Patent ID: 7123984

Claim:
A threading control method for moving a cutting tool and a workpiece in synchronicity with rotation of a main spindle to machine thread grooves in the workpiece, the threading control method comprising: computing the present position of the main spindle; generating a correction amount of the main-spindle position in order to make a single-rotation reference signal of the main spindle synchronous with a control cycle, based on the single-rotation reference signal of the main spindle and the computed present position of the main spindle, and correcting, by this correction amount of the main-spindle position, the position of the main spindle so that the single-rotation reference signal of the main spindle and the control cycle are synchronized; confirming the synchronization of the control cycle and the cycle of the single-rotation reference signal of the main spindle whose position has been corrected; and outputting a command to a threading spindle when the main-spindle single-rotation reference signal and the control cycle are synchronized.