8 I 
 


 
 
 
HOOVER STEEL BALL Co 
 
 ANN ARBOR, MICHIGAN 
 
 MANUFACTURERS OF 
 
 B-A-L-L-S 
 
 STEEL, BRONZE, BRASS 
 COPPER, ALUMINUM 
 
 AND OTHER MATERIALS IN BOTH 
 HIGH AND COMMERCIAL GRADES 
 
 MADE IN AMERICA 
 
 TO THOSE WHO ARE INTERESTED IN OUR PRODUCT WE WILL, 
 UPON APPLICATION, GLADLY FORWARD OUR REGULAR CATALOG 
 AND PRICE LIST, GIVING THE TRADE NAME OF OUR DIFFERENT 
 GRADES OF BALLS, GUARANTEED ACCURACY AND QUALITY, 
 PRICES AND TERMS 
 
TJ/07/ 
 
 FOREWORD 
 
 WE TAKE PLEASURE IN PRESENTING 
 THIS TREATISE ON THE MANUFAC- 
 TURE OF STEEL BALLS AND WISH 
 TO THANK THOSE WHO HAVE SUPPORTED 
 US IN SUCCESSFULLY OVERCOMING THE 
 PREJUDICE AT ONE TIME EXISTING 
 AGAINST AMERICAN MADE BALLS. 
 
 THIS SUCCESS HAS BEEN DUE TO THE 
 QUALITY OF OUR PRODUCT COMBINED 
 WITH EXPERT KNOWLEDGE OF THE 
 REQUIREMENTS OF OUR CUSTOMERS. 
 
 IN THE FOLLOWING PAGES WE HAVE 
 ENDEAVORED TO SHOW STEP BY STEP 
 THE VARIOUS STAGES THROUGH WHICH 
 A BALL PASSES FROM THE ROUGH STEEL 
 BLANK TO THE MIRROR -LIKE FINISHED 
 SPHERE. 
 
 THE OBJECT OF THIS TREATISE IS TO 
 LAY BARE FACTS WHICH HAVE HITHERTO 
 BEEN GENERALLY UNKNOWN AND IF WE 
 SUCCEED IN STIMULATING FURTHER 
 INTEREST IN THE BALL INDUSTRY, THIS 
 WORK WILL NOT HAVE BEEN IN VAIN. 
 
 HOOVER STEEL BALL Co. 
 
 ANN ARBOR, MICHIGAN 
 
 372827 
 
L. J. HOOVER 
 
 PRESIDENT AND GENERAL MANAGER 
 
COMMITTEE OF THREE HAVING ENTIRE CHARGE OF FACTORY 
 MANAGEMENT AND MANUFACTURING 
 
* * 
 
 M 
 
 hi 0} 
 
 \- " 
 
 (fl ,_ 
 
 cr z 
 
 u < 
 
 > -i 
 
 O a- 
 
 H 
 
 1 Z 
 
Manufacture of Steel Balls 
 
 DURING recent years the application of ball 
 bearings in machine design has increased rapidly, 
 and this type of bearing is now used in many 
 machines where plain bearings were formerly 
 considered good enough. Until German export 
 facilities were shut off by the war, the majority of the 
 steel balls used in these bearings were made by the Deutsche 
 Waffen und Munitions Fabriken of Berlin, Germany, and 
 the product of this firm has become so celebrated that many 
 persons think the steel ball industry was developed by the 
 Germans. As a matter of fact, the art of ball making goes back 
 to a very early date, and the development of original methods 
 for doing this work is attributed to the Chinese. To those who 
 have credited the Germans with the development of commercial 
 methods of ball manufacture, it will doubtless be of interest to 
 learn that the first commercial steel balls were made in this 
 country under basic patents granted to Richardson of the 
 Waltham Emery Wheel Co., Waltham, Mass., and that the 
 original ball making machinery for the plant of the Deutsche 
 Waffen und Munitions Fabriken was designed and built in the 
 United States and shipped to Germany ready for use. This 
 will be explained in detail in connection with the following 
 historical outline of important epochs in the steel ball industry. 
 
 HOW THE STEEL BALL INDUSTRY 
 CAME INTO EXISTENCE 
 
 IT HAS been stated that basic patents for dry grinders used 
 in roughing out ball blanks to a spherical form were granted 
 to Richardson of the Waltham Emery Wheel Co., in 1887. 
 These patent rights were subsequently sold to the Cleveland 
 Machine Screw Co., Cleveland, Ohio, which had control of 
 patents on ball making machinery taken out by John J. Grant. 
 One of the first firms to manufacture steel balls on a commer- 
 cial basis was the Simonds Rolling Machine Co., of Fitchburg, 
 Mass., and the Fitchburg Steel Ball Co. was subsquently formed 
 by employes who left the Simonds firm. After a brief career, 
 
the latter firm was taken over by the Cleveland Machine Screw 
 Co., and with facilities acquired through its own development 
 work and purchase from other companies, it was in a position 
 to manufacture the majority of balls used in the bicycle trade. 
 In this connection it will be of interest to note that up to the 
 year 1899 balls one-half inch in diameter were the largest size 
 that were manufactured in quantities. 
 
 About 1890 the Cleveland Machine Screw Co. designed and 
 built for the Deutsche Waffen und Munitions Fabriken, of 
 Berlin, Germany, equipment used in its original steel ball plant 
 and this marked a most important step in the trade, owing 
 to the reputation for making high-grade balls that was later 
 acquired by this firm. The machines built and shipped to 
 Germany had no reference to American manufacturing rights, 
 and the Cleveland Machine Screw Co. continued to operate its 
 plant in the usual way. 
 
 In 1894 when a consolidation of bicycle manufacturers was 
 effected, the Cleveland Machine Screw Co. was sold to the Pope 
 Mfg. Co. of Hartford, Conn., which at that time started to 
 manufacture its own balls for use in bicycle bearings. The 
 requirements of balls for the bicycle trade were not nearly as 
 severe as the standards which must be met by balls used in 
 high-grade annular bearings at the present time. This was 
 largely due to the fact that the cup and cone form of races was 
 employed, allowing compensation to be made, and while this 
 form of race did not enable ball bearings to be operated under 
 the most efficient conditions, it was the means of overcoming 
 discrepancies due to inaccuracies in the size of the balls. Up 
 to this time there had been six or seven firms engaged in the 
 manufacture of steel balls, but with the decline of the bicycle 
 industry a number failed. 
 
 In 1901 the Standard Roller Bearing Co., Philadelphia, 
 Pa., acquired all obsolete and existing plants engaged in the 
 manufacture of steel balls. L. J. Hoover, who was formerly 
 in the employ of the Standard Roller Bearing Co., left that firm 
 in 1906 and formed the Grant & Hoover Co. at Merchantville, 
 N. J. The name of this firm was later changed to Atlas Ball 
 Co., and the plant transferred to Philadelphia, Pa., where it is 
 still in operation. On March 1, 1913, the Hoover Steel Ball Co. 
 of Ann Arbor, Mich., was organized by Mr. Hoover for the 
 
 10 
 
purpose of engaging in the manufacture of high-grade steel balls 
 to take the place of those imported from Germany. When the 
 European war started in 1914, the blockade of German ports by 
 the British Navy shut off the supply of steel balls formerly 
 exported by that country to the United States, and the insistent 
 demand of consumers for balls made in this country imposed 
 a heavy strain upon the facilities of domestic producers. Some- 
 what similar conditions existed in all branches of the machinery 
 trade, making it difficult for the ball manufacturers to increase 
 the capacity of their plants ; but the management of the Hoover 
 Steel Ball Co. showed commendable initiative by contracting 
 for the entire output of machine building firms with which orders 
 were placed for special machinery required in ball manufacture; 
 and these firms were given financial assistance to enable them 
 to handle work with the greatest possible rapidity. As a result, 
 the Hoover Steel Ball Co. has greatly increased its capacity, the 
 grow r th being well illustrated by Fig. 1 and the illustration in the 
 center of the book, that show, respectively, the original factory in 
 which the firm started manufacturing in March, 1913, and the plant 
 as it appears at present. An idea of the magnitude of the business 
 will be gathered from the fact that the consumption of steel 
 runs in excess of 500 tons a month, and calculated on the basis 
 of J^-inch balls, the daily production is between 25,000,000 
 and 30,000,000 balls per day. 
 
 Fig. 1. Original Plant in which Hoover Steel Ball Co. started Manufacturing 
 Operation in March, 1913. 
 
 11 
 
RAW MATERIAL OF THE STEEL 
 BALL INDUSTRY 
 
 THE steel from which balls are made comes to the factory 
 in coils or straight rods, according to its size. Stock 
 less than 11/16 inch in diameter comes in coils and is 
 known as "wire," while all stock exceeding 5/g-inch in diameter 
 comes in straight bars. The size of the stock is referred to in 
 thousandths, i. e., stock ^g-inch in diameter is known as 0.375- 
 inch stock. The following is a specification of steel wire 
 used for making balls: carbon, 0.95 to 1.05 per cent; silicon, 
 0.20 to 0.35 per cent ; manganese, 0.30 to 0.45 per cent ; chromium, 
 0.35 to 0.45 per cent; sulphur and phosphorus, not to exceed 
 0.025 per cent. The following analysis is typical for the larger 
 sizes of stock which comes in straight bars: carbon, 1.02 per 
 cent; manganese, 0.40; silicon, 0.21; chromium, 0.65; sulphur, 
 0.026; and phosphorus, 0.014 per cent. A well equipped 
 laboratory is maintained in which chemical and physical tests 
 are conducted on each shipment of steel to determine its suit- 
 ability for manufacture into balls, and an unloading ticket must 
 be signed by the head of the laboratory before the steel is taken 
 from the cars into the plant. Some very interesting conditions 
 have been brought to light by the laboratory work, and a later 
 section of this article will be devoted to a discussion of tests 
 conducted on the raw material and product, data obtained from 
 these tests, and a description of methods and apparatus used 
 in the laboratory. 
 
 PRODUCTION OF BALL BLANKS 
 BY COLD-HEADING 
 
 BALL blanks made from stock ranging from 1/16 up to and 
 including j^-inch m diameter are formed on special 
 cold-headers designed for the production of ball blanks 
 by the E. J. .Manville Machine Co., Waterbury, Conn. A 
 battery of these machines is shown in operation in Fig. 2, and 
 in this connection it may be mentioned that the Hoover Steel 
 Ball Co. is equipped with machines of the following sizes: 00, 0, 
 1, 2, 3, and 5. Production of ball blanks by the cold-heading 
 process has several advantages in its favor. In the first place, 
 there is practically no waste, with the exception of about 0.040 
 
Fig. 2. General View in Cold-header Department; Blanks for All Sizes of Balls 
 up to Y^-inch Diameter are made on Cold-Heading Machines. 
 
 inch of metal left on the blank to provide for finishing. Blanks 
 can be held to this close limit because the steel is worked 
 cold and there is no tendency for it to become decarbonized. 
 One man can look after three or four machines, so that the 
 cost of labor is almost negligible. Cold-headers used in the 
 production of ball blanks are of the type commonly known as 
 single-blow solid-die machines, and the way in which they 
 operate can best be explained in connection with Fig. 3. These 
 machines consist of a heavy framed which completely surrounds 
 the working parts of the machine, thus insuring a high degree 
 of rigidity. At one end of the machine there is a driving shaft 
 B ; and. at the opposite end of the frame is die-block C. Between 
 the sides of the frame is a movable ram D that actuates the heading 
 punch E. Wire F to be made into ball blanks enters the machine 
 through feed rolls G and then passes through cut-off quill H. 
 At the side of the machine is supported a bracket / in which 
 slide / may be reciprocated by a crank motion from the main 
 driving shaft. Slide J has a cam groove cut in it in which roll K 
 is fitted ; this roll is mounted on cross-slide L, so that a lateral 
 
 13 
 
Fig 3. Plan View of Cold-header Mechanism Illustrating Method of Operation. 
 
 motion is imparted to cut-off knife M located on the end of 
 cutter-bar L. 
 
 A ratchet feed advances the wire through the cut-off quill 
 until it comes into contact with a stop, which is not shown 
 in the illustration. This stop checks forward motion of the stock 
 when a sufficient length has passed the cut-off knife to produce 
 a ball blank of the proper size. Cut-off knife M is advanced in 
 the manner just described, severing the wire, but retaining it on 
 the cut-off blade by means of a spring finger. Advance of the 
 cut-off knife and wire slug is continued until the slug reaches a 
 position directly in front of the opening in die TV. Here it is 
 held stationary long enough for punch E to begin to push the 
 slug of metal into the die, at which time cut-off knife M retreats 
 
 Table I. Capacities of Cold-headers in Ball Blanks per Hour 
 
 Size of 
 Cold- 
 header 
 
 Capacity for 
 Ball Blanks 
 Diameter in 
 Inches. 
 Max. Size. 
 
 Production 
 of Blanks 
 per Hour 
 
 Size of 
 Cold-header 
 
 Capacity for 
 Ball Blanks 
 Diameter in 
 Inches. 
 Max. Size. 
 
 Production 
 of Blanks 
 per Hour 
 
 00 
 
 3/16 
 
 7800 
 
 2 
 
 7/16 
 
 6300 
 
 
 
 9/32 
 
 7200 
 
 3 
 
 1/2 
 
 6000 
 
 1 
 
 3/8 
 
 6900 
 
 5 
 
 9/16 
 
 4800 
 
 Note Due to time loss in setting up, trouble with stock and breakdowns, the actual 
 average rate of production is from 80% to 90% of above values. 
 
Table II. Size of Stock Used for Making Balls on Cold-headers 
 
 Diameter of 
 Ball Inches 
 
 Diameter of 
 Stock Inches 
 
 Diameter of 
 Ball Inches 
 
 Diameter of 
 Stock Inches 
 
 1/8 
 
 .100 
 
 5/16 
 
 .235 
 
 5/32 
 
 .120 
 
 3/8 
 
 .275 
 
 3/16 
 
 .145 
 
 7/16 
 
 .320 
 
 7/32 
 
 .170 
 
 1/2 
 
 .365 
 
 1/4 
 
 .190 
 
 9/16 
 
 .395 
 
 9/32 
 
 .220 
 
 5/8 
 
 .440 
 
 and allows punch E to continue its work by pushing the blank 
 to the bottom of the die cavity. After the slug F has been 
 headed it is ejected by the knock-out pin O which is 
 advanced by the mechanism operated by lever P, which 
 also receives its motion from a crank at the side of the machine 
 connected to the main driving shaft. In this way the ball 
 blank is knocked out of the die and dropped through an opening 
 into a receptacle placed to receive it, this being clearly shown in 
 Fig. 2. Table II gives the diameter of stock used in making 
 blanks for several different sizes of balls, and is presented to 
 show the enlargement that takes place during the heading 
 operation. Various grades of steel* have been used for making 
 dies employed on the cold-headers, but the most satisfactory 
 results have been obtained with the following grades ^'Sander- 
 son" or "Viking Special" made by the Crucible Steel Co. of 
 America; "Intra" made by the Hermann Boker Co.; "Gyro" 
 made by Braeburn Steel Co.; and tool steel made by William 
 Jessop & Sons. 
 
 HOT-FORGING BALL 
 BLANKS 
 
 IT HAS previously been stated that blanks for balls exceeding 
 ^g-inch in diameter are hot-forged from straight bars, and 
 in handling this work multiple dies are employed which 
 produce strings of balls containing up to ten balls, according 
 to the size. The stock is heated in "Frankfort" furnaces made 
 by the Strong, Carlisle & Hammond Co. of Cleveland, Ohio; 
 
 15 
 
Fig. 4. View of Stock Racks in Hot-forging Department where Ball Blanks 
 exceeding Y^-inch diameter are made. 
 
 these are oil furnaces which are operated with oil at a pressure 
 of 8 pounds per square inch, and air at a pressure of 2 pounds 
 per square inch. Twelve bars are arranged in the furnace as 
 shown in Fig. 5. The hammer-man takes out the bar at the 
 left-hand side of the furnace, and after forging a string of balls 
 at the end of this bar and cutting it up into individual ball 
 blanks, returns the bar to the furnace at a point at the extreme 
 right. In this way, the bars are used in rotation, which prevents 
 any bar from becoming overheated. This is a matter of con- 
 siderable importance, because the furnaces are maintained at a 
 temperature somewhat in excess of 1800 degrees F. in order to 
 provide for heating the stock as rapidly as may be necessary; 
 but should it happen that steel was left in the furnace for an 
 undue length of time, there would be danger of burning the steel. 
 
 The multiple forging dies are shown in detail in Fig. 6, 
 in which it will be seen that each die opening is elliptical; the 
 purpose of this is to provide a clearance space at each side into 
 which excess metal will flow. It must be borne in mind however, 
 that while this illustration only shows four die openings, the 
 number of openings runs up to ten, according to the size of ball 
 blanks that are being forged. In the cross-sectional views, 
 the dimensions of the die are indicated by letters, and in Table 
 III are given diameter A of cherrying cutter, distanced between 
 
 16 
 
Fig. 6. Type of Die used for Hot-forging Ball Blanks for Balls exceeding 
 %-inch Diameter. 
 
 Table HI. Dimensions of Hot- forging Dies for Ball Blanks 
 
 Diameter 
 of Ball, 
 Inch 
 
 Diameter 
 A of Die, 
 Inch 
 
 Distance 
 B between 
 Centers, 
 Inch 
 
 Depth C of 
 Die, Inch 
 
 Depth D, of 
 Bridge, Inch 
 
 Diameter E 
 of Stock, 
 Inch 
 
 3/4 
 
 0.775 
 
 0.910 
 
 0.387 
 
 0.065 
 
 0.625 
 
 7/8 
 
 0.905 
 
 1.060 
 
 0.452 
 
 0.065 
 
 0.729 
 
 1 
 
 1.035 
 
 1.210 
 
 0.517 
 
 0.075 
 
 0.823 
 
 centers, and depth C to which the cherrying cutter is sunk in 
 making the dies for three sizes of balls, and these data are 
 presented to indicate how dimensions of the dies vary for differ- 
 ent sizes of balls. The depth D of the gate between adjacent 
 diesis a matter of considerable importance, because, it determines 
 the size of the neck between adjacent balls, which is depended 
 upon to hold the string of balls together until they are sheared. 
 Also this depth must be regulated so that there is no tendency 
 to draw the stock adjacent to the neck and form a pipe in the 
 ball blank, which would have a highly detrimental effect on its 
 structure. A land of approximately one-third the diameter of 
 the ball is provided for clearance at the bottom of the die and 
 the upper die member. The dies are made from a special die 
 steel made by the Ludlum Steel Co. of Watervliet, N. Y., or from 
 
 17 
 
Fig. 5. "Frankfort" Oil-heated Furnaces made by Strong, Carlisle & 
 Hammond Co., in which Bars are Heated for Hot-forging Operation. 
 
 "Firth-Sterling Special," made by the Firth-Sterling Steel Co., 
 McKeesport, Pa. This is not an alloy steel, but a regular tool 
 steel adapted for making hot-forging dies. In order to produce 
 round balls in such dies, the bar is turned between each stroke 
 of the hammer, which results in bringing the balls to a close 
 approximation of the spherical form. Along one side of each 
 die is a pipe with a number of holes drilled in it through which 
 water flows onto the dies and work. 
 
 In purchasing stock for the production of ball blanks for 
 the hot-forging method, it is matter of considerable importance 
 to have all bars of the same length. This is due to the fact that 
 when there is considerable variation in length, some bars will 
 
 18 
 
be used up before others, with the result that it is necessary to 
 finish up a number of short pieces in the furnace before putting 
 in an entire new charge. At the end of each bar there is left 
 what is known as a "short end," and experience has shown 
 that these short ends cannot be forged into ball blanks of the 
 regular size, as they fail to fill out the dies properly. On this 
 account, short ends are collected and forged into ball blanks of 
 the next smaller size. By ordering stock in bars of a specified 
 length, ' 'short-ends" are eliminated. 
 
 After being forged, the hot string of balls is taken to punch 
 presses made by the Ferracute Machine Co., Bridgeton, N. J., 
 which are placed beside the Bradley helve hammers on which 
 the forging operation is performed, the arrangement being 
 clearly shown in Fig. 7. The punch presses are equipped with 
 multiple shearing dies, which consist of a lower die member 
 with holes of the same size as the balls and a multiple punch 
 carried in the ram, one punch being in line with each opening 
 in the die. The string of balls is dropped into place and the 
 
 Fig. 7. 
 
 C. C. Bradley Hammer and Ferracute Power Press in which a String of 
 Ball Blanks is Forged and Cut up into Individual Balls. 
 
 19 
 
press tripped, resulting in pushing the balls through the holes 
 in the die and leaving the scrap metal which is brushed off 
 before the next operation is performed. The bar is then returned 
 to the right-hand side of the heating furnace, as previously 
 mentioned, and is moved to the left each time a heated bar is 
 removed, until it reaches the extreme left ready for another string 
 of balls to be forged from the heated metal at its end. Three 
 sizes of helve hammers made by C. C. Bradley & Son, Inc., 
 Syracuse, N. Y., are used for forging ball blanks, which have 
 capacities for striking blows of 125, 150 and 300 pounds. 
 
 ELEVATION OF DIE AND PUNCHES 
 
 PUNCH. HOLDER 
 
 FLAN OF DIE 
 
 Figure 8. Type of Die used for Shearing String Forgings into Individual Ball Blanks. 
 
