Numerical control method for machining an arc on the curved surface of a cylinder using interpolation of linear and angular data

A numerical control method in which controls around a rotation axis and along a linear axis of a machine tool are simultaneously performed by a numerical control unit which operates in accordance with a machining program, so that a circular arc is formed on a cylindrical surface of a cylindrical workpiece, comprising the steps of:

• (a) calculating a distance interval, in a circumferential direction of the workpiece, between a start point and an end point of a circular arc to be formed on the basis of a moving command value for the rotation axis, the moving command value being indicative of an angular interval between the start and end points of the circular arc in the circumferential direction of the workpiece and represented by a unit of angle;
• (b) executing a circular arc interpolation processing on the calculated distance interval for the rotation axis and a moving command value for the linear axis, which is represented by a unit of length, so as to calculate a first distribution amount for the rotation axis and a second distribution amount for the linear axis, respectively;
• (c) converting the first distribution amount into a third distribution amount which is represented by a unit of angle;
• and
• (d) controlling the linear and rotation axes of the machine tool in accordance with the second and third distribution amounts, respectively.