Control device for machine tool

A control device for a machine tool that includes a tap mounted on a main spindle relatively movable with respect to a workpiece and machines the workpiece using the tap, the control device comprising:

• a parameter preparing unit that preliminarily stores a predetermined parameter relating to a control;
• an evacuation unit that causes the tap to perform an evacuation operation from the workpiece;
• and
• an evacuation diagnosing unit that diagnoses whether the evacuation operation is normal, wherein
• the parameter preparing unit stores a section modulus, a tensile strength, and a safety factor of the tap as the parameters,
• the evacuation diagnosing unit compares a breaking torque threshold value calculated based on the section modulus, the tensile strength, and the safety factor with an operational torque of the tap to diagnose whether the evacuation operation is normal, and
• when the evacuation diagnosing unit diagnoses that the evacuation operation is abnormal, the evacuation operation is cancelled.