Tap phase detection method, female thread processing method in machine tool, and machine tool

A female thread processing method in which halted female thread processing is continuously performed with a tap mounted to a main spindle of a machine tool, the method comprising:

• preliminarily acquiring a relation between a rotation angle of the main spindle and an existence of a screw thread of a reference tap as a tap before a halt by mounting the reference tap to the main spindle, and detecting existence of the screw thread at a position where the screw thread and a root of thread of the reference tap pass through with a sensor from a direction intersecting with an axial direction of the reference tap while rotating the main spindle;
• acquiring a relation between a rotation angle of the main spindle and an existence of a screw thread of an other tap for continuing the female thread processing by mounting the other tap to the main spindle and detecting existence of the screw thread at a position where the screw thread and a root of thread of the other tap pass through with the sensor while rotating the main spindle;
• calculating a phase difference between the reference tap and the other tap based on the relation between the rotation angle and the existence of the screw thread acquired in the preliminarily acquiring and the relation between the rotation angle and the existence of the screw thread acquired in the acquiring of the relation;
• and
• setting a start position for rotating the main spindle to which the other tap is mounted based on the phase difference, and continuously performing the female thread processing from the start position.

A machine tool for continuously performing halted female thread processing with a tap mounted to a main spindle, the machine tool comprising:

• a sensor configured to detect existence of a screw thread at a position where the screw thread and a root of thread of the tap pass through from a direction intersecting with an axial direction of the tap mounted to the main spindle;
• a reference phase acquisition unit that acquires a relation between a rotation angle of the main spindle and an existence of the screw thread of a reference tap as a tap before a halt by detecting existence of the screw thread at a position where the screw thread and a root of thread of the reference tap pass through with the sensor while rotating the main spindle in a state where the reference tap is mounted to the main spindle;
• a measurement phase acquisition unit that acquires a relation between a rotation angle of the main spindle and an existence of a screw thread by mounting an other tap for continuing the female thread processing to the main spindle and detecting existence of the screw thread at a position where the screw thread and a root of thread of the other tap pass through with the sensor while rotating the main spindle;
• a phase difference calculation unit that calculates a phase difference between the reference tap and the other tap based on the relation between the rotation angle and the existence of the screw thread acquired by the reference phase acquisition unit and the relation between the rotation angle and the existence of the screw thread acquired by the measurement phase acquisition unit;
• and
• a processing unit that sets a start position for rotating the main spindle to which the other tap is mounted based on the phase difference, and continuously performs the female thread processing from the start position.