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How to Counterbore on a Lathe

Counterboring on a lathe requires some previous experience working on metal with a lathe, such as the basics of truing the chucks and drilling pilot holes. A counterbore makes room for the head of a bolt or cap head screw to sit flush against the surface of the metal by adding an extra hole. A similar process is used to make a countersink, which is conical rather than cylindrical in shape and is for a flat head screw.

Things You'll Need

Standard twist drill (slightly larger than screw head)
Cutting face
Drill bit (slightly smaller than screw)

Instructions

- 1
  Grind down the end of the twist drill with the cutting face. Grind until it is almost flat, to an angle of about 175 degrees.
- 2
  Drill the pilot hole on your project with the bit. Remember the pilot hole must be slightly smaller than the screw; for example, a number 10 screw would take a number 11 pilot hole.
- 3
  Drill the counterbore with the ground-down twist drill. Take care to keep the counterbore concentric with the pilot hole or the screw won't fit.

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