Machine tool method for deciding if a workpiece surface is concave or convex

A machining method for a machine tool having axes of rotation for performing a first machining operation by moving a tool relative to a workpiece in a first machining direction, thereafter pick-feeding the tool, performing a second machining operation after the pick-feed by moving the tool relative to the workpiece in a second machining direction opposite to that of the first machining direction, and repeating the first and second machining operations and the pick-feed operation to perform desired machining, comprising the steps of:

• (a) obtaining a plane contacting a curve along the external shape of the workpiece at a second machining starting point Ps at which the second machining operation is to begin, by using three-dimensional position data at the second machining starting point Ps of the second machining operation, and obtaining tool central axis direction data at the second machining starting point;
• (b) determining whether a curved surface of the workpiece in the proximity of a first machining end point Pe at the end of the first machining operation is concave or convex;
• (c) performing the following substeps if the curved surface of the workpiece is concave:
• (c1) obtaining an approach plane containing the machining end point Pe and lying parallel to the plane obtained in said step;
• and
• (c2) obtaining a point of intersection Pc between the approach plane and a straight line passing through the second machining starting point Ps of the second machining operation, the straight line coinciding with the direction of the central axis of the tool at the second machining starting point;
• (d) performing the following substeps if the curved surface of the workpiece is convex:
• (d1) adopting the plane obtained in said step (a) as an approach plane;
• and
• (d2) obtaining the point of intersection Pc between the approach plane and a straight line passing through the machining end point Pe and coinciding with the direction of the central axis of the tool by using three-dimensional position data at the machining end point Pe of the first machining operation, and tool central axis direction data at the machining end point;
• (e) moving the tool from the maching end point Pe toward the point of intersection Pc with a path from point Pe to point Pc to point Ps which serves as a pick-feed path;
• (f) performing a pick-feed by moving the tool from the point of intersection Pc to the second machining starting point Ps;
• and
• (g) executing the second machining operation.