Several production requirements should be met when using carbide drills.

The use of drill bushings is recommended. This will insure close hole location and hole size tolerance. Provide sufficient clearance between bushings and work piece to allow chips to be removed before reaching bushing.

The use of a coolant will improve the drilling operation and hole quality. Flood cooling directed at the flutes will insure drill point cooling, reduce flute and point chipping, and remove drill chips. An air blast may be more effective on non-metallic materials.

Selection of the proper drill is dependent on several factors: depth of hole, hardness of material, type of equipment. Always use the shortest tool dimensionally possible. Reduced tool extension will insure hole quality, tool efficiency, and reduce overall cost.

In general you can us the following in selecting the proper drill:

• Twist Drills: Hole depth three (3) to five (5) times drill diameter. Up to Rc 50.
• Roc-50 Drills: Hole depth two (2) to three (3) times drill diameter, Rc 50 to Rc 60.
• Spade Drills: Hole depth one (1) to two (2) times drill diameter, Rc 58 to Rc 63.
• Tri-Flute Drills: Hole depth three (3) to five (5) times drill diameter, up to Rc 50.

Speeds: Carbide drills are run at much higher speeds than HSS dulls. Refer to the following chart. Reduce speed when drilling to maximum depth. Also when corner wear is rapid.

Feed: Generally slightly less than with HSS drills. The increase in speed is the factor controlling increased production rates. Always maintain even feed rates to prevent chipping, excessive wear and work hardening of some materials.

The intervals of sharpening drills are basically the same as with end mills. Do not allow the drill to dull to the point of complete tool failure.