The next point is the carriage, which consists of a platform (L), bridg ing the bed and called the "saddle;" of an apron (_li), containing the means of obtaining motion; of a cross-slide (N); of a swivel-piece (0) and of a tool-slide (P) provided with bolts, to secure the tool. The motion of the tool-slide is effected by a screw worked by the handle Q, and by rotating the swivel-piece 0 it can be moved at any angle to the face plate in a horizontal plane. The cross-slide AT can be moved by a screw, which can be worked either by the handle R or by power through the gears inside the apron controlled by the hand-nut S. Its only motion is parallel to the face-plate. The saddle can be moved along on the bed (only at right angles to the face-plate) in three ways: (i) by hand, with the hand-wheel IV and appropriate gearing in the apron working into the rack seen on the edge of the bed; (2) by power through a train of gearing driven by a groove cut in the lead-screw X and working the rack on the side of the bed, being controlled by the hand-nut (both this power feed and that on the cross-slide can be reversed or stopped by moving the lever U to one side or the other or stopping it in the middle); and (3) by closing a segmented nut (made in two pieces) upon the thread of the lead-screw X by means of the handle V.
The feed is driven from the back end of the live spindle by the gear 1 working into the gear 2 on the shaft 3 carrying three gears keyed fast, as shown. On a shaft (4) below these and meshing with them are three loose gears, any one of which can be fastened to the shaft by a sliding key operated by a clutch-pin (5). On the other end of the shaft is a gear which imparts motion to the lead-screw X through an appropriate train of gears, and thence to the carriage.
The dead or poppet head consists of a spindle (10), of a top piece (11), and of a base piece (72), the whole being firmly clamped to the bed by means of bolts (13). It is necessary for the spindle (10) to have a length wise motion ; and this is imparted by a screw operated by a hand wheel (14) and a pair of gears (15). The whole head can be moved along on the bed by a pinion gearing into the rack on the side of the bed and operated by the ratchet-lever 1G. The top piece 11 can be moved trans versely across the bottom piece 12, thus throwing one end of the work nearer the tool than the other and thereby producing conical surfaces. Both spindles (in each head) have inserted in their ends pointed pieces, called " centres," upon which the work is supported.
When work is slight or cannot be reached by the dead centre or is very long, it is customary to use what is known as a "steady-rest." This con sists of a base piece (?0), which can be firmly clamped to the bed, of a top piece (21), and of three steel pieces (?,?), called "jaws." These pieces, which are adjustable, can be moved by screws until they touch the work, and can then be clamped; they then provide a bearing which supports and steadies the work. To get the work in and out of this conveniently the top piece
21 is made separate and can be entirely removed, thus allowing ample room for handling. It will be seen that this machine provides a variety of speeds of rotation of the work, a variety of rates of power-feed to the tool, supports for the steady running of the work, and movements to the tool by means of which true cylindrical, 3 ngular, or flat surfaces may be produced.
screw-machines one of the best is represented in Figure 3 (f/. 22), which is a lathe having a hollow spindle with a chuck on each end, a carriage having hand and power movement and carrying two tools and a set of open screw-cutting dies, and a slide tool block having four variations of feed and carrying six tools, to be applied to the work successively, these tools being mounted in a " turret," so called because it resembles the turret or tower of the "Monitor" pattern of iron clad vessels of war. This lathe will work upon any kind of pieces which can be held in a chuck and which need the successive operation of several different tools. But, while in many features it resembles a lathe, it is unlike the latter in its treatment of small work. A lathe takes a forged shape awl trims and alters it; the screw-machine takes the roughened bar and finishes the product, doing the work of blacksmith, helper, fire, bolt header, centring-machine, lathe, lathe-chucks, and even making the hole in which the lathesman tries his work. While it wastes iron, it saves labor, which is of much more value than the iron wasted. In this machine there is a chuck (el) with V-jaws, which is fast upon the whole arbor of the machine. There is a steadying-chuck (B) on the rear of the arbor, and an ordinary lathe-carriage (C) slides upon the bed and is worked by the usual hand-wheel (D) and rack-pinion. Across this carriage slides a tool-rest (E) worked by a screw and haying two tool-posts, one in front and one in rear of the work. This tool-rest works upon an intermediate slide, which fits and slides in the carriage, and is moved in and out a short distance by a cam lever (G), an apron on the front end of the slide carrying the lead screw nut H. Resting the cam lever brings the slide outward, and the tool-rest E comes 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 I, which does not extend to the head of the machine, and resetting the tool. The gear is never changed, different lead-screws being used for different threads. The turret 0 turns on a block (lI), which slides on the bed; it has in it six holes, to receive sun dry tools, call be turned to bring any of these tools into action, and is secured by the lock-lever P. The turret slide is quickly moved by hand through the capstan levers U, which also lock it at any point.