NC sentence creation system

A numerical control sentence creation apparatus implemented by a computer for creating a numerical control sentence for a two stage drilling operation by which a hole having a bottom drilled by a first stage drilling operation using a first drill having a first diameter is further drilled by a second stage drilling operation using a second drill having a second diameter smaller than the first diameter of the first drill, said numerical control sentence creation apparatus comprising:

• a memory storing machining configuration data, and machining condition data including a first amount of clearance and a second amount of clearance;
• and
• means for receiving said machining configuration and machining condition data and for creating the numerical control sentence used to control said first and second drills using the computer, where said first drill is moved to a first machining end point of said first stage drilling operation by a predetermined first cutting feed after said first drill has been moved by a first quick traverse to a first point which is spaced from an end of a workpiece by said first amount of clearance when said first stage drilling operation is performed, and where said second drill is moved to a second machining end point of said second stage drilling operation by a predetermined second cutting feed after said second drill has been moved by a second quick traverse to a second point which is spaced from the bottom of the hole drilled by said first stage drilling operation by said second amount of clearance, when said second stage drilling operation is performed.