miners, differences in, 234. Mining, first drill used, 2. Misfires, 247. and how to avoid them, 190. Modderfontein "B" gold mines, driving results, 232. Mohawk bit, 165. Mountings, drill, 39. Muck as staging, 287. handling, 289. Mucking, 244. Ophelia tunnel, 288. Murphy drill, tank, 339. Number 2 hammer drill, 70, 71. Standard drill, 61, 62, 63. steel drills, 173. "National" tappet drill, 20, 21, 22. New Century 00 drill, 334. Ingersoll rock drills, work done, 262. Modderfontein, driving results, 233. Newhouse tunnel, rock-drilling prac- tice, 285. Nitroglycerine, 179. Numa drill sharpener, 157. Number drill, 16. of 3i-inch drills served by standard pipes, 355. Nuts, maintenance, 146. Oilers, rock drill, 118. Oiling, 110. Ophelia tunnel, rock-drilling prac- tice, 286. Optimus compound rock drill, 123, 124. Ore, breaking, Joplin, 307. Davis pyrites mine, 273. extraction system, Caledonia mino, 270. Orebody, Joplin, 307. Overheating drill bits, 156. Pawls of hammer drill, 53. Percussion drills versus rotary pres- sure drills, 134. electric drill, 85. in rock drilling, 129. Philosophy of process of drilling rock, 129. Pillars in quarry stope, Rose Deep, 250. Pipe fittings, 355. lines, 106. maintenance, 357. serving 31-inch drills, 355, 356. sizes, 355. Piston drills, 8, 342. drills, classification, 10. designed to use air exclusively, 122. South Africa, 226. electric air drill, 100. maintenance, 144. INDEX 365 Piston rock drills, 35. rods, maintenance, 144. versus hammer drills, 136. wear of, 142. Plan of work, 108. Plate, rotating, of hammer drill, 53. Plunger, pawl spring, of hammer drill, 53. Portland Gold Mining Co., rock drill practice, 278. Powder charge, ignition, 183. conditions influencing, 186. diameter of sticks, 187. explosive force, 185. fumeless, 186. maximum strength, how produced, 183. storage, 194. susceptibility to detonation, 184. Rack-a-Rock, 179. Raise stoping, Wolverine mine, 294. Rand Collieries, Ltd., geological sec- tion of diamond drill hole, 235. deep levels, record driving, 231. " Little Giant," 13, 276. Model No. 5 drill, 15. "Slugger" rock drill, 29. Repairs, 117. logging, 146. made by contract, 141. rock drill, 141. Reshanking drills, 145. Resistance due to pipe fittings, 356. Respiration, artificial, 208. Respirators, 340. Rifling, 320. Rock-boring systems, 129, 130. character of, Rand Collieries, Ltd. 235. drilling, Aberdeenshire, 266. practice in heavy rock excava- tion, 310. drills, 1. contests, 315. future development, 334. hose for, 357. in tunnels, 291. Rock drills of 1880, 3. practice, America, 269. practice, Broken Hill, 260. practice, examples, 226. tests, 315, 321, 322, 323, 325, 330. used in South Africa, 226. Witwatersrand, 226. Rockers, maintenance, 144. Roosevelt drainage tunnel, rock- drilling practice, 290. Rose Deep, three pillars in quarry stope, 250. Rotary electric drills, 94. pressure drills, versus percussion drills, 134. Rotation, 81. Adams electric drill, 93. modified slip, 36. systems, hammer drills, 50. piston rock drills, 35. Rubislaw quarry, showing working face, 265. Running of machine, 116. Schram, Harker & Co., Optimus compound rock drill, 123, 124. Scotland, rock drill practice, 264. Scott gasolene rock drill, 104. Sergeant drill, section showing parts, 8. rock drills, descriptive table, 9. slip rotation, 35. Set-up, 106, 107, 108. Setting the machine, 110. Shaft, inclined, sinking, 248. Number 1, Rand Collieries, Ltd., 236. sinking, Caledonia mine, 270. Davis mine, 278. frames, 43, 44. Joplin, 303. Long Tunnel mine, 264. method, V-cut, 259. rapid, with air drills, 245. sump and bench system, 244. the Rand, 235. Victoria Reef Quartz Mining Co., 263. C66 INDEX Shaft sinking with machines, 236, 242. Wolverine mine, 300. Shanks on drill steel of hammer drill, 53. Sharpeners for drill steel, machine, 157. Sharpening chisel bits, 156. cruciform bits, 157. tools, 272. Shaw machine, 10A, 78. Shot firing, electric, 204. firing, group electric, 197. weak, 194. Siemens-Halske electric drill, 86, 89, 90. -Schuckert electric drill, 87. Signaling system, Rand Collieries, Ltd., 239. Simmer deep, driving results, 231. Simplex drill