L- S. S. Montu T J LIBRARY OF THE UNIVERSITY OF CALIFORNIA GIFT OF MRS. S.S. MONTAGUE Class i S. S. Montague. RUDIMENTARY TREATISE CONSTRUCTION OF CRANES, MACHINERY FOB EAISING HEAVY BODIES, FOE THE EEECTION OF BUILDINGS, AND FOE HOISTING GOODS. BY JOSEPH GLYNN, F.R.S., MEMBER OP THE INSTITUTION OP CIVIL ENGINEERS, ETC. HONORARY MEMBER OF THE PHILOSOPHICAL SOCIETT, NEWCASTLE-UPON-T1NE, ETC. FOURTH LONDON: VIRTUE BROTHERS & CO., 26, IVY LANE, PATEENOSTER ROW. 1866, ~: CONTENTS. Preface ..:........ v 1'. PRIMITIVE STATE OP MAN 1 Origin of the windlass ........ 3 Improvements on the windlass 4 Original capstan described ....... 8 Original improvements on the capstan ..... 9 Jack-roll 12 Gin, described 12 Application of steam power to collieries 13 Extensive use of the capstan by the Russians .... 14 Cross 16 Hand wheel . 16 Cog and round ......... 16 Lever and axle 17 Block and pulley, origin and use 18 "Dead-eye" . 19 2. APPLICATION OF HOISTING MACHINES, AND EMPLOYMENT OF THE POWER OF MEN 20 Derrick 20 Henderson's derrick 21 Triangle, or " three legs," 22 Calculations, and experiments on the power of men . . 22 3. PROGRESSIVE CONSTRUCTION OF CRANES 26 Walking crane 27 Goods crane 28 Shipwrights' crane ......... 29 Influence of cast iron on the form of the crane 33 Brakes 33 Well cranes 36 Wharf cranes .... 36 Construction of the crane post 36 Foundry cranes 41 4. TRAVEKSING, OR TRAVELLING CRANES 43 Eennie's traversing crane 43 Improved travelling cranes .48 Use of, in the erection of large buildings, &c. ... 48 Use of, in building bridges ....... 49 5. SELF-ACTING HOISTING MACHINES 50 Sack-tackle 51 Hoist, or lift ! 51 Cornish man-machine . 52 117189 IV CONTENTS. Page Hague's vacuum crane 53 Steam crane .......... 53 Armstrong's water crane 58 Murray's lifting apparatus 63 Hydrostatic paradox, explained 64 Bramah's press 65 Bramah's presses, used in the erection of the Conway Bridge . 65 6. STRENGTH OF MATERIALS USED IN THE CONSTRUCTION OF CRANES 67 Beams, strength and forms of 07 Timber beams, experiments on the strength of ... 67 Experiments on the strength of cast iron .... 70 Strength of cast-iron pillars 74 Tables showing the strength of cast iron under various tests . 77 Strength of wrought iron 78 Transverse strength of wrought iron ..... 80 Crane hooks, form and strength of 81 7. DEFLECTION OF MATERIALS 81 Cast iron 81 Timber 82 Table of the strength of timber in general use . . 85 Rules on the strength of timber crane-posts . .88 Lang's masting sheers, their construction described . 90 8. STRESS OR FORCE UPON EACH PART OF A CRANE . . 92 Results of alterations, in the form of, considered . . 94 9. CHAINS AND ROPES OF CRANES AND HOISTING MACHINERY . 97 Chains, strength of ..,.,.... 97 Chains for crane work ........ 97 Barrels of cranes ... ^ ..... 97 Comparison of the strength of chains and ropes ... 99 Huddart's experiments on the strengih of cordage . . . 100 Flat ropes 102 Weight and strength of chain and hempen cables . . .103 Wire ropes . ... . 103 Wire ropes, strength of . . . . . . . .104 Strength of flat wire and hempen ropes . . . . . 105 10. MACHINERY OF CRANES 106 Wheels, strength and proportions of ..... 107 Diameters of wheels and barrels . . . . . .108 Toothed wheels 110 Strength and form of the teeth . . . . . . 110 Willis's method of forming teeth ...... 112 Willis's " Odontograph " 114 11. FOUNDATIONS AND MASONRY FOR FIXING AND SECURING CRAN 7 ES . 114 Works of reference 116 12. REFERENCE TO THE ILLUSTRATIONS 118 PREFACE. THE subject of this Treatise is the construction and use of machines which diminish toil, and facilitate and lessen la- bour without superseding it, enabling men to perform what they could not accomplish without such aid. Deprived of mechanical power, a man's force is limited to his muscular strength, of which he has but little, in proportion to his bulk and weight, when compared with other animals ; his disposable mechanical force, when daily exerted for ten hours, being only about one-tenth of his weight. The old race of millwrights men who designed and constructed their own work may be considered extinct ; and the operative engineers or " fitters " of modern times, although excellent workmen at the vice or the lathe, have, since the introduction of self-acting tools, and by the classification of labour, become almost machines them- selves. One man has been trained to do one thing, in doing which, however skilful he may be, he exercises no discre- tion of his own ; he has nothing to contrive or to propor- tion. But good springs out of evil. Providence did not intend that man should be reduced to a machine; his mind will not rest satisfied in this condition ; he begins to inquire why he finds himself thus ; he desires to know the VI PREFACE. relation between cause and effect, and to understand the principles on which are founded the orders he is called upon to execute. It is hoped that the elementary treatises now put forth may serve as guides to such persons, as well as to young students, in commencing the pursuit of knowledge, and tend to render the course straighter, and the task less difficult. The author has for many years had the direction and management of men in considerable numbers. He is convinced that perfect order, strict discipline, and prompt obedience, are imperatively necessary to ensure success in the combined efforts of many men ; but he is also con- vinced that intelligent and well-informed people are more easily directed than those who are uneducated and ignorant ; and he has never found that a sound education, and a right understanding of first principles, unfitted a man for the station he might hold, although they might tend to raise him above it, and often eventually did so. He has the gratification of seeing many persons, who have acted under his orders, now filling offices of trust and responsi- bility with merited credit, and others deservedly acquiring reputation and wealth, which they owe to the early cultiva- tion of their minds. In every state of society the many must be ruled by the few, and " those who think most must govern those who toil ;" but the relations of society in this countiy at present have the effect of increasing wealth in few hands, and many men labour to make one man rich. This may, in part, be attributed to the use of machines, as substitutes not only for labour, but for the performance of operations formerly requiring skilful workmen. PEEFACE. Vll Machines are employed to make machines, and thus capital increases in a larger ratio in few hands. It may be doubted whether the accumulation of capital in large- masses be a national benefit. If it be otherwise, if it be desirable to improve the condition of " those who have most of the toil and least of its benefits," as has been well said by an illustrious Prince, then will one of the best and most peaceful means of modifying this unequal distribution of comforts be to give to the working-classes a sound and useful education, and to impart to them a know- ledge of first principles in the mechanical arts they are called upon to practise; to elevate their character, and better to fit them not only to fulfil their duty in that station wherein Providence has placed them, but to render them capable of rising above it, when opportunities are presented to them, by peaceful and legitimate means, conducive to the general welfare of society. J. G. ON THE CONSTRUCTION OF CRANES. PRIMITIVE METHODS OF ASSISTING OR COMBINING THE POWER OF MEN OR HORSES. The Windlass. The Capstan and the Gin. The Cross. The Hand wheel. The Cog and Round. The Dead-eye. The Pulley. IF man were furnished with no other means cf defence, or of assistance to his physical strength, than those which his own organisation supply, he would be one of the most helpless creatures existing. But his hand instinctively grasps the club or the stone as ready weapons for his pro- tection; and his further wants, stimulating his ingenuity, teach him to form the objects within his reach into the bow, the spear, and other appliances for the pursuit of game or of fish. He twists the vegetable fibre or the thong into the line or the cord, and the cord into the rope. From the fallen tree he makes the raft and the canoe. He quits the cave which gave him shelter, and builds the more conve- nient hut and the more ample cottage, and he soon finds that he has to deal with materials beyond his unaided strength to fashion or to move. The pole in his hands becomes a lever to remove the trunk of the fallen tree, and the rope of twisted thongs or fibres of bark, thrown over the fork of an extended branch, probably formed the first crane. Although no mechanical power be gained by this arrangement, yet it enables several men to unite their strength, and one man to maintain and hold fast the result of their combined efforts. That either this form, or the rude but useful adaptation 2 ON THE CONSTRUCTION OF CRANES. of the lever, common in all parts of Northern Germany, Fig. 1. and sometimes seen in a more slender and commonplace shipe in our own brickyards, may have been the original crane, seems not improbable ; the name given to the ma- chine being the same as that of the long-necked water-fowl, which, wading in the shallows by a river's side plunges its bill into deeper pools to bring up its food. The Crane, la Grue, der Kranich, la Grua, and Cigonal, indicating in French, German, Italian, and Spanish, that the idea which furnished the name was the same in them as in the English language, or that they all derived the machine and the name from the same source, probably from the Germans. Most persons who have passed through German villages will remember the simple and picturesque mode of raising water from a well by means of a tall fir or poplar tree resting in the fork of an elm growing near the well or brook. The root end of the poplar, assisted perhaps by the weight of a stone, overbalances the top, from which the bucket is suspended; the counterbalance being equal to half the weight to be raised, or thereabout, so that the man ON THE CONSTRUCTION OF CRANES. 55 has to pull down the bucket to make it descend into the \vell ; the counterbalance assisting him in hoisting up the bucket when full ; and thus, by apportioning his efforts, he doubles his effective force at the time he needs it. Fig. 2. The application of the pole as a lever for moving weights, or for turning over the trunk of a tree, might suggest its further use, combined with a rope, to obtain mechanical power; the author has seen old seamen, in case of need, resort to such a contrivance, and make, as they termed it, "a purchase," with a plain wooden roller (part indeed of a fir- tree trunk), a rope, and two handspikes, and, by the skilful combination of these materials over a hatchway, accomplish what the united strength of all hands failed to effect without such assistance. A little in advance of this, is the mode of hoisting timber common throughout all the North of Europe, and some- times used by our woodmen in England, by means of the " lever and axle " attached to the " three legs or triangle " a tripod, formed of three poles, secured by a rope or shackle at the top. The end of one handspike or spoke, being oc- casionally thrust through the axle or windlass, rests upon OK THE CONSTRUCTION OF CRANES. the ground and stops it from unwinding, forming a simple but effectual check. This same primitive windlass is still used by the Chinese for weighing anchor, even in their largest junks. A strong tree of hard wood extends entirely across the vessel from side to side ; it is hewn into an octagonal form, and the ends being reduced and rounded to form pivots, rest in the top timbers of the ship, which are brought up above the deck for this purpose ; consequently the length of their windlass is sometimes 28 or 30 feet. It is stopped from unwinding or turning the wrong way by thrusting a hand- spike through, and allowing its end to bear upon the deck, whereby the descent of the anchor, between the successive exertions of the crew, is prevented, until they can ship their bars and heave again. The next improvement appears to have been " the paul." So late as the year 1776, when Falconer, author of that beautiful nautical poem, the Shipwreck, published his Ma- rine Dictionaiy, the windlass used on board of British mer- chant vessels appears to have advanced but little beyond this primitive form. The differences were two : first, it did not rest on the ship's sides, but was supported and secured in two strong timbers fixed on opposite sides of the main deck, a little behind the foremast, wherein the windlass turns on its axis. These are generally called " the windlass bits," and are each made in two pieces, for more conve- niently getting out the windlass and allowing the bight of the cable to be passed round it, as it commonly is in three turns ; the upper parts of these bits being formerly orna- mented with carved " knights' heads," still retain that name. Secondly, the windlass was furnished with pauls, which Fal- coner thus describes : " The pauls, which are formed of wood or iron, fall into notches cut in the surface of the windlass, and lined with plates of iron. Each of the pauls being accordingly hung over a particular part of the windlass, falls eight times into ON THE CONSTEUCTTON OF CEANES. 5 the notches at every revolution of the machine, because there are eight notches placed on its circumference under the pauls. So, if the windlass is twenty inches in diameter, and purchases five feet of the cable at every revolution, it will be prevented from turning back, or losing any part thereof, at every seven inches,, nearly, which is heaved in upon its surface.. " As this machine is heaved about in a vertical direction, it is evident that the efforts of an- equal number of men acting upon it will be much more powerful than on the cap- stan, because their whole weight and strength are applied more readily to the end of the levers employed to turn it about ; whereas, in the horizontal movement of the capstan, the exertion of their force is considerably diminished. It requires, however, some dexterity and address to manage the handspike to the greatest advantage ; and to perform this, the sailors must all rise at once upon the windlass, and fixing their bars therein, give a sudden jerk at the same instant, in which movement they are regulated by a sort of song or howl pronounced by one of their number." The " song " of the seamen, when raising the anchor for their departure, has always a melancholy and plaintive tone, even " When ten jolly tars, with musical Joe, Heave the anchor a-peak, singing, Yo, heave ho ! " The windlass remained nearly in the same state as described by Falconer, when the author first saw it ; but the windlass necks were then made of iron, so as to prevent loss of power by friction, and the pauls, then placed in the centre of the windlass, were two in number, and of different lengths, or, as the sailors termed them, " paul and half- paul," which, although the number of notches was still only eight, had the effect of dividing the circumference of the windlass into sixteen, and enabled the seamen to retain every three and a half inches of the cable they hove in- This was a great relief to the men, for seven inches on the windlass occasionally lost by the shock of a heavy 6 ON THE CONSTRUCTION OF CKANES. sea, occasioned a severe jerk at the end of a six-feet hand- spike. The advantages arising from this improvement gave rise to the patent pauls, wherein a cast-iron paul-wheel was fixed upon the wooden windlass, and the pauls were made more numerous, and of various lengths. The paul-wheel had sixteen notches ; it was made hollow, and octagonal inside, to slip over and be adapted to the old windlass ; better methods of securing all the parts being introduced at the same time, the announcement in the Newcastle papers became less frequent, that " the Good Intent, of Shields (coal-laden), with windlass upset, and loss of anchors and cables in the Swin, had put into Harwich, and must dis- charge cargo for repair." The principle of dividing a ratchet-wheel by differential pauls, whereby minute division of . circumference can be ob- tained with a comparatively coarse pitch of tooth, is worthy of being borne in mind, and may be made useful in many kinds of machinery. By applying it to the ship's windlass, every inch of cable is retained, much labour is saved, and the men are preserved from hurts, often caused by the vio- lent recoil of their handspikes. Other alterations have been successively made in the windlass ; machinery of various kinds has been attached to it, for some of which patents have been granted. One of these alterations consisted in fixing within the bit-heads a sway-beam of wrought iron, constructed so as to be unshipped at pleasure. Upon the windlass, and imme- diately under .the two arms of the beam, were fixed ratchet wheels, upon which two pauls, one attached to each arm, alternately acted as the beam was raised or depressed, and a wooden pole or handle being passed horizontally through an eye at each end of the sway-beams, they were worked with a pumping action like a fire-engine. This arrange- ment rendered the working of the windlass continuous, or nearly so, as well as much more rapid in its action, and highly useful for lighter work, such as warping the ship out ON THE CONSTRUCTION OF CRANES. of a crowded harbour ; whilst, in case of need, it might be readily removed, and the windlass worked with handspikes as before. By a subsequent improvement, patented by Messrs. Pow and Fawcus,. of North Shields, the ratchet a, a, are wheels with plain surfaces; there are two of these "purchase- wheels" fixed upon the windlass. c, c, the nipping levers confined to the purchase- v.