Method of determining cutting trajectory in N/C machining system

In a numerical control machining system, a method of determining a cutting trajectory for a small diameter ball end mill when cutting a leftover area on a work produced by cutting the work with a larger diameter ball end mill, the leftover area being an area formed of leftover portions which are left uncut on the respective cutting trajectories of the larger diameter ball end mill, said method comprising the steps of

• identifying the leftover portions in the directions of the cutting trajectories for the larger diameter ball end mill which are set at regular pitches,
• obtaining reference cutting trajectories for the small diameter ball end mill which are imaginary cutting trajectories in the same direction as the cutting trajectories for the larger diameter ball end mill,
• dividing each of the reference cutting trajectories at dividing points which are of the same number for all the reference cutting trajectories and which are positioned at regular intervals in the direction of the reference cutting trajectory, and
• plotting the cutting trajectories for the small diameter ball end mill by connecting the corresponding dividing points of the respective reference cutting trajectories with straight lines.