Chapter IV: Machines and Tools for Shrapnel Manufacture (2)

=Using the “Libby” Turret Lathe for Machining Shrapnel Shells.=--One of the many ways of machining a shrapnel shell is illustrated in Figs. 42 and 43. This shows the set-up on the “Libby” turret lathe, manufactured by the International Machine Tool Co., Indianapolis, Ind. In the first chucking, the forging, as shown at _A_, is held on a special solid arbor provided with a series of corrugations where it contacts with the forging. This, in addition to providing a rigid support, assists in gripping, and the shell is also gripped by a pair of chuck jaws that act as drivers. First, a gang tool-holder carrying three stellite turning tools _o_ is brought into position, and the cutting is started, continuing for a distance of one-third of the length turned. To provide additional support, a roller back-rest, carrying a facing tool, is brought in to steady the work, and, as it is fed forward, the end of the forging is faced off and chamfered.

The second operation on the first chucking is shown at _B_. Here the cutter _a_ is brought in first and starts the band groove, after which the under-cutting tool _b_ is brought in to under-cut the edges of the groove. In the meantime, roller _c_ supports the work. Upon the completion of the groove, the holder carrying cutter _d_ is advanced to finish-face the end of the work and chamfer.

The third operation--cutting the waves in the band groove--is of an interesting character and is accomplished as shown at _C_. A cam _e_ which is free to rotate with the work is first brought in contact with it; then the cross-slide is advanced, carrying the waving tool _f_ and the guide _g_. The guide _g_ fits in the cam groove and controls the operation of the waving tool.

In the second chucking on the first operation the shell is reversed in the chuck and is held in the manner indicated at _D_, Fig. 43. The forging is located in the chuck by a stop-collar _h_, and is gripped on the external diameter by the jaws of the chuck. A stepped boring tool carrying five inserted blades is brought in to rough-bore the internal diameters and machine the shell to the proper thickness at the bottom of the powder pocket. This tool also carries a facing cutter that faces off the shell to the proper length. While the boring tool is working, a broad turning tool, held on the cross-slide, is brought in to bevel the nose preparatory to closing-in. The next step is to taper-ream the internal diameter, as shown at _E_. This completes the operations for the second chucking.

The nose of the shell is now heated and closed in, after which the third series of operations is performed. The first step in the third chucking is to bore for the thread and face the end of the shell with a turret tool, as shown at _F_. The next operation is to machine the curved contour of the nose of the shell with a special turret tool as shown at _G_. Here a wide forming cutter _i_, held in a turret tool-holder, is brought in contact with the work, finishing the nose of the shell to the proper form. During this operation, the shell is supported by a roller in the holder.

The next operation is to form the inside of the nose of the shell to the proper shape, as shown at _H_. This is accomplished with a forming blade _j_, held in a holder clamped in the toolpost. Following this, a collapsible tap is brought in from the turret to thread the nose of the shell, as shown at _I_.

=Machining Shrapnel Shells on a Heavy 22-inch Turret Lathe.=--Still another method of machining shrapnel shells in a heavy turret lathe is shown in Figs. 44 and 45. The shell being machined is an 18-pound British shrapnel shell made from a forging. It is held on an expanding arbor for the first operation, as shown in Fig. 46. The arbor is of the three-point support type and is positive in its grip. Around the periphery of the nose-piece are located three pinions _A_ capable of being rotated by a square-ended wrench. These mesh with teeth in bevel gear _B_ which, in turn, is threaded onto arbor _C_. The forward end of this arbor is cone-shaped and operates the three gripping fingers in the open end of the shell, whereas another rod passing through arbor _C_ and connected to plunger _D_ operates, through the coil spring, the three fingers used in gripping the shell by the powder pocket. This arbor holds the shell securely while the machining operations are being accomplished.

