CNC Cutting Tools Solid Carbide Straight Shank Twist Drill Drilling Holes C-twist Drill High Speed Steel Long Working Life

The lowly twist drill is one of the most commonly used tools in the machinist's arsenal. By all accounts, it also has some of the highest material removal rates of any of the tooling available. As such, it's worth getting to know them a little better.

- Irregular or Rough Surface: Cut the feed back to as low as 1/4 the normal feedrate to avoid chipping the twist drill.
- Convex: Convex surfaces are hard to do unless the radius of the convex surface is greater than 4 times the drill diameter and you're entering perpendicular to the convex radius. If this is not the case, mill a flat spot for the drill to get started on before attempting to drill.
- Concave: Don't attempt a concave surface unless the radius is more than 15x the drill diameter and the drill is centered on the concavity and not the wall. You can drill the wall of a concave surface. Reduce feed to 1/3 when entering. If the surface doesn't meet these requirements, mill a flat before attempting to drill.
- Angled: Treat entry and exit of angled surfaces the same. If entering or exiting an angle surface of 2 to 5 degrees angle to the tip or less, reduce feed to 1/3 of normal to accomdate this interrupted cutting condition. For surfaces angled 5 - 10 degrees, ideally use a drill whose point angle matches the angle of the surface. If the angle is more than 10 degrees, you'll need to mill a flat before drilling.