 Fig. 8. shows the construction of shearing punches used 
 for cutting up the string forgings into individual ball blanks. 
 At A is shown the form of punch-holder used, which will be seen 
 to consist of a cast-iron shoe with four set-screws for holding 
 the punches. These are secured in a clamp B which is made 
 by drilling holes of the proper size for the punch shanks in a 
 block of the desired form and then sawing this block in half; 
 the punches are then put in place and the entire clamp secured 
 in punch-holder A . The diameter C of these punches is usually 
 made about J^-inch less than the diameter of the balls in the 
 string forging that is to be cut up. A plan view of the die is 
 shown at D, and it will be evident that the spacing between 
 holes in this die is the same as the center distance between the 
 
die cavities in the forging die. Also a bridge is provided in the 
 shearing die of sufficient depth to retain the neck left between 
 adjacent ball blanks on the string forging while the balls are 
 pushed through the die. After the shearing operation has been 
 completed, the scrap metal is brushed off the shearing die before 
 the next set of ball blanks is cut up. 
 
 In has been mentioned that balls ranging in size from ^-inch 
 up to about 2j^-inches in diameter are made by forging strings 
 of blanks according to the process which has just been described. 
 In the case of the larger sizes of balls from &/% to 4 inches in 
 diameter single blanks are usually forged under a steam 
 hammer, making one blank at a time at the end of the bar. 
 Slugs of the proper size are first cut off to the required length 
 and both ends chamfered, the length of stock being determined 
 by the weight of the finished balls after making a proper allow- 
 ance for the material removed in finishing. These blanks are 
 placed in the oil furnace and heated to a forging temperature; 
 and each time a blank is removed to be forged a new slug of 
 metal is put into the furnace in its place. Dies used for this 
 kind of forging are of an entirely different form from those used 
 in string forging; they are cupped out to the desired diameter, 
 but are only turned to a depth of one-quarter the diameter of 
 the ball to be forged and are not relieved. When the blank has 
 been heated, the hammer-man places it in the die and the hammer 
 is worked very slowly until the blank begins to take a spherical 
 shape, when quicker and heavier blows are struck. Owing to 
 the shallowness of the die, the operator has ample room to turn 
 the ball in all directions, and he can therefore produce an almost 
 perfect sphere. Blanks up to 8 inches in diameter are forged 
 without varying more than 0.005 inch from a true spherical form. 
 
 ROUGH DRY-GRINDING 
 
 THE method of making ball blanks varies according to their 
 size, small blanks being made on cold-headers and large 
 blanks forged from hot metal according to the methods 
 which have just been described. After this preliminary 
 work, all sizes of balls go through essentially the same treatment 
 certain minor modifications being made according to the quality 
 of the balls; and the method of treatment may also vary some- 
 
what in the case of balls of extremely large size. These modifica- 
 tions from standard practice will be taken up in detail. 
 
 Blanks made by either the cold-heading or hot-forging 
 process are first sent to the dry-grinding room, where they 
 
 Fig. 9. Side View of Dry-grinder, showing wheel dropped away from work, a 
 
 Charge of Balls ready to be dropped into Grinding Position, and Ball 
 
 being measured for Size in Test Indicator. 
 
 22 
 
are subjected to a rough-grinding operation before going to 
 the heat-treating department. This rough-grinding results in 
 removing a considerable part of the surplus metal and bringing 
 each ball to a much closer approximation of a truly spherical 
 form than it is possible to obtain in forgings made by either of 
 the methods that have been described. In the case of hot-forged 
 
 Fig. 10. Front View of Grinding Machine, showing Grinding Wheel raised to 
 
 Operating Position and Tray of Ground Balls just removed from Machine; 
 
 Balls seen in Ring are not in Grinding Position 
 
 23 
 
ball blanks, this rough-grinding also removes the decarbonized 
 steel from the surface of the blanks produced in forging. 
 
 An exception to the general method of procedure is made 
 in the case of balls from 1/16 to 3/16 inch in diameter. Such 
 balls are not dry-ground before being heat-treated, but they 
 get a rough and a finish dry-grinding after being hardened. 
 Figs. 9 to 11, inclusive, show the type of machine on which 
 the dry-grinding operation is performed, and the best idea 
 of its construction and method of operation will be obtained 
 by reference to the two views shown in Fig. 11. The main 
 
 Fig. 11. 
 
 Front and Side Views of Dry-grinding Machine, illustrating 
 Principle of Operation. 
 
 parts of this machine consist of a carborundum grinding wheel 
 A and an iron ring B which are driven in opposite directions. 
 Two rings C and D are supported by spiders in such a way 
 that there is a space between the beveled edges of the inner 
 and outer rings sufficient to allow ball blanks that are to be 
 ground to project through this space. In the side view of the 
 machine illustrated in Fig. 11, these rings are shown with the 
 wheel lowered, but when the machine is in operation the balls 
 held between rings C and D are in contact with grinding wheel 
 A ; and ring B presses down and holds them against the grinding 
 
wheel. In order to provide for grinding the balls uniformly, 
 the spindles on which grinding wheel A and driving ring B are 
 carried are placed eccentric to each other, which results in giving 
 the balls an oscillating motion in addition to their motion of 
 rotation ; and as a result of this combined movement all surfaces 
 of the ball blanks are exposed to the action of the grinding wheel, 
 which results in bringing them to a close approximation of the 
 spherical form. The way in which the upper and lower spindles 
 of the machine are driven is best illustrated in Fig. 9, which 
 shows how open and crossed belts are brought to the machine 
 pulleys from an overhead countershaft. 
 
 Probably the best way to describe the operation of one of 
 these dry-grinders is to start at the point where a charge of 
 ball blanks has been ground down to the required size and is 
 to be removed from the machine. To provide for doing this, 
 the head which supports grinding wheel A is carried on a slide 
 on the base of the machine. Secured to the bottom of this slide 
 is a rack E that meshes with a pinion at the end of cross-shaft F. 
 Keyed to the opposite end of shaft F is a worm-wheel G that 
 meshes with a worm actuated by hand-wheel H that provides 
 fine adjustment. Secured to the bed of the machine is a disk /, 
 and in order to drop grinding wheel A out of contact with the 
 work held between rings C and D, the spring latch carried by 
 lever J is withdrawn from a notch in disk / and the lever is 
 moved to the left until the latch engages a stop notch in disk /, 
 which limits the downward motion of the grinding wheel. It 
 will be seen that sufficient clearance is, now provided between 
 grinding wheel A and rings C and D to enable tray K to be 
 swung into position to catch the balls when they are discharged 
 from the holding rings. 
 
 It will be seen that inner ring D is supported by a spider 
 secured to the lower end of rod L, and in order to discharge 
 the ground balls, ring D is dropped by pushing down lever M. 
 This drops the inner ring and allows the ground balls to fall into 
 tray K. When lever M is released, ring D is returned to its 
 original position by means of a compression spring N. During 
 the time that the charge of balls in the machine is being ground, 
 a fresh charge of blanks is placed in the space between driving 
 ring ,5 and outer ring C; a few of these balls will be seen in position 
 in Fig. 9. After the ground balls have been removed and inner 
 
ring D has been returned to the position shown in Fig. 11, it is 
 necessary to place the charge of new blanks in position to be 
 ground. This is done by dropping both rings C and D sufficiently 
 so that the balls held between outer ring C and driving ring B 
 may drop into position, after which the two rings are returned 
 to the location shown in Fig. 11. This result is accomplished 
 by means of lever O that is carried at the end of a cross-shaft 
 which has a pinion at its right-hand end meshing with the rack 
 P cut in the sleeve that supports the spider on which outer 
 ring C is carried. 
 
 In order to drop a charge of balls into place, the spring 
 latch carried by lever is released and this lever is pulled forward 
 which results in dropping both rings C and D, due to the fact 
 that rod Z/, supporting inner ring D, is pinned to the upper end 
 of sleeve P, to which the outer ring is connected by means of the 
 spider. When the balls have been dropped into position as 
 indicated, grinding wheel A is raised into contact with the work 
 
 Fig. 12. Special Grinding Machines for Grinding Rings shown at 
 C and D in Fig. 11. 
 
by raising lever /. Rings C and D are ground to a smooth surface 
 and fine edge in order that the balls may run freely and reach 
 through the space to come into contact with the grinding wheel 
 A. This is done on special grinding machines, the method of 
 grinding the inner and outer rings being clearly illustrated in 
 Fig. 12. Lever Q at the front of the grinding machine operates 
 a clutch that provides for starting or stopping the machine. 
 It will be seen from Figs. 9 and 10 that the grinders are provided 
 with an exhaust system to carry away the dust of the wheel. 
 
 HEAT TREATMENT 
 
 DURING the process of making the steel for the balls and 
 in forging and rough-grinding the ball blanks made 
 from this steel, severe internal strains are likely to be 
 set up in the metal that would often be of sufficient magnitude 
 to cause the balls to be broken when subjected to only a small 
 
 Fig. 13. Charging End of American Rotary Gas Furnaces in which Balls 
 up to One Inch Diameter are Heat-treated. 
 
part of their rated load carrying capacity. Trouble from this 
 source must be eliminated, and this is done by subjecting the 
 balls to a preliminary annealing operation in rotary gas furnaces 
 made by the American Gas Furnace Co. of Elizabethport, N. J., 
 before the final hardening operation. The same type of furnace 
 
 Fig. 14. Discharge End of American Rotary Gas Furnaces, showing Quenching 
 
 Tanks and Deflector through which Balls are delivered to 
 
 Baskets at Bottom of Tanks. 
 
is used for the annealing and hardening operations, but for the 
 former the delivery chute on the furnace is arranged to discharge 
 the balls into pans, as shown at A in Fig. 13, while for the latter 
 the balls are discharged into a quenching tank, as indicated in 
 Fig. 14. The form of retort used in these American gas furnaces 
 is shown in Fig. 15, and it will be seen to have a spiral path 
 
 Fig. 15. Cross-Sectional View of "Nichrome" Retort used in Rotary Gas Furnaces. 
 
 through which the balls pass as the retort is revolved. At the 
 loading end of each furnace there is a hopper that is kept filled 
 with ball blanks, and the retort draws blanks from this hopper 
 and passes them through the furnace at such a rate that the 
 steel is heated to the desired temperature when the balls are 
 discharged. For annealing, a temperature of 1300 degrees F. 
 is employed, and for hardening the balls are raised to a tempera- 
 ture of from 1425 to 1475 degrees F. according to the size and 
 the composition of the steel. Pyrometers made by the Hoskins 
 Mfg. Co. of Detroit, Mich., are used to determine the tempera- 
 ture of each furnace. 
 
 QUENCHING THE STEEL 
 BALLS 
 
 IT HAS been mentioned that the same type of furnace is 
 used for both the annealing and hardening operations, the 
 only change being to place the tube so that the ball blanks 
 are discharged into a pan in the case of annealing, and into 
 the quenching tank in the case of the hardening operation. 
 The retorts used in the furnaces were formerly made of cast 
 iron, and great trouble was experienced through their destruction 
 after they had been in service a short time. This trouble has 
 
been over-come by substituting "Nichrome" in place of cast iron, 
 and retorts made of this material last indefinitely. 
 
 In hardening, there is a difference of practice according to 
 the size of the balls, those of 5/16-inch diameter and less being 
 quenched in oil while balls of larger size are quenched in water. 
 Balls made of some grades of steel are quenched in pure water 
 and others are quenched in brine. In all cases the quenching 
 tanks are provided with a device of the form shown in Fig. 14, 
 which consists of a series of conical sheet metal deflectors through 
 which the balls pass before reaching the wire mesh basket at 
 the bottom of the tank. The purpose of these sheet metal cones 
 is to deflect the course of the balls so that they follow a winding 
 path and are completely cooled before reaching the bottom of 
 the tank. One complete furnace charge can be run into one 
 of these wire baskets and when this is filled, the entire outfit 
 is lifted out of the tank by means of an electric hoist as shown, 
 and the balls are then removed from the basket. The depth of 
 
 Fig. 16. ''Frankfort" Oil Furnaces for use in Heat-treating Balls over One inch 
 
 Diameter, and Quenching Tank in which these Balls are Hardened. Note 
 
 Hoskins Pyrometer for showing Temperature of Furnaces. 
 
 30 
 
the quenching tank is about 14 feet. Rotary furnaces are used 
 for annealing and hardening the smaller sizes of balls, and in 
 the case of balls one inch in diameter and over, ''Frankfort" 
 oil furnaces are employed, into which the balls are introduced 
 on trays as shown in Fig. 16. When the balls are heated to the 
 proper temperature, these trays are withdrawn and the balls 
 are dumped into the quenching tanks provided with the sheet 
 metal cones described. The reason for quenching small balls 
 in oil and large balls in water is that the oil does not absorb the 
 heat as rapidly as the water, and in the case of very small balls, 
 the shock of dropping them into water would result in strains 
 so great that many balls would either be cracked or broken, and 
 the strength of those balls in which there were no visible defects 
 would be seriously impaired. In the case of large balls, there 
 is sufficient heat to prevent trouble from this cause. From 
 time to time sample balls are tested by breaking them on an 
 anvil and examining the structure of the steel to make sure that 
 the heat-treatment is producing the desired results. Provision 
 must be made for preventing over-heating of the oil or water 
 in the quenching baths, and this is done by having a circulating 
 system through which the oil or water passes into a reservoir 
 outside the building and then through a coil in this reservoir 
 and back to the tank. In this way the contents of the quenching 
 tank are kept in continual circulation, preventing overheating. 
 
 SPECIAL TREATMENT TO RELIEVE 
 INTERNAL STRAINS 
 
 DURING the process of hardening, internal strains are 
 set up in the balls, and it is necessary, of course, to 
 relieve the strains without effecting the surface hard- 
 ness of the balls. 
 
 This is done by immersing the balls which are carried in 
 wire baskets, in a tank of boiling water for two hours. The 
 equipment used for this purpose is shown in Fig. 17. 
 
 This practice is only followed in the case of balls that are 
 hardened by quenching in water or brine. 
 
 Besides relieving the internal strains, the hot water prevents 
 the balls from rusting after their removal, as the hot balls dry 
 off very rapidly. 
 
Fig. 17. Water Bath in which Severe Strains are Removed from Balls Quenched 
 in Water by subjecting them to Temperature of Boiling Water for Two Hours. 
 This Treatment also enables Balls to Dry Rapidly and Prevents Rusting. 
 
 FINISH 
 DRY-GRINDING 
 
 AFTER being hardened, the balls are sent back to the dry- 
 grinding room, where they are subjected to what is 
 known as a finish dry-grinding operation. This is the 
 same as the rough dry-grinding that the balls receive before harden- 
 ing, except that it is done with a finer wheel which results 
 in removing the scale produced in hardening and also 
 reducing their diameters a little closer to the finished size. 
 For the rough-grinding operation, wheels of No. 40 grit are 
 employed. On the finish-grinding, the grit of the wheel varies 
 according to the size of the balls. Wheels of No. 60 grit are 
 used for all balls exceeding 5/16-inch in diameter, while for 
 smaller balls wheels of 90 or 100 grit are employed. In all cases 
 the machines are driven at the required number of revolutions 
 per minute to give a surface speed of 4500 to 5000 feet per minute 
 at the point where the ring wheel engages the balls. 
 
A VISITOR who is conducted through the plant of the 
 Hoover Steel Ball Co. finds it exceptionally easy to 
 become acquainted with what is going on in each shop, 
 because, although the plant is large, it is engaged in 
 making a single product, manufacturing operations on different 
 sizes of balls being conducted in essentially the same way through 
 out. This condition stands out in marked contrast to that found- 
 in plants engaged in the production of a variety of different 
 parts, as the manufacturing operations necessarily vary, making 
 it more difficult to see just what is being done. 
 
 c o c e * D m E c> F o 
 
 Fig. 18. (A) String of Hot- forged Bail Blanks. (B}Ball Blanks made by Cold- 
 heading Process. (C) Rough Dry-ground Balls. (D) Rough Dry-ground Balls after 
 Hardening. (E) Finish Dry-ground Balls. (F) Oil-rolled Balls. (G) Oil-ground 
 Balls. (H) Polished Balls ready for Inspection. 
 
 Fig. 18 shows the condition of the product at each step in 
 the process of manufacture, and it will be of interest to study 
 this illustration carefully, as it shows just what is done to the 
 balls by each operation through which they pass before comple- 
 tion. At A is shown a string of hot-forged ball blanks before 
 they have been sheared apart, and at B are illustrated two ball 
 blanks made by the cold-heading process. Blanks produced 
 by either of these methods are first subjected to a rough dry- 
 grinding operation which reduces them to an approximately 
 spherical form, as shown at C, although the surface is covered 
 with a multitude of small flats and scratches left by the grinding 
 wheel. At D are shown two rough-ground blanks after they 
 have been subjected to the process of heat-treatment, and it 
 will be noticed that their appearance is essentially the same as 
 that of the rough-ground blanks shown at C except that the 
 surface is darkened as a result of the heat treatment. Two 
 blanks are shown at E, which have received the finish dry- 
 grinding after being hardened, and it will be noticed that the 
 appearance of these blanks is the same as that of the rough- 
 
 33 
 
ground blanks C except that the flats and scratches are not so 
 pronounced. At F and G are shown two blanks that have gone 
 through a process known as ' 'oil-rolling" and two blanks that 
 have been through the oil-grinding process. The appearance of 
 both these balls is practically the' same except that the oilground 
 balls have been reduced to exactly the desired size. At H are 
 shown two finished balls after being polished, ready to be sent 
 on to the inspection department, where they will be subjected 
 to a series of rigid tests. 
 
 OIL-ROLLING BALLS IN 
 TUMBLING BARRELS 
 
 AFTER receiving the finish dry-grinding, the balls are of 
 approximately spherical form, but the surface is covered 
 with flat spots and scratches left by the grinding wheel 
 and there is still a considerable amount of excess metal on the 
 balls to be removed. The first step is to subject them to a process 
 known as oil-rolling which consists of tumbling a charge of balls 
 in an iron barrel containing oil and abrasive. This oil and 
 abrasive is refuse from machines on which a subsequent opera- 
 tion known as "oil-grinding" is performed; this operation will be 
 
 Fig. 19. View in Oil-rolling Department, showing Special Tumbling Barrels 
 of Large Capacity. 
 
 34 
 
described in detail later, and the nature of the abrasive will be 
 explained at that time. Most of the tumbling barrels used in 
 this department have capacity for a charge of 1500 pounds of 
 balls, and these were built especially for the Hoover Steel Ball 
 Co. ; but some 800-pound barrels made by the Baird Machine Co. 
 of Bridgeport, Conn., are also employed. Some of these barrels 
 are shown in operation in Fig. 19. The purpose of oil-rolling 
 is to smooth off the flats and scratches left by the dry-grinders 
 and to remove excess stock, about 0.004 inch being allowed 
 for removal in the oil-grinding operation. Balls up to 1^2-inch 
 in diameter are given this oil-rolling treatment. 
 
 It is necessary to leave the balls in these tumbling barrels 
 from twenty to thirty-six hours, according to the amount of 
 stock that must be removed, and as each ball rotates in such a 
 way that its entire surface is uniformly exposed to the action 
 
 Fig. 20. Oil-grinding Machine on which Final Grinding Operation is performed 
 
 Attention is called to Dials showing Approximate Time when Grinding 
 
 will be Finished, and Indicator for Testing Size of Balls. 
 
 35 
 
of the abrasive and of the balls adjacent to it, this treatment 
 results in the production of perfect spheres. When the time has 
 almost arrived at which the balls should be removed, a 
 number are selected at random from the contents of 
 each barrel, taken out and measured with a micrometer 
 in order to see how closely they approach the required size. 
 The oil-rolling is then continued with successive gaugings until 
 the balls have been reduced to the required dimension plus 0,004 
 inch, after which they are removed from the barrels, cleaned, 
 and then taken to the oil-grinding department. In reducing 
 balls by the process of oil-rolling, it occasionally becomes neces- 
 sary to add more abrasive to the supply of oil and abrasive ob- 
 tained from the oil-grinders. When this is done, No. 36 carborun- 
 dum is used, as this coarse-grain abrasive increases the speed at 
 which the balls are reduced to the required size. 
 
 HOW THE PROCESS OF OIL-GRINDING 
 IS CONDUCTED 
 
 THERE are two main grades of balls made in the Hoover 
 factory, known as "Micro-chrome" and "Commercial" 
 balls, the former being the better quality. Both grades are 
 reduced to the final size by the process known as "oil-grinding" 
 that is conducted on machines of the form shown in Figs. 20 
 
 Fig. 21. 
 
 Side and Front Views of Oil-Grinding Machine, 
 Illustrating Method of Operation. 
 
 36 
 
and 21. The construction and operation of the oil-grinding 
 machines will be best understood from Fig. 21, which shows 
 details of its construction. These machines are provided with 
 two iron rings A and J3, each of which has an annular groove cut in 
 it of a suitable size to accommodate the balls C to be ground. 
 It will be noted that there is a small groove at the bottom of the 
 annular groove in the lower ring A , which provides for holding a 
 supply of oil and abrasive. Ring A has the annular groove for the 
 balls cut at the bottom of a larger groove, and ring 5 has a flange 
 in which the ball groove is cut that drops into this large groove 
 in ring A ; the arrangement will be readily understood from the 
 illustration. It will, of course, be understood that the grinding 
 ring is rilled with balls, the number that constitutes a complete 
 charge varying according to the size of balls that are being 
 ground. 
 