The first operation performed at the first chucking of the work is shown at _C_ in Fig. 44. Here a turning tool-holder clamped to the turret and carrying two cutters is advanced and takes a roughing cut from the exterior diameter of the shell for practically its entire length. The shell is supported by three roller supports as illustrated. The second operation at the first chucking is performed from the cross-slide, as shown at _D_. Here a forming tool of the tangent type roughs out the rifling band groove, leaving sufficient metal in the center for the production of the wave ribs. The third operation is facing off the closed end of the shell from the turret as shown at _E_, and the fourth operation consists in machining the waved ribs as shown at _F_. The tool for accomplishing this operation is held on the cross-slide and is operated from a face-cam on the nose of the spindle.

In the second chucking the shell is held in a three-jaw scroll chuck. The first operation is to rough-bore the inside of the shell and powder pocket with a tool _G_, Fig. 45, held in the turret; directly after this a finishing tool of the same shape is brought in, finishing the surfaces previously roughed out. The second operation is to face off the open end of the shell and taper-form back of the nose from the cross-slide, as shown at _H_, and at the same time turn that portion of the exterior surface of the shell not machined in the previous operation with a tool clamped to the turret as shown at _I_.

Previous to the third chucking, the nose of the shell is heated and closed in. The shell is then held in a three-jaw scroll chuck provided with special jaws. The first operation, as shown at _J_, consists in boring and turning the nose of the shell with a tool held in the turret. Following this, the hole is reamed with a standard reamer and tapped with a collapsible tap. Both of these tools are held in the turret, but are not shown in the illustration. This completes the machining operations on the shell.

=Threading Shrapnel Shells on “Automatic” Threading Lathes.=--Considerable difficulty has been experienced in cutting the square thread in the nose of the French shrapnel shell. One method which accomplishes this operation satisfactorily is shown in Fig. 47, and is accomplished on a 12-inch “Automatic” threading lathe built by the Automatic Machine Co., Bridgeport, Conn., and equipped with special tools for this purpose. Referring to this illustration, it will be seen that two tools are used--a roughing tool _A_, and a finishing tool _B_. Tool _A_ roughs out the thread to a shape similar to the Acme type of thread, whereas tool _B_ squares it up. The roughing and finishing tools are held on the forward and rear carriages, respectively, and are operated simultaneously, being advanced throughout the length of the thread, withdrawn and returned to start a new cut. The method of operating the tools is one of the chief features of the “Automatic” threading lathe.

The base end of shrapnel shells when made from bar stock is as a rule bored out and a plug inserted to eliminate any piping effect in the bar. Fig. 48 shows the method of accomplishing this operation on a 12-inch “Automatic” threading lathe. The work is held in a three-jaw universal chuck and is supported by a roll steadyrest comprising two rolls that are located beneath the work. On the extended end of the rear roller stud is fastened a swinging stop that is used for locating the base of the shell in the correct position ready for threading. The base of the shell is counterbored in another machine, previous to the threading operation. The threading is done with a circular tool held on a special internal threading tool-holder, the latter being retained in the toolpost carriage. The threading tool-holder can be moved longitudinally to bring it into the proper relation to the work. It is also held so that the cutting edge is turned upside down as this action forces the work down in contact with the roller supports. By handling the work in this manner, a steadyrest of the ordinary type is dispensed with and the operation of the attachment facilitated.

One method of making plugs for the base end of shrapnel shells when made from bar stock is shown in Fig. 49. For this work, a 12 by 4 “Automatic” threading lathe equipped with special tools designed for this purpose is used. The machine is provided with a draw-in collet chuck that holds the rough-forged blank. The order of handling the operations on this machine is to use the rear tool _A_ for turning the external diameter of the plug. This is handled at the same rate of feed as that required for threading, so that it is sometimes necessary to take more than one cut, depending on the amount of material left on the diameter. The vertical slide _B_ is for facing only and carries a cutting tool _C_. This is supposed to finish the face in one cut, but as the work will spring considerably, a light finishing cut is taken when the tool is being drawn back from the center to the circumference of the work. The threading tool _D_ is held on the front toolpost and is of single-point construction. The feed given to this tool is automatically controlled, both as to pitch and depth of cut at each traverse.

