Numeric control device of machine tool

A numeric control device for detecting an error or a defect of a motor or a spindle motor of a machine tool, the numeric control device comprising:

• a first storing part for storing master vibration data of the spindle or the spindle motor, the master vibration data being prepared by associating data of the vibration outputted from a vibration sensor arranged on the spindle or the spindle motor with an operation pattern for detecting the defect of the spindle or the spindle motor, obtained by rotating the spindle or the spindle motor in no-load condition;
• a calculating part for calculating a difference value between newly measured data according to the operation pattern and the master vibration data stored in the first storing part;
• a judging part for determining that the measured data is abnormal when the difference value calculated by the calculating part exceeds a predetermined reference value;
• and
• an outputting part for outputting information regarding the measured data when the judging part determines that the measured data is abnormal.