Bolt circle calculator. Every hole's X and Y.
Enter the bolt circle diameter, how many holes, and where the first one starts. Get the coordinates for every hole, ready to type into the control or check on the CMM.
Hole positions
- Spacing between holes
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- Distance between adjacent holes (chord)
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| Hole | Angle | X | Y |
|---|
Sine and cosine, once per hole.
Each hole sits at an equal angle around the circle. The first hole is at the start angle and the rest follow in the direction you pick.
X = Xc + (D/2) × cos(θ)
Y = Yc + (D/2) × sin(θ)
θ = start ± (hole − 1) × 360° / n
Chord = D × sin(180° / n)
Angles are measured from +X (3 o'clock), counterclockwise positive, the way most controls and CAD do it. Pick CW to number the holes clockwise instead.
The chord is the straight-line distance between two neighbouring holes. It's handy for checking the pattern with calipers.
Good to know
Which way is 0°?
0° is the +X axis, 3 o'clock looking down on the part. Angles go counterclockwise. For a first hole at 12 o'clock, enter 90.
Can I use an offset center?
Yes. Enter the circle's center X and Y relative to your part zero, and the hole coordinates come out relative to part zero too.
How many decimals does it show?
Four in inch and three in mm. Round to whatever your drawing and control need.
Got the drawing too? Balloon it free.
Upload a PDF drawing. Deburr numbers every dimension, GD&T frame and note, and gives you the ballooned PDF and a Form 3 spreadsheet. No account needed.