In actual operation, both the threading and turning tools are in motion all the time on the work, but the tools are independently controlled so that either one can be operated separately. A stop is provided on the back toolpost so as to turn each plug to the same diameter. The automatic throw-out for the feed of the threading tool is set from the front handle on the ratchet and pawl as regularly furnished on the “Automatic” threading lathes.

=Grinding Shrapnel Shells.=--An increasingly large number of shrapnel shell manufacturers are finishing the steel shell by grinding instead of finish-turning. That is, the exterior surface of the shell is rough-turned to within from 0.030 to 0.080 inch of the finished size and is then finished to the required limits and shape by grinding, as shown in Fig. 50. It is claimed by the advocates of grinding that the finishing operations are more speedily performed in this manner and that a more accurate and concentric shell is produced. They also point out the fact that portions of the shell are so hard that it is extremely difficult, if not impossible, to turn it in the allowable time.

The varied heat-treatment given to the shell on the closed end and nose leaves it harder in some sections than others, as indicated in Fig. 51. The section _E_, 2¹⁄₂ inches from the closed end of the shell, must strike from 42 to 50 on the scleroscope, and the section _A_ at the nose must strike between 20 and 25. The section marked _D_, or that part of it to the left of the line that marks the limit of the heat-treating on the closed end, has not been heat-treated at all, and partly on this account, and also because of the gradually diminishing thickness of the shell along this section, it strikes between 40 and 45, decreasing as the thickness of the wall diminishes, until at _C_ the section strikes but 35. Section _B_, adjacent to the annealed nose of the shell, strikes about 30 on the scleroscope.

On the other hand, some manufacturers are not putting the shell through this heat-treating and tempering process, and omit the annealing and machining of the nose after the nosing-in operation. This leaves the nose with considerable stock to remove and in such a condition as regards hardness that the grinding machine becomes a necessity. In the face of these varying degrees of hardness of the shrapnel shell, it will be seen that it is difficult to secure wheels of the right grain and grade to suit all of these conditions. With this information in mind, we can more intelligently take up the actual grinding of the shell. The Norton Grinding Co., Worcester, Mass., has been actively engaged in developing methods of grinding shrapnel shells and the following illustrations and descriptions apply to this work.

Fig. 52 shows the two-operation method of grinding the shrapnel shell. Section _A_ at the open end of the shell is covered by a wide-faced wheel formed to shape, that finishes the radius on the nose at one in-feeding of the wheel. Sections _B_, _C_, and _D_ are covered by a wide-faced wheel, formed to shape so as to finish these three surfaces at one in-feeding of the wheel. Section _E_ at the closed end of the shell is finished completely by turning.

Some manufacturers use a three-operation method of grinding the shrapnel shell as illustrated in Fig. 53. In this case, the sections _A_ and _D_ are first ground with the same wheel, as American manufacturers deem it advisable to grind surface _A_ rather than to finish it by turning. The second stage in this grinding is the finishing of the nose _E_ with a formed wheel, and the third stage is the finish-grinding of the body at points _B_ and _C_.

=Two-operation Method of Grinding Shrapnel Shells.=--The procedure followed in grinding shrapnel shells by the two-operation method is first to screw plugs into the open end of the shells, as shown in Fig. 52. The outer ends of these plugs are centered, and the projection left on the closed end of the shell with the center intact acts as a means of supporting the shell. Some of the Canadian manufacturers vary this practice by cutting off the center projection on the closed end of the shell and fitting a cap with a center hole over the closed end. Others use a ball-bearing cup center to carry the closed end. American manufacturers, however, leave the center projection on the shell until after the grinding has been finished.

In grinding the nose end of the shell, the amount of metal removed varies from 0.020 to 0.090 inch on the diameter. The grinding wheel operates at from 6000 to 6250 surface feet per minute. The speed of the work is 75 revolutions per minute, or a surface speed of practically 75 feet, and the machine used is a Norton 6 by 32 plain grinder. The wheel used is generally 14 inches in diameter by 2¹⁄₄-inch face. The wheel requires truing for every five to twenty shells, depending upon the amount of metal removed and the hardness of the shell. For truing, a simple radius fixture carrying a diamond is used. Fig. 54 shows this wheel-truing device clamped on the grinding machine bed. It is applied in the same manner as the usual steadyrests used for supporting the work. The diamond is mounted in a swinging arm that is operated by a hand lever as shown. By successive cuts across the wheel, the desired shape is attained.