- 1 eels ly flat iron rings, or discs, called travellers, which, in descending, move freely round. d, d, the travellers with the cheek-plates of the nipping levers bolted to them ; the levers bite upon the purchase-wheels, and, acting alternately, force the windlass round in their ascent. e, the cross-head of the sway-beam shown in plan, with sockets to receive the levers. /,/, the levers,, which are bent forward to clear the knees of the bit-heads. Fig. 4. wheels are dispensed with, and a nipping lever, acting on a wheel with a plain surface, is substituted, so that the noise of the ratchets is avoided, and all the length of cable hove 8 ON THE CONSTRUCTION OF CRANES. in is held fast. Other alterations consisted in the appli- cation of toothed wheel-work in various ways, sometimes to the ends, and sometimes to the middle of the windlass, so that at last it has, in fact, become a powerful compound piece of crane-work. The ancient mariner, howevery looks on all these altera- tions with jealousy and suspicion, prudently rejecting all such as may not, in case of emergency, be laid aside for the trusty handspike of tough ash or hiccory, which never has its teeth broken by a heavy strain in a gale of wind, like the cast-iron wheel-work. He also knows the import- ance of having such tackle as the ship's carpenter may repair, and for which materials may be found in any port whither, in stress of weather, his vessel may be driven. As it is often inconvenient, and sometimes dangerous, to ship and unship the handspikes in a ship's windlass, be- sides causing much loss of time, and as by it the united strength of many men cannot be employed, the capstern or capstan is used instead of it, hi large vessels, to weigh the anchor, and in ships of war, when despatch is needful, a large body of men act together, walking round the cap- stan, their efforts being rendered simultaneous and uniform by the sound of music, and the cable of the gallant ship, on her return home from a foreign station, is merrily rounded in. " A fair wind, and off she goes." The original capstan or crab was, something like the primitive windlass, set on end through a round hole in the deck ; it was formed of a single piece of timber ; the lower end of it, reduced to a pivot, and shod with iron, was stepped into the vessel's kelson; the upper part of it had two holes morticed through it, one above the other, crossing each other at right angles. The machine in this form may still be occasionally seen in small coasting ves- sels from the bye ports in the West of England, or on board of French luggers ; and it is sometimes used for hauling up the larger fishing craft upon the beach. It ON THE CONSTRUCTION OF CRANES. 9 gradually, however, assumed a more important shape, and instead of being only one piece of wood, it was composed of several parts ; namely, the " drum-head," the " barrel," the " whelps," and the " spindle," all, in the first instance, made of timber. The spindle, as before, was shod with iron, to form the pivot, and worked through a round hole ; but this was formed in a strong wooden stock, called " the step," which rested upon and was bolted to beams placed for the purpose ; the spindle was hooped with iron to pre- vent abrasion of the wood, and it revolved in an iron socket or collar, called " the saucer," which was fixed in the step. Two strong pauls of wood or iron were bolted at the deck to the beams above mentioned, and acting against the lower end of the whelps, prevented the recoil of the cap-, stan. A man-of-war has two capstans ; the main capstan being, as it were, a double one, like two capstans on the same spindle, the one on the main deck and the other on the upper deck, so that two tiers of bars can be worked at once upon the two decks. Many improvements have also taken place in the capstans ; the spindle is now made entirely of iron, and, wheel- work being applied to it, the capstan also has become a compound machine, displaying in some instances much ingenuity. In this sketch, the drum-head is fixed upon the spindle, and turns it round. An iron bolt passing through the drum-head, locks it to the barrel, and the whole capstan turns round with the spindle, forming a simple machine, or " single purchase." When the locking bolt is withdrawn, the wheel- work, shown in plan, acts between the spindle and the barrel, and a power of three to one is gained; the spindle makes three turns, while the barrel makes one, and they revolve in opposite directions. The mode of locking the drum-head is shown in the sectional elevation of the capstan. The mechanism, has, however, this general character in all its phases, namely, that there is a toothed pinion upon B 3 10 ON THE CONSTRUCTION OF CRANES. Fig. 5. the spindle, and a wheel with external teeth attached to the lower part of the barrel. Fig. 6. ON THE CONSTEUCTION OF CRANES. 1.1 The working of capstans is subject to an inconvenience, arising from the tendency of the rope which is wound upon them to advance in a spiral direction towards the end of the barrel, there being generally two and a half or three turns of the rope taken round the capstan, and one part of the rope is wound off the barrel as the other part is wound on. It therefore becomes necessary to " surge the cap- stan," that is to say, suddenly to slack the rope so as to bring it back to its original position ; the barrel and whelps being formed lik^ a truncated cone to facilitate the opera- tion. But this being always inconvenient, and often hazardous, especially where very great weights must be dealt with, a plan has been devised which may be seen in use at the great masting shears in Her Majesty's Dockyard, at Wool- wich, to obviate this objection. Two capstans are fixed near to each other, and are connected by a pair of toothed wheels, so that they revolve together, but in contrary direc- tions ; one only has a drum-head to receive the capstan bars, the other is made low to allow the bars to pass over it, and the rope is passed round both in the form of the figure of 8. The crab or capstan, on a large scale, is often used at mines and coal-pits to raise and lower the heavy cast- iron pumps, to draw the pump-rods, and other similar work; it has generally four arms permanently fixed, instead of bars, to which a large number of the miners apply their strength, and they are sometimes assisted by horses. The mine capstan is a simple, and, in early times, has been a very useful machine ; but, since the mines have been sunk deeper, it often causes frightful accidents: the men not being accustomed to act in concert like the well- trained crew of a man-of-war, and being hastily called together to raise great weights of pumps, or, what is more dangerous, to lower them, are occasionally overcome by the descending load, and this accelerating in its descent, "the 12 ON THE CONSTRUCTION OF CRANES. capstan spins," flinging the miners from its arms with fearful violence, when broken limbs and even death ensue. In these days, when safe and powerful machinery may be substituted, the cheapness of the mine capstan is the chief inducement to retain it. Wherever the author could exercise sufficient influence, he has erected a combination of wheel-work for deep pits instead of the mine capstan; so that a small number of men suffice, and accidents are avoided. There is scarcely any limit to the powers that may be gained by compound wheel-work, and the additional time it takes is of little moment in heavy mining operations. During the early periods of mining in Cornwall, when pits began to be sunk in those places where the manifest abundance and richness of a vein led the miner to pene- trate beneath the surface, the produce was raised by being thrown upon successive stages or platforms, or " shammels," as the Cornish miners call them, by men stationed at different elevations. The introduction of the jack-roll or windlass, in its rudest shape, was a great improvement; this contrivance, which probably came from Germany, not only facilitated the raising of the excavated material, but enabled them to clear the mine of water by means of buckets, with a degree of despatch not before practicable. In the Derbyshire lead mines, the jack-roll or "wal- lower," as they term it there, is still used, as it is also at some of the ironstone pits ; but at many of these, as in the collieries, it has been superseded by " the gin," which is worked by horses. The gin consists of an upright wooden axle, on which is fixed a hollow cylinder of wood-work, called the cage, round which a rope winds horizontally; the ends of the rope being directed down the pit by two pulleys. A trans- verse beam, seven or eight yards long, is secured across the axle, to each end of which is yoked a horse. The horse ON THE CONSTRUCTION OF CRANES. 13 track should not be less than seven or eight yards in diameter, so that the horse may not expend his force in an oblique direction, but get a fair pull on the " starts." An ordinary horse produces the greatest mechanical effect in working at a gin, or drawing a load on a tramway, when he travels at the rate of two and a half miles an hour or 220 feet in a minute ; he can then exert in regular work day by day for eight hours, a steady pull of 150 pounds. Hence arises our familiar term of "horse's power;" the speed of 220 feet multiplied by 150 pounds being equal to 33,000 pounds raised a foot high in a minute, a standard which engineers have by common consent adopted as the expression for mechanical powers employed for practical and manufacturing purposes. This limit to the use of horses for winding coals, the adaptation of the steam engine to a rotatory motion, and its successive improvements having made it perfectly ma- nageable, the increasing depth of the pits, and the demand for coal, have caused the steam-engine in most cases to supersede the gin, and its use has enabled the coal-owners to expend large capital in sinking deep pits, where thick and valuable coal might be obtained ; so that the power of the engines has, of late years, been continually augmented. A company of gentlemen, having recently sunk a pit to a depth of 220 yards, at Cinder-hill Colliery, near Notting- ham, with some difficulty and much expense, found coal of good quality and ready sale ; and, being desirous to meet the demand in the market without sinking additional pits, they applied to the Butterley Company to furnish them with such an engine as might raise what coal they could sell. The author was desired to make the requisite calcu- lations, and to prepare such plans as should effect this object. He found that it would be necessary to draw from this depth a ton of coal in every successive minute for ten hours a day ; that the coal should be brought up in two of the small underground waggons, to be unloaded " at bank," each of which contained half a ton ; and that, in order to 14 ON THE CONSTRUCTION OF CRANES. allow time to land each load and to reverse the engine, it was requisite to bring up the ascending " cage " as fast as the descending one would with safety and certainty go down. Taking into account the resistance of the air and the friction of the " guides," it was not considered prudent to attempt a speed greater than 16 feet in a second. A heavy body, unchecked by the friction of slides or guide rods, falls about 16 feet in the first second; but as the engine, when reversed, does not immediately regain full speed, it permits the requisite acceleration of the falling or empty cage, which descends as the full one rises. The weight of the flat rope, the friction of the cage, and the weight to be drawn at such a speed, rendered it necessary to construct a non-condensing steam-engine of 200 horses' power. The result was quite successful ; and, in the col- lier's week of five days, or 50 hours' work, 3000 and some- times 3500 tons of coal are raised with ease. Much more than this is performed at several of the collieries in the counties of Northumberland and Durham, where engines of great power are employed at larger pits. Referring to the practice of heaving at the capstan on board of ship to the sound of music, it may be remarked that, by this means, a number of those machines, actuated by large bodies of men, may be made to exert their force at once upon the same object; and that the Russians of the present day employ them in moving those immense blocks of stone, of which their public buildings display so many examples ; and, also, that they are employed in moving their line-of-battle ships, often built on shallow water at a distance from the sea, until they are fairly floated upon the caissons or "camels," which are used to buoy them up and enable them to come down the Neva to the Gulf of Finland, towed by a flotilla of 'row-boats. The rock on which stands the colossal statue of Peter the Great, was moved from Lachta, in Finland, to the Russian capital by the aid of many capstans worked at the same time by a large body of soldiers, who kept step ON THE CONSTEUCT10N OF CRANES. 15 to the sound of the drum. The impression which the sight of this immense monument made on the author's memory, many years ago, is still fresh and vivid. The rock, when brought to St. Petersburgh, is said to have weighed 1100 tons, which corresponds with the ori- ginal dimensions of the stone. These were 42 ft. long at the base, 36 ft. at the top ; 21 ft. thick, and 17 ft. high. The transit of this enormous block of granite was facili- tated by a kind of anti-friction railway, laid down as it pro- ceeded onward, and taken up from behind ; it consisted of large beams of timber, wherein grooves were formed to receive large cannon-balls, the stone resting upon cor- responding grooved timbers, so that the two beams formed a kind of channel for the balls. The taste of the sculptor unfortunately led him to dress the stone,, and partially to change its form, by which its size was reduced and its rude grandeur impaired, to the great chagrin of the Empress Catherine ; but still it is a noble work. Few monuments can be compared with the Bronze Sta- tue at St. Petersburgh ; the animated figure of the rampant horse, standing 17 ft. high, with his imperial rider 11 ft. in height, admirably designed and skilfully executed, poised upon their massy pedestal, produce an effect hardly to be surpassed. It is much to be regretted that some of the best machine capstans that have been introduced on board ship have failed from the weakness of their wheel-work and the im- perfection of their workmanship, thus 'creating a prejudice among seamen to such mechanism, and tending to delay, if not to prevent, its more extended use. In all- such cases the stress should be ascertained, and the strength of the machinery calculated, making allowance for contingencies, instead of taking it for granted, as is too often done, that wheels and teeth of a certain size and pitch will answer the purpose. The constant inconvenience and frequent danger incurred in shipping and unshipping the handspikes, or 16 ON THE CONSTRUCTION OF CRANES. spokes, caused them, in small windlasses, to be permanently fixed, and eventually the cross or the hand-wheel became, for many purposes, parts of machines, as we see them still on the copperplate printing rollers and the steering wheels of ships, by which mechanical power is gained in the pro- portion of the radius of the spoke to the semi-diameter of the barrel. The same rule holds good in all the simple forms of the wheel and axle, whether windlass, capstan, jack-roll, or gin. The spokes of the hand- wheel were generally eight in Fig. 7. number, but it was" not difficult to perceive, that if their number were increased, or if a second wheel and axle could be brought to act upon the first, much greater power might be gained. Hence " the spokes " were multiplied into " cogs" and upon the second axle was fixed a small wooden wheel or " lantern" composed of two discs or trenchers, in which were inserted six or more staves or " rounds" of hard wood like the rounds of a ladder. The figure here given was taken from an old deep well in the county of Kent. ON THE CONSTRUCTION OF CRANES. 