Vibration suppressing method and vibration suppressing device for us in machine tool

A vibration suppressing device provided in a machine tool having a rotary shaft for use in rotating a tool or a workpiece, for suppressing chatter vibrations generated during rotation of the rotary shaft, the vibration suppressing device comprising:

• a vibration detection unit configured to detect chatter vibrations;
• a storage unit configured to store a plurality of stable rotation speeds at which the chatter vibrations are expected to be suppressed, and at least one switching rotation speed across which a dynamic characteristic of a rotary shaft system changes;
• an optimum rotation speed selection unit configured to select an optimum rotation speed from the plurality of stable rotation speeds, the optimum rotation speed being a rotation speed to which a rotation speed of the rotary shaft is changeable without crossing the switching rotation speed;
• and
• a rotation speed change unit configured to change the rotation speed of the rotary shaft to the optimum rotation speed.