Patent ID: 8042436

Claim:
A method for preparing an NC machining program used in an NC machining apparatus which includes: a workpiece main shaft to which a workpiece is attached; a bite holder provided so as to be movable along a second axis which is orthogonal to a first axis corresponding to an axis of said workpiece main shaft; said workpiece main shaft or said bite holder being provided so as to be rotatable around a turning axis which is in parallel to a third axis orthogonal to the first axis and the second axis; and the workpiece attached to said workpiece main shaft being cut by a rotary tool provided in said bite holder while said workpiece main shaft is rotated around the first axis; said preparing method comprising: a first step of preparing an NC machining program including a position instruction of a cutting portion of said rotary tool at a time of cutting, on the basis of a two-dimensional workpiece coordinate system having the first axis and the second axis as coordinate axes; a second step of inputting a first angle around said turning axis with respect to said workpiece main shaft or said bite holder at a time of cutting, and a second angle formed by a line extending between the center line of the workpiece and the point of contact of the rotary tool against the workpiece during the cutting operation and the third axis to said NC machining apparatus; and a third step of converting said NC machining program prepared in the first step into an NC machining program including a position instruction of a three-dimensional workpiece coordinate system having the first axis, the second axis and the third axis as the coordinate axes, the third step being done in such a manner that the workpiece can be cut while keeping the posture of the rotary tool expressed by the first angle and the second angle.