Patent ID: 8874255

Claim:
A method of control of rotation of a spindle device of a machine tool comprising the steps of: storing spindle rotational speed change data, which changes a rotational speed of a spindle repeatedly in accordance with an instructed speed, linked with stability limit data, which indicates a stability limit for machining in accordance with the rotational speed of the spindle, selecting, from an instructed spindle rotational speed and the stored stability limit data, spindle rotational speed change data giving less vibration, and using the selected spindle rotational speed change data as the basis to change the rotational speed of the spindle repeatedly, wherein said spindle rotational speed change data is data for changing the rotational speed of the spindle so that timings at which cutting edges of an equal pitch cutting tool which is attached to the spindle strike the workpiece are timings by which the workpiece is struck when using a tool of variable pitch cutting edges.