Patent ID: 7613541

Claim:
A threading control method for performing a threading operation on a workpiece by moving, in synchronization with rotation of a main spindle on which the workpiece is mounted, either a cutter or the workpiece in a feeding spindle direction which is a central axis direction of the workpiece rotated by the main spindle, the method comprising: outputting a thread-pitch command value and a programmed main-spindle rotation frequency by using a machining program; calculating a first servo feed rate of a feeding spindle that controls the cutter based on the thread-pitch command value and the programmed main-spindle rotation frequency; calculating a second servo feed rate of the feeding spindle based on the thread-pitch command value, the programmed main-spindle rotation frequency and a main-spindle override value received from an external source; calculating, when the workpiece is threaded either at a second feed rate different from a previous first feed rate, or on a second machine different from a previously used first machine, a main-spindle threading-start timing shift based on the first servo feed rate, the second servo feed rate, and a servo-spindle acceleration time-constant of the feeding spindle; and altering a threading-start timing to thread the workpiece based on the calculated main-spindle threading-start timing shift.