Drill Geometry Cheat Sheet for Common Materials

The two most important drill geometry features are point angle and helix angle. Point angle controls how the cutting edge engages the work, while helix controls chip evacuation. Matching these to your material prevents breakage, poor hole quality, and premature wear.

For mild and alloy steels, use a standard 118° point angle with a conventional helix. This is a versatile geometry that handles most steel jobs. When drilling harder steels or stainless, switch to a 135° point angle with a split point. The flatter point reduces thrust and the split point prevents walking.

Aluminum and plastics need a sharper point angle around 90° to 100° with a high helix. The sharp point cuts cleanly and the high helix pulls chips out fast, which is critical for gummy materials. Without it, chips pack and break drills.

Cast iron is abrasive but brittle, so use a 90° point angle with a low helix. The low helix reduces grabbing and prevents the drill from pulling into the work. Keep speeds moderate and use a coolant or mist to control dust and heat.

In short, remember: steels like standard or split points, aluminum likes sharp and high helix, cast iron likes flat and slow. Adjusting these two angles alone will improve your drilling success more than any other single change.

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