Controller for a machine tool for executing tapping

A device for controlling a machine tool which executes a tapping by using a rotary main shaft to which a tap is attached and a feed shaft which feeds the main shaft, the device comprising:

• a program reader for identifying an index of the size of said tap;
• a temperature detector for detecting the temperature of a motor which drives said main shaft;
• an acceleration storage for storing the acceleration of said main shaft corresponding to the index of the size of said tap;
• a rate storage for storing the rate of varying the acceleration of said main shaft depending upon the temperature of said motor;
• and
• an acceleration calculation unit operated on a processor of the device for calculating a new acceleration of said main shaft by multiplying an acceleration determined from the index of the size of said tap identified by said program reader and from said acceleration storage by a rate determined from said temperature detected by said temperature detector and from said rate storage.