17 Machines of this kind were common forty years ago, and some may still be in existence, although the general intro- duction of cast-iron machinery and its toothed wheels has now superseded the old " cog and round." The mechanical power gained by the wheel and axle, or level and axle, which are the same things, has been already mentioned ; there is, however, another form of the axle, by which much greater power is gained for a short lift. It is obvious that the only way to gain more power with the simple lever and axle, is to increase the length of the lever; but this can. only be done within a very limited range. Fig. 8. If, however, the axle be made of two different diameters, one-half of the barrel's length being a little larger in diameter than the other half; if a single pulley or block be put upon the middle or "bight" of a rope, and the two ends of the rope be wound round the two ends of the barrel in opposite directions, so that one end will wind off as the other end winds on ; then, if the smaller part of the barrel be 7 in. in diameter, or 22 in. in circumference, and the larger part be 8 in. in diameter, or about 25 in. in cir- cumference, every turn of the barrel will wind up the dif- ference, or about 3 in. of rope ; which difference, being divided by the use of the pulley, would raise the weight suspended to it about an inch and a half, so that with a winch or lever of 18 in. radius the workman's hand would move in a circle of 3 ft. in diameter, or about 113 in. 18 ON THE CONSTRUCTION OF CRANES. in circumference ; and consequently a power of about 75 to 1 would be gained. But, as one complete turn of the barrel winds on 25 inches of rope, it requires nearly 17 ft. of rope to raise the load 1 ft. high. The quantity of rope required limits the use of the differential axle or barrel to a short range ; but there are many cases in which so sim- ple and powerful a machine may be very usefully em- ployed. In the machine last described the block or pulley formed an essential part, and added to the power of the machine. As it is used in the construction of many cranes as a means of gaining mechanical power, it may be well to show, briefly, how it does so. When ropes or cordage came into use, it was found to be a convenient mode of raising any round object up a slope or inclined plane from the water-side; or of lowering it down in similar situations, to pass the middle of the rope about a tree or a post, and the two ends of it round the object to be raised or lowered. In this way a heavy spar may be hoisted from the river upon a quay or wharf, or a water cask lowered hi to a ship's boat with comparative ease, the power gained being two to one, independent of the inclined plane, the cask itself serving as a pulley. This arrangement of the rope, by sailors termed a "par- buckle," is also used by the draymen in London with great skill and dexterity ; they will sometimes lower a cask of half a ton in weight into a cellar without any apparent dif- ficulty, by making it form a part of the mechanism. The combinations of ropes and rollers to gain mechani- cal power, which invention sharpened by necessity would soon suggest, led to the contrivance of " the block," which at first was merely a piece of hard wood with a hole in it, to reeve the rope through, such as are still used to " set up " or heave tight the shrouds and standing rigging of ships. These blocks have three holes in them, through which the rope or "laniard" is passed, and then greased, to reduce the friction, until it is hove tight and made fast. The ON THE CONSTRUCTION OF CRANES. 19 round shape of the block, and the position of the three holes, give it somewhat the resemblance of a death's head, and hence its name, " the dead-eye." In blocks constantly used, the friction and rigidity of the cordage causing so great a loss of power, induced the addition of a roller or " sheave " in the block itself; and successive improvements have brought the crane blocks, used in some of the steam- engine manufactories, to their present state of excellence. The blocks now employed in the leading establishments of the present day,\vith iron shells, brass sheaves, and steel pins, their wrought-iron straps or side links, swivels, and hooks all carefully calculated, so as to give sufficient strength of materials for the load to be hoisted, and at the same time to avoid superfluous weight, and to reduce the friction by proportion of parts and superior workmanship, greatly di- minish labour, and increase despatch in the manufacture of heavy machinery. The introduction of iron blocks and pulleys admits the use of chains instead of ropes ; arid as the links of chains are now made almost exactly uniform in size and shape, they have been substituted for ropes in most foundries and engine works. The power gained by any combination or system of blocks or pulleys, is proportionate to the distance travelled by the moving force, compared with the height to which the load is raised in the same time, without deducting loss by friction ; so that, if mechanical power of two, four, or six to one be gained, the force applied must move through so many times the space that the weight is lifted, and in the same time ; for in this, as in all other machinery, speed is lost in proportion to power gained, besides the loss arising from friction of the mechanism and other resistances ; con- sequently, no force descending can ever raise an equal weight to the same height in the same time. Simple and obvious as these things seem, they have been too often forgotten, and much time and money have been spent in contriving and constructing complicated machines to no purpose. 20 ON THE CONSTRUCTION OF CRANES. APPLICATION OF HOISTING- MACHINERY, AND EMPLOYMENT OF THE POWER OF MEN. Having traced the early development of mechanism for raising or lowering heavy bodies, its application to practical purposes in different situations must next be considered. In this there are several points to be determined, namely, the weight to be raised, the height to which it must be hoisted, and the time in which it must be done must also frequently form an element in the calculation, to determine the power to be employed, the machinery to be used, the mode of fixing or attaching the machinery, and of suspend- ing the weight. When the weights to be raised are those of ordinary merchandise, to be hoisted from the hold of a trading ship, and lowered into a barge alongside, it is usual to raise a single pole, frequently a spare topmast or boom, and to step it over end, immediately before the mainmast, and inclining over the main hatchway of the vessel, or, in sailor's phrase, " to rig a derrick." The foot of the derrick is stepped into a piece of wood secured to the deck and hollowed to receive it, and the heel of the derrick is provided with " a lashing" of rope to pre- vent the foot from tripping. The head of the derrick is furnished with a strong rope called " the stay," the end of which is made fast to the head of the mainmast ; and there are also two other ropes called " guys," made fast to the head of the derrick, and thence extending one to each side of the ship; so that, by hauling in the one guy and slackening the other, the derrick is made to turn so far upon its heel, and the head, with the load suspended from it by a pulley or blocks, describes the segment of a circle from the hatchway of the ship to the barge which receives the goods. The winch or barrel which winds up the rope is commonly attached to the fore part of the mainmast, and as the current weight of merchants' goods is seldom ON THE CONSTRUCTION OF CRANES. 21 more than a ton, as, for instance, a sugar hogshead, this arrangement is found very convenient and useful. A mode of combining the advantages of the derrick with those of the crane has been patented by Mr. Henderson. The jib of his crane is fitted with a joint at the foot, and has a chain instead of a tension bar attached to it at the top, so that the inclination of the jib, and consequently the sweep or radius of the crane, may be altered at pleasure. A similar crane, in a rude form, has long been used in stone quarries ; but Mr. Henderson has introduced a para- bolic barrel, similar to the fuzee of a watch, upon which the chain winds as it raises the jib, and the barrel decreases in diameter as the jib approaches the horizontal line, so that the power to raise or depress the point of the jib is equalised at all times. When the weights to be lifted are heavy, and the height to which they must be raised is considerable, as in the masting of a ship of war, or in placing the boilers on board of a steam-frigate, it is customary to employ two strong spars set apart at the foot, but meeting together at the top in an acute angle, where they are secured to each other by a rope lashing, or for permanent purposes by an iron bolt and shackle, from which the requisite blocks are suspended. These spars are stepped, like the derrick, near to the edge of a quay or wharf, or upon the gunwale or side of some large old ship or hulk ; from their crossing each other when lashed together at top, something like a pair of large scissors, or " shears," they have received and still retain that name, although in most modern examples no resemblance remains to the original shears. The weights to be lifted at the royal dockyards have of late years become so heavy, and the bulk of the materials, such as the boilers of the war steamers, so great, as to render the employment of the "shear hulk" inconvenient; and permanent shears have, therefore, been fixed upon the quays, and those at Woolwich Dockyard are a good example of the kind. The shears, however, have only one motion in their step, which 22 ON THE CONSTKUCT10N OF CEANE8. serves as a centre ; the spars, as the radius, describe a ver- tical arc, inclining their heads over the water, whereas the derrick has two motions, and can describe a vertical and a horizontal arc also. The machinery used with the shears is generally a powerful capstan. When the weight requires to be lifted perpendicularly, and the height is not great, as, for instance, when some massy stone or beam of timber, iron girder, or the like, must be raised from the ground, so that a waggon may be run under it for convenient loading, it is usual to employ three spars, meeting at the top and spreading asunder at the foot, an arrangement which workmen call the " three legs " or " triangle." In this instance no motion can be obtained beside that of the perpendicular lift. It is, how- ever, a veiy useful arrangement, easily made in most situa- tions, often enabling a few men and horses to load and remove the largest timber trees and blocks of stone which their waggon is capable of carrying. The machinery used in such cases when men's power is applied, is generally a windlass and a pair of threefold blocks, the windlass being fixed to two of the "legs." When horses are em- ployed, the rope from the blocks or " tackle fall " is passed through a leading block or " snatch block " attached to one of the legs, in order to give the rope a horizontal direction, and the horses being yoked to it, gaining by the threefold blocks a power of six to one, can raise great weights with much facility. The horses regularly engaged on such work display great sagacity and obedience to a word or sign, to hoist, to lower, or to stop. The power of horses has been already mentioned ; the power of men is next to be considered. The late Mr. John Walker, an able assistant of Mr. Eennie, made many and repeated experiments on the power of men employed in raising weights for driving piles in the Eoyal Dockyard at Sheerness, and he found that the force exerted by an ordi- nary labourer, in average daily work, frequently did not ex. ceed 12 Ibs., and that 14 Ibs. was as much as could be ON THE CONSTRUCTION OF CRANES. 23 reckoned upon as the power of a labourer working daily at a winch or crane handle, for ten hours a day, moving at the rate of 220 ft. per minute. It is important to remember facts like this, because most writers rate the power of men much higher. This is an error into which they were likely to fall when manual force was exerted for the purposes of experiment, for a short period, or even for a single day. Mr. Joshua Field (late President of the Institution of Civil Engineers) some years ago tried a series of experiments on the strength of men working at a crane of the usual construction, in ordinary use, and not prepared in any manner for the experiments, having two toothed wheels of 92 and 41 cogs, and two pinions of 11 and 10 cogs; the diameter of the barrel, measuring to the centre of the chain, was llf in., and the diameter of the circle described by the crane-handle was 36 in. ; the ratio of the weight to the power by this combi- nation was 105 to 1. The weight was raised in all cases through 16 ft., and so proportioned in the different experiments as to give a resistance against the hands of the men of 10, 15, 20, 25, 30, and 35 Ibs., plus the friction of the apparatus. The resistance occasioned by the friction of the apparatus being a constant element in all machines, and of much the same amount in most cranes, and the object being to ob- tain some practical results on the power of men in raising weights by a system of machinery, it was not thought necessary to make any experiment for ascertaining the amount, of this resistance in the present instance. The following table shows the resistance at the handle, the weight raised in each experiment, the time in which the weight was raised, and the remarks which were made at the time with respect to the men. A column also ex- pressing the power or effect, by the number of pounds raised one foot high in one minute, is added. It will be necessary to add a few words respecting the construction of this column. In order to compare these experiments with each other, 24 ON THE CONSTRUCTION OF CRANES. the results must be reduced to a common standard of com- parison, and it is very convenient to express the results of such experiments by the pounds raised one foot high in one minute, this being the method of estimating horses' power. The number is in each case obtained in the followin manner. Take the first experiment. Here 1050 Ibs. were raised 16^ ft. high in 90 seconds; this is equivalent to (1050 + 16'5 =) 17325 Ibs. raised 1 ft. high in 90 seconds, which is equivalent to (17325 -r- 1*5 =) 11550 Ibs. raised 1 ft. high in one minute. In this case the man's power is equal to 11550, and, the same calculations being pursued in the other cases, give the numbers constituting the last column in the folio whig TABLE. No. of the Experiment. Statical Resistance at the handle. ft Time in Seconds. Time in minutes. REMARKS. Man's Power. I. II. III. IV. V. vi. VII. VIII. IX. X. XI. 10 15 20 25 30 35 1050 1575 2100 2625 3150 3675 90 135 120 150 150 132 150 170 180 243 35 1-5 2-25 2 2-5 2-5 2-2 25 2-83 3 4-05 Easily by a stout Englishman Tolerably easily by the same 11550 11505 17325 17329 20790 27562 24255 21427 20212 15134 Not easily by a sturdy Irish- man . With difficulty by a stout Englishman ... With difficulty by a London man With the utmost difficulty by a tall Irishman With the utmost difficulty by a London man. Same as Experiment V. With extreme labour by a tall Irishman With very great exertion by a sturdy Irishman. Same as Experiment III With the utmost exertion by a Welshman . Given up at this time by an Irishman. ON THE CONSTRUCTION OF CRANES. 