Bolt Circle Layout
Hole coordinates (X, Y) for a circle of N evenly spaced holes from a bolt-circle diameter, start angle, and center, plus the angular spacing and adjacent center-to-center chord (first-principles circle-of-holes trigonometry).
Formula and source
R = dia/2; hole i at angle start + i*(360/N): x = cx + R*cos(angle), y = cy + R*sin(angle); angular spacing = 360/N; adjacent center-to-center chord = 2*R*sin(180/N).
Circle-of-holes (bolt-circle) layout - the standard hole-pattern coordinate geometry as in Machinery's Handbook (Industrial Press), by name; first-principles trigonometry.
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