Regrinding Instructions for Gun Drill N-8 & Half Round Drill HA-1:

Grinding

1. Position horizontal register at +30º , (half round drills at +20º), vertical register at +12º. Grind until all wear is removed.
2. Position horizontal register at +29º, (half round drills at +19º), vertical register at +20º. Grind to establish the primary relief width of approximately 5% of the diameter.
3. Position horizontal register at -20º, (half round drill at -15º), vertical register at +12º. Grind to establish the point position width of drill diameter. (Dia./4).
4. Position horizontal register at 0º, vertical register at +25º. Grind front clearance until the triangle created reaches the rear edge of the primary relief.
5. For gun drill only. Position horizontal register at -25º, vertical register at -12º. Grind until the triangle formed reaches the center of the tip "V".
6. Remove drill and freehand a periphery chamfer around the radial surface at approximately 20º, stopping just short of the primary relief.