25 Experiment IV. may be considered as giving a near ap- proximation to the maximum power of a man exerted for two minutes and a half ; for, in all the succeeding experi- ments, the man was so exhausted as to be unable to let down the weight. The greatest effect produced was that in Experiment VI. This, when the friction of the machine is taken into the account, Mr. Field considered to be fully equal to a horse's power, or 33,000 pounds raised 1 ft. high in one minute. Thus it appears that a very powerful man, exerting himself to the utmost for two minutes, comes up t the constant power of a horse; that is, the power which a horse can exert for eight hours per day. Mr. Field's experiments show what a man can do for a short time ; Mr. Walker's showed what he can do, day by day, the whole day through The men employed by Mr. Field were strong and athletic ; Mr. Walker's were ordinary labourers, and their power, expressed by multiplying 220 ft. per minute by 12 or 14 Ibs., is 2640 or 3080, which must be regarded as the limit of an ordinary, man's force con- stantly exercised at a crane-handle. The author has erected many cranes of various kinds for various purposes ; and he has found, practically, that although a man may exert a force of 25 pounds for short periods, yet it is not prudent to reckon upon more than 15 pounds in constant action upon a crane-handle moving at the rate of 220 ft. in a minute. The power of a man will, in that case, be repre- sented by (15 + 220 =) 3300. Mr. Smeaton, in one of his reports, directs that the water left in the dock at Port Glasgow, which at a medium tide amounted to 2141 cubic feet, or 627 tons, shall be pumped out by manual labour; and, in describing the pumps, he says : " This quantity to be raised in four hours to the mean height of 4 ft, will require six men working at a time ; and good English labourers will continue at the same rate for the whole time , but as the labourers to be employed will probably be such as can be promiscuously 26 ON THE CONSTRUCTION OF CRANES. picked up, it will be proper to have two sets to relieve each other." Reducing these figures to the general standard of me- chanical power, 4 feet + 627-5 tons + 2240 lbs._ 4 hours 4- 6 men + 60 minutes ~~ will represent Mr. Smeaton's value of a good English labourer's power, which he estimates as twice that of ordi- nary persons "promiscuously picked up." Mr. Smeaton further states, in the same report, that, " If the employment of twelve men for four hours be thought too much, the work may be done in three hours twenty minutes by two ordinary horses." This is calculat- ing rather closely ; but it may be taken to mean that he considers the power of a horse equal to that of six men when they work four hours. The dynamical standard of 83,000, however, may be reckoned equal to the power of ten men ; and it has been thought right to place this evi- dence in detail before the reader, that he may make it practically useful. PROGRESSIVE CONSTRUCTION OF CRANES. The Walking Crane. Goods Crane. The Shipwright's Crane. Wharf Cranes Foundry Cranes. Tn the first construction of machines it is seldom that a complete adaptation and fitness for the intended object is at once attained ; they are frequently cumbrous and com- plicated contrivances, and it is not until practice has clearly shown the relation of the means to the end, that machines become simplified, and divested of superfluous material and useless adjuncts. At all times,' and in all circumstances, this is to some extent the case, but in no instance has it been more so than in that of the first cranes which were erected on quays and wharfs for landing and shipping merchandise. ON THE CONSTRUCTION OF CRANES. 27 The cranes of the last century, especially in the first half of it, were rude and clumsy devices borrowed from the Dutch, many of them worked by men walking within a large hollow wheel, as the turnspit-dog used to do at the same period. Some of these machines lately were, and probably still may be, remaining on the banks of the Thames; and, in the school days of the author, such cranes were used for unloading ships at the quay of New- castle-upon-Tyne, of which some idea may be formed from Fig- 9. Fig. 9. The wheel was about 15 ft. in diameter, and that part of its axle upon which the rope was wound was about 14 in. : the rope then passed over guide rollers to the jib of the crane, which projected over the hatchway of the ship and c o 28 ON THE CONSTRUCTION OF CRANES. turned upon a pivot, so that it could move round about three-fourths of a circle, and so deliver the goods upon the quay. In order to lower the goods the men walked backward ; but as it sometimes happened that they were overbalanced by the descending weight, a bar or pole of wood was sus- pended from the axle, so that hi such case they might lay hold of it, and save themselves from being whirled round in the wheel. The great wheel and the framing which supported it were contained in a wooden building, or rather the beams of the framing covered with weather boarding formed the house, and served also to support the jib, which was at- . tached to one corner of the house. The first improvement on these primitive cranes seems to have been the liberation of the men from the wheel, which, being reduced in size, was fixed upon the jib ; the Fig. 10. ON THE CONSTRUCTION OF CBANES. 29 N jib being produced behind the upright to receive and carry it. The upright or crane-post was fixed in the ground like a mast, with a pivot on the top of it upon which the jib turned. This crane is still in use, and as it may be em- ployed with advantage in the colonies and in new settle- ments, where timber may readily be had, but where foundries have not been established, it may be well to illustrate the description by a sketch. (Fig. 10). This crane is almost entirely of wood, with a smav quantity of smith's work, easily forged and fitted, the only part of the iron requiring skill to forge being the crane- handle, in place of which a wooden cross may be used. The second advance seems to have been the shipwright's crane, fitted with a wheel and pinion ; it still retains its original shape^ and is an excellent machine for its peculiar purposes, the landing and shifting of timber, and the hoist- ing of the various pieces to form the frame of the ship whilst building. The jib is long and lofty, and is firmly secured to the upright or crane-post by a strap of iron on the back, and supported in front by an oak-tree, and a stay of timber morticed into the post, and extending nearly to the point of the jib ; a frame behind the post carries the barrel and wheel-work. The post, generally of oak, is placed in a well, and turns upon a pivot at the 1 foot, and in a collar of timbers at the well-top ; the collar is lined with iron, and the post is hooped at this part to prevent abrasion and lessen friction. Although the general form of this crane remains un- altered, yet, in many cases, posts, first made of wood, have been gradually superseded by cast-iron work. The knee, the collar, and the crane-post are, one or more of them, now frequently made of cast iron, and these last-named parts are often bored and turned in the lathe, or fitted with anti-friction wheels, so that the post may more easily re- volve in the collar. 30 ON THE CONSTRUCTION OF CRANES Fig. 11. FIVE-TON CKANE. SIDE ELEVATIQK. ON THE CONSTRUCTION OF CRANES. Fig. 11. FIVE-TON CRANE. SIDE ELEVATION. 82 ON THE CONSTBUCTION OF CRANES. Fig. II a. FIVE-TON CRANE. BACK "View. ON THE CONSTRUCTION OF CKANES. 33 The introduction of cast iron for the posts of cranes led to other alterations in their structure ; the jib has some- times been brought down from the top of the crane-post to the foot of it, and the stays of timber formerly below the jib have been replaced by wrought iron "tension bars" above it, extending from the top of the cast-iron post or frame-work to the outer end of the wooden jib, which then acts on the thrust ; so that a crane thus made is composed of three different materials cast iron, wrought iron, and wood. Sometimes the jib also was made of cast iron, as shown in the 5 ton crane. (See Figs. 11, and 11 a.) " Brakes," or as the word is sometimes written, " breaks," have been applied to facilitate the lowering of the goods. These are levers which bring into close contact with a plain wheel, generally fixed on the barrel of the crane, a seg- ment of tough wood strengthened by an iron strap, which by its friction prevents the weight from accelerating as it is lowered. Thus it is evident that to construct a crane properly a knowledge of the strength and application of materials is necessary; and to calculate the stress to which they are subject, some acquaintance with the composition and reso- lution of forces is also requisite ; and to proportion the power applied to the due performance of its work, it is needful that the mechanical powers should be studied and learned, so that the greatest mechanical effect may be ob- tained; and also that the construction of wheels and pinions in all their parts, especially that of their teeth, should be well and carefully considered; Until all these things have been learned, and not before, the making of a crane, simple as the machine may seem, will be little better than guess work ; and when cranes are intended to raise such heavy weights as they have now fre- quently to sustain, their construction should never be en- trusted to ignorant and unskilful men, whose mistakes may endanger both property and human life. c 3 ON THE CONSTKUCTION OF CRANL.8. Fig. 12. TEN-TON CRASK. OK THE CONSTRUCTION OF CRANES. Fig. 12. TEN-TON CRANB. Za&esrs ff o fleet 36 ON THE CONSTKUCTiON OF CRANES, It is not possible in this brief treatise to explain these subjects fully, but they cannot altogether be passed over, and the reader will be referred to those works in which farther information is clearly and explicitly given.* And here it may be remarked, that brakes ought to be applied and used with great caution ; and that, as a general rule, they ought not to be attached to cranes for lowering loads greater than ordinary merchandise, or building stones of average size and weight. Cranes fixed in a well or pit may take a great variety of shapes in their superstructure ; sometimes the jib may be long and lofty, as in the shipwright's yard ; sometimes it may form a right angle with the post. In some cases it is supported by stays, or struts, in others it is sustained by tension rods ; sometimes it is made of timber, and some- times of cast iron, the form changing with the purpose to which the crane is to be applied ; and it is in this adaptation that the skill of the constructor is displayed. The well-crane having been found inconvenient for raising great weights, because of the insufficient resistance of the ground at the well top, which needed to be strongly secured by framework or by masonry to sustain the pres- sure against the collar, and the use of cast iron having become better understood, another change of construction took place The crane-post became a strong hollow pillar of cast- iron, stepped into a massy cross of the same material, bedded in a block of masonry, and held down by strong bolts passing through the mass of masonry to its founda- tion. A wrought-iron pivot, steeled and hardened upon the point, supported the superstructure, also of cast iron, which turned upon this pivot, revolving round the post, which re- mained fixed. A cap of steel or of bell metal prevented the abrasion of the pivot; and machinery was in many cases applied to make the crane turn round the post. In cranes of this kind, the stress borne by the post imme- diately above the cast-iron cross is very great ; the action is * Papers of the RoyiU Engineers in 4to, Vol. 4. ON THE CONSTRUCTION OF CRANES. 37 like the claws of a hammer applied to draw a nail, the weight acting at the jib end as upon a lever, tends to break the post at the level of the ground, or to overturn the mass of masorry in which it is fixed. An adequate degree of strength is therefore requisite, and in order to obtain it with the least expenditure of material, the post is made hollow. The works of creation, 'which alone are perfect, teach us by variour examples, as in the stalks of corn, and the feathers and bones of birds and other animals, that a hollow cylinder, or prism, is much stronger than one made solid with the same quantity of material ; and also, that if the hollow beam have the hollow or pipe not in the middle, but nearest to that side where the fracture is to end, it will be so much the stronger, as we may see in the wings of sea-fowl, and other birds of rapid flight. This principle has been adopted and initiated in one of the boldest works of modern times, the hollow railway bridges over the Menai Straits and Conway River, designed by Mr. Eobert Stephenson. The strength of a solid cylinder to resist lateral stress, is as the cube of its diameter ; but if the cylinder be hollow, its strength is represented by the difference between the cubes of its external and internal diameters. For example, in a crane intended to carry a load of 10 tons, of which engravings are given, See Fig. 12, the crane-post is made 18 inches diameter outside, and 3 inches thick, so that its internal diameter is 11 inches The cube of 18 being 5832, and the cube of 11 = 1331 ; their difference, 4501, represents the proportional strength of the hollow crane-post. A solid post of equal strength must be made full 16 J inches in diameter, for the cube of 16 - 5 is 4492*126; but the section of the hollow crane-post contains only 160 square inches of iron, whilst the solid post contains nearly 214, making a difference of 54 inches, or about one-third more metal than there is in the hollow post, although it is equally as strong as the solid one 38 ON THE CONSTRUCTION OF CRANES B Fig. 13. FIFTEEN-TON CRANE. Section akA * Scale 1 2 S 4- 3 ON THE CONSTRUCTION OF CRANES. Fig. 13. FIFTEEN-TON CRANE. Inches Scale 40 ON THE CONSTRUCTION OF CRANES. ENLARGED SCALE OF DETAILS. Inches 12 O ON THE CONSTRUCTION OF CBANES. 41 When marine steam-engines had so much increased in size and power that it became necessary to construct cranes specially to deliver and to land their machinery and boilers cranes calculated to lift weights of 20 or 30 tons it was no longer safe or practicable to throw so great a stress on the post ; it was, therefore, used merely as the centre of a strong circular track of iron, bended upon solid masonry, sometimes built of granite, upon which a massive carriage or framework of cast iron, containing the wheel-work, re- volved. To this framework strong tension bars are attached, and the jib acts as a " strut," resisting the principal part of the stress upon the thrust ; wheels, which move upon the circu- lar track, are used to diminish the friction, and machinery is applied to turn the crane round about the central pivot. Such cranes as these are obviously few in number, their use being limited to the larger seaports frequented by steam ships, most of which have not more than one or two of them. Probably there are not two exactly alike ; and as considerable skill is required to make such powerful ma- chines with economy of materials and labour, no opportu- nity should be lost by the young student or practitioner in examining such examples as may present themselves. In each of them he may find something to learn and some- thing to avoid in his future practice. The demand for large and heavy cast-iron materials re- quired the erection of powerful cranes in the foundries, and caused them to assume a peculiar form, which may be de- signated as that of "the foundry crane." These machines are used not only to lift and move the heavy iron castings, but also to put together and adjust the moulds in which the melted metal will receive its shape. These moulds are sometimes made of dried loam, and sometimes of damp sand, rammed into a frame of cast-iron, which workmen call a flask or box, although it resembles neither of these, but is more like the skeleton cases used for packing glass. Such moulds are both heavy and fra- 42 ON THE CONSTRUCTION OF CRANES, gile ; the damp sand detaches itself with the slightest jerk, and great accuracy is requisite in putting the parts of the mould together. In such cranes the upright or post is generally equal in height to the side walls of the building, with pivots at each end, the one turning in a footstep fixed in masonry upon the ground, thn other in a collar secured by framework to the roof and side walls of the building. The jib is hori- zontal, secured to the post nearly at the top, and at right angles with it. The jib is usually made in two parts, at- tached to each side of the post, and parallel to each other, and is supported by two stays springing from the front of the post, near to the lower end of it, and fixed to the jib about half way between the end of it and the crane-post. In order that the crane may work easily and smoothly, the chain must not be large or heavy, as it might be apt to jerk as the links come upon the barrel ; therefore, to obtain the requisite strength with a comparatively slender chain, blocks, generally threefold, are used, or rather the lower block has three sheaves or pulleys, and the upper block has four. This fourth pulley permits one end of the chain to be carried to the point of the jib, and fastened there, whilst the other end, after being reeved through the block, passes over a single guide pulley fixed near the middle of the jib, and is rolled upon the barrel of the crane. By this arrangement, the upper block may traverse along half the length of the jib, that is, from the point to the junction of the stays ; and by means of traversing machinery, worked by an endless chain descending to the floor of the foundry, the position of ihe upper block, and consequently of the suspended load, may be regulated with the greatest exact- ness and facility, the load being neither raised nor lowered while the block travels along the jib. This description will be better understood by referring to the engravings of a crane designed by the author for the foundry of Messrs. Miller, Kavenhill and Co., at Blackwall See Fig. 13, &c. ON THE CONSTRUCT] ON OF CRANES. 