For grinding the body either a 10 by 24 special-purpose or 10 by 36 Norton grinding machine is employed. The amount of metal removed from the body varies from 0.030 to 0.075 inch on the diameter, and the limits vary from 0.002 to 0.010 inch, depending largely on the requirements of the plant in which the work is being done. The wheel used on the body is 20 inches in diameter and is of the ring-wheel type. It will be noticed in Fig. 52 that the wheel for grinding the body is also formed to shape. The method of truing the wheel for shaping the shrapnel shell body is shown in Fig. 55. This attachment is clamped to the front of the grinding machine bed and at the top of the bracket is fitted a slide _A_ operated by handwheel _B_. Upon the face of this slide nearest the grinding wheel is pivoted an angular arm _C_ that supports the diamond _D_ at its lower end. Under the end of the upper arm is a spiral spring that keeps the diamond normally back from the wheel. A plate former _E_ clamped to the bottom face of the bracket is shaped to agree with the form to be given the wheel. At the lower extremity of the arm and behind the diamond is mounted a roll _F_ that bears constantly against form _E_. When the diamond slide is reciprocated by turning the handwheel, the diamond is made to traverse a path conforming with the cam that guides it. By moving the wheel in toward the diamond and making successive traversings of the diamond, the wheel is given the desired shape.

For grinding the body, the wheel must be trued after every ten to twenty-five shells are ground, depending upon the amount of metal removed and the hardness of the shell. In grinding shrapnel shells, the usual method is to fit a lot of the shells with the driving plugs and carry them all through to completion before removing the plugs.

=Removing Center End From Shrapnel Forgings.=--For performing practically all the machining operations on the shell, a center projection is left on the closed end of the shell for supporting it. This, of course, must be removed before the shell is completed. One method of doing this is to use a Besly No. 14 ring-wheel grinder equipped with a special fixture. A Besly grinder fitted up for this work is shown in Fig. 56, and the fixture used for holding the shell is shown in Fig. 57. The machine, as furnished, is arranged for wet grinding, but is not so fitted up in the illustration. The fixture is fastened to the geared lever feed table and is of simple design. It is provided with a backing-up stop _A_, the work resting in two semi-spherical groove projections on the fixture. The operator simply holds the shrapnel shell in place by hand and then feeds it in against the wheel and traverses it past in the usual manner. The time for removing a ⁵⁄₈-inch diameter stub end projecting ³⁄₈ inch from the body of the shell is less than a minute.

=Press Tools for Making Powder Cup.=--In the British shrapnel shell, the powder in the base of the shell used for exploding it and ejecting the lead bullets, etc., is held in a tin-plate powder cup. This is completed in the punch press in the manner shown in Figs. 58 and 59, and comprises two parts, a base and a top. The base is made from tin plate 0.022 inch thick, whereas the top is made from 0.036 inch thick tin plate. The bottom of the cup is completed in one operation with the punch and die shown in Fig. 58, which is held in a single-action press. It is turned out from a blank 3⁷⁄₃₂ inches in diameter and is cut out and formed in one operation. The completed size is 2¹⁄₄ inches diameter by ⁷⁄₈ inch high. After cupping, the top edge is trimmed in a turret lathe. The press operations on the top, as shown in Fig. 59, are a little more complex. The first operation consists in cutting out a blank 2¹⁹⁄₃₂ inches in diameter. Then the edge is turned up with another punch and die shown in the center of the illustration. The next operation is piercing the center with the punch and die at the right, and the last operation is drawing out a flange around the pierced hole. The tools for this operation are shown to the extreme right, as is also a completed powder cup. The final operation on the cup consists in soldering the top to the base.