 To provide for loading and unloading the machine, lower 
 ring A is drawn out onto a table D which is provided for that 
 purpose, and after a fresh charge of balls has been put in place 
 this ring is pushed back into position under the upper ring B 
 that is secured to the spindle of the machine. A sheet metal 
 shield is then pushed into place in front of the rings in order to 
 prevent splashing of the oil. Ring A is located in approximately 
 the desired position by means of a hole in the machine bed 
 into which an extension on the under side of ring A drops, but 
 the extension on this ring is a loose fit in the hole to allow ring 
 A to align itself properly with ring B. 
 
 The upper ring is secured to the spindle, and in order to 
 start the grinding operation it must be lowered into contact 
 with the balls carried in the annular groove of ring A. This is 
 accomplished by a rack on the spindle sleeve that meshes with 
 pinion E secured to lever F. 
 
 In order to raise ring B out of contact with the work so that 
 ring A may be drawn out onto turntable D, lever F is pulled down 
 into the horizontal position shown in the illustration. In this 
 position spring latch G drops into a notch on ring H that is 
 secured to the frame of the machine, thus holding ring B in the 
 suspended position. After the machine has been reloaded and 
 it is desired to drop ring B into contact with the work preparatory 
 to starting the grinding operation, spring latch G is withdrawn 
 
from the notch in ring H by pulling back grip / that is connected 
 to the end of the rod on which latch G is carried. Then the wheel 
 is lowered by gravity, care being taken to hold tight to the 
 crank at the end of lever F so that it is slowly raised to a vertical 
 position instead of flying up and allowing ring B to drop heavily 
 onto the balls carried in the lower ring. 
 
 It will be seen that there are three grinding heads provided 
 on each machine, and these are furnished with independent 
 tight and loose pulley drives, so that any head may be stopped 
 without interfering with the operation of the other two. This 
 is done by throwing the belt from the tight to the loose pulley 
 by means of lever /, which actuates the belt shifter. The oil- 
 grinders are provided with a dial similar to that of a clock, 
 so that the time for grinding can be observed; the grinding 
 operation usually takes from twenty to forty-five minutes, ac- 
 cording to the size of the balls and the amount of stock that 
 must be removed. When the machine is set up ready to start 
 the grinding operation, this dial is set to the approximate time at 
 which the grinding operation will be completed, and a little while 
 before this time is reached several balls are selected at random 
 from different points around the ring, and are measured with an 
 indicator to see how near they come to the required size. The 
 dials on the machine and the test indicator are shown in Fig. 20. 
 
 Fig. 22. Small Tumbling Barrels for Cleaning Balls in Sawdust, and Riddles foi 
 Separating Sawdust from Balls. 
 
 38 
 
CLEANING AND POLISHING 
 OIL-GROUND BALLS 
 
 AS SOON as the balls have been ground down to the desired 
 diameter, they are removed from the machine and taken 
 to tumbling barrels containing hardwood sawdust, in 
 which they are rolled for a sufficient length of time to clean off 
 all oil and abrasive. The charge in each tumbling barrel is then 
 taken out and put into riddles through which the sawdust is 
 sifted, as shown in Fig. 22, to separate it from the balls; the 
 balls next go to the tumbling barrels containing a mixture of oil 
 
 Fig. 23. Kegs in which Balls are Polished by Rolling in Leather. 
 
 39 
 
and Vienna lime. They are rolled in this mixture for a sufficient 
 length of time to give them a preliminary polish, after which 
 they are removed and again cleaned in tumbling barrels filled 
 with hardwood sawdust. The sawdust is sifted from the balls 
 in riddles, after which they are rolled for from twenty to twenty five- 
 minutes in kegs containing strips of kid similar to that from which 
 gloves are made, the arrangement of this polishing equipment 
 being shown in Fig. 23. Rolling the balls in this way gives them 
 a high polish, which is the final step in the process ; and the finished 
 balls are then ready to be taken to the inspection department. 
 
 The following data concerning conditions under which 
 oil-grinders are operated and abrasives and oils used on these 
 machines will prove of interest. It has been mentioned that 
 two main grades of balls are made, which are known as ' 'Micro- 
 chrome" and ' 'Commercial" the former being the better quality. 
 On the "Micro-chrome" balls the grinders are run at 195 revolutions 
 per minute and the abrasive used is a mixture of No. 3-F car- 
 borundum and "Atlantic Red" machine oil made by the Standard 
 Oil Co. On "Commercial" balls, the grinders are run at a speed of 
 325 revolutions per minute and the abrasive is an equal mixture 
 of Nos. 180 and 150 carborundum to which No. 4 "Road Oil" 
 is added, this oil also being the product of the Standard Oil Co. 
 Used oil and abrasive from the grinding machines is collected 
 and used in the tumbling barrels. 
 
 SPECIAL TREATMENT FOR 
 LARGE BALLS 
 
 CERTAIN variations from the practice described in the 
 preceding paragraphs are necessary in the case of large 
 sized balls which would be too heavy to handle in tumbling 
 barrels. For instance, "Commercial" balls over 1^-inch in diameter 
 and "Micro-chrome" balls over 5/g-inch in diameter are burnished 
 on oil-grinders running at high speed and in which very fine 
 abrasive and light oil are used instead of being subjected to a 
 tumbling operation in barrels containing a mixture of oil and 
 lime, as previously described. If large balls of this kind were 
 put in a tumbling barrel, there would be too much shock from 
 the balls striking one another; hence the variation in practice. 
 
 40 
 
PRODUCTION OF OIL- 
 ROLLED BALLS 
 
 IT HAS been explained that in the regular process of manu- 
 facture the balls go from the tumbling barrels to the oil- 
 grinders on which they are reduced to the required size 
 ready for polishing. There are some cheaper grades of balls, 
 however, that do not go to the oil-grinders; these balls are reduced 
 to size by oil-rolling in the tumbling barrels, after which they 
 are polished and sent to the inspection department. The method 
 of polishing is the same as that to which the better grades are 
 subjected, which was previously described. In oil-rolling the 
 balls, a mixture of No. 36 carborundum and No. 4 "Road Oil" 
 is used in the tumbling barrels. 
 
 MANUFACTURE OF BRASS, BRONZE 
 AND COPPER BALLS 
 
 IN ADDITION to its regular product, the Hoover Steel Ball 
 Co. does quite an extensive business in the manufacture of 
 brass, bronze and copper balls of various sizes. One important 
 use of these balls is for various forms of valves, although they find 
 a number of other applications. The general features of the 
 methods used in producing these balls are the same as those 
 employed in making steel balls, but there are certain modifications 
 which will prove of interest. Brass, bronze and copper ball blanks 
 up to 1 ^-inch in diameter are produced on Manville cold-headers, 
 and blanks for balls exceeding this size are cast. In the case 
 of very large balls the practice is often adopted of making the 
 blanks hollow, which is done by casting them with a sand core 
 that is subsequently removed. Then in order to prepare the 
 blank for finishing, the holes left by the core prints are drilled, 
 reamed and tapped so that threaded plugs may be screwed in. 
 These hollow ball blanks are then subjected to the regular process 
 of manufacture, and it is a difficult matter to detect the place 
 where the plugs have been screwed in. 
 
 As in the case of steel balls, these blanks are first subjected 
 to a process of dry-grinding to make them approximately spheri- 
 cal. Brass, bronze and copper balls are too soft to stand treatment 
 in tumbling barrels, as they would be covered with bruises from 
 impact with each other. After being dry-ground, they receive 
 
 41 
 
the regular process of oil-grinding and are then polished in 
 machines of the same design as those used for oil-grinding; but 
 in polishing, the balls are rolled in oil without any abrasive, 
 which results in giving them quite a high polish, although the 
 surface produced is not as highly finished as in the case of steel 
 balls which are subjected to burnishing and polishing operations 
 after being oil-ground. In treating brass, bronze and copper balls 
 in the oil-grinding machine, care must be taken not to subject 
 them to too great pressure, and in order to guard against this 
 the rings on the machine are filled with brass and steel balls 
 arranged alternately; the steel balls support the pressure of the 
 upper ring and the head on which it is carried, and allow the 
 balls to be ground and polished without being subjected to 
 sufficient pressure to flatten them. 
 
 INSPECTION OF FINISHED 
 BALLS 
 
 AFTER each step in the process of manufacture, the balls 
 receive a general inspection to make sure that nothing 
 is wrong with the adjustment of the machines or with the 
 material from which the balls are made that will prevent the 
 production of balls that come up to the standard. After receiv- 
 ing their final polish, the finished balls go to the inspection 
 department, where they are subjected to a number of searching 
 tests in order that all defective balls may be eliminated and 
 that those balls which pass inspection may be divided into 
 various grades according to the accuracy of their dimensions. 
 
 The first step is to clean the balls thoroughly, which is done 
 by placing them in metal baskets provided with long handles 
 so that the load of balls may be dipped into gasoline to remove 
 grease and particles of leather carried over from the polishing 
 department. After this washing, the balls are put into canvas 
 bags and rolled on a table so that the bags will absorb the 
 gasoline and wipe off the dirt. The balls are given a preliminary 
 wiping in one of these bags, after which they are placed in a 
 second bag that is cleaner and insures the removal of the last 
 traces of gasoline and dirt. 
 
MAKING PLATE 
 INSPECTION 
 
 AFTER cleaning, the first actual examination is conducted 
 on what are known as "inspection plates, "one of which is 
 shown in Fig. 24. These plates are used on benches that 
 run all the way around the two inspection rooms, so that ad- 
 vantage may be taken of the liberal amount of daylight provided 
 by the windows which extend from below the bench up to the 
 ceiling. The plates are made of glass and painted black. A 
 reflector is set up at the back of each inspection plate which 
 throws light on the balls; and a strip of thin flexible cardboard is 
 drawn back and forth beneath the balls to rotate them and 
 bring all surfaces into view. Several times while making this 
 inspection all the balls on the plate are rubbed with a cloth 
 to change their axes of rotation and insure exposing the whole 
 surface. The first step is to pick out balls having cracks, flats, 
 etc., and these are sold as seconds or scraps. 
 
 Fig. 24. Type of Glass Plate on which Preliminary Inspection is Conducted. 
 
 43 
 
During the next step in the process of inspection, attention 
 is paid to a white spot on each ball that is thrown from the 
 reflector at the back of the inspection plate. As previously 
 mentioned, a card is drawn back and forth under the plates 
 to make them revolve, and the inspectors first pick out what 
 are known as "wigglers," which is the name given to balls 
 that are out of round and go through a series of contortions 
 while being rolled. After this has been done, the balls on the 
 plate are gone over carefully and all those that show any defect 
 are picked out. During this process of inspection, the balls 
 are sorted into eight grades, as follows: (1) "Cracked," balls 
 that have received their cracks from any cause, (2) "Junk," 
 balls which have flats, holes, etc.; (3) "Rubbish," same 
 defects as (2) but not so bad; (4) "Dead soft," balls that 
 are covered with small pits caused by impact with hard balls 
 during the process of tumbling; (5) "Out of round," balls known 
 as "wigglers" by the inspectors; (6) "Fifth grade," balls with 
 small cuts and scratches on them; (7) "Fourth grade," balls 
 showing same defects as "Fifth grade," but not of so serious a 
 character; (8) Balls having no defects sufficiently serious to 
 be visible to the eye. The inspectors engaged in making the 
 plate inspection are provided with small magnets somewhat the 
 shape of a pencil with which they handle the balls with amazing 
 dexterity. 
 
 Disposal of the defective balls varies somewhat according to 
 their size. Many of the small balls with defects of the kind 
 referred to are sold to various manufacturers, according to the 
 class of service required of them. For instance, very poor balls 
 are sold to novelty makers. Other balls that are not good enough 
 for use in high-grade ball bearings are plenty good enough for 
 the use of certain manufacturers of hardware specialties, such 
 as roller bearing castors for furniture, roller bearing roller skates, 
 etc. Large balls that are found defective are returned to the 
 manufacturing department, where they are ground down to a 
 smaller size in order to remove the defects from the surface of 
 the metal ; and these balls are again carried through the regular 
 process of manufacture. 
 
 44 
 
GAUGING BALLS FOR 
 SIZE 
 
 BALLS that are used in annular bearings must be of abso- 
 lutely the same size in order to give satisfactory results. 
 If this is not the case, the large balls will support all the 
 load, and the undue amount of service to which they will be 
 subjected will cause them to be destroyed more rapidly than 
 would otherwise be the case. In order to fit properly in" the 
 races, it is desirable for the balls to be of exactly the specified 
 size, but provided all the balls are of the same size, they are 
 capable of giving very satisfactory results even though they 
 are either slightly over or under the specified size. In the 
 final process of inspection, the balls are gauged and sorted out 
 into different grades, according to whether they are of exactly 
 the specified size or somewhat under or over this size. Attention 
 is called to the fact that this variation in high-grade steel balls 
 does not exceed- a few ten- thousandths inch. As balls of the 
 different grades are all of the same size, they are capable of 
 giving perfectly satisfactory results. Some users of balls gauge 
 them at their own plants and make this sub-division, while others 
 buy gauged balls ready for assembly. 
 
 In gauging those balls which show no defects in conducting 
 the plate inspection, practice varies according to the size of 
 the balls, but in all cases the object is the same, namely, to 
 sort the balls out into those which are of absolutely the desired 
 size and those which vary by different degrees either above or 
 below the standard. Balls up to and including ^-inch in diameter 
 are gauged on automatic machines which sort them into seven 
 different grades, as follows: balls exceeding 0.0002 inch over size; 
 balls 0.0002 inch over size; balls 0.0001 inch over size; balls of the 
 specified size; balls 0.0001 inch under size; balls, 0.0002 inch 
 under size; and balls more than 0.0002 inch under size. Auto- 
 matic gauging machines are used for this grading, two batteries 
 of such machines being shown in Figs. 25 and 26. The balls 
 are placed in hoppers A, at the bottom of each of which there 
 is a plate in which a number of holes are drilled in a ring, these 
 holes being of slightly larger size than the balls to be gauged. 
 The plates are revolved, and as each hole comes into line with 
 the delivery tube, the ball carried in this hole drops into the 
 
 45 
 
Fig. 25. Close View of Battery of Automatic Gauging Machines 
 with Inclined Blades. 
 
 tube and runs down over gauge blades B which are set at a slight 
 angle to each other so that balls of the different sizes referred to 
 will drop between the gauge blades and enter tubes that carry 
 them to the proper drawers in the cabinets beneath. 
 
 It will be seen that two types of machines are shown in 
 Figs.. 25 and 26. In Fig. 25 the gauge blades are placed on an 
 incline so that the balls run over them by gravity, and as the 
 balls are always in contact with the gauge blades, the tubes lead- 
 ing to the drawers of the cabinet can be placed much closer 
 together than on the type of machine shown in Fig. 26, where 
 
 46 
 
Fig. 26. Close View of Battery of Automatic Gauging Machines 
 with Horizontal Blades. 
 
 the gauging blades are in a horizontal position. On the latter 
 type of machine an agitator is necessary to keep the balls moving 
 over the gauge blades. This agitator consists of a crank C and 
 connecting-rod D that actuates a link mechanism which causes 
 a horizontal bar to rise in the space between the gauging blades. 
 This bar rises slightly and then moves forward, carrying the 
 balls with it, after which the agitator bar slowly drops and 
 leaves the balls once more supported on the gauging blades. In 
 
 47 
 
this way the balls are moved along over successive tubes and 
 finally drop through between the gauging blades the position 
 being determined by the size of the balls so that different sizes 
 of balls are sorted out as previously described. A stop checks 
 the progress of the ball as it passes onto the gauging blades, and 
 prevents it from rolling too fast. The gauging blades are set by 
 master balls, in order to have the desired angle between them; 
 and before the balls are packed, the accuracy of the blade setting 
 is tested. 
 
 SPECIAL INDICATOR FOR 
 TESTING BALLS 
 
 FOR gauging balls larger than 5/s-inch in diameter use is 
 made of. an instrument of the form shown in Fig. 27. 
 This will be seen to consist of an ordinary Brown & 
 Sharpe dial test indicator accurate to 0.0001 inch, that is set 
 
 Fig. 27. 
 
 Dial Indicator with 10 to 1 Leverage Ratio, for Testing 
 Accuracy of Balls to 0.0001 Inch. 
 
 48 
 
up on the table on which is also carried a holder for the ball to 
 be tested. Connection between the ball and the dial test indicator 
 is made by a lever, the fulcrum of which is so placed as to give 
 a ratio of 1 to 10, and in this way readings obtained are accurate 
 to 0.0001 inch. The girls who conduct this inspection handle 
 the balls very rapidly and sort them out into different sizes 
 according to the amount of deviation from the normal size. 
 
 COUNTING AND PACKING 
 BALLS 
 
 IT IS necessary to use great care in handling finished balls to 
 prevent them from becoming rusty. On this account it 
 would not do to have the balls touched by the fingers. 
 For these reasons, several methods of mechanical counting have 
 been developed which give extremely satisfactory results. The 
 apparatus used for this mechanical counting is shown in 
 Fig. 28. The balls are placed in hopper A and dropped 
 down in holes in sliding plate B, which is pushed forward 
 so that the holes are under the hopper during the "loading" 
 
 Fig. 28. Methods used for Counting Balls Preparatory to Packing. 
 
 49 
 
period. The plate is then drawn forward to allow the balls to 
 drop out into a box placed to receive them. Each stroke of the 
 plate counts out one hundred balls, and plates for counting balls 
 of various sizes are made interchangeable so that all of them 
 may be used on a given machine. Balls up to J^-inch in diameter 
 are counted by the machine, and balls from 9/16 to J/g-inch in 
 diameter are counted mechanically by means of board C, into 
 the grooves of which the balls are loaded up to an index line. 
 Plates of this kind are made for various sizes of balls, and each 
 plate holds 500 balls. Large balls are counted by hand, care 
 being taken not to touch the balls with the bare fingers. After 
 counting, the balls are packed in cartons lined with waxed paper, 
 and these are packed in substantial wooden boxes for shipment. 
 
 RESEARCH 
 DEPARTMENT 
 
 IT IS obvious that in the tonnage manufacture of a product 
 that must meet such exact requirements as balls for use 
 in high-grade annular bearings, the greatest care must be 
 taken in the selection of raw material and in conducting each 
 step in the process of manufacture in order to produce balls 
 that will pass the inspection department. In addition to the 
 requirements of high-grade balls that were referred to in the 
 description of various examinations that are conducted by the 
 inspectors, it is absolutely necessary for the balls to be of uniform 
 hardness and strength because this is the only way of being 
 sure that all balls will possess the necessary durability and 
 elasticity. 
 
 Assurance must be obtained that the steel received at the 
 factory is of a suitable grade to produce balls that will fulfill 
 the specifications before manufacturing operations are started, 
 because if the balls were finished before it was found that they 
 were defective, the raw material and the labor involved in 
 converting this material into finished balls would be lost. Data 
 showing that the steel fulfills these specifications 'are obtained 
 from the results of tests conducted in the testing department 
 which is equipped with all the necessary apparatus for making 
 physical and chemical tests upon the raw material. In addition, 
 this department is referred to by heads of the various manufac- 
 
 50 
 
turing departments when any case of trouble arises, such as failure 
 of the balls to harden properly, the production of more than the 
 usual number of balls with cracks, and other troubles of this 
 kind. Some exceptionally interesting facts have been brought to 
 light as the result of work conducted in the metallurgical 
 department and chemical laboratory. 
 
 TESTING 
 
 RAW MATERIAL 
 
 THERE are sidings from the Ann Arbor Railroad entering 
 the plant so that cars may be run directly to the building 
 in which the raw material is received and to the building 
 where the finished balls are packed for shipment. The method 
 of procedure in testing raw material is the same for both bar 
 stock and coil, and consists of taking at random a number 
 of each kind in proportion to the quantity received and from 
 the end of each of which is cut a sample. One end of this 
 sample is etched in dilute hydrochloric acid for fifteen minutes. 
 After this has been done, the surface of the metal is carefully 
 examined to see that it is free from seams. The acid tends to 
 accentuate any surface defects that may be present, so that 
 those that might be invisible in the bar as it comes to the 
 plant can be quite easily seen after the treatment. In ball 
 manufacture it is highly important for the stock to have a 
 flawless surface, because any slight defects are carried right 
 through the process of manufacture and are likely to become 
 accentuated, with the result that balls produced from this stock 
 will be rejected by the inspectors. 
 
 The regular routine tests of the raw material inspected in 
 the laboratory also include a Brinell hardness test. This is 
 especially important in the case of "wire" under 11/16 inch in 
 diameter that is converted into ball blanks by the cold-heading 
 process, because excessive hardness of this material is likely 
 to give trouble through the breakage of the cut-off knives or 
 the dies used on the cold-headers. In order to give the best 
 possible results, stock for the cold-heading machine should have 
 a Brinell hardness of not over 170. A sufficient number of 
 samples to represent the average uniformity of the shipment 
 are examined for pipes, segration or decarbonization, and when 
 
 51 
 
necessary microphotographs are made, which together with 
 their accompaning reports, put definitely on record the condi- 
 tion of each shipment. Samples are also taken for chemical 
 analysis from each shipment and the percentage of the most 
 important elements determined, this being influenced by the 
 kind of material received and the effect of these elements on the 
 finished product. In cases where laboratory tests do not show 
 that the stock is defective, an "unloading ticket" is made out 
 and sent to the stock- room, authorizing the material to be 
 taken from the cars and placed in storage, ready to be drawn 
 out on requisition by the manufacturing department. 
 
