L is an adjustable stop which determines the position of the carriage in cutting off, facing, etc. K is an arm pivoted to the rear of the carriage, and carrying three open dies like a bolt-cutter head. is a block sliding on the bed. X is a gauge screw attached to this block and provided with two nuts. The stop lever shown in the cut turns up to strad dle this screw, and the position of the nuts determines how far each way the block may slide. 0 is the turret fitted to turn on the block. It has six holes in its rim to receive sundry tools. It can be turned to bring any of these tools into action, and is secured by the lock lever, 1'.
The turret slide is moved quickly by hand, by means of the capstan levers, U, which by an in-and-out motion also serve to look the turret at any point. The turret slide is fed in heavy work by the hand wheel, .R, on its tail screw. This tail screw carries, inside the hand wheel, two gears, 8, which are driven at different speeds by a back shaft behind the machine. These two gears are loose on the tail screw, and a clutch operated by lever, 7', locks either one to the screw.
Turret TooL9.—The different forms of tools used in the turret on ordinary shop work are illustrated in Figs. 3, to 9.
The end gauge shown in Fig. 4 is simply a hollow shank, A, fitting the turret. and a gauge rod, II, fitting the shank. The shank may be set further in or out of the tur ret, and the rod may be set further in or out of the shank. The end gauge is so set that when the turret is clear back against its stop the end of the rod B will gauge the proper projections of the bar iron from the chuck of the machine. The center, shown in Fig. 5, explains itself ; it is used only in chasing long work in steel. The turner, shown in Fig. (I, consists of hollow shank, A, fitting the turret ; a hardened bushing, B, held in its front end by a set-screw : a heavy, mortised bolt, 0, in the front lug of the shank ; an end-cutting too], li, shaped like a carpenter's mortising chisel, and clamped by the mortised bolt ; a collar screw E. to hold the tool endwise, and a pair of set-screws, F, to swivel the tool and its bolt. Bushing B is to snit the work in hand. The tool, D, is a piece of square steel. hardened throughout. It is held by its bolt with just the proper clearance on its face.
It cuts with its end without any springing, and will on this account stand a very keen angle of cutting edge. It will cut an inch bar away at one trip with a coarse feed. It does not do smooth work, and is, therefore, used only to remove the bulk of the metal, leaving the sizer to follow.
The sizer, shown in Fig. consists of a hollow shank, A. fitting the turret and carrying in its front end It 1111 rdened bushing, B, and it flat tool, a The sizer follows the turner and takes a light water or oil cut, giving size and finish with a coarse feed. Having only light, clean work to do, it holds its size nicely.
The die holder, shown in Figs. 8 and ft, is arranged to automatically stop cutting when the thread is cut far enough. It will cut a full thread cleanly up against a solid shoulder. It
consists of a hollow shank, A, fitting the turret ; a sleeve, B, fitted to revolve and slide ou the front end of the shank, C; a groove, E bored inside the sleeve ; pin, D. on the shank, fitting freely in the groove, E; a keyway, F, at one point in the groove and leading out each way from it, and a thread die, G, held in the front end of the sleeve. When the turret is run for ward the thread die takes hold of the bolt to be cut.
but it revolves idly instead of standing still to cut, until the pin, D, comes opposite the keyway, F, when, the turret still being moved forward, the pin enters the back of the keyway. The sleeve now stands still, the die cuts the thread and pulls the turret along' by the friction of the pin in the keyway. Finally the turret comes against its front stop and can move forward no further. Consequently the sleeve is drawn forward on its shank, C, and the instant the pin, D, reaches the groove, E, the die and sleeve commence to revolve with the work and cease cutting. The machine is then run backward and the turret moved back a trifle. This - causes the pin to catch in the front end of the keyway, and the sleeve is again locked. The die then unscrews, and, in so doing, pushes the turret back. A tap holder may be inserted in place of the (lie, and plug taps may be run to an exact depth without danger.
The following cuts show the operationsperformed in making a machine screw : First Operation.—The bar is inserted through the open chuck. Second turret being clear back against its stop and revolved to bring present the end gauge, the bar is set against the end gauge and the chuck is tightened. This chucks the bar and leaves the proper length projecting from the chuck. Third Operation.—The front tool in the car riage, a beveled side tool, cones the end of the bar so turret tools will start nicely. Fourth Operation.—The turret being revolved to present the turner, the bar is reduced at one heavy cut to near the proper size, the turret stop determining the length of the reduced portion. Fifth Operation.—rhe turret being revolved to present the sizer, the body of the bolt is brought to exact size by a light, quick, sliding cut. Sixth open die arm being brought down, the bolt is threaded, the left carriage stop indicating the length of the threaded part. Seventh Operation.—The turret being revolved to present the die holder, the solid die is run over the bolt, bringing it to exact size with a light cut, and cutting full thread to the exact point desired. Eighth front tool in the carriage chamfers off the end thread. Ninth back tool of the carriage, a parting tool, cuts off the bolt, the left carriage stop determining the proper length of head. Dna Operation.— The bolt being reversed in chuck, the top of the head is water-cut finished by a front tool in the carriage. This operation is deferred till all the bolts of the lot are ready for it.
Screw Propeller : see Engines, Marine.
Screw-threading Machine : see Nut-tapping Machine.