Machine tool

A machine tool, comprising:

• a gripping unit configured to grip a shaft-shaped workpiece;
• a tool movable in a radial direction and an axial direction with respect to the workpiece;
• a processing control unit configured to perform a threading by repeating a tool path in which the tool cuts into the workpiece in the radial direction, moves in the axial direction of the workpiece, and moves away from the workpiece in the radial direction, while the workpiece and the tool are relatively rotated around an axis line of the workpiece;
• a rotation speed control unit configured to vary the relative rotation speed of the workpiece and the tool in units of the tool path;
• and
• a rotation speed calculation unit configured to calculate the rotation speed of each of the tool paths, wherein
• the rotation speed control unit does not continuously vary the rotation speed within one path, but varies the rotation speed to a varied maximum speed higher than a reference rotation speed set value by a variation width set value or a varied minimum speed lower than the reference rotation speed set value by the variation width set value, or varies to any one of a plurality of rotation speed candidate values, and
• the rotation speed control unit refers to speed condition information that indicates a condition of preliminarily stored reference rotation speed and variation width, or the rotation speed candidate value assuming that a chatter vibration is to be reduced, and when at least one of the reference rotation speed set value and the variation width set value, or the rotation speed candidate value does not satisfy the condition, the rotation speed control unit varies at least one of the reference rotation speed set value and the variation width set value, or varies the rotation speed candidate value so as to satisfy the condition, or the rotation speed control unit indicates on a display unit that varying should be made.