CH669920

Machining the circumferences of workpieces, particularly piston rings, in a variety of out-of-round contours and diameters requires only a single copying disc having a basic out-of-round contour. The copying disc is driven in synchronism with the angle of rotation alpha of piston rings to be machined by a direct current servomotor and, in order to generate the desired out-of-round contour, is caused to deviate from its synchronous movement by pulses received from a computer for the leading and lagging difference angles of rotation delta phi. An adjustable coupling member is provided between a copying disc sensor (such as a double lever) and the tool holder for transferring the out-of-round contour from the copying disc to the workpiece.