Numerical control system providing graphic machining simulation

A numerical control system comprising:

• a controller for controlling a machine tool and a graphics display unit connected to said controller, said graphics display unit comprising:
• a circuit interface for entering display data from said controller;
• a memory for storing said display data through said circuit interface;
• a central processing unit for issuing commands to a graphics interface in accordance with said display data;
• display memories for storing graphics patterns;
• and
• a CRT for displaying said graphics patterns from said display memories in accordance with said commands;
• said central processing unit processing said graphics patterns in said display memories through said graphics so as to display a workpiece shape as a shaded image on said CRT in accordance with a first user selection, a tool shape with said workpiece shape on said CRT in accordance with a second user selection, and movement of said tool shape on said CRT;
• said numerical control system further comprising means for machining the workpiece in a simulated fashion in accordance with said movement of said tool shape with respect to said workpiece shape on said CRT so as to change a shape of said shaded image in said display memories based on calculations by said central processing unit;
• said central processing unit further processing said graphics patterns so as to remove, from said CRT, an interference area in which a tool tip shape of said tool shape interferes with the workpiece shape displayed as the shaded image as simulated machining of said workpiece by said tool shape proceeds.