Generate the hole positions for any bolt circle. Enter the pitch circle diameter, number of holes and a start angle, and the calculator lists X and Y coordinates for every hole relative to the centre, the angular spacing and the chord distance between adjacent holes, with a scaled pattern diagram for marking out or CNC programming.
What it gives you
- X/Y coordinates for each hole
- Angular pitch and chord length between holes
- Bolt circle radius
- Scaled pattern drawing
- Start angle offset for straddled or in-line patterns
Method and standards
Each hole sits at the PCD radius at an angle of the start angle plus its index times 360 over the number of holes. The chord between adjacent holes is PCD times the sine of half the pitch angle, which is the useful figure for marking out with dividers. Flange bolt holes conventionally straddle the centrelines, which corresponds to a start angle of half the pitch.
How to use it
- Enter the PCD and number of holes.
- Set the start angle: 0 for a hole on the axis, half the pitch to straddle it.
- Copy the coordinate table or use the chord for marking out.
Questions engineers ask
- Absolute or incremental coordinates?
- Absolute, relative to the circle centre. Add your part datum offset for CNC.
- Why straddle the centreline?
- Flange standards place bolt holes either side of the centrelines so that pipework can run square to the joint. Set the start angle to half the angular pitch.
- Does it link to the flange tables?
- The flange size lookup gives PCD and hole count for standard flanges; enter those values here.
Need this calculation done properly, with a signed-off calculation pack or FEA behind it? Forgepoint provides mechanical design, analysis and pressure equipment engineering from Manchester, UK-wide.
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