 On the following pages are given our specifications for 
 coil and bar stock, and a consideration of these will show the 
 care taken in the selection of raw material used in the manu- 
 facture of Hoover steel balls. 
 
HOOVER STEEL BALL CO. 
 
 SPECIFICATION NO. 1. 
 Chrome-Carbon Steel Wire Cold Drawn. 
 
 ANNULMENTS: 
 
 1. This specification supercedes all previous specifications, or letters of instruction, 
 covering this material. 
 
 MANUFACTURE: 
 
 2. The material must be made by the Electric or Crucible process. 
 
 QUALITY: 
 
 3. The material must be of highest quality in every respect, of uniform composition, 
 and free from slag or other segregation. 
 
 The wire must be free from imperfections, such as pipes, seams, checks or lamina- 
 tions either on the surface or in the section of the wire. 
 
 WORKMANSHIP AND FINISH: 
 
 4. The wire must be of good workmanship, must have a good surface finish, and 
 must be true to diameter ordered within the limits of plus .002" and minus .002". 
 If the wire is out-of-round, the mean of the largest and smallest measured diameter 
 must be equal to the size ordered, but in no case can they exceed the limits of 
 plus .002" and minus .002". 
 
 COMPOSITION: 
 
 5. Upon receipt of the material at destination, drilling may be taken from the 
 several coils, selected at random, for analysis, and must show the composition 
 of the material to be uniform and within the following requirements. 
 
 Carbon .95 % to 1.05 % 
 
 Chromium .35% to .45% 
 
 Manganese .80% to .45% 
 
 Silicon .20% to .35% 
 
 Phosphorus under .025 % 
 
 Sulphur under .025% 
 
 CONDITIONS: 
 
 6. The material must be thoroughly and uniformly annealed and the fracture 
 must be close grained. 
 
 The Brinnell hardness (5 m/m Ball under 1000 Kg. pressure) must not exceed 
 170 at any point in the length or any point in the cross section of the wire, so 
 that when blanks made therefrom are cold upset into the form of a Ball, no 
 defects will open up in the outside surface of the Ball. 
 
 The wire must be free from any decarbonized surface and after hardening must 
 show a close grained velvety fracture. 
 
 COIL SIZE, WEIGHT AND CONDITION: 
 
 7. Coils must be reeled uniformly and the layers must be bound together securely 
 with separate tie wires to keep them in good shape during transportation so that 
 they can be unwound properly without tangling. If the ends of the coil are 
 tapered down or imperfect in any way, they must be "cropped" off. 
 
 Coils may be covered with a coating of oil or grease to protect them from excessive 
 
 rusting during transportation, but the coils must be free from any hard or gritty 
 
 foreign matter that would interfere with their proper operation in the heading 
 
 machine. 
 
 The coils must not be less than 18" inside diameter or greater than 34" outside 
 
 diameter. Wire of heavy cross section should be wound in as large a coil as 
 
 possible, but within the outside diameter limit given above. 
 
 The coils should weigh not less than 90 pounds or more than 110 pounds for wire 
 
 above .235" diameter. Coils of wire below .235" diameter may weigh as low as 
 
 70 pounds. 
 
 REMARKS: 
 
 8. Material which fails to meet the above requirements will be rejected and returned. 
 The manufacturers must pay all transportation charges on rejected material. 
 Ann Arbor, Mich., January 1st, 1917. 
 
 53 
 
HOOVER STEEL BALL CO. 
 
 SPECIFICATION NO. 5. 
 Chrome-Carbon Steel Bars Hot Rolled. 
 
 ANNULMENTS: 
 
 1 This specification supercedes all previous specifications or letters of instruction 
 covering this material. 
 
 MANUFACTURE: 
 
 2. The material must be made by the Electric or Crucible process. 
 
 QUALITY: 
 
 3. The material must be of highest quality in every respect, of uniform composition, 
 and free from slag or other segregation. 
 
 The bars must be free from imperfections such as pipes, seams, checks or lamina- 
 tions either on the surface or in the section of the bar. 
 
 WORKMANSHIP AND FINISH: 
 
 4. The bars must have as good a surface finish as is consistent with good hot rolling 
 practice. They must be free from excessive scale, and must be true to diameter 
 ordered within the following limits. 
 
 Minus and plus .005" for sizes under 13/16" diameter. 
 
 Minus and plus .010" for sizes over 13/16" diameter. 
 
 If the bar is slightly out-of-round, the mean of the largest and smallest measured 
 diameter must be within the minus and plus limits given above. 
 Appended to this specification is a table giving the prevailing sizes (diameter) 
 of stock which we use, and the corresponding decimal sizes. We reserve the 
 right to change this list from time to time when necessary but the order or contract 
 calling for the material will specify the size wanted. 
 
 As an example, if our order calls for 13/16" plus .010" (Decimal .823"), the 
 manufacturer may supply this as large as .833" diameter but no smaller than 
 .823" Diameter. 
 
 COMPOSITION: 
 
 5. Upon the receipt of material at destination, drillings may be taken from the 
 several bars, selected at random for analysis, and must show the composition 
 of the material to be uniform and within the following requirements. 
 
 Carbon .90% to 1.00% 
 
 Chromium .60% to .70% 
 
 Manganese .30 % to .45 % 
 
 Silicon .20% to .35% 
 
 Phosphorus under .025 % 
 
 Sulphur under .025 % 
 CONDITIONS: 
 
 6. The material must be thoroughly hotvworked to produce a fine grain and must 
 not, subsequent to this hot working, be subjected to a high temperature such 
 as would produce a coarse grain. 
 
 The surface of the bars must be free from decarbonization to the extent that upon 
 removing .005" from the diameter of the bar, the remaining section will retain 
 its full quota of carbon as called for under composition. 
 
 The bars must be cut to uniform lengths as ordered. A preferred length will be 
 specified on the order, also a minimum length and a maximum length, but in no 
 case may intermediate lengths be supplied. For example, a 13/16" plus .010" 
 diameter bar will be ordered cut to lengths 64", 73" and 82" with 73" as the 
 preferred length. 
 
 SHIPPING: 
 
 7. When two or more different sizes are shipped together in the same car, they must 
 be so arranged and located in the car that they will not become mixed during 
 transportation . 
 
 REMARKS: 
 
 8. Material which fails to meet the above requirements will be rejected and returned. 
 The manufacturers must pay all transportation charges on rejected material. 
 Ann Arbor, Mich., January 1st, 1917. 
 
 54 
 
TESTS OF SEAMY COLD- 
 DRAWN WIRE 
 
 IN DESCRIBING the inspecting of balls, reference was made 
 to the rejection of those in which cracks are found. 
 These exist almost entirely in balls up to and including 
 5/8-inch in diameter, the blanks for which are made by the cold- 
 heading process; it seldom happens that cracked balls are 
 found in sizes over j^-inch, blanks for which are made by the 
 process of hot-forging. A study of this subject reveals the 
 fact that after cold-heading, ball blanks very often had some 
 sort of crack, and in a great many cases these were quite 
 deep. At first it was thought that this was due to faulty 
 annealing or to some element in the steel, which had a tendency 
 to make the metal brittle, but subsequent investigation showed 
 that this was not the case. 
 
 STUDY OF SEAMS IN STEEL 
 BARS AND WIRE 
 
 DEFECTS revealed by etching the metal in dilute hydro- 
 chloric acid run lengthwise of the bar; sometimes these 
 extend for the entire length of the coil, while in other cases 
 only one end is found to be defective. For want of a better 
 name, the laboratory has called these defects ' 'seams," and it 
 has been proved that wire with seams will in all cases be split 
 to some extent during the process of cold-heading, while that 
 without seams will produce perfect balls in the cold-heading 
 machines. In some cases the cracks opened up in the balls while 
 cold-heading are not so deep that they cannot be eliminated dur- 
 ing the subsequent treatment to which the blanks are subjected ; 
 but in other cases it may happen that these splits in the blanks 
 are so deep that they reach below the surface of the finished 
 balls, in which case the balls will be rejected by the inspectors. 
 The investigation conducted in the laboratory relative to 
 troubles resulting from stock having seams or scratches have 
 developed the following information: (1) Cold-drawn wire 
 on which the surface is apparently quite smooth, and on which 
 no seams are visible, is found in many cases to possess minute 
 laps or seams which are made visible by etching with dilute 
 
 55 
 
hydrochloric acid. (2) Although these seams may not be deep 
 on the original wire, they are accentuated by the stretch which 
 the surface of the wire undergoes during the cold-heading 
 operation. (3) Such cracks are likely to be still further ac- 
 centuated in hardening, and in many cases they will cause the 
 ball to split in half. 
 
 In making a study of the effect of seams on the steel, 
 it is the practice, as previously mentioned, to etch the stock 
 with dilute hydrochloric acid for fifteen minutes. 
 
 The action of the acid first lays open any surface defects 
 which may be closed so tightly by the pressure of the cold- 
 drawing operation that they will be invisible to the eye 
 unless subjected to the acid treatment. The acid also makes 
 the cracks black, and subsequent grinding exposes the white 
 surface of the adjacent metal so that the crack is brought into 
 as great prominence as possible. 
 
 TESTING FOR SEAMS IN STOCK BY 
 APPLICATION OF PRESSURE 
 
 RECENTLY another test for revealing these seams has 
 been developed, which consists of upsetting short blanks 
 cut from the bars. These test blanks for wire having a 
 diameter of .275", are 7/16-inch high and are ordinarily 
 
 B 
 
 Fig. 33. (A) Samples cut from Steel with Seam in Surface, and Same Samples 
 
 partially and fully upset, indicating how Seam opens up through Application 
 
 of Pressure; (B) Similar Samples from Steel without Seam, which 
 
 show No Tendency to Split. 
 
 56 
 
subjected to a pressure of 20,000 pounds, which results in 
 flattening them out to a height of 3/16-inch, or to a 
 pressure of 50,000 pounds, which flattens them out to a 
 height of 3/32-inch. In all cases where there are seams in the 
 wire, these test samples are split open by this pressure, while a 
 perfect wire without any seams is not damaged by the treat- 
 ment. At A in Fig. 33 is shown a sample cut from wire con- 
 taining a seam and the same blank partially and fully upset; 
 it will be noticed that, although the seam in the wire is small, 
 it has been widened out considerably by the upsetting. At B 
 in the same illustration is shown a similar set from perfect wire, 
 comprising a blank and partially and fully upset samples, and 
 it will be seen that the upset sample does not show any tendency 
 to split. 
 
 In order to give some idea of the extent to which the seam 
 at A was deepened by the upsetting treatment, section a-b 
 through the blank and section c-d through the flat disk were 
 polished, and photomicrographs of these are shown in Fig. 34. 
 At A in Fig. 34 the seam in the original wire was about 0.010 
 inch in depth, while at B the depth of the seam after the blank 
 has been upset has been increased to approximately 0.050 inch. 
 From this it will be apparent that seams in the wire that do 
 not appear to be of sufficient depth to give trouble may become 
 very objectionable because of the tendency to deepen during 
 the conversion of the stock into ball blanks. Upset disk B 
 is of about the same diameter as a ball blank made from this 
 wire by the cold-heading process, so that it has been subjected 
 to about the same amount of stretch in upsetting that would 
 ordinarily take place in making a ball blank by the cold-heading 
 process. To show how trouble may develop in this way, a 
 ball 0.375-inch in diameter is produced from a blank 0.400 
 inch in diameter, so that the blank is reduced 0.025-inch on 
 the diameter, or approximately 0.013-inch on the radius. This 
 leaves 0.050 minus 0.013, or 0.037-inch of the split extending 
 below the surface of the finished ball, which will certainly lead 
 to its rejection by the inspectors. 
 
 It appears that hardness of the wire does not cause splitting 
 of the upset blank. Tests conducted with a view to establish- 
 ing this fact have shown that blanks made from seamless steel 
 
 57 
 
Fig. 34. Photomicrographs of Sections on Lines a-b and c-d in Fig. 33, 
 indicating Increase in Size of Seam through stretching of 
 Metal Surface in Upsetting. 
 
 with a high Brinell hardness number did not split under the 
 most severe conditions of upsetting, while blanks of metal 
 with a low Brinell hardness number, but with seams on their 
 surfaces, were frequently split during the process of cold-heading. 
 Specifications under which steel is purchased for the production 
 of ball blanks in cold-heading machines call for metal with 
 a hardness number not exceeding 170 as determined by the 
 Brinell method, but slightly harder stock is capable of being 
 worked with fairly satisfactory results. 
 
 HOW SEAMY STOCK ACTS IN 
 COLD-HEADING MACHINE 
 
 IN ORDER to confirm the accuracy of the conclusions reached 
 in regard to the action of seamy stock when worked up into 
 ball blanks in the cold-heading machines, tests were 
 conducted by placing coils that had bad seams in them on the 
 cold-headers and observing the kind of ball blanks that were 
 produced. In every case it was found that the blanks produced 
 from such stock showed bad cracks, as shown at A in Fig. 35. 
 In the inspection department, cracks found in finished balls 
 were at one time commonly referred to as "fire cracks" on the 
 assumption that they were developed during the process of heat- 
 treatment, but they are now designated as ' 'header cracks." In 
 
 58 
 
this illustration attention is called to the fact that at the top 
 and bottom of each ball blank there is a small projection formed 
 by pressing the metal into the knock-out pin hole in the header 
 dies. These have been termed ' "poles," and it will be noted 
 that the poles lie on the axis of the wire. Midway between 
 the two poles there is a band or "fin" caused by the metal being 
 forced out between the two header dies; and this fin has been 
 termed the "equator" of the ball. 
 
 Fig. 35. (A) Cold- header Ball Blanks, showing Splits running from Pole 
 
 to Pole, (B) Finished Balls produced from Blanks Split during 
 
 Cold- heading Operation. 
 
 It will be noted at A in Fig. 35 that the header cracks run 
 from pole to pole. At B in the same illustration are shown 
 some finished balls with the same kind of cracks, and it has 
 always been found that cracks in the finished balls have been 
 lengthened to a considerable extent, the ends of these cracks 
 terminating in very fine lines. This can be readily understood 
 when we consider that a small crack or fine sharp tool mark on a 
 piece to be hardened causes a weak spot which in many cases 
 will result in splitting the piece during the process of heat- 
 treatment. At A in Fig. 36 are shown some balls that were 
 picked out in the inspection department because they had fire 
 cracks; these were sent to the laboratory and fractured to 
 reveal the grain of the metal. It will be noticed particularly 
 in the third ball of the third line that at the extreme left of 
 the fracture there is a dark spot near the surface, which is 
 
 59 
 
the mark left by the original crack produced during the cold- 
 heading operation. Then to the extreme right there is a 
 fresh fracture which represents all the metal that the ball had 
 to hold it together after being hardened. 
 
 Attention is called to the fact that the middle of the ball is 
 black and oily; this is the hardening crack into which the oil 
 and abrasive have found their way during the oil-rolling and 
 
 rveo 
 
 Fig. 36. (A) Fractures of Balls shown at (B) in Fig. 35, showing Original 
 
 Header Crack, Fire Crack and Fracture of Uncracked Metal, (B) Etched 
 
 Balls, showing Crack from Pole to Pole and Crack on Equator. 
 
 grinding operations. The crack produced in cold-heading was 
 the cause of a further cracking of the ball during the process 
 of heat-treatment. At B in Fig. 36 are shown some finished 
 balls that were rejected by the inspectors because of cracks. 
 Before being photographed these balls were etched with dilute 
 hydrochloric acid, and it will be noticed that the cracks run 
 from pole to pole, and in some cases there are also secondary 
 cracks following the line of the equator. The way in which 
 these equatorial cracks are produced can best be explained by 
 reference to Fig. 37. At A is shown a longitudinal section of 
 the wire which has been etched with hydrochloric acid to 
 reveal the structure of the metal. Attention is called to the 
 lamellar structure, which is characteristic of any steel and is no 
 reflection upon its quality. These laminations run lengthwise of 
 the coil. At B is shown a section of a headed ball blank made 
 from a piece of this wire and etched with acid to bring up the 
 
 60 
 
Fig. 37. (A) Section of Steel Stock, showing Lamellar Structure; (B) Cross- 
 section of Cold-header Ball Blank, showing Distortion of Steel Structure; (C) 
 Cross-section of Header Cracked Ball Blank; (D) Ball Blank shown in Cross- 
 Section at (C); (E) Cold-header Ball Blank with Large Fin; (F) Perfect Cold- 
 header Ball Blank; (G) Etched Ball, showing End Grain of Steel at Equator; 
 (H) Etched Ball, showing End Grain of Steel at Pole. 
 
 structure of the metal. Here it will be seen that the lamina- 
 tions have arranged themselves in a manner similar to magnetic 
 lines of force running from pole to pole. 
 
 At D and E are shown header-cracked ball blanks, and it 
 will be noticed that blank E shows an unusually large fin on 
 one side. Blank D shows the split on one side and also a por- 
 tion of the split extending into the fin. Blank F is properly 
 headed and shows no crack or excessively large fins. Referring 
 to the view shown at C, which is a cross-section of blank D, 
 it will be seen that the split extends into the fin, and it will 
 also be noted that the crack extends below the surface of the ball, 
 although it comes to the surface at each end at points near 
 the poles. This is due to the fact that the split does not penetrate 
 the ball at right angles to the surface, but runs on a slant. Instead 
 of compressing and filling up the open space in the ball, material 
 has been pressed outward and made a large fin; when this fin 
 
 61 
 
is ground away, the crack is quite evident. At G and H are 
 shown finished balls that have been etched with acid to show the 
 grain at the equator and at the poles, respectively. 
 
 HEADED BLANK 
 
 FINISHED BALL 
 
 Fig. 38. Diagram illustrating Distortion of Steel Structure in Cold-header 
 Ball Blank similar to that shown at (B) in Fig. 37. 
 
 Referring again to the sectional view of the wire shown 
 at A in Fig. 37, and also to the cross-section of a ball blank 
 made from this wire shown at B, it will be seen that the structure 
 of the steel has been greatly disturbed during the process of 
 cold-heading to produce the ball blank. In Fig. 38 is shown 
 diagrammatically the way in which this disturbance takes 
 place. It will be seen that the ends of the fibers come to the 
 surface at the poles and at both sides of the equatorial fin; 
 and when the ball is etched the steel is attacked more rapidly 
 at these points. The peculiar marks shown at G and H in Fig. 37 
 are the result of this disturbance of structure. The conclusion has 
 been reached that when a ball with so-called ' 'header cracks" is 
 etched with acid and shows two end poles and two equatorial marks 
 with a wide crack running from pole to pole or possibly a secondary 
 crack running between the two equators, this crack is a header 
 crack which is caused by a seam or lap in the steel from which 
 the ball was made. The internal stress due to the structural 
 distortion illustrated in Fig. 38 is completely normalized by the 
 
annealing treatment to which all Hoover balls are subjected. 
 A number of these headed balls with header cracks were 
 heated in an electric furnace in the laboratory and quenched 
 in water at 1500 degrees F. ; every ball was further cracked by 
 this treatment, and several of them fell in half or were easily 
 broken by a light hammer blow. Another lot of headed balls 
 with no header cracks was heated in the electric furnace and 
 quenched in water at 1600 degrees F., and not a ball was cracked 
 in hardening. Balls quenched in water at 1500 degrees F. that 
 broke during the process of heat-treatment are shown at A in Fig. 
 39, while the balls quenched in water at 1600 degrees F., without 
 damage are shown at B in the same illustration. At this excessive 
 temperature the grain of the metal was coarsened, but no hard- 
 ening cracks were produced and it required considerable force 
 to break the balls. Several finished balls were next selected 
 in the inspection department that showed very slight header 
 cracks. These balls were hardened at 1500 degrees F. and cracked 
 in the process of hardening exactly as before. The characteristic 
 black mark left by the original header crack is shown at one side 
 of the balls at C in Fig. 39. Another lot of finished balls showing 
 no header cracks was hardened at 1600 degrees F. and none 
 of the balls was cracked, views of the fractured surfaces of these 
 balls being shown at D in Fig. 39. This confirmed the accuracy 
 of previous tests, and from these data the following conclusions 
 were drawn: (1) The header crack forms a weak spot, so that 
 when the ball is hardened, even at the proper temperature, 
 
 
 
 ? 
 
 
 
 Fig. 39. (A) Fractures of Header Cracked Balls that Split when re-heat-treated 
 in Laboratory at 1500 Degrees F., (B) Fractures of Perfect Balls that did not 
 Split when re-heat-treated at 1600 Degrees F.; (C) Fractures of Balls with 
 Slight Cracks which broke when re- heat-treated at 1500 Degrees F., (D) 
 Fractures of Perfect Balls that did not break when re- heat-treated at 1600 
 
 Degrees F. 
 
 63 
 
what the inspectors call a "fire crack" is likely to be produced. 
 (2) A ball with no header cracks can be hardened at an excessively 
 high temperature without producing a fire crack. 
 
 Another hardening test was made with four samples of wire, 
 two pieces of which showed seams, and two pieces that did not. 
 The seamy pieces of wire were quenched at a temperature of 
 about 1500 degrees F. in water and hardening cracks developed 
 along the seams. The two pieces without seams were quenched 
 in water at a temperature of 1600 degrees F. and no cracks 
 developed. All these tests show that with small blanks with- 
 out any header cracks, it is practically impossible to produce 
 fire cracks in the automatic hardening furnaces; when cracks 
 are produced they are started in cold-heading and not through 
 the process of heat-treatment. The shape of the ball is in its 
 favor, as it insures uniform quenching and a minimum of internal 
 strain. Application of too high a temperature would tend to 
 increase the size of the grain in the steel and make it brittle 
 and unfit for use, but it would not produce hardening cracks. 
 
