Now i is attached to a shaft having journal bearing (and capable of end motion) at the back of the lathe head, and on this bar is attached the slide rest j, in which the turning or threading tool may be placed. The shaft above referred to having end motion, may be operated (when the nut in the lever i is lifted clear of the collar) laterally by means of the lever i; hence to traverse j to the right, or for the back traverse, i is raised and pulled to the right, i is then lowered, the nut engages with the collar, and the tool is traversed to the cut. The cut is adjusted for diameter by the slide rest, which is provided with an adjustable stop to determine the depth to which the tool shall enter the work.
It is obvious that this part of the machine, may be employed for ordinary turning operations, if the collar be of suitable pitch for the feed.
Fig. 693.
[Figs. 692] and [693] represent a screw machine for general work.
a is a chuck with hardened steel V-shaped jaws. It is fast on the hollow arbor of the machine. b is a steadying chuck on the rear end of the arbor. The arbor has a two and one-sixteenth hole through it and its journals are very large and stiff. It is of steel, and runs in gun-metal boxes. The cone pulley and back gear is of the full proportion and power of an eighteen-inch lathe. c is an ordinary lathe carriage fitted to slide on the bed, and be operated by hand-wheel d and a rack pinion as usual. Across this carriage slides a tool rest e operated by screw as usual, and having two tool posts, one to the front and one to the rear of the work. This tool rest, instead of sliding directly in the carriage as is the case with lathes, slides on an intermediate slide which fits and slides in the carriage. This intermediate slide is moved in and out, a short distance only, by means of cam lever g. An apron on the front end of this slide carries the lead screw nut h. When the cam lever is raised it brings the slide outward about half an inch, and the tool rest e comes out with it and at the same time the nut leaves the lead screw. The inward movement of the slide is always to the same point, thus engaging the lead screw and resetting the tool. In cutting threads with a tool in the front tool post the tool is set by moving the tool rest as usual, and at the end of the cut the cam lever serves to quickly withdraw the tool and lead screw nut so that the carriage can be run back. The tool rest is then advanced slightly and the new cut taken. By this means threads are cut without any false motions, and the threads may be cut close up to a shoulder.
i is the lead screw. This screw does not extend, as is usual, to the head of the machine. It is short and is socketed into a shaft which runs to the head of the machine and is driven by gearing as usual. The lead screw is thus a plain shaft with a short, removable, threaded end. The gearing is never changed. Different lead screws are used for different threads, thus permitting threads to be cut without running back. The lead screws are changed in an instant by removing knob j. The lead screw nut h is a sectional nut, double ended, so that each nut will do for two pitches, by turning end for end in the apron. l is an adjustable stop which determines the position of the carriage in cutting off, facing, &c. k is an arm pivoted to the rear of the carriage and carrying three open dies like a bolt cutter head. At m is a block sliding or capable of being fed along the bed. n is a gauge screw attached to this block and provided with two nuts. The stop lever shown in the cut turns up to straddle this screw, and the position of the nuts determines how far each way the block may slide. o 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 p.
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 lock the turret at any point. The turret slide is fed, in heavy work, by the crank-wheel r on its tail screw. This tail screw carries, inside the crank-wheel, two gears s, 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 t locks either one to the screw. Both the carriage and turret are provided with oil pots not shown in the cuts.