43 TRAVERSING OR TRAVELLING CRANES, For Stacking Timber or Stone, and for Erecting Buildings, Bridges, and other Engineering Works. All the cranes hitherto noticed turn upon a centre, and describe a circle with a radius seldom exceeding 25 feet, they can therefore lift only those objects that come within their sweep, and then but such as are within a very short distance of the circumference of the circle they describe, with the exception of the foundry crane, which will lift any- thing within the area comprised between the two circles drawn by the point of the jib and a radius of half that length, because the upper block travels along the outer half of the horizontal jib. The fixed centres greatly limit the utility of these cranes, for the load to be lifted must be brought to them, conse- quently their chief employment is the loading or unlading of heavy goods and materials into ships or waggons, and they cannot distribute their burdens over any extent of sur- face. It was, therefore, very desirable that the cranes them- selves should be capable of moving to certain distances. r One of the earliest examples of the traversing crane was designed by the late Mr. Rennie for the Mahogany Sheds at the West India Docks, where several of them may now be seen at work. A kind of railway is constructed in the roof, upon parallel frames of timber extending across the Huilding, and upon this a carriage, which is fitted with the wheel-work of a powerful crane, and mounted upon low wheels, travels from side to side of the house. Several of these railways are placed across the shed, so that the largest logs of mahogany can be stacked in rows across the house. The chain comes down to the floor between the two lines of rails, and the carriage, with the log of mahogany sus- pended from it, is moved by machinery attached to the carriage, and worked by the men at the crane. 44 ON THE CONSTRUCTION OF CRANES. But these cranes have only one motion, that is to say, across the building, and several of them are required for Fig. 14 a. TRAVERSING CRANE. ON THE CONSTEUCTION OF CRANES. 45 the service of one long shed ; so, in course of time, persons began to consider that, if, by some further contrivance, the Fiy. 146. TEA VERSING CRANE. END ELEVATION. 46 ON THE CONSTRUCTION OF CRANES. framework which earned the railway could be made to move along the building at the same time the carriage was Fig. 14 c. TRAVERSING CRANE. SIDE ELEVATION. OH THE CONSTRUCTION OF CRANES. 47 travelling across it, they could, by combining the two mo- tions, command the whole area of the floor ; and that such Fig. 14 d. TRAVERSING CRANE. HALF PLAN. 43 ON THE CONSTRUCTION OF CRANES. a system of machinery would be most valuable in many cases, but especially in the erection of large marine steam- engines. In designing new buildings for steam-engine manufactories, the side walls are now generally made of sufficient strength to cany a line of rails on each wall, upon an offset in the masonry On these rails rest two parallel frames of timber, mounted on low wheels at each end, and bolted together at a proper distance apart, so that the 'frames travel along the building from end to end. Upon these frames of timber, extending across the build- ing a railway is laid, and a carriage travels as before de- scribed, similar to those in the mahogany shed, fitted with crane-work, from which the chain depending may reach the floor at the place desired. The usefulness of such a combination has caused its in- troduction in many public works and in several private establishments. Mr. Cubitt, and other eminent builders, perceiving the advantages resulting from it, have employed it extensively, not only in their building contracts, but also in landing and stacking heavy blocks of stone. In these cases the longitudinal railways are carried upon beams of timber resting upon uprights ranged in rows along each side of the stone-yard, or of the building to be erected ; in which instance the uprights, being lofty, are secured both by horizontal and diagonal ties. Indeed, so many and so great are the benefits derived from such a system of framing and machinery, that Mr. Grissell thought it right to con- struct framework the full height of the Nelson Column, in Trafalgar Square, with a travelling crane at the top strong enough to place the statue on the pinnacle. Mr. Grissell has presented a model of this framework to the Institution of Civil Engineers, in order that others may profit by his experience ; and similar machinery is also used in building the new Houses of Parliament. Other cases, however, have arisen in the modern practice ON THE CONSTRUCTION OF CRANES. 49 of engineering that render it desirable to dispense with framing, as not only expensive but inconvenient. In the erection of cast-iron bridges, the parts of which are fitted together at the iron works where they are made, it is neces- sary, both for convenience and despatch, that the hoisting machinery should embrace the whole fabric, and pass along at the same time. The Butterley Company, in the erection of cast-iron bridges, use cranes of this kind, which are strong, simple, and easily managed, with less machinery than has been generally thought necessary for such operations, the whole of which can be worked from below. The travelling or traversing crane, shown in the en- gravings (See figs. 14 , 146, 14 c, 14d), was used to erect the large cast-iron drawbridge over the river Ouse, at Selby, designed by Messrs. Walker and Burgess, for the Hull and Selby Eailway Company. It is composed of two triangular frames of timber, based on cast iron plates set edgewise, and mounted on wheels similar to those of railway waggons. These frames support two parallel beams of timber, trussed underneath by wrought-iron tie-bars an inch and a quarter in diameter, and cast-iron struts ; on these beams is laid a railway, upon which travels a carriage containing the pulleys for the chain, and constituting a fourfold purchase block, the chain passing between the two beams to the lower blocks. The ends of the chain pass along and above the beams to the fixed pulleys at each end, and thence down to the winches, which are secured upon the cast-iron bases of the two triangles. By winding one of these winches, and unwinding the other at the same time, the carriage and the load suspended from it travel from one end of the beams to the other ; and by winding or unwinding one of the winches only, the load is raised or lowered. The waggon-wheels, on which the triangular end frames are mounted, have toothed wheels and pinions attached to D 50 ON THE CONSTRUCTION OF CRANES. them ; by turning the pinion handles the waggon- wheels are made to revolve, and the whole fabric, with its load, travels like a locomotive engine along the two parallel lines of railway on which it is placed ; these rails are of the strong kind used on the London and Birmingham Railway, and are laid 30 feet apart. This transverse distance may be called the span of the crane ; the longitudinal distance is, of course, limited only by the length of the railway on which the crane travels. The crane here represented will lift a weight of eight tons, arid the cost of it, including the chain and blocks, was 150/. It is readily taken to pieces for removal; and, by the combination of its movements, every point within the area comprised between the rails may be commanded with the greatest exactness and facility. Hence the utility of this crane for the purpose of fitting together the heavy portions of large work, which cannot be done by a crane moving round a fixed centre. It may also be made very useful in storing and stacking heavy materials, as stone, timber, anchors, or cannon. The traversing crane is used with great advantage in working the diving bell, when it is employed for laying the foundations of sea-walls under water, as the bell by this means may be made to travel along the line of wall ; and the stones may be lowered so nearly into their places, that they require but little adjust- ment by the divers. SELF-ACTING HOISTING MACHINES. TUe Sack Tackle. The Lift. The Cornish Man- Machine. The Vacuum Crane, Steam Crane, Water Crane, &c. The successive improvements of the crane, already de- tailed, have not been sufficient to satisfy the minds of inge- nious mechanics, and many attempts have been made to render cranes self-acting ; so that manual labour might be ON THE CONSTRUCTION OF CEANES. 51 dispensed with, and intelligence alone be required to direct their operations Some of these attempts have been attended with consi- derable success. Skilful millwrights, engaged in the con- struction of extensive corn mills, have, in many instances, made most ingenious mechanism for transferring the grain and the flour to various parts of the mill; and hoisting tackle for raising the wheat and delivering the meal in sacks, worked by the machinery of the mill, has been used for a long time past. The machinery of the sack tackle is called into action by pulling a cord held in the hand of the miller ; and it continues in motion until he slackens his hold, whilst the heavy sack of corn, no longer carried on his shoulders, but becoming as it were obedient to his will, rises through successive trap-doors and lays itself at his feet. The lift or hoist is also used in cotton mills to raise a kind of ascending room, in which not only the materials, but the workpeople themselves, are carried from floor to floor ; and the waste of their physical strength, otherwise expended in repeatedly climbing the stairs, is avoided. Persons rising from the ground floor in the ascending chamber, are landed on any of the upper floors they please, by disengaging the machinery of the hoisting tackle, which much resembles that of the corn-mill. The waste of strength arising from the exertion of climbing a long flight of stairs or a series of ladders is very great, so much so that in the Cornish mines, where the miners had to ascend crooked shafts by means of ladders from their daily labour, their strength was often so far spent, when they reached the top, that they were fain to lay themselves exhausted on the ground. The ascent from the mine was the most severe portion of the day's work. It was difficult in many of the mines, when the shafts were neither straight nor perpendicular, to find a remedy for such unprofitable toil, as ropes could .not be applied in such shafts. 52 ON THE CONSTRUCTION OF CRANES. The mining companies, therefore, offered a premium to the inventor of the best machine for " bringing the men to grass." Many ingenious plans were proposed, but the best was one in which two rods of timber move with a pumping action parallel to each other, and only so far asunder that a man may step without danger between the two rods, work- ing like pump rods, with a stroke of about 12 or 14 ft., and an alternating motion, one rod moving upward as the other moves downward. They are fitted with suitable guides and rollers to keep them steady in work, and to prevent need- less friction, and each rod makes 3 or 4 strokes per minute. Upon each of these timbers is fixed, at regular distances equal to half the length of stroke, whatever that may be, say 6 or 7 ft. apart, a series of steps or small project- ing scaffolds, whereon one man may stand, and there are also long staples or holdfasts which he may grasp with his hands. The rods are almost stationary for a second of time, when the crank which moves them is turning past its centres, and at this period, which is the termination of a stroke, the stages upon the two rods coincide with each other; a man, therefore, can step upon a stage of the ascending rod, and he is earned up 12 or 14 ft. ; he passes over to the other rod which has just descended, and finds the stage upon it ready to receive him and carry him up another stroke ; thus, by stepping alternately from rod to rod, he rises with a zigzag movement, and with very little fatigue, in a short time to the mouth of the pit, travelling about 250 fathoms in 20 minutes. As soon as he has quitted the first stage of ascent another miner takes his place, and thus a body of men continues rising from the mine, the rods being loaded with people for their entire length, until the whole party has ascended, the relief party descending at the same time on the alternate steps. A model of this man-machine may be seen at the Museum ON THE CONSTEUCTION OF CEANEP. 58 of Practical Geology, an institution that ought to have more numerous and frequent visitors. This machine is worked by steam power, and is mentioned in this place somewhat out of its regular order, as it is a recent invention. The first successful attempt to work detached cranes by mechanical power, and without manual labour, appears to have been that of Mr. Hague of London, who, by means of an air-pump worked by steam power, exhausted the air from a receiver, and continued by pumping to maintain a vacuum in it. From this receiver pipes were laid under ground to several cranes in one of the docks, and each of these cranes was fitted with a small cylinder, vibrating or oscillating upon hollow pivots behind the crane-post, with the piston-rod acting upon the pinion shaft of the crane's machinery, which was fitted with a crank and fly-wheel for that object. The cylinder resembled that of an oscillating high pres- sure steam-engine, except that its power was derived from the exhaustion of the air and not from the pressure of steam. There are, however, several objections to machinery worked by means of an exhausted receiver; it is very liable to derangement from the leakage of joints and fittings, and difficult to manage and adjust in the hands of ordinary workmen. The vacuum cranes therefore went out of use, although similar machinery for winding coals is still employed underground in pits where the presence of in- flammable air renders it unsafe to place the fires of a steam-engine boiler, the vacuum pipes being carried down the pit. While the vacuum apparatus remained in abeyance, it occurred to another ingenious mechanist that if high-pres- sure steam were applied directly in the cylinder attached to the crane, he might dispense with the air-pump, the re- ceiver, and their adjuncts. This idea was carried into effect, and cranes., with small steam-engines fixed to them, 54 ON THE CONSTRUCTION OF CBANES. Fig. 16. PLAN OF PISTON, &c. L = the length in feet, 20. B, b, D, d = the breadths and ~ depths shown in the figure, all in Q inches. No account is taken of the top ,.... B = 12 _._ J " flanch in this calculation in fact, it adds so little to the strength of the beam that it is practi- ON THE CONSTEUCT10N OF CRANES. 71 cally of no value in that respect; but it is necessary, in casting the beam, to make it with such a flanch, in order to prevent its distortion in cooling, and also to insure the soundness of the rib at top, that it may serve as a fulcrum to the lower portions of the beam which act by tension. Thus, if the beam have the following dimensions, namely, the breadth of the lower flanch 12 in., and its thickness 2 in. ; the depth of the beam 10 in., and the thickness of the web or middle part 1 in. ; the width of the top flanch 5 in., and its thickness also 1 in. ; then the whole sectional area of the beam will be 36 in. at the centre, and the lower flanch will contain 24 in., or two-thirds of the section. Suppose the beam to be supported at both ends, and to be 20 ft. long between the supports, then The cube of the depth or D 3 is . . = 1000 The breadth . . . . B . . . = 12 The reduced breadth B b = 11 12000 The reduced depth fr or 8 3 = 512 X 11 = ^5632 The length L, or 20 feet, X D = 10 or 200)6368 Of which take f, which will be equal to 3)31-84 the ultimate weight W that the beam 10-61 will bear in tons. 2 Tons 21/22 that is to say, the load that will just break the beam. Mr. Hodgkinson also, in his evidence concerning the fall of a cotton mill at Oldham, gave the following approximate rule for beams of similar section. Multiply the area of the section of the lower flanch in the middle of the beam by the depth of the beam there, both in inches, and divide the product by the length of the beam between its supports in feet ; the quotient multiplied by 2-14 will give the breaking weight in tons. This rule applied to the same beam will give the following result: Area of the lower flanch 12 X 2 = 24 inches. Depth of the beam in the middle 10 Divided by the length in feet . . 