 EFFECT OF HARDNESS 
 OF WIRE 
 
 WHEN the wire used in making ball blanks on cold-headers 
 is too hard, there is a tendency for it to break off instead 
 of shearing as it should. When trouble of this sort is 
 encountered, it is likely to be accentuated by the fact that the 
 blank is often carried to the heading die in a sidewise position, 
 which results in the development of abnormal pressure in the 
 die. Working hard stock of this kind results in breaking the 
 cut-off knife or the dies on the cold-heading machine. This 
 condition of excessive hardness does not usually exist for 
 the entire length of the coil ; wire may shear off and head nicely 
 for some time, when suddenly a hard spot will be reached and 
 then the dies or the cut-off knife is likely to suffer. After this 
 hard spot has been passed, the wire may be all right for another 
 period of considerable duration. With the view of showing 
 the relative condition of hard and soft spots in the wire, slugs 
 of metal were selected at a point where trouble was encountered 
 from this cause, and again at a point where the operation of 
 the cold-header was entirely satisfactory. These were tested 
 
 64 
 
Fig. 40. (A) Fracture of Hard Metal Slug; (B) Fracture of Normal Metal Slug; 
 
 (C) Etched Surface of Hard Steel magnified 5.25 Diameters Attention is 
 
 called to Decarbonization at Circumference; (D) Etched Surface of Normal 
 
 Steel with No Decarbonization at Circumference. 
 
 by the Brinell method and it was found that the hard slugs 
 had a Brinell hardness number of 215, while the soft slugs only 
 showed a Brinell hardness number of 190. The latter is really 
 higher than it should be, as 170 is specified for steel to be used in 
 cold-heading machines. 
 
 "Fig. 41. (A) Decarbonized Surface shown at (C) in Fig. 40 magnified to Sixty- 
 two Diameters; (B) Same Magnification as at (A), showing Condition of 
 Practically No Decarbonization. 
 
 65 
 
At A in Fig. 40 is shown the fresh fracture of a slug of hard 
 metal and attention is called to the coarse grain as compared 
 with the finer grain of the normal steel shown at B. The hard 
 specimen was very brittle and easy to break, while the normal 
 steel was tough and capable of bending considerably before 
 being broken. Specimens of these two steels were next polished 
 and etched, with the result shown at C and D, respectively. 
 These are transverse sections cut through the wire, and attention 
 is called to the coarse grain of the steel shown at C\ the ring at the 
 surface is a band of decarbonized steel apparently produced by 
 the application of too high an annealing temperature. The 
 normal steel shown at D has a fine grain and there is no 
 indication of decarbonization. 
 
 At A in Fig. 41 is shown the decarbonized band of steel sur- 
 rounding section C in Fig. 40, which is magnified to 62 diameters, 
 instead of 5.25 diameters, as in the case of the previous illustra- 
 tion. It will be noted that the extreme edge of this photomicro- 
 graph is somewhat indistinct, owing to the slightly rounded 
 edge formed while polishing the specimen. The decarbonized 
 surface of this stock would not be entirely removed in the process 
 of grinding, and would result 'in the production of either soft 
 balls or balls with soft spots. AtB, Fig. 41, we have the condition 
 where there is practically no loss of carbon at the surface. 
 At A and B in Fig. 42 is seen a decided contrast between the 
 
 Fig. 42. (A) Pronounced Pearlitic Structure with large cells and Boundaries 
 of excess Cementite, indicating Application of too High an Annealing Temper- 
 ature; (B) Fine-grained Structure, showing Condition obtained with Proper 
 Annealing Temperature. Both Samples magnified to 225 Diameters. 
 
 66 
 
structure of the slug of hard metal and that taken from the 
 normal wire. At A there is a pronounced pearlitic structure 
 with large cells and distinct boundaries of excess cementite, 
 which also indicates the application of too high an annealing 
 temperature. At B the structure is fine grained, which is the 
 condition produced by employing the proper annealing 
 temperature. Where lack of uniformity is discovered in 
 the hardness of the wire, it is probably due to application of too 
 high an annealing temperature. 
 
 CAUSE OF SOFT SPOTS 
 ON BALLS 
 
 SOME valuable discoveries have been made in the laboratory 
 as a result of work that was started with some other object 
 in view. For instance, an investigation that was started 
 with the view of determining the effect of slight seams found in 
 a certain shipment of steel at the time of the preliminary tests. 
 These seams were not considered serious enough to justify rejec- 
 tion of the steel, but after the first lot of blanks had been finish 
 dry ground, tests were made. This was done by etching a number 
 of balls in dilute hydrochloric acid, to see if the seams had been 
 removed in grinding. The balls were immersed in the solution, 
 and after being etched for fifteen or twenty minutes they were 
 removed, and cleaned. 
 
 When treated in this way, the balls are usually a light gray 
 color over their entire surface, but the particular lot of balls 
 referred to could not be uniformly etched. At first it was thought 
 that a film of grease or some other foreign matter was interfering 
 with the action of the acid, but a second trial resulted in the 
 same mottled appearance of the etched balls. Part of the surface 
 was light gray, while other parts were dark gray and almost black. 
 Balls with these spots are shown in Fig. 43 and no matter how 
 often they were re-etched, the same spots always appeared and 
 they were of the same outline as those developed by the pre- 
 vious etching. Some of the unetched samples were examined, 
 and it was found that a considerable quantity of black scale 
 was left on the balls, i. e., the forging had not been cleaned 
 up properly after the finish dry-grinding. At this stage the ball 
 
 67 
 
Fig. 43. Finish Dry-ground Balls after being etched with Hydrochloric Acid, 
 showing Mottled Appearance due to Soft Spots produced by Decarbonization 
 
 of Steel. 
 
 consistently measured 1.135 inch, i. e., within 0.010 inch of the 
 finished size -\Y% inch. 
 
 Thus far results seemed to indicate that the forging blanks 
 were under size, so five samples were selected at random and 
 measured. The measurements of these five blanks are given 
 in Table 4, reference to which will show that dimensions A across 
 the poles and dimension B near the poles were of ample size; 
 and the surfaces at or close to the poles were also smooth and 
 well filled out. However, these conditions did not exist around 
 the equator, where it will be seen that dimension C was scant 
 in many balls, and additional trouble was caused by the fact 
 that the surface was very rough and covered with "hills" and 
 ' Valleys." In making these equatorial measurements with a 
 micrometer, the distance is taken across the tops of the ' 'hills," 
 while the dimensions in the 'Valleys" will obviously be consider- 
 ably less. It is doubtful, therefore, whether three out of five of 
 
 68 
 
these samples would clean up in the rough dry-grinding. A 
 re-examination of the etched dry-ground balls showed that the 
 peculiar black spots did not appear at the poles as frequently 
 as they did at the equator; and when a new file was applied to 
 the black spots shown in Fig. 43, it was found that they were 
 dead soft, while the light gray spots were very hard. The 
 sclerescope hardness of ten of these balls was taken and averaged 
 as follows: black spots, 48; gray spots, 70. 
 
 Table IV. Measurements of Balls across Poles, near 
 Poles and at Equator. 
 
 1.168 
 1.169 
 1.170 
 
 1.166 
 1.161 
 1.151 
 1.175 
 1.152 
 
 1.161 
 1.167 
 1.145 
 1.172 
 1.170 
 
 1.160 
 1.163 
 1.145 
 1.170 
 1.158 
 
 1.166 
 .162 
 .150 
 .159 
 
 .167 
 
 The reason for these spots will be understood from the 
 photomicrographs presented at A and B in Fig. 44, which are 
 taken from polished surfaces at the extreme outer surface of 
 the black and white spots on the balls. These surfaces were 
 prepared and photographed in exactly the same way; instead 
 of polishing a flat on the ball, the spherical surface was polished, 
 because a flat surface having any width whatever would also 
 be at a considerable depth below the surface of the ball, and 
 would not reveal conditions that it was desired to investigate. 
 Difficulty was experienced in polishing this spherical surface, 
 and so the photographs reproduced in Fig. 44 show polish marks 
 rather too distinctly, but these have no bearing upon the accuracy 
 of the results obtained in the investigation. At A is shown a 
 large percentage of free ferrite, indicating a hypo-eutectoid 
 structure of about 0.30 to 0.40 per cent carbon; in other words, 
 the metal is similar to a mild steel. On the other hand, the 
 condition revealed at B is practically a pure eutectoid structure 
 of pearlite, this steel having from 0.85 to 0.90 per cent carbon. 
 Specifications under which the steel is purchased call for from 
 0.95 to 1.05 per cent of carbon, so that in this regard it fulfills 
 requirements. 
 
 69 
 
Fig. 44. (A) Photomicrograph of Black Soft Spots on Balls shown in Fig. 43, 
 
 showing Large Percentage of Free Ferrite or Hypo-eutectoid Structure; (B) 
 
 Photomicrograph of Hard White Spots on Balls shown in Fig, 43, indicating 
 
 the Desired Eutectoid Structure. 
 
 A further test was conducted by preparing flat surfaces of 
 considerable depth on the balls and examining these under the 
 microscope; and in both cases it was found that photomicro- 
 graphs obtained in this way indicated metal containing its full 
 percentage of carbon. Hardness tests show that the metal 
 directly under the decarbonized spot is soft and indicate 
 not only that the decarbonized surface fails to harden, but that 
 it also forms a sort of insulator and retards the proper 
 hardening of the eutectoid steel beneath it. Therefore, the 
 decarbonization plus its effects means a soft area of decided 
 depth, so deep, in fact, that when the ball is finished the 
 soft spot still appears. Having reached this conclusion, specimens 
 of the raw material were prepared by cutting sections trans- 
 versely from the bar, and these were prepared and photographed 
 Fig. 45 illustrating the conditions that were revealed in this way. 
 It will be noted that the steel shown at A is decarbonized to a 
 depth of 0.010 inch 0.020 inch on the diameter of the ball- 
 while in the sample shown at B there is no decarbonization. It 
 was this steel with the decarbonized surface that produced balls 
 showing soft spots in the tests. 
 
 Fifty of these balls showing soft spots were taken to the 
 laboratory, where they were again heat-treated, and the result 
 was that the balls came out hard. It was not considered, how- 
 ever, that this indicated defective heat-treatment in the process 
 
 70 
 
Fig. 45. (A) Photomicrograph of Transverse Section of Decarbonized Edge of 
 Steel Magnification, 125 Diameters; (B) Photomicrograph of Transverse 
 Section of Steel showing No Decarbonization Magnification, 125 Diameters. 
 
 of manufacture, because it might have happened that the 
 operation of finish dry-grinding removed enough metal from 
 the surface so that the balls would harden properly, although 
 they were prevented from doing so at the time of the original 
 treatment by the decarbonized steel that covered the surface 
 of the balls. Because of the oval shape of the forgings, the depth 
 of decarbonization varies at different spots on the rough-ground 
 surface of the balls; for example, at the poles there is little or no 
 decarbonization, while around the equator the decarbonization 
 is quite deep. When a ball is reduced to the finished size, the 
 following conditions will be found : (1) decarbonized areas where 
 the original decarbonization on the rough ball was deep; (2) 
 soft areas where the original decarbonization on the rough ball 
 was shallow; (3) hard areas where there was little or no de- 
 carbonization on the rough ball. In cases (2) and (3) the steel 
 has its full percentage of carbon, and when the balls are rehard- 
 ened some of the soft spots disappear, while the spots devoid 
 of carbon still remain soft. It would be possible to reduce these 
 balls to a smaller size and reclaim them by rehardening, but this 
 subsequent heat-treatment has a tendency to roughen their 
 surface slightly, which necessitates subsequent grinding opera- 
 tions jhat would probably reduce the diameter from 0.015 
 to 0.020 inch, so that allowance must be made for this 
 reduction in size. 
 
 71 
 
To overcome trouble from the use of stock that is decarbon- 
 ized at the surface, special forging dies were made which produce 
 oversize ball blanks, so that the diameter at the equator measures 
 from 0.060 to 0.080 inch more than that of the standard finished 
 balls. The same stock forged in a regular die would make a 
 blank 0.025 inch to 0.035 inch larger than the finished size. In 
 the present case it is found that these would not clean up, but 
 left soft and decarbonized spots on the surface of the finished 
 ball. For this reason, the special forging dies were produced. 
 This practice was adopted because, owing to the slow deliveries 
 made by the steel mills, it was desired not to reject any steel of 
 this size that could possibly be used. 
 
 DEVELOPMENT OF A DEVICE FOR 
 SEPARATING HARD AND SOFT BALLS 
 
 OWING to shipment to the factory of a large quantity of 
 low carbon steel through an error made at the steel mills, 
 and which escaped the rigid sampling to which every 
 car of steel received at the Hoover plant is subject, about 
 seven tons of this material was converted into ball blanks 
 before it was attempted to harden them. This was due to 
 the fact that a large supply of blanks of the same sizes 
 had accumulated, and these were naturally sent through the 
 heat-treating department ahead of blanks made from this 
 shipment of steel. When the blanks had been heat-treated, they 
 were tested in order to determine the nature of the results 
 obtained, and while a number of balls broke with a fine-grained 
 fracture and showed a hardness that was all that could be desired, 
 almost 10 per cent of the balls were found to be dead soft. When 
 these balls were subjected to pressure they flattened out instead 
 of breaking in the usual way. A peculiar mottled effect was 
 noted on the balls found to be file hard, while the soft balls 
 were a dull black color ; but this difference in appearance was not 
 sufficiently marked to enable the balls to be separated, and even 
 had this been possible, the length of time required to eliminate 
 defective balls by this method would have been prohibitive. 
 With a view to overcoming this difficulty, a device was de- 
 veloped which is shown in diagrammatic form in Fig. 46. Its 
 principle of operation is based on the fact that when balls are 
 
dropped on a hardened steel anvil there is considerable difference 
 in the height of the rebound of hard and soft balls. The balls 
 to be tested roll down an incline plane and drop upon a hardened 
 steel block, from which they rebound; the hard balls rise high 
 enough to pass over a "hurdle" into a box, while the soft balls 
 do not reach this height and are deposited in a second box. To 
 test the efficiency of this device, 119 balls taken from one of the 
 tote pans in the shop were run through the drop test; 79 dropped 
 into the "hard bin" and 40 into the "soft bin." These balls were 
 once more thoroughly mixed and again run through the ap- 
 paratus with the same result as in the previous case. Additional 
 trials confirmed the accuracy of the apparatus. This method of 
 separation proved so satisfactory that a regular equipment 
 has been built for use in the dry-grinding room, where it is 
 used for separating hard and soft balls. 
 
 
 / ! 
 
 
 1 
 
 HARD O 
 BALLS , f : 
 
 "ji^lr 
 
 ZT\ 47" i 
 
 _,__47 .4 >, 
 
 -t - \ 
 
 i S& / <**' 
 3lW x \ t 
 
 
 
 SOFT- 
 BALLS 
 
 \\ / 
 
 X 
 
 
 
 yn&sj 
 
 HARD 
 
 A ANVIL" | 
 
 
 
 Fig. 46. Diagram illustrating Principle of Apparatus developed for 
 Automatic Separation of %-inch Hard and Soft Balls. 
 
 CONCLUSION 
 
 MANY of the cases of trouble to which reference has been 
 made are of rare occurrence, but it is obvious that they 
 exert a powerful influence on the quality of the product 
 turned out in the factory. Also, the conditions brought to light 
 by these investigations are exceptionally interesting. It was on 
 
 73 
 
this account that they were selected for discussion in the present 
 treatise, in connection with the regular work of the laboratory, 
 and not because they really belong to a description of routine 
 work of testing the raw material and product of a factory en- 
 gaged in the manufacture of steel balls. 
 
 CRUSHING AND DEFORMATION 
 TESTS 
 
 THE old method of determining the crushing load of a 
 ball was to test a single ball between two hardened steel 
 plates. It is obvious that if the plates were not of uniform 
 hardness the crushing loads would also lack uniformity, because 
 the plates would be indented during the test and the softer plate, 
 being indented the greater, would present more supporting area 
 to the ball, and thereby increase its resistance to crushing. 
 Inability to produce plates of absolute uniformity puts this 
 method out of the question as a standard test. 
 
 The Hoover Steel Ball Co. has developed the Three-Ball 
 test as a standard. Three balls super-imposed, as shown in 
 the illustration, are subjected to a gradually increasing pressure 
 until rupture occurs, and the amount of pressure is recorded at 
 this point. 
 
 We wish to emphasize that testing by the Three-Ball method 
 will yield results somewhat lower than by the plate test by 
 reason of the fact that the contact points are very minute and 
 therefore the pressure per unit of area is tremendous. 
 
 The plate test is very often used by some ball manufacturers 
 to deceive the buyer by making him believe he is getting a better 
 ball by reason of the high crushing load. 
 
 Believing that a table of crushing loads would be of very 
 little value to our customers, as a guide to determine the safe 
 working load of the ball, and that such a table might be mislead- 
 ing, we refrain from publishing same. 
 
 It is evident that the safe working load that a ball will 
 carry depends not only upon the quality of the ball, but also 
 upon the type of bearing in which it is to run, the shape, material 
 and finish of the ball race, etc. 
 
 74 
 
We stand ready at all times, however, to give our customers 
 information as to crushing strength and elastic strength, and 
 to give our opinion as to the most suitable size and type of 
 ball for any particular work, after we have received full particulars 
 of the bearing and the nature of the work for which it is required, 
 load, speed, etc. 
 
 Ball Crushing Apparatus 
 
 75 
 
76 
 
I 
 I 
 
 I* 
 
 Is 
 
 Cft; 
 Sfe 
 
 ii 
 
 77 
 
78 
 
Fracture of a hard surface tough center ball. Note the flattening and cone of rupture at the points 
 of contact, formed when the balls were crushed. 
 
 HOOVER STEEL BALLS HAVE A HARD 
 SURFACE AND A TOUGH CENTRE 
 
 CO-OPERATION with our customers and extensive service 
 tests of our balls have developed a method of heat 
 treatment which while simple in its theory is difficult of 
 practical control, and this control is only made possible by 
 automatic hardening machines which eliminate the personal 
 element. 
 
 It is not a difficult matter to harden a ball clear through 
 to the centre, as it is merely a question of quenching at a tempera- 
 ture sufficiently high to harden the interior, but this method is 
 without due regard to the exterior. Hardening a ball under 
 these conditions produces an over-heated exterior which is 
 necessarily brittle, and strength cannot be restored by tempering. 
 
 Hoover balls are heat-treated to produce a sufficiently 
 hard exterior and a tough semi-hard interior, producing the 
 qualities most needed in ball bearings. The surface is sufficiently 
 hard to withstand wear, without being so brittle as to flake or 
 peel. The interior is sufficiently tough and elastic to stand the 
 strain of heavy loads. 
 
 This type of ball must not be confused with a low grade 
 steel ball "case hardened" on the surface and with a soft core. 
 
 When we speak of hard surface and tough centre we refer 
 to a high grade alloy steel in which there is a gradual merging 
 of hardness at the surface to semi-hardness at the core, without 
 a distinct line of demarkation as in the "case hardened" ball. 
 
 The above photograph shows the fracture of a hard surface* 
 tough centre ball, of which the Hoover Steel Ball Co. is the 
 exponent. 
 
SMOOTH AND MIRROR-LIKE surface finish must be maintained in every ball 
 leaving our plant and to this end extensive microscopic examinations are regularly 
 made. The constancy and effect of the many abrasive materials used are kept under 
 rigid control. 
 
 Microphotographs 1, 2, 3 and 4 show the highly magnified surfaces of several 
 makes of balls for comparison. 
 
 No. 1 shows the Hoover standard. 
 
 At the top of this page is shown the apparatus on which microscopic examinations 
 and photographs are made. 
 
 80 
 
CHEMICAL 
 LABORATORY 
 
 WE HAVE an up-to-date Chemical Laboratory which co- 
 operates with the Metallurgical Department in the 
 control of the raw material which is used in the pro- 
 duction of the Hoover Steel Balls, as well as the solution of the 
 different problems which are constantly arising in a plant that is 
 aiming to produce a product as near perfect as scientific methods 
 and human efficiency can make it. 
 
 Drillings, and in some cases millings, are taken from the 
 samples which are brought to the Metallurgical Department 
 from each shipment of steel which is received at the plant, 
 whether for the production of balls or to be used for the produc- 
 tion of machine parts that may be required in the plant. These 
 drillings, or millings, as the case may be, are analyzed in the 
 Laboratory. The percentage of carbon, manganese, phosphorus, 
 sulphur and chromium is determined in all steel used for the 
 production of balls. In the case of Header Die Steel, which is 
 used to make the dies that forge the balls, the percentage of 
 carbon is determined on each bar, and if it should be an alloy 
 steel other elements are determined, and a complete analysis 
 is made on one sample taken from the shipment. 
 
 Samples are also taken from each shipment of Brass and 
 Bronze Wire or Rod, which is received at the plant, and from 
 which are made our Brass and Bronze Balls. These are analyzed 
 to determine the quantities of tin, lead, copper, iron, zinc, and 
 also any elements that might have an injurious effect on the 
 service rendered by the finished balls. As the composition in 
 a great measure controls the hardness, resistance to abrasion, 
 resistance to corrosion, and therefore the life of the finished balls, 
 it can be seen how very important it is that a careful analysis 
 should be made of all raw material from which these balls are 
 produced. 
 
