Fig. 4. Rear View of Lathe Apron
The drive for the cross-feed is from gear C to gear F which can be engaged through a friction clutch (operated by knob l, [Fig. 1]) with gear G meshing with a pinion H. The latter rotates the cross-feed screw, which passes through a nut attached to slide D ([Fig. 1]), thus moving the latter at right angles to the ways of the bed. The cross-feed is also reversed by means of lever r. As previously explained, lead-screw S is only used for feeding the carriage when cutting threads. The carriage is engaged with this screw by means of two half-nuts N ([Fig. 4]) that are free to slide vertically and are closed around the screw by operating lever u. These half-nuts can only be closed when lever r is in a central or neutral position, so that the screw feed and the regular turning feed cannot be engaged at the same time. As previously mentioned, lead-screw S, [Fig. 1], is rotated from the lathe spindle, through gears a, b and c, called change gears. An assortment of these gears, of various sizes, is provided with the lathe, for cutting screws of different pitch. The gears to use for any pitch within the range of the lathe are given on the plate I.
Fig. 5. Plan View showing Work Mounted between Centers of Lathe
Example of Cylindrical Turning.—Having now considered the principal features of what might be called a standard lathe, the method of using it in the production of machine parts will be explained. To begin with a simple example of work, suppose a steel shaft is to be turned to a diameter of 21/4 inches and a length of 141/2 inches, these being the finished dimensions. We will assume that the rough stock is cut off to a length of 145/8 inches and has a diameter of 25/8 inches. The first step in this operation is to form conically shaped center-holes in each end of the piece as indicated at c in [Fig. 5]. As all work of this kind is held, while being turned, between the centers h and h1, holes corresponding in shape to these centers are necessary to keep the work in place. There are several methods of forming these center-holes, as explained later.
After the work is centered, a dog A is clamped to one end by tightening screw s; it is then placed between the centers of the lathe. The dog has a projecting end or “tail,” as it is commonly called, which enters a slot in the faceplate F and thereby drives or rotates the work, when power is applied to the lathe spindle onto which the faceplate is screwed. The tailstock center h1, after being oiled, should be set up just tight enough to eliminate all play, without interfering with a free rotary movement of the work. This is done by turning handle n, and when the center is properly adjusted, the tailstock spindle containing the center is locked by tightening handle p. (Ordinary machine oil is commonly used for lubricating lathe centers, but a lubricant having more “body” should be used, especially when turning heavy parts. The following mixtures are recommended: 1. Dry or powdered red lead mixed with a good grade of mineral oil to the consistency of cream. 2. White lead mixed with sperm oil with enough graphite added to give the mixture a dark lead color.)