20)240 120 Multiplied by the given number 2'14 Gives as the weight to break it 25-68 tori. 72 ON THE CONSTEUCTION OB CRANES. The author has found by many experiments on cast-iron of good quality, that rectangular bars supported at both ends, when reduced to a general standard of an inch square and a foot long, broke with 1 ton on the middle of the bar. If, therefore, the same beam be supposed to form part of a rectangular parallelogram, at its middle section, which is 12 in. broad and 10 in. deep, and from which two beams, each 5 \ in. broad and 8 in. deep, be cut out, disregarding in this case also the top flanch, the following will be the result. (See jig. 29.) 10 2 X 12 = 120(T 8 8 X 5$ X 2 . . . 704 Divide by length in feet 20)496 Weight that just breaks it 24'8 tons. In no case should a cast-iron beam be loaded with more than one-fifth of the weight that will break it, even where the load is quiescent, as in the floors of warehouses. It has been the practice of some persons in building cotton mills to load the beams with one-third of the breaking weight, but in time they often give way, and cause frightful accidents. The fall of a cotton mill at Oldham, in the county of Lancaster, from the failure of the cast-iron beams and pillars, and some other casualties of a similar nature, caused an inquiry to be made under a Royal Commission by Sir Henry de la Beche and Thomas Cubitt, Esq., which elicited some very important evidence, and induced some valuable experiments, to which the author has made frequent re- ference. Cast-iron cranes should not be loaded with more than one-tenth of the weight that will break them, and when those cranes are intended to lower heavy bodies by means of brakes, their load should not be more than one-twentieth of the breaking weight. When a weight is rapidly lowered, and checked in its descent by the brake, it acts like a fall- ing body upon the chain at the end of the jib. A civil engineer of acknowledged talent designed several cast-iron ON THE CONSTRUCTION OF CRANES. 78 cranes for shipping blocks of stone ; they were found quite strong enough to hoist the intended load, but failed when the blocks of stone were suddenly stopped in their descent into the hold of the ship. Besides, it often happens, when heavy objects lie beyond the sweep of the crane, that the chain is carried out be- yond the perpendicular, and the jib is thus virtually length- ened. On beams loaded at the middle the stress decreases to- wards the ends, and at the points of support the beam re- quires, theoretically, no depth: this diminution of depth from the centre to the ends is proportionate to the square root of the stress at each point, and. consequently, forms parabolic curves, terminating when they reach the supports ; practically, however, they cannot so terminate ; but, when the beam is made half the depth at the ends that it is in the middle, it includes the parabolas. Or, if the beam project from a wall or a crane post, and be loaded at the end so that fracture shall begin at the upper side, the stress on the beam next to the wall will be four times the load upon the end. If the depth of the beam next to the wall or prop be re- presented by 10, and the stress at the end by 100; and if the length of the beam be divided into 8 parts, then the stress upon the beam and the depths required to resist it will be in these proportions. Fig. 30. The same principle is often carried still further by cast- is 74 ON THE CONSTRUCTION OF CRANES. ing the beams, or crane jibs, like a piece of open frame- work, by which the effect, if increased, may to some extent be obtained, as is shown in the construction of the 10-ton crane. (See Fig. 12.) When cast-iron is subject to tension, the strength is in proportion to the areas of the transverse section of the bars, but it is seldom applied to resist tensile stress, wrought- iron being generally used for that purpose on account of its greater toughness and strength. It is, therefore, only necessary to state that the mean of many experiments shows that the average tensile strength of cast-iron is nearly 7-2 tons to each square inch of section. $ When cast-iron is subjected to a crushing action, the force required to crush a prism of a height varying from 3 to 6 times its radius is on the average 6^ times as much as will tear it asunder, or about 48 tons upon a square inch. When the height exceeds 3 times the diameter of a solid cylindrical column, it is partially bent as well as crushed, and, when its height is less than 1J times its diameter (or rather 1 -42), the portions crushed cannot detach themselves, because the material splits off at an angle of 55' with the plane of the crushing surface. But, when cast-iron is used for pillars, many circumstances must be taken into account which materially affect the results, for not only are the crushing and bending actions combined, but their effects vary with their peculiar application. As, for instance, long pillars with their ends perfectly flattened, firmly fixed, bore three times as much as when their ends were rounded, and made capable of turning like a universal joint. When one end was rounded and the other flat, the strength was a mean between the two ; so that in three long pillars, all of equal diameter and length, one of them with both ends made round, another with one end rounded and the other end flat, and the third with both ends flat, the strength was as 1, 2, 3, or very nearly so ; but the enlargement of the flat ends with a disc beyond the diameter of the pillar, ON THE CONSTRUCTION OF CRANES. 75 so as to give increased breadth of bearing, although neces- sary in many cases for practical purposes, gives no additional strength to the pillar, but stability only. A long pillar with both ends flat, or firmly fixed, has nearly the same strength with one of the same diameter and half the length, with both ends rounded. A solid pillar, enlarged at the middle, as 3 to 2, or upwards of the diameter of the ends, and tapering from the middle to the ends, like the frustums of two cones with bases united, has its strength increased more than the weight of the metal by about a seventh of the whole, whether the ends be round or flat. In practice, however, it is proper that the form of para- bolic spindles be given instead of the conical shape, for the following reasons, in respect of similar pillars a shape something like the main yard of a ship. For, if long pillars be cast and turned perfectly similar, the diameter being to the length in a constant proportion, the strength of the larger pillars is found to increase in the ratio of the 1-865 power of the diameter, or nearly as the squares. If a pillar have flat ends, but the pressure it sustains acts diagonally through it, that is to say, from the extrem- ity of the diameter at one end to the opposite extremity of the diameter at the other, the strength is reduced in the proportion of 1 to 3, which has been proved by experiment, as in the case of pillars rounded at the ends. These properties apply to pillars of such a length that fracture may be considered as having been produced wholly by the flexure of the column, that is to say, to cast-iron pillars with rounded ends, in which the length is more than 15 times the diameter; and to those with flat ends, whereof the length is more than 30 times the diameter ; but, if the pillars be shorter, fracture takes place partly by flexure and partly by crushing, so that both these actions must be taker! into the calculation. Professor Hodgkinson found the strength of long cast- iron columns with rounded ends to increase as the 3-76 76 ON THE CONSTRUCTION OF CRANES. * power of the diameter nearly, and those with flat ends as the 3*55 nearly, the length in each case being given. But when the length varied, and the diameter remained the same, he found that the strength was inversely as the 1-7 power of the length, or nearly so. Taking, therefore, 3*6 as the mean between 3*76 and 3*55, and the coefficients obtained by a series of experiments, he deduced the following rules for columns fixed at the ends : For solid columns D 3-6 W = 44-] 6 y 1<7 = the strength of a cylinder. For hollow columns 3-6 __ ^.,. 6 ne g^jjtk of a no n ow W = 44-34 = ^ = cylinde. W is the breaking weight in tons, D the external and d the internal diameter in inches, and L the length in feet. If both ends of the pillars be rounded, divide the result by 3. If one end be rounded and the other flat, take two-thirds of the result as to strength. If pillars with flat ends be shorter than 30 times then- diameter, or if the ends be rounded they be less than 15 times the diameter, they will be crushed as well as bent, and the value of W must be modified thus : W + I c c is the weight that would crush the pillar in tons, if it were so short as to be broken without flexure. To find c, Mr. Hodgkinson multiplies the area of the section of the pillar in inches by 49, because the iron he used (Low Moor, No. 3 Iron) required 49 tons to crush a prism whose base was one inch square. * The relative strength of cast-iron pillars, as compared with other materials used in cranes, may be thus stated : representing the strength of cast-iron columns by 1000, the strength of wrought-iron was found to be 1745 ; cast steel, ON THE CONSTRUCTION OF CRANES. 77 2518; Dantzic oak, 108-8; red deal, 78-5. (Philosophical Transactions, 1840, Part 2nd, page 430.) From what has been already stated, it is evident that all crane jibs, acting on the thrust, should have their diameter largest on the middle and tapering in a curved form, approx- imating to the parabolic, toward the ends, which should' be about | the diameter of the middle, and also in order to obtain the greatest strength with the least material, in a cast-iron crane jib, acting on the thrust, it should be made hollow, and the ends should be fixed, so that the stress shall be taken directly through the axis of the pillar, or that the ends of the pillar shall be flat, and their planes a& right angles with its axis. So that all the contrivances of ball and socket ends, and other methods of compensating for imperfection and want of truth in the construction and adjustment of pillars and struts, should be abandoned, as worse than useless. The following tables, delivered in evidence by Mr. Hodgkinson and Mr. Fairbairn, show the results of many experiments made by them on the tensile, crushing, and transverse strength of cold and hot-blast iron. FOECE IN POUNDS REQUIRED TO TEAR ASUNDER A BAR OF CAST IRON, ONE INCH SQUARE. Description of Iron. Cold Blast. Hot Blast. Ratio of Strength, that of Cold Blast Iron being 1000. Buifery, No. 1. ... 17466 (1)* 13434 (1) 1000 ' 769 Carron, No. 2. ... Coed Talon, No. 2. . . Carron, No. 3. ... 16683 (2) 18855 (2) 14200 (2) 13505 (2) 16676 (2) 17755 (2) : 809 : 884 1250 Devon, No. 3. ... 21907 (1) 99 n * The numbers between parentheses show the number of experiments. 78 ON THE CONSTKUCTION OF CRANES. FORCB IN POUNDS REQUIRED TO CRUSH A PRISM; THE BASE ONK INCH SQUARE; THE HEIGHT, 1 INCH. Description of Iron. Cold Blast. Hot Blast. Ratio of Strength, that of Cold Blast Iron being 1000. Buffery, No. 1. ... Carron, No. 2. ... Coed Talon, No. 2. . . Carron, No. 3. ... 93366 (4) 106375 (3) 81770 (4) 115442 (4) 86397 (4) 108540 (2) 82734 (4) 133440 (3) 1000 : 925 : 1020 : 1012 : 1156 Devon, No. 3. ... 145435 (4) ' n TRANSVERSE STRENGTH OF BARS, ONE INCH SQUARE, LAID ON SUPPORTS 4 5 FEET ASUNDER, AND BROKEN BY A WEIGHT IN THE MIDDLE. Description of Iron. Cold Blast. Hot Blast. Ratio of Stiength, that of Cold Blast Iron being 1000. Buffery, No. 1. . . . Carron, No. 2. ... 463 (3) 476 (3i 436 (3) 463 (3) 1000 942 973 Coed Talon, No. 2. . Do. do. No. 3. . Carron, No. 3. . . Devon, No. 3.' . . Muirkirk, No. 1. . . Elsicar cold and Milton hot blast, No. 1. . . 408-7 (3) 538 (2) 444 (3) 448 (2) 444 (2) 430 (2) 409-2 (2) 496 (2) 520 (3) 537 (2) 418 (2) 352 (2) 1001 922 1170 1190 942 819 Wrought iron is seldom used on the thrust in constructing cranes ; but its strength, compared with that of cast-iron, applied as a pillar, is nearly 75 per cent, greater. It has, however, been found, by experiments carefully made, that it is permanently compressed with about 1 1 tons on the square inch of transverse section ; with loads below that weight, the bar or pillar regained its original length. It is, almost invariably, in large cranes, upon the stretch, and mostly in the manner shown in the 5-ton crane. (See Fig. 1 1 .) Its tensile strength is directly proportionate to the area of its transverse section. ON THE CONSTRUCTION OF CRANES. 79 A series of experiments were tried by the late Mr. John Kingston, in the dockyard at Woolwich, which are given in all their details in the Transactions of the Society of Arts, Volume 51, 1837. Inches. A bar 1 inch with 5 tons stretched -Oil in 100 10 -054 15 -110 26-5 1-35 broke. A bar 1 inch diam. 5 tons stretched -025 in 100 10 '060 U '093 23 2-502 broke. A bar 1 inch square 11 ' 8 12 T03 A bar 1 inch diam. 9 1-03 A bar 2 inches sq. 40 1-05 40 -90 These and various other experiments show the breaking strength of bar iron to vary from 23 to 28 tons per square inch of section, and that the average weight which breaks the bars, when they are of a fair quality, is about 25 tons for each square inch of section; that it is permanently stretched and its elasticity destroyed by about two-fifths of the strain that breaks it, or about 10 tons, the strain varying from 8-25 to 12 tons. It has also been ascertained that bar iron stretches, within the limits of its elasticity, about "000096, or one ten- thousandth part of an inch, by each ton of strain, and it is permanently stretched when the extension reaches one- thousandth part of its length. Consequently, it should never be subjected, for any practical purpose, to a stress of more than 5 tons on each square inch of section with a quiescent load or steady pull. In cranes where tension rods are used (he stress should 80 ON THE CONSTRUCTION OF CRANES. not exceed 3 tons per square inch, and if brakes be used for lowering the load, not more than two tons per square inch of section ; otherwise considerable reaction may take place when the descending load is checked suddenly in lowering. The lateral or transverse strength of wrought iron was carefully tried by Professor Barlow, at the request of the Directors of the North Western, or London and Birming- ham Railway Company. His principal experiments were made on bars about 3 feet long, supported at both ends, the distance between supports being 33 inches ; and he found that bars Ij inches broad and 3 inches deep would bear 4^ tons of stress at the middle of the bar, as their ultimate load ; with any further load the bar was permanently bent, and its elasticity destroyed. The ultimate deflection in on 9 case was '148 inches, and the mean deflection for each half ton of load '0103 inches ; in another it was '124, and the mean for each half ton -0108 inches. The author's practice gives the lateral strength of wrought iron, as compared with cast iron, to be about 14 to 9, and in the disposition of the metal the same rules apply to both ; but wrought iron cannot be run into moulds, nor can the same forms always be given to it by forging. Fig. 81. There is one part of a crane subject to severe transverse strain, that is too often neglected by the engineer and left to the smith; more lives are lost and more goods are ON THE CONSTBUCTION OF CBANES. 