 A great many oils and greases are used in the plant for 
 various purposes, and these must be all carefully tested and 
 graded. For instance, the finished balls are packed in a mixture 
 of an oil and a grease and it is very important that these should 
 be absolutely free from any element such as acids, sulphides or 
 water, as any of these would etch and oxidize the surface of the 
 
 81 
 
balls in a short time so that they would be rendered useless for 
 our customers. The same thing applies to the paper used in 
 lining the boxes in which the balls are packed for shipment. The 
 leather used to put the final polish on the balls must also be free 
 from acid and moisture, or they would be rejected by the Inspec- 
 tion Department on account of rust spots. A surface so highly 
 finished is very sensitive and must be carefully protected not 
 only during production but in the packing, and this is the reason 
 the surface of the balls is so carefully covered with oil to prevent 
 even the atmospheric moisture affecting them. 
 
 Fuels in the form of coal, oil and gas are also graded and 
 combustion problems investigated in this department. The effect 
 on the finished product of the different modes of handling the 
 balls during production must be considered, and even the humi- 
 dity of the room in which they are inspected has to be reckoned 
 with. It can, therefore, be seen that besides the routine control 
 of raw material, etc., a number of interesting questions arise 
 from time to time which the Chemical Laboratory must assist 
 in solving. 
 
* 
 
 gS 
 
 S-2 
 c e,sc 
 
 g 
 s l: 
 
 a 
 
 S B te 
 
 II 
 
 s ? 
 S g! 
 
 ^ C o, 
 
 
 
 c o^S e e 
 
 84 
 
I: 
 
 li 
 
 if 
 
 * 
 
 I* 
 
 IS 
 
 s! 
 
 5* 
 
 si 
 
 5! 
 a 
 
 <> c 
 
 ! 
 
 Sl 
 
 
11: 
 
 "S.B 
 
 I Is 
 
 
 
 
 86 
 
s 
 si 
 
 h 
 
 I! 
 
 ti 
 
 87 
 
88 
 
89 
 
e fc 
 
 a v. ^~ 
 
 ill! 
 
 5 h *S 
 
 . 
 
 1111! 
 
 
 t 
 
 il 
 
 90 
 
91 
 
5-8 
 
 cc > 
 
 1 
 
 5*1 
 
 H* 
 
 o S o 
 
 8is& 
 
 lol 
 
c 
 
 .'= 
 
 
 c-o 
 
 
 S > 
 8? 
 
 =- o 
 
 I 
 
 I! 
 
 51 
 
 
TUMBLING BARREL ROOM This room is equipped with a variety 
 of tumbling barrels, cleaning barrels and rotary kegs, all of which serve some 
 special purpose, depending upon the size of ball or the grade of finish desired. 
 
 94 
 
I? 
 
 *!! 
 Ill 
 
 ts 
 
 OQ S- 
 
 ^ c c 
 
96 
 
97 
 
98 
 
$2 
 
 ""* a> 
 
 I! 
 
 ?* 
 
 i"B 
 
 i c 
 
 I! 
 
 > c 
 
 100 
 
IS 
 
 ** 
 
 11 
 
 a h 
 
 80 
 
 i] 
 
 I! 
 ft 
 
 = 
 = i 
 
 l 
 
 101 
 
- * 
 
 II 
 
 31 
 
 
 102 
 
i! 
 
 103 
 
104 
 
105 
 
106 
 
107 
 
108 
 
109 
 
WEIGHTS OF STEEL BALLS 
 
 Diameter of Decimal 
 Ball (Inches) (Inches) 
 
 WEIGHT PER BALL 
 
 Grammes 
 (Metric) 
 
 Ounces 
 
 (Avoir) 
 
 Pounds 
 
 (Avoir) 
 
 1-16 .0625 
 
 .0166 
 
 .00096 
 
 .00006 
 
 3-32 .09375 
 
 .0547 
 
 .00193 
 
 .00012 
 
 1-8 .125 
 
 .1302 
 
 .00457 
 
 .00029 
 
 5-32 
 
 .15625 
 
 .2552 
 
 .00898 
 
 .00056 
 
 3-16 .1875 .4408 
 
 .01552 
 
 .00097 
 
 7-32 .21875 
 
 .6993 
 
 .02461 
 
 .00154 
 
 1-4 .25 
 
 1.0463 
 
 .03680 
 
 .00230 
 
 9-32 .28125 
 
 1.4865 
 
 .05231 
 
 .00327 
 
 5-16 .3125 
 
 2.0415 
 
 .07184 
 
 .00449 
 
 11-32 .34375 2.7141 
 
 .09550 
 
 .00597 
 
 3-8 
 
 .375 3.5226 
 
 .12400 
 
 .00775 
 
 7-16 
 
 .4375 5.5871 
 
 .19722 
 
 .01229 
 
 1-2 
 
 .50 8.3498 
 
 .29392 
 
 .01837 
 
 9-16 .5625 
 
 11.8923 
 
 .41856 
 
 .02616 
 
 5-8 . 625 
 
 16.2947 
 
 .57520 
 
 .03585 
 
 11-16 .6875 
 
 21.6873 
 
 .76336 
 
 .04771 
 
 3-4 . 75 
 
 28.1872 
 
 .99200 
 
 .06200 
 
 13-16 .8125 
 
 35.7585 
 
 1.25872 
 
 .07867 
 
 7-8 
 
 .875 
 
 44.7872 
 
 1.57648 
 
 .09853 
 
 15-16 
 
 .9375 55.0169 
 
 1.93664 
 
 .12104 
 
 
 66.8257 
 
 2.35232 
 
 .14702 
 
 -1/16 
 
 .0625 80.1379 
 
 2.8199 
 
 .17626 
 
 -1/8 
 
 .125 
 
 95.1271 
 
 3.3473 
 
 .20923 
 
 -3/16 
 
 .1875 
 
 111.8809 
 
 3.9369 
 
 .24608 
 
 -1/4 
 
 .25 
 
 130.4965 
 
 4.5919 
 
 .28702 
 
 -5/16 
 
 .3125 151.0656 
 
 5.3157 
 
 .33226 
 
 -3/8 
 
 .375 
 
 173.6764 
 
 6.1113 
 
 .38199 
 
 -7/16 
 
 .4375 
 
 198.4563 
 
 6.9833 
 
 .43649 
 
 -1/2 
 
 .50 
 
 225.4820 
 
 7.9343 
 
 .49594 
 
 -9/16 
 
 .5625 
 
 254.8682 
 
 8.9683 
 
 .56057 
 
 -5/8 
 
 .625 
 
 286.6917 
 
 10.0881 
 
 .63056 
 
 -11/16 .6875 
 
 321.0544 
 
 11.2973 
 
 .70614 
 
 -3/4 .75 
 
 358.0711 
 
 12.5998 
 
 .78756 
 
 -13/16 .8125 
 
 397.8185 
 
 13.9985 
 
 .87498 
 
 -7/8 .875 
 
 440.398 
 
 15.4968 
 
 .96864 
 
 1-15/16 .9375 
 
 485.939 
 
 17.0993 
 
 .06880 
 
 2 
 
 2. 
 
 534.491 
 
 18.8077 
 
 .17559 
 
 2-1/8 
 
 2.125 
 
 641.101 
 
 22.5591 
 
 .41007 
 
 2-1/4 
 
 2.25 
 
 761.019 
 
 26.7788 
 
 .67382 
 
 2-3/8 
 
 2.375 
 
 895.037 
 
 31.4947 
 
 .96859 
 
 2-1/2 
 
 2.50 
 
 1043.924 
 
 36.7340 
 
 2.29608 
 
 2-5/8 
 
 2.625 
 
 1208.474 
 
 42.5239 
 
 2.65798 
 
 2-3/4 
 
 2.75 ' 
 
 1389.436 
 
 48.8916 
 
 3.05600 
 
 2-7/8 
 
 2.875 
 
 1587.727 
 
 55.8691 
 
 3.49213 
 
 3 
 
 3. 
 
 1803.881 
 
 63.4751 
 
 3.96755 
 
 3-1/8 
 
 3.125 
 
 2038.920 
 
 71.7457 
 
 4.48451 
 
 3-1/4 
 
 3.25 
 
 2293.482 
 
 80.7033 
 
 5.04440 
 
 3-3/8 
 
 3.375 
 
 2568.460 
 
 90.3792 
 
 5.64920 
 
 3-1/2 
 
 3.50 
 
 2864.492 
 
 100.7960 
 
 6.30031 
 
 3-5/8 
 
 3.625 
 
 3183.875 
 
 112.0345 
 
 6.99997 
 
 3-3/4 
 
 3.75 
 
 3523.164 
 
 123.9734 
 
 7.74903 
 
 3-7/8 
 
 3.875 
 
 3887.462 
 
 136.7923 
 
 8.55028 
 
 4 
 
 4. 
 
 4275.876 
 
 150.4599 
 
 9.40458 
 
 4-U4 
 
 4.25 
 
 5128.882 
 
 180.4756 
 
 11.28073 
 
 4-1/2 
 
 4.50 
 
 6088.179 
 
 214.2314 
 
 13.39065 
 
 4-3/4 
 
 4.75 
 
 7160.402 
 
 251.9608 
 
 15.74896 
 
 S 
 
 5. 
 
 8351.420 
 
 253.4605 
 
 18.36854 
 
 C = Contents in Cubic Inches. 
 = 4/3 TT R 3 = 4.1888 R 3 = .5236 D 3 
 
 W = Weight of Steel Balls in pounds. 
 
 = R 3 (.28065 X 4.1888) = 1.17558 R 3 = .14695 D 
 
 110 
 
FORMULA FOR DETERMINING PITCH DIA. 
 
 OF BALL CIRCLE AND CLEARANCE 
 
 BETWEEN BALLS 
 
 Notation: 
 
 Di = Pitch Dia. of Ball Circle. 
 
 D2 = Dia. of Circumscribed Circle. 
 
 Ds = Dia. of Inscribed Circle. 
 
 d = Dia. of Balls. 
 
 N = Number of Balls in the Ring. 
 
 S = Clearance Between Each Pair of Balls. 
 
 Di = (d+S)XCSC. 
 
 180 \ 
 N / 
 
 /ISO 
 
 )3 = Di-d 
 
 /180 
 = DiXSIN. f 
 
 180 \ 
 
 IT)-' 
 
 The following table gives the value of the CSC. and SIN. for "N" Balls. 
 
 No. of Balls 
 
 "N" 
 
 Angle a 
 180 
 
 CSC. 
 180 
 
 SIN. 
 180 
 
 N 
 
 N 
 
 N 
 
 6 
 
 30 
 
 2.00000 
 
 .50000 
 
 7 
 
 25 42' 51.43" 
 
 2.30476 
 
 .43388 
 
 8 
 
 22 30' 
 
 2.61313 
 
 .38268 
 
 9 
 
 20 
 
 2.92381 
 
 .34202 
 
 10 
 
 18 
 
 3.23607 
 
 . 30902 
 
 11 
 
 16 21' 49.09" 
 
 3.54947 
 
 .28173 
 
 12 
 
 15 
 
 3.86370 
 
 .25882 
 
 13 
 
 13 50' 46.16" 
 
 4.17858 
 
 .23932 
 
 14 12 51' 25.72" 
 
 4.49396 
 
 .22252 
 
 15 12 
 
 4.80973 
 
 .20791 
 
 16 
 
 11 15' 
 
 5.12583 
 
 . 19509 
 
 17 10 35' 17.65" 
 
 5.44219 
 
 . 18375 
 
 18 10 
 
 5.75877 
 
 . 17365 
 
 19 9 28' 25.26" 
 
 6.07554 
 
 . 16459 
 
 20 9 
 
 6.39247 
 
 .15643 
 
 21 8 34' 17.14" 
 
 6.70950 
 
 . 14904 
 
 22 8 10' 54.55" 
 
 7.02667 
 
 .14231 
 
 23 7 49' 33.91" 
 
 7.34394 
 
 .13617 
 
 24 7 30' 
 
 7.66130 
 
 .13053 
 
 25 7 12' 
 
 7.97873 
 
 .12533 
 
 26 
 
 6 55' 23.08" 
 
 8.29623 
 
 .12054 
 
 27 
 
 6 40' 
 
 8.61380 
 
 .11609 
 
 28 
 
 6 25' 42.86" 
 
 8.93140 
 
 .11196 
 
 29 
 
 6 12' 24.82" 
 
 9.24907 
 
 .10812 
 
 30 
 
 6 
 
 9.56677 
 
 . 10453 
 
 111 
 
THE CIRCLE 
 
 d = Diameter of Circle. 
 
 C = Circumference of Circle. 
 
 C=7rd =3.141593 d 
 
 A = Area of Plane Surface. 
 7r = 3.141593 
 
 Trd 2 
 
 A = = .785398 d 2 
 
 4 
 
 Areas of Circles are to Each other as the Squares of their Diameters. 
 THE SPHERE 
 
 V = Volume of Sphere. 
 
 d = Diameter of Sphere. 
 
 S = Area of Convex Surface. 
 
 d 2 
 
 V 
 
 .523599 d 3 
 
 Surfaces of Spheres are to each other as the Squires of their Diameters. 
 The Volume of a Shpere = 2/3 the Volume of its Circumscribing Cylinder. 
 Volumes of Spheres are to each other as the Cubes of their Diameters. 
 
 BALL DIA. 
 IN INCHES 
 
 C RCUM. 
 N INCHES 
 
 AREA 
 
 VOLUME 
 CU.- INCHES 
 
 SECTION 
 SQ. INCHES 
 
 CONVEX SURFACE 
 SQ. INCHES 
 
 /SZ 
 
 .09818 
 
 .00077 
 
 .00307 
 
 .00002 
 
 /16 
 
 . 19635 
 
 .00307 
 
 .01227 
 
 .00013 
 
 /SZ 
 
 .29452 
 
 .00690 
 
 .02761 
 
 . 00043 
 
 /8 
 
 . 39270 
 
 01227 
 
 .04909 
 
 .00102 
 
 /SZ 
 
 .49087 
 
 .01917 
 
 . 07670 
 
 .00200 
 
 /16 
 
 . 58905 
 
 .02761 
 
 .11045 
 
 .00345 
 
 /32 
 
 .68722 
 
 . 03758 
 
 . 15033 
 
 . 00548 
 
 /4 
 
 .78540 
 
 .04909 
 
 .19635 
 
 .00818 
 
 /32 
 
 .88357 
 
 .06213 
 
 .24851 
 
 .01165 
 
 16 
 
 .98175 
 
 .07670 
 
 . 30680 
 
 .01598 
 
 11 32 
 
 1.0799 
 
 .09281 
 
 .37123 
 
 .02127 
 
 3 8 
 
 
 .1781 
 
 .11045 
 
 .44179 
 
 . 02761 
 
 IS SZ 
 
 
 .2763 
 
 . 12962 
 
 .51848 
 
 .03511 
 
 7 16 
 
 
 .3744 
 
 .15033 
 
 .60132 
 
 .04385 
 
 15 32 
 
 
 .4726 
 
 . 17257 
 
 
 . 05393 
 
 1 Z 
 
 
 .5708 
 
 .19635 
 
 .78540 
 
 . 06545 
 
 9 16 
 
 
 .7671 
 
 .24850 
 
 . 99403 
 
 .09319 
 
 5 8 
 
 
 .9635 
 
 .30680 
 
 
 .2272 
 
 .12783 
 
 11 16 
 
 
 .1598 
 
 37122 
 
 
 .4849 
 
 .17014 
 
 S 4 
 
 
 .3562 
 
 .44179 
 
 
 .7671 
 
 . 22089 
 
 
 
 .5525 
 
 .51849 
 
 
 .0739 
 
 . 28084 
 
 7/8 
 
 
 .7489 
 
 .60132 
 
 
 .4053 
 
 .35077 
 
 15/16 
 
 
 .9452 
 
 .69029 
 
 
 .7611 
 
 .43143 
 
 1. 
 
 
 .1416 
 
 .7854 
 
 
 .1416 
 
 .52360 
 
 1/16 
 
 
 .3379 
 
 .8866 
 
 
 .5466 
 
 . 62804 
 
 1/8 
 
 
 .5343 
 
 .9940 
 
 
 .9761 
 
 .74551 
 
 3/16 
 
 
 .7306 
 
 
 .107J 
 
 
 .4301 
 
 .87681 
 
 I/* 
 
 ,- 
 
 .9270 
 
 
 .2272 
 
 
 .9088 
 
 
 .0227 
 
 
 
 .1233 
 
 
 .3530 
 
 
 .4119 
 
 
 .1839 
 
 3/8 
 
 
 .3197 
 
 
 .4849 
 
 
 .9396 
 
 
 .3611 
 
 7/16 
 
 
 .5160 
 
 
 .6230 
 
 
 .4919 
 
 
 .5553 
 
 1/Z 
 
 
 .7124 
 
 
 .7671 
 
 
 .0686 
 
 
 .7671 
 
 /16. 
 
 
 .9087 
 
 
 .9175 
 
 .6699 
 
 
 .9974 
 
 /8 
 
 
 .1051 
 
 
 .0739 
 
 
 .2957 
 
 
 .2468 
 
 1 /16 
 
 
 .3014 
 
 
 .2365 
 
 
 .9461 
 
 
 
 /4 
 
 
 .4978 
 
 
 .4053 
 
 
 .6211 
 
 
 .8062 
 
 1 /16 
 
 
 .6941 
 
 
 .5802 
 
 1 
 
 .321 
 
 
 .1177 
 
 /8 
 
 
 .8905 
 
 
 .7612 
 
 
 .044 
 
 
 .4514 
 
 1 /16 
 
 
 .0868 
 
 
 .9483 
 
 1 
 
 .793 
 
 
 .8083 
 
 2. 
 
 
 .2832 
 
 
 .1416 
 
 1 
 
 .566 
 
 
 .1888 
 
 /16 
 
 
 .4795 
 
 
 .3410 
 
 1 
 
 .364 
 
 
 .5939 
 
 
 
 .6759 
 
 
 .5466 
 
 
 .186 
 
 
 .0243 
 
 /16 
 
 
 .8722 
 
 
 7583 
 
 1 
 
 .033 
 
 
 .4809 
 
 /4 
 
 
 .0686 
 
 
 .9761 
 
 
 .904 
 
 
 .9641 
 
 /16 
 
 
 .2649 
 
 
 .2000 
 
 1 
 
 .800 
 
 
 .4751 
 
 n 
 
 
 .4613 
 
 
 .4301 
 
 
 .7Z1 
 
 
 .0144 
 
 /16 
 
 
 .6576 
 
 
 .6664 
 
 1 
 
 .666 
 
 
 .5829 
 
 /Z 
 
 
 .8540 
 
 
 .9087 
 
 1 
 
 .635 
 
 
 .1813 
 
 /16 
 
 
 .0503 
 
 
 .1572 
 
 20 629 
 
 
 .8103 
 
 /8 
 
 
 .2467 
 
 
 .4119 21.648 
 
 
 .4708 
 
 1 /16 
 
 
 .4430 
 
 
 .6727 22.691 
 
 1 
 
 .164 
 
 It 
 
 
 .6394 
 
 
 .9396 
 
 23.758 
 
 1 
 
 .889 
 
 I /16 
 
 
 .8357 
 
 
 .2126 
 
 24.850 
 
 1 
 
 .649 
 
 /8 
 
 
 .0321 
 
 
 .4918 
 
 25.967 
 
 1 
 
 .443 
 
 1 /16 
 
 
 .2484 
 
 
 .7771 
 
 27.109 
 
 1 
 
 .272 
 
 3 
 
 
 .4248 
 
 
 .0686 
 
 28.274 
 
 | 
 
 .137 
 
 1/16 
 
 
 6211 
 
 
 3662 
 
 29.465 
 
 1 
 
 
 1/8 
 
 
 .8175 
 
 
 .6699 
 
 30.680 
 
 I 
 
 '979 
 
 3/16 
 
 
 .014 
 
 
 .9798 
 
 31.919 
 
 
 .957 
 
 1/4 
 
 
 .210 
 
 
 .2958 
 
 33.183 
 
 ] 
 
 974 
 
 i/l 
 
 
 .407 
 
 
 .6179 
 
 34.472 
 
 I 
 
 .031 
 
 S/8 
 
 
 .60S 
 
 
 .9462 
 
 35.784 
 
 20.129 
 
 7/16 
 
 
 .799 
 
 
 .2806 
 
 37.122 
 
 21 . 268 
 
 1/Z 
 
 
 .996 
 
 
 .6211 
 
 38.484 
 
 22.449 
 
 
 
 .192 
 
 
 .9678 
 
 S9.872 
 
 23.674 
 
 
 
 .388 
 
 
 .321 
 
 41.283 
 
 24.942 
 
 11/16 
 
 
 .585 
 
 
 .680 
 
 42.719 
 
 26.254 
 
 3/4 
 
 
 .781 
 
 
 
 44.179 
 
 27.611 
 
 13/16 
 
 
 977 
 
 
 .tit 
 
 45 . 664 
 
 29.016 
 
 7/8 
 
 
 174 
 
 
 .798 
 
 47.173 
 
 SO 466 
 
 15/16 
 
 
 .370 
 
 
 
 48.708 
 
 3 .965 
 
 4. 
 
 12.566 
 
 12 566 
 
 50.465 
 
 33.510 
 
 112 
 
DECIMAL EQUIVALENTS OF FRACTIONS 
 OF AN INCH 
 
 Fract. 
 
