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Standard Basic 60° Center Drill Dimensions

Center Drills, or as they are also called, combination drill and countersinks, are a very popular tool in the machining industry.

The main purpose of the 60° center drill is to drill a countersunk hole in a part to accommodate a live center on a lathe.  Although they are commonly used as a spot for a drill.

Below is a “Dimension” chart for standard 60° center drills and also formulas for calculating a desired countersink diameter using a center drill.

Center Drill No.

“A” Body Diameter

“D” Pilot Diameter

“C” Pilot Length

00000

0000

000

00

0

1

2

3

4

5

6

7

8

9

10

.125”

.125”

.125”

.125”

.125”

.125”

.188”

.250”

.313”

.438”

.500”

.625”

.750”

.875”

1.0”

.010”

.015”

.020”

.025”

.031”

.047”

.078”

.109”

.125”

.188”

.219”

.250”

.312”

.344”

.375”


.030”

.030”

.030”

.038”

.047”

.078”

.109”

.125”

.188”

.219”

.250”

.312”

.344”

.375”

60° Center Drill Countersink Diameter Formulas

No.1 Center Drill :

No.2 Center Drill :

No.3 Center Drill :

No.4 Center Drill :

No.5 Center Drill :

No.6 Center Drill :

No.7 Center Drill :

No.8 Center Drill :

No.9 Center Drill :

No.10 Center Drill :

( C-Sink Dia - .047) / 2) x 1.7321) + .061 = Drill Depth

( C-Sink Dia - .078) / 2) x 1.7321) + .100 = Drill Depth

( C-Sink Dia - .109) / 2) x 1.7321) + .140 = Drill Depth

( C-Sink Dia - .125) / 2) x 1.7321) + .161 = Drill Depth

( C-Sink Dia - .188) / 2) x 1.7321) + .242 = Drill Depth

( C-Sink Dia - .219) / 2) x 1.7321) + .282 = Drill Depth

( C-Sink Dia - .250) / 2) x 1.7321) + .322 = Drill Depth

( C-Sink Dia - .312) / 2) x 1.7321) + .402 = Drill Depth

( C-Sink Dia - .344) / 2) x 1.7321) + .443 = Drill Depth

( C-Sink Dia - .375) / 2) x 1.7321) + .483 = Drill Depth

Center Drill Depth Calculation Example:

To make a .375” Diameter Countersink with a No. 5 Center Drill:

.375” Desired Countersink Diameter - .188” = .187”

Divide .187” by 2 = .0935”

Multiply .0935” by 1.7321 = .162”

Add .242” to .162” = .404” Drill Depth

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.404”

.375”

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Below is a screen shot of the Center Drills Dimensions Calculator that is included in the Web Machinist Software program.

Web Machinist Software:

Web Machinist Software

“Center Drill Measurements  Calculator” Provides the Dimensions of Center Drills #00000 to #10 and can Calculate the Program Depth to Obtain a Desired Counter Sink Diameter.

Center Drill Measurements Calculator

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