The main parts of a typical screw cutting lathe are clearly shown in Fig. 318. The view at A is from the end showing screw cutting and feed gears, that at B is a front view showing the parts convenient to the operator. While the various important lathe parts have been outlined in other portions of the book it may be well to review these so the novice operator can understand the parts and what they are for. The main portion of any lathe is the bed which is supported at the right height from the floor by cast iron legs. The bed supports the head stock at one end, this in turn carries the spindle to which face plate or chuck is fastened. The spindle is supported by bearings and is driven by either of two methods. With the back gears out, the cone pulley group may be locked to the spindle by a simple clutch pin, which gives the highest spindle speed. With the clutch pin out, the pulley group will turn without turning the spindle. With the back gear in and the clutch pin out, the spindle will be turned at a low speed determined by the back gear reduction. Some work can be done better with the spindle turning fast, such as wood and brass turning, filing, finishing, etc., while "hogging" or removing much metal by taking heavy chips always requires the use of the back gears. The carriage consists of two parts, a portion resting on the ways of the lathe bed carrying the cutting tool and an apron attached to it that carries the mechanism used in moving the carriage back and forth under the action of the lead screw. The lead screw determines the lateral feed or movement of the carriage from end to end of the lathe.

The tail stock of all lathes is adjustable along the ways and supports one center. The center is mounted in a movable barrel in the tail stock. This barrel may be moved back and forth by a screw turned by hand wheel A and locked absolutely in place at any position by lever C. The tail stock may be locked by a suitable lever which clamps it to the bed. The lead screw may be driven at various speeds by varying the gear ratios and may be turned in either direction by moving lever E. The tool post is usually carried by a compound rest attached to the carriage. A compound rest makes it possible to feed the tool in or out in a direction parallel to the ways by lever A and in a direction at right angles to the ways by lever B and also to set the tool at any desired angle with the work. Both levers may be worked simultaneously. The reverse gear is brought in action by lever E on the end of the head stock. The carriage may be moved manually when desired by hand wheel B. The small knob on wheel C actuates a clutch for the carriage cross feed, while lever D makes the connection between the half nuts carried by the carriage and the lead screw in thread cutting.

Fig. 318.   Views of Typical Screw Cutting Lathe with Important Parts Depicted.

Fig. 318. - Views of Typical Screw Cutting Lathe with Important Parts Depicted.

The parts of the countershaft assembly overhead are easily identified. The countershaft carries a pulley cone group to drive that on lathe head stock. The small step of the countershaft cone is belted to the large step of the spindle drive cone. Two friction clutches are used, one being driven by a crossed belt to obtain reverse motion. The shipper handle actuates the clutch cone and is in turn operated by a shipper bar making it easy to operate the clutches from any part of the lathe.

An interior view of the usual form of automatic apron furnished on South Bend lathes is shown at Fig. 319-A. It will be noted that the lead screw is provided with a spline which drives the worm operating the power cross feed and the automatic longitudinal feed. The half nuts, which are used in screw cutting, are clearly shown. The various levers and wheels previously described are also indicated. The reverse of the South Bend Lathe is shown at Fig. 319-B. The reverse gear carrier may be rocked so either gear A or B is in mesh with spindle gear C or it may be left in a neutral position with both gears out of mesh when it is desired to run spindle on the direct drive for polishing, etc. The graduated compound rest is shown at 319-C. In addition to enabling both cross and longitudinal tool post feed, the rest swivels in a complete circle and is clamped in any position desired by T head bolts. The graduation is such that it may be set for any angle.

Modern Lathe Practice

Fig. 319.   Views of Important Lathe Part Assemblies Making Design and

Fig. 319. - Views of Important Lathe Part Assemblies Making Design and Location of Components Clear.