chuck, 240. Sinclair hammer drill, 69, 70. valveless hand drill, 61. Siskol drill, 333. "Slugger" rock drill, 29. Sommeiller machine, 1, 2. South Africa, drills in use, 226. Africa, rock drill practice, 226. Spares, fitted up, 146. Speed, boring, 332. drilling, 332. Spitting, side, 195. Sprays, 340. Holman, 340. Spring, pawl, of hammer drill, 53. Squibbing, 302. Standards, 146. Starter, Leyner patent, 172. Starting steam drill, 115. the machine, 111. Statics of fluids and gases, 216. Steam drill, starting, 115. in rock drill work, 351. Steel, 150. drill, 150, 310. size of, 234. for drilling dry up-holes, 168. hollow drill, 62, 176, 342. sizes, 240. Steel twisted drill, for removing broken rock, 169. vanadium, used in hammer of drill, 79. Stephens & Son, R., 65. chuck, 48. Climax Imperial hammer drill, 65, 66, 67. tappet valve drill, 23. double chisel drill, 176. patent Climax dust allay er, 341. Sticks, powder, diameter of, 187. Stools, jack, maintenance, 146. Stope-cut, 260, 261. drill, Cleveland, 75. competition, 333, 336, 337. , tests, 331. -face showing run of benches, 256. with benches for drills, 255. ideal arrangement, 255. overhand, 257. shape, 252. underhand, 257. with benches at angle to drift, 253. pillar cut on lower side at drive, 253. Stoping, back versus underhand, 275. Caledonia mine, 269, 271. drift, 307. Findley Consolidated mine, 285. hard ground, 302. Lake Superior, 295, 298. on the Witwatersrand, 249. overhand, on 15 to 45 degree reef, 252. raise, 299. underhand, Davis mine, 274. with large machines, 284. Wolverine mine, 292. Storage of powder, 194. Stretcher bar, 40. Sullivan D-21 air-hammer drill, 72, 73. differential spool valve, 29. valve rock drill, 27, 28. drill on double-screw mining col- umn, 41. on single-screw mining column, 41. INDEX 367 Sullivan guide on cradle, 39. hand hammer drill, 60. rock drill bits, 155. tappet valve rock drill, 18. valve hand drill, 61. Sump and bench system of shaft sinking, 244. Surface operation of drills, 105. Tamping, 220. high explosives, 187. Tank for Murphy drill, 339. Tappet, automatic, Waugh drill, 76. maintenance, 144. valve drills, 12. Tempering drill bits, 154. steel, 150. Temple-Ingersoll electric air drill, 95, 100. Tests, drill, 317, 329, 334. electric and air drills, 89, 90. horse-power, 325. rock drill, 315, 321, 322, 323, 325, 330. stope drill, 331. Testing hammer drills, 147. Time, drilling, 257. Tonite, 179. Tools, 105. blacksmith's, 156. sharpening, 272. swaging, for Kimber sharpener, 161. Torpedo drill, 30, 31. Transvaal stope drill, competition, 333. Tripod for mounting drills, 42. working drill with, 115. Tuckingmill Foundry Co., Dunstan's drill sharpener, 158. Tunnel driving speed, 291, 292. Tuneling, first drill used, 2. rock drills in, 291. U-bolt chuck, 45, 48. Underground drilling, 105. Utah, rock drill practice, 308. Valve, auxiliary, 31. auxiliary, maintenance, 144. Valve chests, maintenance, 143. design in hammer drill, 81. drills, 10. auxiliary, 31. piston, maintenance, 143. remedy for sticking, 116. slide, maintenance, 143. spool, 29, 33. Sullivan differential spool, 29. throttle, maintenance, 143. Valveless drills, 50, 79. Van Dyke mines, driving results, 232. Ryn Gold Mines Estate, Ltd., rock drill tests, 325. Vanadium in drill steel, 177. Vibration of arm and bar, 107. Victoria Reef Quartz Mining Co., record shaft sinking, 263. Vogelstrius Consolidated Deep, driv- ing results, 233. Wages, miners', South Africa, 256. Warren-Tregoning chuck, 46. Water blast, variation of James's, 342. device for passing through drill steel, 347. jets, 338. Leyner hammer drill, 51, 52. .Waugh drifting and stoping drill, 76, 77. drills, 174, 175. Wear between cylinder and piston, 142. causes, 139. effects, 147. on cradle guides, 142. Wedges, 105. Weight of parts of hammer drill, 139. Western lubricating valve, 119, 120. Witherbee-Sherman iron mines, N. Y., rock drill practice, 273. Wolverine bit, 165. mine, rock drill practice, 292. Word drill sharpener, 157, 167. Work done by electric air drills, 101. done with multiple arrangement of drills, 228. 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