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Countersink Spot Drill Depth Formula and Calculator

 

Countersink and Spot Drill Depth Formula and Calculator

Preview: Countersink and Spot Drill Depth Calculator

The following formulas are for countersinks and spot drills that have been sharpened to a point, allowances on tool depth will have to be made if the countersink or spot drill is not sharpened to a point.

For countersinks and spot drills that have been sharpened to a point
For countersinks and spot drills that have been sharpened to a point

To find the tool travel “Z” required for any sharp-point countersink or spot drill angle, use either of the following formulas:

Z = ( D / 2 ) [ 1 / tan ( α / 2) ]
or
Z = ( D / 2 ) cot ( α / 2)

α = countersink angle
D = countersink diameter
Z = depth of tool travel required from surface of part


For countersinks and spot drills that are a truncated cone

To find the tool travel “Z−a” required for any truncated countersink or spot drill angle, use either of the following formulas:

Z - a = ( D - T ) / 2 · [ 1 / tan ( α / 2 ) ]

Z - a = ( D - T ) / 2 · cot ( α / 2 )

a = allowance for truncated countersink tool
d = diameter of through hole
T = diameter of small end of truncated tool

The table below is a quick reference for some predefined To calculate the tool travel “Z”, multiply the factor by the countersink diameter.

Countersink Angle
α, degrees
Factor
(Imperial or Metric Units)
Countersink Angle
α, degrees
Factor
Imperial or Metric Units)
60
0.866
118
0.3004
82
0.5752
120
0.2887
90
0.5000
135
0.2071
100
0.4195
142
0.1722

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