Corner cutting method and NC controller

A corner cutting method in which a rotary tool having a cutting edge at least on a bottom surface thereof and on an outer periphery thereof is used, the rotary tool and a workpiece are relatively shifted on a plane parallel to the bottom surface of the tool so that an outer end of the cutting edge of the rotary tool rotated by a spindle creates a shifting path meeting a desirable shape of a corner to be machined, and the rotary tool is shifted while cutting in an axis direction of the rotary tool, the method comprising the steps of:

• inputting information on coordinate values and a direction and an angle of a corner to be machined and information on the rotary tool, to an NC controller;
• internally calculating coordinate values at a corner cutting starting point where the outer end of the cutting edge is positioned, and a spindle rotating angle in this position, and coordinate values of a corner cutting end point, based on the input information;
• internally calculating a spindle rotating angle at a coordinate position where the outer end of the cutting edge is positioned at a subsequent point sequence position in each sampling, the subsequent point sequence position being obtained by an interpolation calculation, letting a section between the corner cutting starting point and the corner cutting end point be a section to be machined;
• internally calculating coordinate values of the spindle at the subsequent point sequence position based on the spindle rotating angle and a substantial diameter of the rotary tool;
• and
• relatively shifting the rotary tool and the workpiece based on the coordinate values of the spindle on a plane parallel to the bottom surface of the tool while controlling the spindle rotation in synchronization with the shifting.