=Shrapnel Bullets.=--The most deadly and effective parts of a shrapnel are the lead bullets which are held in the shell. When the timing fuse explodes the powder in the base of the shell, the nose is blown off and the bullets are thrown out in a cone shape. The range covered by these bullets in the 18-pound shrapnel shell is about 250 square yards. The lead bullets, which in most shrapnel are ¹⁄₂ inch in diameter, are made from several different compositions, but consist chiefly of 87¹⁄₂ parts lead and 12¹⁄₂ parts antimony. The number of bullets carried in shrapnel shells of the different governments varies. There are 252 in the American 15-pound shell, and 235 or 236 in the British 15-pound shell. The bullets used by the U. S. government have six flattened sides, to facilitate packing, whereas those used by foreign governments are spherical.

There are several methods of making shrapnel bullets. One is to cast the bullets in iron molds, which are split in the center, so that the bullet can be removed when cast. Another is to cut off slugs from lead wire and strike these between dies in a heading machine. The bullet heading machine takes the wire from a reel, cuts it off, forms it and trims off the resultant flash automatically. In making the American bullets, a second operation follows, consisting in flattening the sides. The Waterbury Farrel Foundry & Machine Co. furnishes unit equipments for doing this work. For the flattened bullets, the unit consists of one hydraulic wire extruding press and fourteen heading machines capable of giving a production of 850 bullets per minute. For the spherical bullet, the unit equipment consists of one hydraulic extruding press and eight heading machines, giving a production of 950 bullets per minute.

The method of casting lead bullets in ordinary molds is antiquated, and another method somewhat similar to that just described has taken its place. The first step is to produce the wire from which the bullets are eventually made. This is accomplished in two ways. The first is the hot metal process and consists in pouring the molten lead into a cylinder, from which it is extruded through a die by a plunger advanced into the cylinder. By this method, it is necessary to allow the metal to settle before the press can operate. An improvement over this is utilized in presses built by a hydraulic lead press manufacturer of Brooklyn, and consists in first casting ingots of the required diameter and length and then charging the press with these instead of pouring the molten lead into the press chamber. Two presses have been designed for this process. One has a capacity of 700 tons and is charged with ingots weighing 150 pounds, whereas the other has a 900-ton capacity and is charged with 200-pound ingots. The product from these two machines is 1800 pounds of lead wire from the small and 2500 pounds from the large press per hour. The wire as it is extruded from the die is wound on a reel carrying 2000 pounds of wire.

There are two principal types of swaging machines used for making these lead bullets from wire. One carries a single set of dies, whereas the other carries twelve sets of tools. The operation of the latter will be described. Referring to the diagram, Fig. 60, twelve reels of lead wire--not shown--are arranged in tandem on stands behind the press, six reels in a row. The wire is conveyed from these reels to the dies by a feeding mechanism, being guided to the individual tools by a plate _A_, having twelve U-shaped impressions in its top edge. The wire now passes over a spring _B_ which serves to lift it up slightly at each stroke of the press. The tools _C_ and _D_, as shown, are provided with half-spherical depressions in their adjacent faces and are set so that they come within ¹⁄₆₄ inch of meeting. The dies are guided and controlled in action by a special mechanism, and the press in which they are carried operates at 70 revolutions per minute. This gives a rated production of 840 bullets per minute. As is clearly indicated in the illustration, considerable scrap is formed in making lead bullets by this process--in fact the scrap is about 33 per cent of the reel of wire; also owing to the setting of the punches a slight fin is formed around the periphery of the bullet.

After forming, the bullets are taken to a tumbling machine where they are tumbled for one hour. No other material is put into the tumbling barrel, but the action of the bullets working on themselves satisfactorily removes all the fins. Both the swaging and tumbling operations must be carefully watched because of the necessity of having the bullets a certain weight. The allowable variation on one pound of bullets is one dram, and there are forty-one bullets to the pound. Ten pounds of lead rod make 6¹⁄₂ pounds of bullets, and the scrap resulting from the swaging operation is remelted and used over again. After tumbling, the bullets are inspected and are then ready for use.