Center Drill Depth Calculation

The following shows how to calculate how deep to drill, using a No.4 center drill, to give a desired hole size.

The basic calculation is,

Drill Depth = 0.125 + (Desired Hole – .125) / (2*SquartRoot(3))

Or, Drill Depth = .125 + (Desired Hole – .125) / 3.4641

For 0.125 < Desired Hole < .3125

For desired hole sizes less that 0.125 use:

Drill Depth = (Desired Hole / 2) / Tan(59deg)

Or, Drill Depth = (Desired Hole / 2) / 1.6643

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