81 damaged by the breaking of the crane hook than by any other part of the machine. The hook at the end of a crane chain may frequently be seen formed by simply bend- ing a bar of round iron into a double crook or " ram's head," a shape not at all calculated to resist the stress to which it is liable. The proper form and disposition of material are shown in Fig. 31, contrasted with the older shape of the inverted "Aries ;" but, when very heavy weights must be lifted, it is best to substitute a shackle for a hook. The same remarks apply to the fastening of the chain at the end of the crane jib, and also to the crane barrel. THE DEFLECTION OF MATEEIALS To be taken into Account in constructing Cranes, or in calculating their Strength. Timber acting on the Thrust. In what has been stated respecting the strength of ma- terials, their deflection has not been taken into account; and, on the construction of a crane, the form given to cast iron to afford the requisite strength is also generally suffi- cient to give the required stiffness. But, in a course of experiments on cast-iron beams, the author found that a beam of 4 ft. long, which broke with 12f tons, deflected one-eighteenth of an inch with a load of 12^ tons; whereas a similar cast-iron beam, 9 ft. long, which broke with a load of 13 tons, deflected half an inch with 18 1 tons. From a series of experiments, tried on beams or battens of deal, he was led to the conclusion that, although the strength of a rectangular beam be as the square of the depth, multiplied by the width, and divided by the length multiplied into the load laid upon the middle of the beam, when supported at the ends, yet that the deflection of the beam increases directly in proportion to the load and to the cube of the length, and inversely as the cube of the depth multiplied by the width, a rule confirmed by the experiments E 3 82 ON THE CONSTRUCTION OF CRANES. of Professor Barlow. It is, therefore, important in all works, constructed on a large scale, that the deflection of the material used shall enter into the calculation, but more especially in those cases in which timber may be employed in the form of rectangular beams, or some combination of them. In order to do this, it is requisite to know what amount of deflection the material will bear, and what load will pro- duce that deflection, so that it may be kept within proper limits. The elaborate experiments of Professor Barlow, made by order of the Admiralty in the dockyard at Woolwich, and reduced by him into the form of tables in his excellent work on "The Strength of Timber and other Materials,"* afford data for calculating the dimensions of most kinds of wood likely to be used in works of strength. These tables are the more valuable, as the experiments were numerous and exact, and the timber on which they were made was of considerable scantling, the pieces being generally 7 ft. long and 2 in. square ; but, as the wood was of the best quality, well seasoned, and free from knots, sap, and other defects, allowances must be made in applying the results to practice, to compensate for such imperfections. The beams were fixed at one end and loaded at the other ; the greatest amount of deflection they could sustain without injury was taken as the elastic strength of the par- ticular kind of wood under examination, and then the load was increased until the beam broke. It is obvious that, when the elasticity of the beam was destroyed, or, as a carpenter would say, " when it was crippled," it became useless to pursue the inquiry further, as affording data for calculation ; and it appears to be a good general rule that the greatest load to which the beams should be subjected is one-fourth of the weight that ulti- mately breaks them. These experiments also prove that the deflection of a * In 8vo, edition 1851. ON THE CONSTRUCTION OF CEANES. 83 beam, fixed at one end and loaded at the other, is to that of a beam of the same length, supported at both ends, and loaded at the middle with the same weight, as 32 to 1 ; the stress, as has before been shown, being as 4 to 1. The elastic strength of the timber, that is to say, the greatest load it will bear without having its elasticity de- stroyed, he represents by the letter E. The ultimate strength of the timber, that is to say, the stress that breaks it, he represents by the letter s, and has arrived at the value of these letters in the following manner : A beam of teak timber, 2 in. square, fixed at one end and projecting horizontally 7 ft. from its support, was loaded on the other end, and by careful and repeated trials, such wood, which hi this experiment had the specific gravity of 745, had its strength and deflection ascertained, the load being gradually increased until the beam broke. The mean results were as under : Greatest weight sustained while the elasticity remained perfect in Ibs. .... 300 Deflection at that time, in inches . . .1-151 Breaking weight, in Ibs. ..... 938 Ultimate deflection before fracture, inches . 4-320 To find the value of E, cube the length hi inches, namely, 84* = 592,704, and multiply this by the load in pounds = 300, which gives a product of 177,811,200. Divide this product by the breadth, 2. inches, multiplied into the cube of the depth, or 2 :) = 8, multiplied into the deflection 1-151, multiplied by 32, or a total divisor, 589,312, and the quotient will be 301,800, very nearly; this is the value of E, which, for the sake of simplifying opera- tions, is not carried out exact beyond the fourth figure. The value of s is thus found : Multiply the length in inches, 84, by the breaking weight in Ibs., 938, and their product is 78,792. Divide the product by that of the breadth, 2 in., multi- 84 ON THE CONSTRUCTION OF CRANES. plied into the square of the depth, = 4 in., multiplied by 4, or a total divisor of 32, and the quotient will be 2462, which is the value of s, and represents the ultimate strength of the timber. All the dimensions are here taken in inches ; but, if the length be taken in feet, the number 301,800, which repre- sents the value of E, must be divided by the cube of 12 in., or 1728; this reduces it to 174, and represents the load in pounds that a piece of teak, 1 in. square, and 1 ft. long, will bear when supported at both ends, and weighted on the middle, without destroying its elasticity. In like manner, if the number 2462, which represents the value of s, be divided by 12 in., it is reduce'd to 205, and shows the weight in pounds that will just break the same piece of wood. Practical men have great objections, and very properly so, to the use of tabular numbers, when they are arbitrarily given ; but the experiments, in this instance, being given with them, enable persons to judge of their applicability to practice, and to make allowances for accidental defects in the timber they have to employ. The following table shows the elastic strength (E) and the ultimate strength (s) of those kinds of timber in general use, which are calculated by this formula : Z } x w* I x w = E ; and .,,,, = s ; b x d 3 x 32 x D - "b x tf x 4 I being the length, b the breadth, d the depth, w the load or weight carried, and D the deflection ; all the dimensions being taken in inches. If a beam of Eiga fir, 4 in. broad and 6 in. deep, be fixed at one end, and project 5 ft. over the point of support, and be loaded at the end, if it be required to determine what is the greatest load it can bear without injury, deflec- tion not being considered, find the value of s for Eiga fir, which is 1108, multiply this by the breadth and by the square of the depth, and divide the product by 60 in., the ON THE CONSTKUCTION OF CRANES 85 OOOOOOOOOOOOOOt^OO^O <35r-(OOCOt-OO(N COOCOOaO! It (N Ill CO y 2* 31 7 21 an eighth of an inch in 2 t Ji 9 27 each succeeding size of 2 5* 11 13 33 39 rope, but it has been 3 7^ 15 45 thought sufficient in this 3* 3| 8* 10 12 17 20 24 51 60 72 table to advance by \ of an inch, and to omit 4* 14 28 84 the intermediate sizes. 41 15 30 90 4 16 32 96 4 18 36 108 ON THE CONSTRUCTION OF CRANES. 105 The following scale shows the size, weight, and strength of flat wire ropes, and of equivalent flat hempen ropes, as stated by the same makers : HEMP. A WIRE. j. Size in Ibs. Weight Inches, per Fathom. r Size in Ibs. Weight^ Inches, per Fathom. Breaking Strain Tons. Working Load Cwts. 4 Xl 16.V 2Xi 9 16 36 4i-xH 20 24x4 10 18 40 5 XH 24 2jX| 12i 22 50 SiXlf 26 3 X| 15 27 60 6 Xl 28 3iX| 18 32 72 7 Xl 36 4 X| 20 36 80 S^X2 40 4^Xl 224 40 90 8^X2^ 45 5 X| 25 45 100 It has been recommended that, instead of using a single chain or rope of large size, several parts of a smaller one should, by means of pulleys, be made to sustain the weight. It is an advantage resulting from such an arrangement, that the crane or sheers may be used with greater facility for lifting smaller and more current weights than their maximum load, which it is not often needful to hoist. Thus, by making the rope or chain form part of the machinery, it may not only be less ponderous itself, but toothed wheel-work of a lighter description may also be employed. Eeferring to the engraving of the 1 0-ton crane (see Fig. 12), it will be observed that the occasional use of a single move- able pulley or " monkey block" in the bight or double of the chain, doubles the strength of the chain, and the power of the crane also ; the power gained being equal to the number of moving parts of the chain or rope which suspend the weight, and are shortened as it is hoisted, or as the space through which the weight rises is to the length of rope hauled in. The engraving of the 15-ton (see Fig. 13), shows a gain of 6 to 1 in power, by three pulleys in the lower block. F 3 106 ON THE CONSTRUCTION OF CRANES. The upper block has four pulleys, but one them is for the purpose of leading the chain to the end of the jib, where it is made fast ; so that this upper block may travel along the jib as upon a railway, without either hoisting or lower- ing the weight ; and it will also be perceived that machinery is attached to the upper block, by which it may be made to traverse inwards or outwards, by a man who stands upon the ground, and hauls upon an endless chain acting on a sprocket-wheel above. It is seldom the practice to gain more power by pulleys than 6 to 1, because it is inconvenient to place more than three pulleys, side by side, in the moveable block ; but, when it becomes necessary to gain greater power with one pair of blocks, the pulleys are ranged in two heights, the upper tier of pulleys in the lower block being smaller than those in the lower tier, in order that the ropes or chains may work clear of each other. In Mr. Armstrong's cranes, where great power is applied, in the first instance, by water-pressure, mbving only through a short space, pulleys are used for the opposite purpose of increasing the height of the lift, power being lost in propor- tion to the distance through which the weight is raised, as compared with that through which the piston travels. (See Figs. 15, 16, &c.) The author has observed that crane chains, in constant use, undergo- a change in their internal structure; the iron, which was at first tough and fibrous, gradually be- comes hard and crystalline ; and he has then found them liable .to break ; he therefore recommends that every three years they should be taken down and heated to a bright red in the fire, and slowly cooled in ashes, or sawdust, to anneal the iron. THE MACHINERY OF CRANES. Wheels their Proportion and Teeth Cycloidal, Involute. Professor Willis's Teeth. Axles and Barrels, &c In order that the power applied to cranes may be em- ployed with the greatest effect, it is necessary that the ON THE CONSTRUCTION OF CRANES. 107 wheelworK shall be properly designed and executed, other- wise power is expended to no purpose. This power should be so proportioned to the work to be done, that, if manual labour be used, the men shall exert due disposable strength upon the work, at the speed of 220 feet per minute. If the power gained be too great, time is lost ; if too small, the men's strength is overburdened, and eventually overcome ; the work is too hard for them, and they must give it up. The radius of the winch, or handle, should not be less than 15 inches nor more than 18 inches, varying with the size of the men to be employed ; 1 6 or 1 7 inches being the best average for ordinary labourers, and the height of the axle from the ground should not be less than 3 feet, nor more than 3 feet 3 inches. The best aver- age is 3 feet 2 inches for the muscular exertion of a middle- sized man, and the pinion on the axle of the winch may have from 8 to 1 2 teeth. The pitch of the first motion- wheels may be 1^ or 1^ inch, and their width from 3 to 4 4 inches. The pitch and strength of the succeeding wheels must be proportioned to the stress which each has to bear, the stress increasing as power is gained by the wheelwork. The power gained is thus calculated. In the 5-ton crane, the handles or winches have a radius of 17 inches, and the semi-diameter or radius of the barrel, measured to the centre of the chain rolled upon it, is 7 J , say 8 inches. The , load, 5 tons, is equal to ll,2001hs., and the wheelwork is as under, namely The first pinion, 4| inches diam., 11 teeth 1^ pitch. wheel, 3 feet 89 1^ Second pinion, 6 inches 12 ,, 1| ,, wheel, 4 feet 96 1J Barrel 8 x 11 x 12 X_11200 Ibs. _ 30800 Winch 17 x 89 x 96~ x 4 men = 1513 = which is the statical resistance against each of the four men at the crane handles. If this crane were constantly employed in lifting weights 108 ON THE CONSTRUCTION OF CRANES. of 5 tons, the machinery would not be sufficiently powerful, and the men would be overworked ; but as it stands on a wharf to land and deliver general goods, which seldom weigh more than a ton, and rarely exceed 25 cwt., it is gene- rally worked by two men, and the statical resistance to each man is from 10 to 12^ Ibs. When a load of 5 tons comes, the additional force of two canal boatmen enables the crane men readily to overcome a resistance of 20 Ibs. for a single lift. The packages, however, being chiefly about 4 cwt, the winch is transferred to the axle of the second pinion, and the first is disengaged ; the combination is then 8x12x448^224 17x96x2 TT or 1 3 Ibs. for each man. The diameter of the wheels should be large, as com- pared with the axles and barrel, in order to avoid loss of power by friction, and the necks or journals should have sufficient length, say Ij times to twice their diameter, to preserve them from wearing or cutting, which is a mis- chievous expenditure of power. The diameter and length of the barrel should be so pro- portioned to the lift of the crane that the length of the channel, cut like a square-threaded screw upon its surface, may be equal to the length of chain to be wound upon it, so that the latter part of the chain hoisted in may not ride or roll upon the first part ; and the diameter of the barreJ should, in any case, be such as to prevent any bending action or tendency to distortion of the links, as they apply their fiat sides to the cylindrical surface of it, while the edge of every alternate link is received in the spiral groove. If the edges or circumference of the pulleys be turned with a naiTOw groove in the middle, to receive the edge of the link while the flat of the alternate links rolls upon the pulleys, which should be turned, bored, and run upon a steeled or hardened pin, the chain will be prevented from ON THE CONSTRUCTION OF CRANES. 