Bolt circle and hole patterns

Pick a pattern, enter its size, and read off the coordinates — for a DRO, a CNC program, or layout by hand. Angles are measured counter-clockwise from the +X axis (3 o’clock), as on a machine; choose clockwise numbering if you prefer.

Bolt circle — n holes evenly spaced on a pitch-circle diameter (PCD), the first at any angle, around any centre. Holes sit at (cx + R·cos θ, cy + R·sin θ). The chord between neighbouring holes is PCD × sin(180°/n).
Arc — holes spread over part of a circle, with the first and last on the ends of the arc.
Linear — a row of holes at a spacing, in any direction.
Grid — columns × rows at pitch, optionally staggered; ordered back and forth (serpentine) to keep travel short.

Exports: copy or download the coordinates as CSV, and a G-code drilling program using a canned cycle — G81 (single plunge), G83 (full-retract peck by Q), or G73 (chip-breaking peck) — with safe Z, R plane, final depth, feed, spindle speed, and an optional tool change. The program uses absolute positioning (G90), the XY plane (G17), and G21/G20 for the chosen units.

Starting points — verify with your machine and controller documentation. Check the work offset, simulate or dry-run the program above the part, and confirm the canned-cycle conventions (R plane, G98/G99) of your control before cutting.

Share link copies a URL that opens this tool exactly as you have it set up. It carries the pattern, holes and G-code settings. Opening a link replaces your own saved settings for the tool; a Restore my settings button brings them back. To write a link by hand, use mode, units — for example /tools/bolt-circle/?mode=circle&units=mm.

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