Abstract: A computer numerical control system for controlling a lathe or similar machine tool in the cutting of threads. One computer is used as an interpolator to produce speed commands in real time for producing a smooth cutting tool motion. A second computer is used as an axis controller for receiving said speed commands and for controlling the servo circuits of up to six machine tool axes. A resolver attached to the rotating spindle is utilized to synthesize a tachonometric signal, and is also connected to an interrupt circuit to measure the spindle speed and position. The interpolator then uses this spindle information to synchronize the cutting tool motion with the spindle angular speed and position to enable multiple passes of the cutting tool along the same thread line.