Chamfer and countersink calculator
Work out how far to feed a countersink or spot drill to reach a set diameter, or the sizes of a chamfer at any angle.
Safety: countersinks chatter if run fast. Use a low speed, a firm feed and set a depth stop.
How it works, guides and notes
How it works
A countersink is a cone. Each unit you feed in opens the diameter by 2 × tan(half-angle): about 2 for a 90° tool, so feed half the diameter you want to gain. If a hole is already there, the cutter touches at the hole edge, so measure from there; from the tool tip, it is the full cone depth.
For a chamfer, the radial size and the angle set how far it runs along the work: at 45° the two legs are equal; at 30° to the axis it runs 1.732 × further along.
Worked example: a 10.4 mm countersink in a 5.5 mm hole with a 90° tool: depth from the hole edge = (10.4 − 5.5) ÷ 2 ÷ tan 45° = 2.45 mm.
Spotted a mistake? Report an error.