Method of correcting error on involute interpolation

A method of correcting an error on involute interpolation in an numerical control system, comprising the steps of:

• when an insufficient cut or an excessive cut occurs in an actual configuration of a workpiece which is machined along a first involute curve that is commanded, determining a radius of curvature from a base circle to a starting point of said insufficient cut or said excessive cut on said first involute curve, and an error which occurs at an ending point of said first involute curve in a direction normal to said insufficient cut or said excessive cut;
• setting said radius of curvature and said error as parameters in the numerical control system;
• changing a first offset at the time said first involute curve is interpolated to a second offset which differs from said first offset by said error, on interpolation from said starting point of the insufficient cut or the excessive cut to said ending point of said first involute curve;
• and
• dividing said first involute curve into a second involute curve having an ending point which is the same as said starting point of the insufficient cut or the excessive cut, and a third involute curve having a starting point which is the same as said starting point and an ending point which is spaced said error from said ending point of said first involute curve in a direction normal thereto.