 Dec. 
 
 Fract. 
 
 Dec. 
 
 Fract. 
 
 Dec. 
 
 Fract. 
 
 Dec. 
 
 1 
 
 
 17 
 
 
 33 
 
 
 49 
 
 
 
 
 .015625 
 
 
 
 . 265625 
 
 
 
 .515625 
 
 
 
 .765625 
 
 64 
 
 
 64 
 
 
 64 
 
 
 64 
 
 
 I 
 
 
 9 
 
 
 17 
 
 
 25 
 
 
 
 
 .03125 
 
 
 
 .28125 
 
 
 
 .53125 
 
 
 
 .78125 
 
 32 
 
 
 32 
 
 
 32 
 
 
 32 
 
 
 3 
 
 
 19 
 
 
 35 
 
 
 51 
 
 
 
 
 .046875 
 
 
 
 .296875 
 
 
 
 .546875 
 
 
 
 .796875 
 
 64 
 
 
 64 
 
 
 64 
 
 
 64 
 
 
 1 
 
 
 5 
 
 
 9 
 
 13 
 
 
 _ 
 
 .0625 
 
 __ 
 
 .3125 
 
 _ 
 
 .5625 
 
 .8125 
 
 16 
 
 
 16 
 
 
 16 
 
 16 
 
 
 5 
 
 
 21 
 
 1 37 
 
 i 53 
 
 
 mm 
 
 .078125 
 
 _ 
 
 .328125 
 
 .578125 ! 
 
 .828125 
 
 64 
 
 
 64 
 
 ! 64 
 
 ! 64 
 
 
 3 
 
 
 11 
 
 
 19 
 
 27 
 
 
 __ 
 
 .09375 
 
 H 
 
 .34375 
 
 
 .59375 
 
 .84375 
 
 32 
 
 
 32 
 
 . 
 
 32 
 
 32 
 
 
 7 
 
 
 23 
 
 
 39 
 
 
 55 
 
 
 
 
 . 109575 
 
 
 
 .359375 
 
 
 .609375 
 
 
 
 .859375 
 
 64 
 
 
 64 
 
 
 64 
 
 64 
 
 
 1 
 
 
 3 
 
 
 5 
 
 
 7 
 
 
 
 .125 
 
 
 .375 
 
 
 .625 
 
 
 .875 
 
 8 
 
 
 8 
 
 . 
 
 8 
 
 
 8 
 
 
 9 
 
 
 25 
 
 
 41 
 
 
 57 
 
 
 _ 
 
 . 140625 
 
 _ 
 
 . 390625 
 
 
 .640625 
 
 _ 
 
 .890625 
 
 64 
 
 
 64 
 
 
 64 
 
 
 64 
 
 
 5 
 
 
 13 
 
 
 21 
 
 
 29 
 
 
 __ 
 
 . 15625 
 
 _ 
 
 .40625 
 
 _ 
 
 .65625 
 
 __ 
 
 . 90625 
 
 32 
 
 
 32 
 
 
 32 
 
 
 32 
 
 
 11 
 
 
 27 
 
 
 43 
 
 
 59 
 
 
 
 
 .171875 
 
 
 
 421875 
 
 
 .671875 
 
 
 
 .921875 
 
 64 
 
 
 64 
 
 
 64 
 
 
 64 
 
 
 3 
 
 
 7 
 
 
 11 
 
 
 15 
 
 
 
 
 .1875 
 
 
 
 .4375 
 
 
 .6875 
 
 
 
 .9375 
 
 16 
 
 
 16 
 
 
 16 
 
 
 16 
 
 
 13 
 
 
 29 
 
 
 45 
 
 
 61 
 
 
 _ 
 
 .203125 
 
 __ 
 
 .453125 
 
 __ 
 
 .703125 
 
 _ 
 
 .953125 
 
 64 
 
 
 64 
 
 
 64 
 
 
 64 
 
 
 7 
 
 
 15 
 
 
 23 
 
 
 31 
 
 
 __ 
 
 .21875 
 
 _ 
 
 .46875 
 
 _ 
 
 .71875 
 
 _ 
 
 .96875 
 
 32 
 
 
 32 
 
 
 32 
 
 
 32 
 
 
 15 
 
 
 31 
 
 
 47 
 
 
 63 
 
 
 
 
 .234375 
 
 _ 
 
 .484375 
 
 _ 
 
 .734375 
 
 _ 
 
 .984375 
 
 64 
 
 
 64 
 
 
 64 
 
 
 64 
 
 
 1 
 
 
 1 
 
 
 3 
 
 
 
 
 
 
 .25 
 
 
 5 
 
 
 .75 
 
 1 
 
 
 4 
 
 
 2 
 
 
 4 
 
 
 
 
 TABLE OF DECIMAL EQUIVALENTS OF MILLI- 
 METERS AND FRACTIONS OF MILLIMETERS 
 
 1/100 mm. = .0003937". 
 
 mm. Inches mm. Inches mm. Inches | mm. Inches mm. Inches 
 
 1/50 = .00079 
 
 "/50 = .00866 
 
 21/50= .01654 
 
 31/50= .02441 
 
 41/50= .03228 
 
 2 /50= .00157 
 
 i/50 = .00945 
 
 22/50 =.01732 
 
 3*/50 = . 02520 
 
 42/50 =.03307 
 
 3/50= .00236 
 
 13/50 =.01024 
 
 23/50=. 01811 
 
 33/so =.02598 
 
 43/50 = . 03386 
 
 4/50 =.003 15 
 
 14/50 = .01102 
 
 24/ 5 o= .01890 
 
 34/50 = . 02677 
 
 44/so = . 03465 
 
 5 /50=. 00394 
 
 15/50=. 01181 
 
 25/50= .01969 
 
 35/50 = . 02756 
 
 45/50= .03543 
 
 6/50 =.00472 
 
 16/50 = .01260 
 
 26/50= .02047 
 
 36/50 =.02835 
 
 46/ 5 o =.03622 
 
 , 7 /50= . 00551 
 
 17 /50= .01339 
 
 27/50= .02126 
 
 37/50= .02913 
 
 47/50= .03701 
 
 8/50 = . 00630 
 
 18/50 =.01417 
 
 28/50 = . 02205 
 
 38/M>=. 02992 
 
 48/so =.03780 
 
 9/50= .00709 
 
 19/50= .01496 
 
 29/50= .02283 
 
 29/50= .03071 
 
 49/50 = . 03858 
 
 I0/ 5 o= .00787 
 
 S/50= .01575 
 
 so/so =.02362 
 
 40/50= .03150 
 
 
 10 mm. = l Centimeter = 0.3937 inches 
 
 10 cm. =1 Decimeter = 3.937 inches 
 
 10 dm. =1 Meter =39.37 inches 
 
 25. 4 mm. = 1 English Inch. 
 
 113 
 
CONVERSION TABLE 
 
 DECIMAL EQUIVALENTS OF MILLIMETERS IN INCHES 
 
 1 m/m to 500 m/m. 
 1 m/m = .03937027" 
 
 nun. 
 
 Inches 
 
 m.m. 
 
 Inches 
 
 m.m. 
 
 Inches 
 
 m.m 
 
 Inches 
 
 m.m 
 
 Inches 
 
 man 
 
 Inches 
 
 m.m 
 
 Inches 
 
 ] 
 
 .03937027 
 
 7ft 
 
 2.87402971 
 
 145 
 
 5.70868915 
 
 eii 
 
 8.50397832 
 
 287 
 
 11 .29926749 
 
 358 
 
 14.09455666 
 
 429 
 
 16.88954583 
 
 2 
 
 .07874054 
 
 74 
 
 2.91339998 
 
 14(i 
 
 5.74805942 
 
 217 
 
 8.54334859 
 
 288 
 
 11 .33863776 
 
 359 
 
 14.13392693 
 
 430 
 
 16.92921610 
 
 3 
 
 .11811081 
 
 7* 
 
 2.95277025 
 
 147 
 
 5.78742969 
 
 -218 
 
 8.58271886 
 
 289 
 
 11 37800803 
 
 300 
 
 14.17329720 
 
 431 
 
 16.96858637 
 
 
 .15748108 
 
 7(i 
 
 2.99214052 
 
 14S 
 
 5.82679996 
 
 -219 
 
 8.62208913 
 
 291 
 
 11 41737830 
 
 301 
 
 14.21266747 
 
 432 
 
 17 00795664 
 
 
 .19685135 
 
 77 
 
 3 03151079 
 
 149 
 
 5.86617023 
 
 221 
 
 8.66145940 
 
 -291 
 
 11.45674857 
 
 302 
 
 14.25203774 
 
 433 
 
 17.04732691 
 
 
 .23622162 
 
 78 
 
 3.07088106 
 
 150 
 
 5.90554050 
 
 -2-21 
 
 8 70082967 
 
 292 
 
 11.49611884 
 
 563 
 
 14 29140801 
 
 434 
 
 17.08669718 
 
 
 .27559189 
 
 79 
 
 3.11025133 
 
 151 
 
 5.94491077 
 
 2-2-2 
 
 8.74019994 
 
 2!)3 
 
 11 53548911 
 
 304 
 
 14.33077828 
 
 435 
 
 17 12606745 
 
 
 .31496216 
 
 80 
 
 3.14962160 
 
 152 
 
 5.98428104 
 
 2-23 
 
 8.77957021 
 
 2!) 4 
 
 1 1 . 57485938 
 
 505 
 
 14.37014855 
 
 430 
 
 17.16543772 
 
 
 .35433243 
 
 81 
 
 3 18899187 
 
 153 
 
 6.02365131 
 
 -2-24 
 
 8.81894048 
 
 2!)5 
 
 11 61422965 
 
 500 
 
 14 40951882 
 
 437 
 
 17 20480799 
 
 10 
 
 .39370270 
 
 82 
 
 3 22836214 
 
 154 
 
 6.06302158 
 
 -2-2.-, 
 
 8 85831075 
 
 296 
 
 1 1 65359992 
 
 507 
 
 14.44888909 
 
 438 
 
 17.24417826 
 
 11 
 
 . 43307297 
 
 88 
 
 3.26773241 
 
 1 55 
 
 6 10239185 
 
 22 (i 
 
 8.89768102 
 
 297 
 
 11.69297019 
 
 568 
 
 14.48825936 
 
 439 
 
 17.28354853 
 
 18 
 
 .47244324 
 
 84 
 
 3.307102C8 
 
 156 
 
 6.14176212 
 
 -227 
 
 8 93705129 
 
 298 
 
 11 73234046 
 
 309 
 
 14.52762963 
 
 440 
 
 17.32291880 
 
 19 
 
 .51181351 
 
 85 
 
 3.34647295 
 
 157 
 
 0.18113239 
 
 2-2S 
 
 8.97642156 
 
 2!)!) 
 
 11 77171073 
 
 370 
 
 14.56699990 
 
 441 
 
 7.36228907 
 
 14 
 
 .55118378 
 
 86 
 
 3.38584322 
 
 15S 
 
 6.22050266 
 
 22!) 
 
 9.01579183 
 
 Kin 
 
 11.81108100 
 
 571 
 
 14.60637017 
 
 44-2 
 
 17 40165934 
 
 1.5 
 
 .59055405 
 
 87 
 
 3 42521349 
 
 159 
 
 6.25987293 
 
 230 
 
 9.05516210 
 
 301 
 
 11 85045127 
 
 37-2 
 
 14.64574044 
 
 443 
 
 7.44102961 
 
 10 
 
 . 62992432 
 
 88 
 
 3.46458376 
 
 160 
 
 6.29924320 
 
 -231 
 
 9 09453237 
 
 i()-2 
 
 11.88982154 
 
 373 
 
 14.68511071 
 
 444 
 
 17.48039988 
 
 17 
 
 .66929459 
 
 89 
 
 3.50395403 
 
 K.I 
 
 6 33861347 
 
 -2:! 2 
 
 9.13390264 
 
 503 
 
 11 92919181 
 
 574 
 
 14.72448098 
 
 145 
 
 17.51977015 
 
 IS 
 
 .70866486 
 
 90 
 
 .54332430 
 
 162 
 
 6.37798374 
 
 2:!:! 
 
 9 17327291 
 
 504 
 
 1 1 . 96856208 
 
 575 
 
 14.76385125 
 
 440 
 
 7.55914042 
 
 1!) 
 
 .74803513 
 
 91 
 
 .58269457 
 
 1 63 
 
 6 41735401 
 
 234 
 
 9 21264318 
 
 505 
 
 12.00793235 
 
 570 
 
 14.80322152 
 
 447 
 
 7.59851069 
 
 20 
 
 .78740540 
 
 98 
 
 . C2206484 
 
 K!4 
 
 6.45672428 
 
 235 
 
 9 25201345 
 
 500 
 
 12.04730262 
 
 377 
 
 14.84259179 
 
 44S 
 
 7.63788096 
 
 21 
 
 .82677567 
 
 93 
 
 .66143511 
 
 Ki5 
 
 6.49609455 
 
 230 
 
 9.29138372 
 
 507 
 
 12.08667289 
 
 !78 
 
 14.88196206 
 
 149 
 
 7.67725123 
 
 2-2 
 
 .86614594 
 
 94 
 
 . 70080538 
 
 100 
 
 6.53546482 
 
 -237 
 
 9 . 33075399 
 
 ios 
 
 12 12604316 
 
 379 
 
 14.92133233 
 
 150 
 
 7.71662150 
 
 *S 
 
 .90551621 
 
 95 
 
 .74017565 
 
 107 
 
 6.57483509 
 
 238 
 
 9 37012426 
 
 !()!) 
 
 12 16541343 
 
 580 
 
 14.96070200 
 
 451 
 
 7.75599177 
 
 24 
 
 .94488648 
 
 !>o 
 
 . 77954592 
 
 168 
 
 6.61420536 
 
 23!) 
 
 9 40949453 
 
 510 
 
 12.20478370 
 
 581 
 
 15.00007287 
 
 452 
 
 7.79536204 
 
 5 
 
 .98425675 
 
 97 
 
 .81891619 
 
 169 
 
 6 65357563 
 
 240 
 
 9.44886480 
 
 ill 
 
 12.24415397 
 
 iS -2 
 
 15.03944314 
 
 153 
 
 7.83473231 
 
 20 
 
 .02362702 
 
 98 
 
 . 85828646 
 
 170 
 
 6 69294590 
 
 241 
 
 9 . 48823507 
 
 312 
 
 12 28352424 
 
 383 
 
 15.07881341 
 
 454 
 
 7.87410258 
 
 87 
 
 . 06299729 
 
 !! 
 
 .89765673 
 
 171 
 
 6 73231617 
 
 21-2 
 
 9 52760534 
 
 313 [ 12 32289451 
 
 384 
 
 15.11818368 
 
 155 
 
 7.91347285 
 
 88 
 
 . 10236756 
 
 100 
 
 93702700 
 
 17-2 
 
 6.77168644 
 
 243 
 
 9.56697561 
 
 314 12.36226478 
 
 585 
 
 15.15755398 
 
 450 
 
 7.95284312 
 
 *9 
 
 .14173783 
 
 101 
 
 .97639727 
 
 173 
 
 6 81105671 
 
 244 
 
 9 . 60634588 
 
 3 la! 12 40163505 
 
 580 
 
 15.19692422 
 
 457 
 
 7.99221339 
 
 SO 
 
 .18110810 
 
 102 
 
 01576754 
 
 174 
 
 6 85042698 
 
 245| 9.64571615 
 
 316|l2. 44100532 
 
 387 
 
 15.23629449 
 
 158 
 
 8 03158366 
 
 :u 
 
 .22047837 
 
 103 
 
 05513781 
 
 175 
 
 6.88979725 
 
 246 
 
 9.68508642 
 
 517 12.48037559 
 
 5S8 
 
 15.27566476 
 
 15!) 
 
 8.07095393 
 
 3-2 
 
 .25984864 
 
 104 
 
 . 09450808 
 
 176 
 
 6.92916752 
 
 247 
 
 9.72445669 
 
 31812.51974586 
 
 18!) 
 
 15 31503503 
 
 400 
 
 8.11032420 
 
 33 
 
 .29921891 
 
 10.-, 
 
 .13387835 
 
 177 
 
 6 96853779 
 
 248 
 
 9.76382696 
 
 319 12.55911613 
 
 .390 
 
 15.35440530 
 
 401 
 
 8.14969447 
 
 34 
 
 .33858918 
 
 100 
 
 .17324862 
 
 17S 
 
 7 00790806 
 
 249 
 
 '9.80319723 
 
 320 12.59848640 
 
 5!)! 
 
 15.39377557 
 
 40-2 
 
 8.18906474 
 
 85 
 
 .37795945 
 
 107 
 
 .21261889 
 
 17!) 
 
 7.04727833 
 
 250 
 
 9.84256750 
 
 321 12.63785067 
 
 392 
 
 15.43314584 
 
 403 
 
 8.22843501 
 
 30 
 
 .41732972 
 
 108 
 
 .25198916 
 
 ISO 
 
 7 . 08664860 
 
 251 
 
 9.88193777 
 
 322 
 
 12.67722694 
 
 393J 15. 4725 1611 
 
 404 
 
 8 . 26780528 
 
 SI 
 
 . 45669999 
 
 109 
 
 29135943 
 
 181 
 
 7.12601887 
 
 252 
 
 9 92130804 
 
 i23 
 
 12 71659721 
 
 39415.51188638 
 
 165 
 
 8 30717555 
 
 98 
 
 . 49607026 
 
 110 
 
 .33072970 
 
 18-2 
 
 7.16538914 
 
 253i 9.96067831 
 
 i-24 
 
 12 75596748 
 
 595 
 
 15.55125665 
 
 400 
 
 8.34654582 
 
 39 
 
 .53544053 
 
 111 
 
 . 37009997 
 
 183 
 
 7.20475941 
 
 254'lO. 00004858 
 
 525 
 
 12 79533775 
 
 590 
 
 15.59062692 
 
 407 
 
 8 38591609 
 
 40 
 
 .57481080 
 
 11-2 
 
 40947024 
 
 184 
 
 7.24412968 
 
 255 
 
 10.03941885 
 
 520 
 
 12.83470802 
 
 597 
 
 15.62999719 
 
 108 
 
 8 42528636 
 
 41 
 
 .61418107 
 
 11.'! 
 
 44884051 
 
 185 
 
 7 . 28349995 
 
 256 
 
 10.07878912 
 
 i-27 
 
 12 87407829 
 
 598 
 
 15.66936746 
 
 469 
 
 8.46465663 
 
 4-2 
 
 .65355134 
 
 114 
 
 .48821078 
 
 186 
 
 7.32287022 
 
 -257 
 
 10.11815939 
 
 528 
 
 12 91344856 
 
 i!)!) 
 
 15 70873773 
 
 470 
 
 18 50402690 
 
 43 
 
 .69292161 
 
 115 
 
 52758105 
 
 187 
 
 7.36224049 
 
 258 
 
 10 15752966 
 
 529 
 
 12.95281883 
 
 400 
 
 15 74810800 
 
 471 
 
 18.54339717 
 
 44 
 
 .7?229188 
 
 116 
 
 56695132 
 
 188 
 
 7.40161076 
 
 2;,i) 
 
 10 19689993 
 
 ;:!(i 
 
 12 99218910 
 
 401 
 
 15.78747827 
 
 47-2 
 
 8.58276744 
 
 4.) 
 
 .77166215 
 
 117 
 
 .60632159 
 
 18!) 
 
 7.44098103 
 
 -2(10 
 
 10 23627020 
 
 !31 
 
 13 03155937 
 
 40-2 
 
 15.82684854 
 
 473 
 
 18.62213771 
 
 4(i 
 
 .81103242 
 
 US 
 
 .64569186 
 
 190 
 
 7.48035130 
 
 -261 
 
 10 27564047 
 
 532 
 
 1 3 07092964 
 
 403 
 
 15.86621881 
 
 474 
 
 18.66150798 
 
 47 
 
 .85040269 
 
 11!) 
 
 68506213 
 
 11)1 
 
 7.51972157 
 
 262 
 
 10 31501074 
 
 133 
 
 13.11029991 
 
 404 
 
 15.90558908 
 
 475 
 
 18.70087825 
 
 48 
 
 .88977296 
 
 120 
 
 72443240 
 
 192 
 
 7.55909184 
 
 203 
 
 10.35438101 
 
 534 
 
 13 14967018 
 
 105 
 
 15 94495935 
 
 470 
 
 8 74024852 
 
 4!) 
 50 
 
 .92914323 
 .96851350 
 
 121 
 122 
 
 . 76380267 
 .80317294 
 
 193 
 1!)4 
 
 7 59846211 
 7.63783238 
 
 201 
 -265 
 
 10 39375128 
 10 43312155 
 
 i:i.-, 
 
 530 
 
 13 18904045 
 13.22841072 
 
 407 
 
 15 98432962 
 16.02369989 
 
 477 
 478 
 
 8 77961879 
 8 81898906 
 
 51 
 
 00788377 
 
 123 
 
 .84254321 
 
 195 
 
 7 67720265 
 
 200 
 
 10.47249182 
 
 537 
 
 13 26778099 
 
 408 
 
 16.06307016 
 
 479 
 
 8 85835933 
 
 52 
 
 .04725404 
 
 124 
 
 .88191348 
 
 196 
 
 7 71657292 
 
 207 
 
 10 51186209 
 
 i:is 
 
 13 30715126 
 
 40!) 
 
