So far, high accuracy in-process sensors have been used for controlling the cutting tool, but the method followed in this new system is guite different form previous processes. In this system, after the rough cut the mark indication the pasition of the finished size in put on the cutting surface of the workpiece by ultrasonic or vibration cutting. The cutting is then continued until the mark just disappears, This position being observed by the used of a simple in-proces sensor, The in-prosess sensor in used only to detect the existence or dis apperance of the mark.