Bolt Circle DXF Generator

A bolt circle (also called a bolt hole pattern or pitch circle) is the imaginary circle that passes through the centers of a set of equally spaced holes. Its diameter is the bolt circle diameter (BCD). Flanges, wheel hubs, gear blanks, mounting plates and circular sensor housings all specify their hole patterns this way because it is compact and unambiguous.

The formula

For n holes, hole i (counting from 0) is placed at angle ai = start + i × 360° / n, measured counter-clockwise from the +X axis. With the pattern centered at (cx, cy) and radius R = BCD ÷ 2, each hole center is:

x = cx + R·cos(ai)    y = cy + R·sin(ai)

This generator applies that formula exactly and writes every hole as a circle entity, plus the bolt-circle reference and a center mark, into a plain R12 DXF you can open in any CAD system.

Choosing a start angle

A start angle of 0° puts the first hole on the +X axis. Use 90° when you want the first hole at the top (12 o'clock), or any value to clock the pattern to match an existing feature. The generator preserves your start angle in the output.