 16. 10244043 
 
 480 
 
 8 89772960 
 
 53 
 
 .08662431 
 
 1-25 
 
 92128375 
 
 197 
 
 7.75594319 
 
 20S 
 
 10 55123236 
 
 i:59 
 
 13.34652153 
 
 410 
 
 16 14181070 
 
 481 
 
 8.93709987 
 
 ,U 
 
 .12599458 
 
 126 
 
 . 96065402 
 
 IDS 
 
 7.79531346 
 
 26!) 
 
 10.59060203 
 
 540 
 
 13 38589180 
 
 411 
 
 16.18118097 
 
 48-2 
 
 8.97647014 
 
 55 
 
 .16536485 
 
 127 
 
 . 00002429 
 
 HI!) 
 
 7 . 83468373 
 
 270 
 
 10.62997290 
 
 341 
 
 13 42526207 
 
 41'2 
 
 16 22055124 
 
 483 
 
 9 01584041 
 
 56 
 
 .20473512 
 
 1-2S 
 
 . 03939456 
 
 -200 
 
 7.87405400 
 
 271 
 
 10.66934317 
 
 54-2 
 
 13 46463234 
 
 413 
 
 16.25992151 
 
 484 
 
 9 05521068 
 
 57 
 
 24410539 
 
 129 
 
 .07876483 
 
 -201 
 
 7.91342427 
 
 27-2 
 
 10.70871344 
 
 343 
 
 13 50400261 
 
 414 
 
 16.29929178 
 
 485 
 
 9 09458095 
 
 58 
 
 .28347566 
 
 130 
 
 .11813510 
 
 -20-2 
 
 7.95279454 
 
 273 
 
 10.74808371 
 
 544 
 
 13 54337288 
 
 415 
 
 16.33866205 
 
 480 
 
 9 13395122 
 
 53 
 
 .32284593 
 
 131 
 
 . 15750537 
 
 20:! 
 
 7.99216481 
 
 274 
 
 10.78745398 
 
 545 
 
 13.58274315 
 
 410 
 
 16.37803232 
 
 487 
 
 9 17332149 
 
 (i() 
 
 .36221620 
 
 132 
 
 .19687561 
 
 -204 
 
 8.03153508 
 
 275 
 
 10.82682425 
 
 340 
 
 13 62211342 
 
 417 
 
 16 41740259 
 
 488 
 
 9 21269176 
 
 61 
 
 .40158647 
 
 133 
 
 23624591 
 
 205 
 
 8 . 07090535 
 
 27 (i 
 
 10 86619452 
 
 547 
 
 13 66148369 
 
 4 IS 
 
 16.45677286 
 
 48!) 
 
 9 25206203 
 
 62 
 
 44095674 .134 
 
 .27561618 
 
 206 
 
 8 11027562277 
 
 10 90556479 
 
 348 
 
 13.70085396 
 
 419 
 
 16 49614313 
 
 490 
 
 9 29143230 
 
 03 
 
 .48032701 135 
 
 31498645 
 
 207 
 
 8 14964589 
 
 278 
 
 10.94493506 
 
 549 
 
 13 74022423 
 
 420 
 
 16 53551340 
 
 491 
 
 19 33080257 
 
 04 
 
 .51969728 
 
 136 
 
 35435672 208 
 
 8.18901616 
 
 279 
 
 10.98430533 
 
 550 
 
 13 77959450 
 
 421 16 57488367 
 
 492 
 
 19.37017^54 
 
 65 
 
 55906755 
 
 137 
 
 .39372699209 
 
 8.22838643 
 
 280 
 
 11.02367560 
 
 351 
 
 13.81896477 
 
 422 16 61425394 
 
 493 
 
 19 40954311 
 
 6(i 
 
 .59843782 
 
 138 
 
 43309726 210 
 
 8.26775670 
 
 281 
 
 11.06304587 
 
 552 
 
 13.85833504 
 
 42316.65362421 
 
 494 
 
 19.44891338 
 
 67 
 
 68 
 
 .63780809 139 
 .67717836:140 
 
 47246753211 
 .51183780212 
 
 8.30712697 
 8.34649724 
 
 282 
 2 S3 
 
 11 10241614 
 11 14178641 
 
 553 
 554 
 
 13 89770531 
 13 93707558 
 
 424'ie. 69299448 
 425 16 73236475 
 
 495 
 496 
 
 19 48828365 
 19.52765392 
 
 69 
 
 71654863!l41 
 
 .55120807213 
 
 8 38586751,284 
 
 11.18115668 
 
 555 
 
 13 97644585 
 
 426 
 
 16.77173502 
 
 497 
 
 19.56702419 
 
 70 
 
 .75591890142 
 
 59057834214 
 
 8.42523778 285 
 
 11.22052695 
 
 550 
 
 14.01581612 
 
 4-27 
 
 16.81110529 
 
 498 
 
 19 60639446 
 
 71 
 
 79528917 143 
 
 62994861 
 
 215 
 
 8.46460805286 
 
 11.25989722 
 
 357 
 
 14 05518639 
 
 428 
 
 16.85047556 
 
 491) 
 
 19.64576473 
 
 72 
 
 .83465914 144 
 
 66931888 
 
 
 
 
 
 
 
 
 500 
 
 19.68513500 
 
 114 
 
CONVERSION TABLE 
 
 MILLIMETER EQUIVALENTS OF FRACTIONAL INCHES 
 & inch to 12% Inches 
 
 
 1* 
 
 2* 
 
 3' 
 
 4* 
 
 5" 
 
 6" 7' 
 
 8' 
 
 9* 
 
 10' 11' 
 
 12' 
 
 1 
 
 25 3995 
 
 50.7990 
 
 76.1986 
 
 101.598 
 
 126.998 
 
 152.397ll77.797 
 
 203.196 
 
 228.596 
 
 253.995279.394 
 
 304.794 
 
 1/64 0.3968 
 
 25.7964 
 
 51 1959 
 
 76.5954 
 
 101.995 
 
 127.394 
 
 152.794178.193 
 
 203.593 
 
 228.992 
 
 254.392279.791 
 
 305.191 
 
 1/32 0.7937 
 
 26.1932 
 
 51.5928 
 
 76.9923 
 
 102.391 
 
 127.791 
 
 153.190178.590 
 
 203.990 
 
 229.389 
 
 254. 7891280.188 
 
 305.588 
 
 3/64J .1906 
 
 26 5901 
 
 51.9896 
 
 77.3892 
 
 102.788 
 
 128.188 
 
 153.588178.987 
 
 204.386 
 
 229 . 786 
 
 255s 1861280. 585 
 
 306.985 
 
 1/161 .5874 
 
 26 9870 
 
 52.3865 
 
 77.7860 
 
 103.185 
 
 128.585 
 
 153.984J179.384 
 
 204 . 783 
 
 230.183 
 
 255. 5821280. 982 
 
 306.381 
 
 5/64 .9843 
 
 27 3838 
 
 52.7834 
 
 78.1829 
 
 103.582 
 
 128.982 
 
 154.381179.781 
 
 205.180 
 
 230.580 
 
 255. 9791281. 379 
 
 306.778 
 
 3/32' 3812 
 
 27.7807 
 
 53 1802 
 
 78.5798 
 
 103.979 
 
 129.378 
 
 154.778180.177 
 
 205.577 
 
 230.977 
 
 256.376^281.776 
 
 307.175 
 
 7 /64 7780 
 
 28.1776 
 
 53.5771 
 
 78.9766 
 
 104.376 
 
 129.775 
 
 155.175180.574 
 
 205.974 
 
 231.373 
 
 256.773i282.173 
 
 307.572 
 
 1/8 .1749 
 
 28.5744 
 
 53.9740 
 
 79.3735 
 
 104.773 
 
 130.172 
 
 155.572 180.971 
 
 206.370 
 
 231.770 
 
 257.170;282.569 
 
 307.969 
 
 9/64 .5718 
 
 28 9713 
 
 54.3708 
 
 79.7704 
 
 105.169 
 
 130.569 
 
 155.969181.368 
 
 206.768 
 
 232.167 
 
 257.567,282.966 
 
 308.366 
 
 5/32 9686 
 
 29 3682 
 
 54.7677 
 
 80.1672 
 
 105.566 
 
 130.966 
 
 156. 365181. 765 
 
 207.164 
 
 232.564 
 
 257. 964(283. 363 
 
 308.763 
 
 11/64 .3655 
 
 29.7650 
 
 55.1646 
 
 80.5641 
 
 105.963 
 
 131.363 
 
 156. 762182. 162 
 
 207.561 
 
 232.961 
 
 258. 360^283. 760 
 
 309.160 
 
 3/16 .7624 
 
 30.1619 
 
 55.5614 
 
 80.9610 
 
 106.360 
 
 131.760 
 
 157.159 182.559 
 
 207.958 
 
 233.358 
 
 258.757J284.157 
 
 309.556 
 
 13/64 1592 
 
 30.5588 
 
 55.9583 
 
 81.3579 
 
 106.757 
 
 132.156 
 
 157.556182.956 
 
 208.355 
 
 233.755 
 
 259. 154(284. 554 
 
 309.953 
 
 7/32 .5561 
 15/64 .9530 
 1/4 ! .3498 
 17/64 .7467 
 
 30.9556 
 31.3525 
 31.7494 
 32.1462 
 
 56.3552 
 56.7520 
 57.1489 
 57.5458 
 
 81.7547 
 82.1516 
 82.5485 
 82.9453 
 
 107.154 
 107.551 
 107.948 
 108.344 
 
 132.553 
 182.950 
 133.347 
 133.744 
 
 157. 953 183. 3521208. 752 
 158. 350183. 749 209. 149 
 158.747184.146209.546 
 159.143 184.543209.943 
 
 234.152259.551284.951 
 234. 5481259. 948'285. 347 
 234. 9451260. 3451285. 744 
 235 . 342 ! 260 . 742 286 . 141 
 
 310.350 
 310.747 
 311.144 
 311.541 
 
 9/32J .1436 
 
 32.5431 
 
 57.9426 
 
 83.3422 
 
 108.741 
 
 134.141 
 
 159. 540(184. 940 
 
 210.339 
 
 235.739 
 
 261.139 : 286.538 
 
 311.938 
 
 19/64 .5404 
 
 32 9400 
 
 58.3395 
 
 83.7391 
 
 109.138 
 
 134.538 
 
 159.937185.337 
 
 210.736 
 
 236.136 
 
 261.535'286.935 
 
 312.334 
 
 5/16 7.9373 
 
 33.3368 
 
 58.7364 
 
 84.1359 
 
 109.535 
 
 134.935 
 
 160.334 185.734 
 
 211.133 
 
 236.532 
 
 261.9321287.332 
 
 312.731 
 
 21/641 8 3342 
 
 33.7337 
 
 59.1333 
 
 84.5328 
 
 109.932 
 
 135.331 
 
 160.731 186.131 
 
 211.530 
 
 236.930 
 
 262.329287.729 
 
 313.128 
 
 11/32; 8.7310 
 
 34.1306 
 
 59.5301 
 
 84.9297 
 
 110.329 
 
 135.728 
 
 161.128186.527 
 
 211.927 
 
 237.326 
 
 262.726 ! 288.126 
 
 313.525 
 
 23/64- 9. 1279 
 
 34 . 5274 
 
 59.9270 
 
 85.3265 
 
 110.726 
 
 136.125 
 
 161.525186.924 
 
 212.324 
 
 237.723 
 
 263. 123^288. 522 
 
 313.922 
 
 3/8 9 5248 
 
 34 9243 
 
 60 3239 
 
 85.7234 
 
 111.122 
 
 136.522 
 
 161.922187.321 
 
 212.721 
 
 238.120 
 
 263.520288.919 
 
 314.319 
 
 25/64 1 9.9216 
 13/3210 3185 
 
 35.3212 
 35.7180 
 
 60.7207 
 61.1176 
 
 86.1203 
 86.5171 
 
 111.529 
 111.916 
 
 136.919 
 137.316 
 
 162.318 187.718213.118 
 162.715188.115|213.514 
 
 238.517263.9171289.316 
 238. 914 264. 3131289. 713 
 
 314.716 
 315.113 
 
 27/6410.7154 
 
 36.1149 
 
 61.5145 
 
 86.9140 
 
 112.313 
 
 137.713 
 
 163.112;188.512 
 
 213.911 
 
 239.311 
 
 264.710290.110 
 
 315.509 
 
 7/1611.1122 
 
 36.5118 
 
 61.9113 
 
 87.3109 
 
 112.710 
 
 138.109 
 
 163.509188.909 
 
 214.308 
 
 239.708 
 
 265.107290.507 
 
 315.906 
 
 29/6411.5091 
 
 36.9087 
 
 62.3082 
 
 87.7077 
 
 113.107 
 
 138.506 
 
 163.906189.305 
 
 214.705 
 
 240.105 
 
 265.504'290.903 
 
 316.303 
 
 15/32H1.9060 
 
 37.3055 
 
 62.7051 
 
 88.1046 
 
 113.504 
 
 138.903 
 
 164.303189.702 
 
 215.102 
 
 240.501 
 
 265. 901 j29 1.300 
 
 316.700 
 
 31/6412.3029 
 
 37.7024 
 
 63.1019 
 
 88.5015 
 
 113.901 
 
 139.300 
 
 164.700190.099 
 
 215.499 
 
 240.898 
 
 266.298i291.697 
 
 317.097 
 
 1/2 12.6997 
 
 38.0993 
 
 63.4988 
 
 88.8983 
 
 114.297 
 
 139.697 
 
 165.097190.496 
 
 215.896 
 
 241.295 
 
 266.695,292.094 
 
 317.494 
 
 33/6413.0966 
 
 38.4551 
 
 63.8957 
 
 89.2952 
 
 114.694 
 
 140.094 
 
 165.493190.893 
 
 216.292 
 
 241.692 
 
 267.092292.491 
 
 317.891 
 
 17/3213.4934 
 
 38.8930 
 
 64.2925 
 
 89.6921 
 
 115.091 
 
 140.491 
 
 165.890191.290 
 
 216.689 
 
 242.089 
 
 267.488j292.888 
 
 318.287 
 
 35/6413.8903 
 
 39.2899 
 
 64.6894 
 
 90.0989 
 
 115.489 
 
 140.888 
 
 166.287191.687 
 
 217.086 
 
 242.486 
 
 267.885293.285 
 
 318.684 
 
 9/1614.2872 
 
 39.6867 
 
 65.0863 
 
 90.4858 
 
 115.885 
 
 141.284 
 
 166.684192.084 
 
 217.483 
 
 2-I2.SS3 
 
 268. 282:293. 682 
 
 319.081 
 
 37/6414.6841 
 
 40.0836 
 
 65.4831 
 
 90.8827 
 
 116.282 
 
 141.681 
 
 167.081192.480 
 
 217.880 
 
 243.279 
 
 268.679294.079 
 
 319.478 
 
 19/3215.0809 
 
 40.4805 
 
 65 . 8800 
 
 91.2795 
 
 116.679 
 
 142.078 
 
 167.478192.877 
 
 218.277 
 
 243.676 
 
 269.076294.475 
 
 319.875 
 
 39/6415.4778 
 
 40.8773 
 
 66.2769 
 
 91.6764 
 
 117.075 
 
 142.475 
 
 167.875il93.274 
 
 218.674 
 
 244.073 
 
 269.473,294.872 
 
 320.272 
 
 5/8 115.8747 
 
 41.2742 
 
 66.6737 
 
 92.0733 
 
 117.472 
 
 142.872 
 
 168.271193.671 
 
 219.071 
 
 244.470 
 
 269.870295.269 
 
 320.669 
 
 41/6416.2715 
 
 41.6711 
 
 17.070(1 
 
 92.4701 
 
 117.869 
 
 143.269 
 
 168.668194.068 
 
 219.467 
 
 244.867 
 
 270.266295.666 
 
 321.066 
 
 21/3216.6684 
 
 42.0679 
 
 67.4675 
 
 92.8670 
 
 118.266 
 
 143.666 
 
 169.065194.465 
 
 219.864 
 
 245.263 
 
 270.663296.063 
 
 321.462 
 
 43/6417.0653 
 
 42.4648 
 
 67.8643 
 
 93.2639 
 
 118.663 
 
 144.063 
 
 169.462194.862 
 
 220.261 
 
 245.661 
 
 271.060|296.460 
 
 321.859 
 
 11/1617.4621 
 
 42.8617 
 
 68.2612 
 
 93.6608 
 
 119.060 
 
 144.459 
 
 169.859195.258 
 
 220.658 
 
 246.058 
 
 271.457'296.857 
 
 322.256 
 
 45/6417.8590 
 
 43.2585 
 
 68.6581 
 
 94.0576 
 
 119.457 
 
 144.856 
 
 170. 256 I 195. 655 
 
 221.055 
 
 246.454 
 
 271. 8541297. 253 
 
 322.653 
 
 23/32 18. 2559 
 
 43.6554 
 
 69.0549 
 
 94.4545 
 
 119.854 
 
 145.253 
 
 170.653196.052 
 
 221.452 
 
 246.851 
 
 272.251297.650 
 
 323 . 050 
 
 47/6418.6527 
 
 44.0523 
 
 69.4518 
 
 94.8513 
 
 120.250 
 
 145.650 
 
 171.050196.449 
 
 221.849 
 
 247.248 
 
 272.648298.047 
 
 323.447 
 
 3/4 19.0496 
 
 44.4491 
 
 69.8487 
 
 95.2482 
 
 120.647 
 
 146.047 
 
 171.446196.846 
 
 222.245 
 
 247.645 
 
 273. 0451298.444 
 
 323.844 
 
 49/6419.4465 
 
 44 . 8460 
 
 70.2455 
 
 95.6451 
 
 121.044 
 
 146.444 
 
 171.843197.243 
 
 222.642 
 
 248.042 
 
 273.441:298.841 
 
 324.241 
 
 25/3219.8433 
 
 45.2429 
 
 70.6424 
 
 96.0419 
 
 121.441 
 
 146.841 
 
 172.240197.640 
 
 223.039 
 
 248.439 
 
 273. 8381299. 238 
 
 324.638 
 
 .51/5420.2402 
 
 45.6397 
 
 71.0393 
 
 96.4398 
 
 121.838 
 
 147.237 
 
 172.637198.037 
 
 223.436 
 
 248.836 
 
 274.235i299.635 
 
 325.035 
 
 13/1620.6371 
 
 46.0366 
 
 71.4362 
 
 96.8357 
 
 122.235 
 
 147.634 
 
 173.034198.433 
 
 223.883 
 
 249.232 
 
 274.632300.032 
 
 325.431 
 
 53/64 21.0339 
 
 46.4335 
 
 71.8330 
 
 97.2326 
 
 122.632 
 
 148.031 
 
 173.431 198.830 
 
 224.230 
 
 249.629 
 
 275.029300.428 
 
 325.828 
 
 27/3221.4308 
 55/6421.8277 
 7/8 22.2245 
 
 46.8303 
 47.2272 
 47.6241 
 
 72.2299 
 72.6267 
 73.0236 
 
 97.6294 
 98.0263 
 98.4232 
 
 123.029 
 123.425 
 123.822 
 
 148.428 
 148.825 
 149.222 
 
 173 . 828 199 . 227 224 . 627 
 174. 224 199. 624i225. 024 
 174. 6211200. 021 225. 420 
 
 250:026!275.426;366.825 
 250.423,275.823,301.222 
 250.820276.220:301.619 
 
 326.225 
 326.622 
 327.019 
 
 57/6422.6214 
 29/3223.0183 
 
 48.0209 
 48.4178 
 
 73.4205 
 73.8173 
 
 98.8200 
 99.2169 
 
 124.219 
 124.616 
 
 149.619 
 150.016 
 
 175. 0181200. 418J225. 817 
 175. 415200. 815 ! 226. 214 
 
 251 .217)276 . 616;302 . 016 
 251. 614 277.013;302. 413 
 
 327.415 
 327.812 
 
 59/6423.4151 
 
 48.8147 
 
 74.2142 
 
 99.6137 
 
 125.013 
 
 150.412 
 
 175.8121201.211 
 
 226.611 
 
 252.011 
 
 277.410!302.810 
 
 328.209 
 
 lD/16'23.8120 
 
 49.2116 
 
 74.6111 
 
 100.011 
 
 125.410 
 
 150.809 
 
 176.209201.608 
 
 227.008 
 
 252.407 
 
 277.807i303.207 
 
 328.606 
 
 61/6424.2089 
 
 49 . 6084 
 
 75.0080 
 
 100.408 
 
 125.807 
 
 151.206 
 
 176.606202.005 
 
 227.405 
 
 252.804 
 
 278.204303.603 
 
 329.003 
 
 31/3224.6057 
 
 50 . 0053 
 
 75.4048 
 
 100.804 
 
 126.203 
 
 151.603 
 
 177.003202.402 
 
 227.802 
 
 253.201 
 
 278.601304.000 
 
 329.400 
 
 63/6425.0026 
 
 50.4021 
 
 75.8017 
 
 101.201 
 
 126.600 
 
 152.000 
 
 177.399202.799 
 
 228.198 
 
 253.598,278.998304.397 
 
 329.797 
 
 115 
 
DICKINSON BROS GRAND 
 

 

 UNIVERSITY OF CALIFORNIA LIBRARY 
 BERKELEY 
 
 Return to desk from which borrowed. 
 This book is DUE on the last date stamped below. 
 
 3 1972* 
 
 00 
 
 LD 21-100m-9,'48(B399sl6)476 
 
 72 -1 PM 4