A machine tool produces a tapered slot by moving a tool laterally of the workpiece as well as directly into it. The lateral movement is shortened at the end of each half reciprocation, so as to form the taper. The shortened stroke is achieved by use of electronic circuitry in which transducers are utilized to indicate by voltage output, the magnitude of movement of the tool into the workpiece relative to the magnitude of the movement of the tool laterally thereof and on positive or negative numerical pair being noted, deriving a further signal therefrom and utilizing it to change the direction of reciprocation.