Tapered thread numerical control system for a lathe

Claim 1

A numerical control system for use with a lathe to produce a tapered thread on a workpiece mounted for rotational movement comprising means for supporting a thread cutting tool for movement along a first axis for setting the lead of a thread and a second axis for setting the taper of the thread, means for receiving a command for the extent of movement along the first axis for each revolution and the extent of movement along the second axis for each revolution, motor means connected to each axis for producing an incremental movement on each axis essentially simultaneously with receipt of a command pulse, means for producing a fixed number of encoder pulses for each rotation of the workpiece, first means for receiving the encoder pulses and producing command pulses numerically equal to the extent commanded to the first axis for each fixed number of encoder pulses, second means for receiving encoder pulses and producing command pulses numerically equal to the extent commanded to the second axis for each fixed number of encoder pulses, means for causing both the first and second means to receive encoder pulses simultaneously and in which the first means and the second means each includes an error register having a terminal for indicating one direction of its count with each appearance of the indication producing a command pulse, means for changing the error register count in its one direction a number equal to the extent commanded for its axis for each encoder pulse and means for changing the count of the error register in the other direction a number equal to the fixed number of encoder pulses for each command pulse.