109 twisting, and will work almost as smoothly as a leather belt. The diameter of the toothed wheel upon the barrel-axle must be determined by the circumstances already stated, care being taken to make it as great as they may conve- niently admit; the dimensions of the wheels of the 5-ton, 10-ton, and 15-tori cranes are good practical examples ot proportion in similar cases. In proportioning the diameters of axles, regard must be had to their length, to the diameter or radius of the wheel or lever to which the force is applied, and to the weight or stress at the end of the lever. It is important that no practically sensible twist or torsion should take place in the axles, and it is found that the full force of four men (say 120 Ibs.) may be exerted at winches having 18 inches radius at the ends of an axle 2 feet long and 1^ inch diameter, without practically causing it to spring by twisting. As a bar of iron subjected to twist is, in that respect, like a rope, the number of twists, and consequently the angle of torsion, will be directly proportionate to the length of the axle, to the radius of the lever that twists it, and to the weight or stress at the end of the lever. And, as the springing of the axle by such twisting is radial deflection, the angle of torsion formed by the lever is, inversely, as the fourth power of the axle's diameter. The ultimate strength of axles is as the cubes of their diameters. All pivots or journals subject to lateral stress should have their diameters in proportion to the cube roots of the weights upon them, and, for large pivots made of cast-iron, the cube root of the stress in hundredweights may be taken as the minimum diameter of the neck. Thus, if one pivot or journal of cast-iron sustain a stress of 5 tons, or 100 cwt, the cube root is 4-64, and the dia meter in inches must be 4 j or 5 inches. But, if the neck or pivot be of wrought- iron, the propor 110 ON THE CONSTRUCTION OF CRANES. tionate strength, as compared with cast-iron, is 14 to 9, or 1 00 to 64, the cube root of which is 4, the least diameter in inches which it is prudent to make a wrought-iron pivot, to carry 5 tons; as, for instance, at the end of a crane barrel: say, therefore, 4^ in. These bearings sustain no twisfc. Very few experiments have been made on the resistance of metals to torsion, especially on their elastic resistance. The best are those of Mr. George Eennie, who found that cast-iron bars, 1 in. square, were broken by a mean weight of 211 Ibs. at a radius of 3 ft., which twisted the bar asunder close to the bearing, so that the broken bars may be considered as having no length. These experiments, in many respects interesting and valuable, are not applicable to the present subject ; but, from the data here given, it is hoped that no difficulty will be found in assigning to each axle and pivot its right dimensions. By the pitch of a toothed wheel is meant the distance from centre to centre, between two teeth measured upon the pitch line, which is the circle drawn through that paint where two wheels, working together, come into contact with each other. The widths of crane- wheels are from twice to three times as much as their pitch of teeth, that is to say, a wheel of 1^-inch pitch is from 3 to 4| inches wide upon the face. The pitch is determined by the stress to be borne by the teeth ; and it is important, that every single tooth shall be fully capable of supporting the entire strain to which the wheel may be subject. The strength of the tooth is calculated as that of a beam or lever fixed at one end and loaded at the pitch line, that is, about three-fifths or two-thirds of its length from the root of the tooth, where it may be said to grow out of the periphery of the wheel ; for, although three teeth may be engaged at the same time, it is impossible that they can all be in perfect contact with their fellows, even with the best workmanship. ON THE CONSTRUCTION OF CRANES. Ill This is a point which should never be neglected or left to subordinates, who are too apt to take such models as the ironfounder may happen to have by him. The failure of a tooth may strip off others, and the wheel be broken, so that serious and fatal accidents may arise from such an, oversight. The next consideration is the form of teeth best adapted for crane-wheels ; but it is to be observed that the thick- ness of the rim ought to be at least equal to that of the tooth, and be strengthened by a rib equal in section to a tooth; that the arms, at their point, should at least be equal in section to the rim ; that they should be placed in the middle of the wheel, and be feathered on both sides. Of the various methods which have been used to deter- mine the forms of teeth for crane- wheels, the author has generally employed the epicycloidal curve produced by rolling a circle equal in diameter to the radius of the pinion upon another circle equal in diameter to the radius of the wheel, the diameters being taken at the pitch lines, which are the circles described by the wheel and pinion at their point of contact. The curves so struck, commencing at the pitch lines, form the points of the teeth. They are struck in opposite directions, the space between their starting points being the thickness of the tooth; and from these two points radial lines were drawn to the centres of the wheel and pinion, which formed the sides of the teeth included be- tween them, within the pitch line. This form, it will be observed, made the tooth smallest at the root by the con- vergence of the radial lines, and consequently tended to weaken it ; this was remedied in the pinion by casting a plate upon the teeth, which, forming part of them, served not only to bind, as it were, all the teeth together, but to strengthen the body of the pinion, perforated and weakened by the axle passing through it. " The roots of the teeth" upon the wheel were strengthened J J 2 ON THE CONSTKUCTION OF CRANES. by small angle pieces, for which space was found without the curved line described by the tooth of the pinion. Such teeth worked freely and equably together. But it will be observed that the side of each tooth of the wheel consisted partly of a radial line, partly of an epicycloidal curve, and partly of such a concave angle piece as might be found to clear the pinion ; and it will also be observed that the wheel and pinion were adapted to each other; consequently another pinion, differing much in diameter from the first, would not act well, or, as a workman would say, pleasantly, with the same wheel. Professor Willis, of Cambridge, has recommended a mode of forming the teeth of wheels by which this incon- venience is obviated. It was well known that the teeth of wheels, struck by the involutes of circles corresponding with their respective wheels, would work correctly with any other wheel of the same pitch made with involute teeth ; but the obliquity of these teeth is often very inconvenient, although the writer has used them advantageously, when, from peculiar circumstances, as in rolling mills for making heavy bar iron, rails, &c., the wheels have, at times, more or less hold of each other, and the teeth work deep or shallow in gear. These teeth arc struck by unwinding a string or ribbon from a roller, equal in diameter to the wheel, and describing the tooth by a tracing point at the end of the string. The obliquity of teeth of the involute shape renders them useless for cranework, owing to the thrust caused by it, which tends to force the wheels asunder, and throws undue stress upon the axles and bearings. The writer can state, from practice, the superiority of the form of tooth recommended by Professor Willis, which is thus produced. If for a set of wheels of the same pitch a constant de- scribing circle be taken to trace those parts of the teeth which project beyond each pitch line by rolling on the exterior circumference, and those parts which be within it ON THE CONSTRUCTION OF CRANES. 113 by rolling on the interior circumference, then any two wheels of the set will work correctly together. The describing or " Pitch Circle " should be equal in diameter to the radius of the smallest pinion, which, in this case, should not have less than twelve teeth. When rolled upon the interior circumference of a circle equal in diameter to the pinion, a point upon the periphery of the pitch circle will describe radial lines through the centre of the larger circle representing the pinion, which is twice the diameter. So that the form of the pinion teeth within the pitch line may be at once drawn in straight lines from the centre. When rolled on the exterior circumference, epicycloidal curves, forming the teeth of the pinion beyond the pitch line, are described by the tracing point. But, when these operations are performed by rolling the pitch circle upon another of much larger diameter repre- senting the wheel, the interior and exterior epicycloids form a tooth of very different shape : it is no longer con- tained within radial lines, but spreads out at the root, giving great strength and firmness at the point where they are most needed. The exterior epicycloid forms the point of the tooth in a manner similar to that described in the first instance ; but any wheel or pinion having teeth de- scribed by a common pitch circle will work together ; even the teeth of a rack, which, being placed upon a straight line, may be regarded as the segment of a wheel of infinite radius, can be formed in the same manner, and will work equally well with the wheels. Professor Willis has introduced another form of tooth, excellent for heavy machinery revolving always in the same direction, as the writer has experienced in practice, but not applicable to the wheels of a crane which work both ways round. To enter further into this subject would be to pass the limits of this work ; but those who wish to do so may refer to Professor Willis's treatise on this sub- ject, and to his paper in the Second Volume of the Trans- 114 ON THE CONSTRUCTION OF CRANES. actions of the Institution of Civil Engineers. For the various other modes of striking the teeth of wheels they may consult Practical Essays on Millwork, edited by G. Rennie, Esq. Professor Willis has also constructed an ingenious and useful instrument for striking the teeth of wheels with greater facility, which he has named " the Odontograph ;" it is made both in card paper and metal, by Messrs. Holt- zapfel, of Charing Cross. OF THE FOUNDATIONS AND MASONRY FOR FIXING AND SECURING CRANES, AND REFERENCE TO VARIOUS BOOKS AND AUTHORS FOR MORE COMPLETE AND DETAILED INFOR- MATION. Having thus briefly noticed the different parts which compose a crane, it is requisite to add a few words respect- ing the foundation for it, and the means of securing it to masonry, or buildings, or framework. Referring to Fig. 39, which shows the foundation for the 10-ton crane, it will be seen that a mass of stonework forms the counterpoise to the suspended load ; the strong cast- iron cross, into which the crane is stepped, lays hold of the masonry by means of the holding-down bolts and washer- plates, and, as it were, grasps the whole block. Reckoning the weight of the masonry, a light limestone, at the rate of 15 cubic feet to the ton, the diameter at 16 ft., and the depth 6 ft., the mass will weigh about 80 tons. The centre of gravity coincides with that of the crane-post, and the jib may be regarded as a lever, the fulcrum of which is placed under the end of the cross, 6 ft. from the centre of the mass The sweep or radius of the crane being 191 ft^ the arms of the lever are as 13| to 6 ft., the longest ~arm loaded with 10 tons, plus the projecting jib, pulleys, and ciiam, or about 2 tons more, gives the following statement, namely As 6 ft. : 131 ft. : : 12 tons : 24 tons, the weight required to balance the crane. Fig. 39. THE MASONRY FOR THE 10-TON CRANE. SECTION. CRANE PLATFOKM A WHARF WAIL, AT THE UEVEt OF VH. OF WASHER C.C.C C. EL OF THE UNDER COURSE P SCALE OC FEET. 116 ON THE CONSTRUCTION OF CRANES. But the crane and its load must not only be balanced, but firmly held, without risk of disturbing its foundation ; and, taking into account that the chain is sometimes car- ried beyond the perpendicular line, the weight of masonry, 80 tons, is not in excess. A marine engine boiler, wedged by its own weight into a narrow boat, or some similar over- sight, sometimes doubles the load, and it is needless to say the crane is not calculated for such a strain ; occurrences of this kind must be anticipated and provided for, or fatal accidents may ensue. In like manner, when cranes are attached to buildings, care must be taken that the re- sistance shall more than counterbalance the stress ; and, if there be not ample weight and mass to do so, wrought- iron ties should be extended to lay hold of some further counterpoise. Enough, perhaps, has been said on this point to warn the young practitioner against talcing it for granted that build- ings and roofs are secure, under such circumstances, with out making careful and minute examination of the quantity, weight, and position of the resisting material. For information on the manufacture of ropes and cables, he is referred to the " Professional Papers of the Eoyal Engineers," Volume 5th; and for their proportion and adaptation, to the calculations made in a very elaborate work, by John Edye, Esq., Assistant Surveyor of the Navy, entitled, " The Equipment and Displacement of Ships of War." The " Professional Papers of the Royal Engineers " con- tain many important and interesting notices of the appli- cation of cranes and hoisting machinery, as, for instance, that of the travelling crane, with its tackle and framing for working the Diving Bell, in Volume 1st, and for the lifting and transport of heavy timber at Chatham Dockyard, by Sir Mark Isambard Brunei, in Volume 6th, besides many ON THE CONSTRUCTION OF CEANES. 117 other cases, given in all their details throughout others of these volumes, which manifest the skill and judgment of the officers of that distinguished corps in then* adaptation and use of mechanical means in the execution of works of utility as well as in military operations. Buchanan's "Essays on Millwork," edited by George Eennie, Esq., and the papers of Professor Willis, already mentioned, are worthy of more especial notice ; since it is rarely the case that persons so much occupied as these gen- tlemen are, either can or will devote their intervals of lei- sure to works on mechanical subjects. The author has to express his thanks to several gentle- men connected with Government works for facts kindly communicated, and to the manufacturers of ropes and chain cables, who, without exception, liberally answered such in- quiries as were made, especially to Joseph Crawhall, Esq., proprietor of St. Ann's Ropeworks, Newcastle-on-Tyne, whose extensive establishment contains a variety of in- genious mechanism, which it would be difficult to surpass, in the uniformity and excellence of the cordage it pro- duces. He is also greatly obliged to Messrs. Pow and Fawcus, chain cable-makers and anchorsmiths of North Shields, successors to Mr. Robert Flinn. The iron prepared by that gentleman for making harpoons for the Northern Whale Fisher}' has probably never been excelled in tenacity and strength ; the shank of the barbed weapon was often bent into all forms by the exertions of the wounded whale, whose capture depended upon that slender rod of iron. Messrs. John Abbott and Co., of the Park Iron Works, Gateshead-on-Tyne, kindly offered to make any experiments on chains which might be thought necessary; and Mr. William George Armstrong, of the Elswick Works, New- castle, readily supplied drawings and details of his powerful water cranes. This work has been written, in such intervals of profes- J 1 8 ON THE CONSTRUCTION OF CRANES. sional engagement as presented themselves, from a wish to diffuse information respecting a class of machinery which the author has had constantly to employ and to construct for many years past ; and also to second the views of the publisher, by contributing to a series of books for beginners, to be published at a cheap rate : for the first of these reasons the work will be found unequally written, and, for the last, it has been written almost in the same conversa- tional manner in which he has been used to address his pupils and assistants. REFERENCE TO THE ILLUSTRATIONS. FIVF-TON CRANE. This is shown by a Side-Elevation (Fig. 11), and a Baqk View (Fig. 11 a), and the mechanism may be described as follows: A, the principal Wheel, fixed on the barrel-axle, is in diameter 4 ft., and has 96 teeth, lin. pitch. B, the Pinion, 6 in. in diam., 12 teeth, 1^ in. pitch. c, the Wheel on Second Motion, 3 ft. ; 89 teeth, 1 in. pitch. D, the Pinion, or "Winch-axle, 4 in.; 11 teeth, 1 in. pitch. E, the Friction, or Brake Wheel. F, the Barrel. G, Guide-rollers for the chain. H, the Collar, fitted with anti-friction rollers. TEN-TON CRANE, also similarly shown (Fig. 12), has the wheel-work pro- portioned as follows : The principal Toothed Wheel, mounted on the barrel-axle, is in diameter 4 ft. 9 in., with 92 teeth, 2 in. pitch, and 4 in. broad. Pinion, working in do., 7 in. ; 11 teeth, 2 in. pitch, 4 in. broad. 2nd Motion Wheel, do. 3 ft. ; 72 teeth, 1 in. pitch, 3 in. broad. 1st Motion Pinion, do. 6 in. ; 12 teeth, 1 in. pitch, 83 in. broad. Machinery for turning the Cranes : Wheel on Crane-post, 2 ft. 8 in. ; 52 teeth, 2 in. pitch, 3| in. broad. Pinion working in do. 7 in. ; 11 teeth, 2 in. pitch, 3| in. broad. Bevel- wheel on same axle, 1 ft. 4^ in.; 32 teeth, 1 in. pitch, 3 in. broad. Do. Pinion working in do., 5 in. ; 12 teeth, 1^ in. pitch, 3 in. broad. FIFTEEN-TON CRANE (Fig. 13), with horizontal jib and traversing blocks, has the wheelwork the same as the ten-ton crane, but additional power is gained by the blocks, part of which is lost by the increased diameter of the barrel. The machinery of the Traverse-Gear for moving the blocks is E, a Toothed Wheel, diameter 2 ft. 5 in. ; 72 teeth, 1 in. pitch. F, Pinion in do., diameter 4 in. ; 10 teeth, 1^ in. pitch. Sprocket or chain wheel, 2 ft. 6 in., worked by an endless chain. ENLARGED SCALE OF DETAILS of the fifteen-ton Crane shows a Side View of the Guide Roller; of the Traversing Back, upon a portion of the ON THE CONSTEUCTION OF CEANES. 119 Crane-Jib ; a section of the Crane-Jib, Guide Roller, Traverse Pinion and Rack, with other parts of the Machinery of the Traverse-Gear for moving the Blocks along the Jib. THE TRAVELLING CRANK (Figs. 14 a, 14 6, 14 c, 14