Considerable ingenuity is displayed by automobile repairmen in overcoming various machining difficulties, and an instance of a useful lathe attachment is described in a current issue of the Commercial Motor, an English publication. The repairman had occasion to replace parts of a badly damaged torque tube and ball universal joint and, when he came to turn the ball and its seating, was confronted by a problem, inasmuch as the only machine available was a 12-inch center lathe.

The sketches at Fig. 338 show the attachment constructed and applied, and demonstrates how the concave and convex surfaces required were turned. The upper drawing shows the attachment for turning the concave surface; the lower depicts the ball being machined. The diagram underneath each lathe illustrates the path of the cutting tool. The attachment consisted of flat mild steel strips, the sections being .5 inch by 1 inch. Six lengths were cut off to obtain the necessary travel, and at the base of the angle pieces were drilled two .375-inch diameter holes. The plain ends were drilled out .5 inch.

The swiveling connecting rods, two in number, were drilled out and tapped .5 inch Whitworth at each end, the centers being carefully marked out equal to the radius of the ball and spherical seating; that is, four inches. Permitting these to swing at the end of each angle piece enabled the necessary arc of the cutting tool to be effected.

It will be noted that for either machining operation, one angle strip is bolted to the tail stock of the lathe, and another piece to the top slide under the tool rest. Cross feed only is used, the transverse feed being free altogether so that without touching the handwheel the carriage may readily be pushed along the lathe bed. The cutting tool may then be made to follow the required circular path.

Fig. 338.   Device for Machining Concave and Convex Surfaces on Lathe.

Fig. 338. - Device for Machining Concave and Convex Surfaces on Lathe. A-Path of Cutting Tool for Ball Seating. B - Swivelling Links for Securing Radii. C - Path of Cutting Tool for Sphere.