Numerical control device

A numerical control device that controls a machine tool including:

• a work rotating shaft configured to rotate a work;
• a first cutter holder configured to machine a front surface of the work when the work is rotating;
• and a second cutter holder configured to be capable of moving on a surface having an axis direction of the work rotating shaft as a normal and machine the work from a side opposed to an end face of the work, the numerical control device comprising:
• a machining-program storage region having stored therein a machining program including a first command for controlling the rotation of the work rotating shaft while performing front surface machining using the first cutter holder and a second command described using a relative coordinate with respect to the work and for performing position control on the second cutter holder;
• an arc-superimposition-interpolation control unit configured to rotate the work rotating shaft in accordance with the first command and, at the same time, subject the second cutter holder to the position control on a second machining route obtained by superimposing the rotation of the work rotating shaft on a first machining route in accordance with the second command,
• a maximum-speed calculating unit configured to calculate a maximum speed of the work rotating shaft such that speed of the second cutter holder moving on the second machining route does not exceed a maximum allowable speed set in advance;
• and
• a speed clamp unit configured to clamp rotating speed of the work rotating shaft with the maximum speed calculated by the maximum-speed calculating unit.