Fig. 30. Attachment for Turning Spherical End of Gasoline Engine Piston
Another spherical turning attachment is shown in [Fig. 30]. This is used for machining the ends of gasoline engine pistons. The cross-slide has bolted to it a bar A carrying a roller which is pressed against a forming plate B by a heavy spring C. The forming plate B, which is attached to a cross-piece fastened to the ways of the lathe bed, is curved to correspond with the radius required on the piston end, and when the tool is fed laterally by moving the cross-slide, it follows the curve of plate B. The piston is held in a special hollow chuck which locates it in a central position and holds it rigidly.
In connection with lathe work, special attachments and tools are often used, especially when considerable work of one class must be turned; however, if a certain part is required in large quantities, it is usually more economical to use some semi-automatic or automatic turning machine, especially designed for repetition work.
Fig. 31. Front and Rear Tools used for Roughing
Turning with Front and Rear Tools.—In ordinary engine lathe practice, one tool is used at a time, but some lathes are equipped with tool-holders at the front and rear of the carriage so that two tools can be used simultaneously. [Fig. 31] shows a detail view of a lathe in which front and rear tools are being used. These tools are of the inserted cutter type and the one at the rear is inverted, as the rotary movement of the work is, of course, upward on the rear side. This particular lathe was designed for taking heavy roughing cuts and has considerable driving power.
The part shown in this illustration is a chrome-nickel steel bar which is being roughed out to form a milling machine spindle. It is necessary to reduce the diameter of the bar from 57/16 inches to 33/4 inches for a length of 27 inches, because of a collar on one end. This reduction is made in one passage of the two tools, with a feed of 1/32 inch per revolution and a speed of 60 revolutions per minute. The use of two tools for such heavy roughing cuts is desirable, especially when the parts are required in large quantities, because the thrust of the cut on one side, which tends to deflect the work, is counteracted by the thrust on the opposite side.