Machine tool and moving position determining method

A moving position determining method for a machine tool provided with a spindle rotating around a spindle axis along with a workpiece and a tool post to which a tool having a cutting edge cutting the workpiece is attached, the method moving at least one moving object including the spindle and the tool post in a moving direction perpendicular to the spindle axis to perform a true-circular machining of an eccentric radius (rc) around an eccentric center position (Pc) in the moving direction as the spindle rotates,

• the method comprising:
• a first step determining an intermediate center position (Pi) in the moving direction for each divided rotation angle (E) smaller than a single rotation of the spindle and an intermediate eccentric radius (ri) around the intermediate center position (Pi) according to an initial position (Po) of the cutting edge in contact with the workpiece in the moving direction, the eccentric center position (Pc), and the eccentric radius (rc) to keep the cutting edge in contact with the workpiece as the moving object moves in the moving direction within a predetermined maximum feed speed (F) until the true-circular machining around the eccentric center position (Pc) is complete on the workpiece, and
• a second step determining the moving position of the moving object in the moving direction as the spindle rotates to perform a cutting of the intermediate eccentric radius (ri) around the intermediate eccentric center position (Pi) for said each divided rotation angle (E) on the workpiece.