CNC Machining Bolt Circle Calculator

A CNC machining bolt circle calculator generates nominal X and Y coordinates for equally spaced hole centers on a pitch circle. The user defines circle center, pitch-circle diameter, whole hole count, first-hole angle and ordering direction. The result lists each hole in order with its normalized angle and Cartesian coordinates.

The coordinate convention is explicit: zero degrees points along positive X at three o’clock, 90 degrees points along positive Y, and counterclockwise angles are positive. Clockwise ordering subtracts the equal angular step. This matches the cited Haas bolt-circle convention while keeping the output controller-neutral.

The page does not emit G-code. Coordinates alone do not identify units mode, work offset, absolute or incremental programming, drilling cycle, safe Z, tool, fixture or control syntax. Keeping geometry separate makes the table useful for checking CAM or a drawing without pretending it is a reviewed machine program.

Pitch-circle diameter is divided by two to obtain radius. Angular spacing equals 360 degrees divided by the whole hole count. Starting with index zero, the calculator adds spacing for counterclockwise order or subtracts it for clockwise order.

Each hole angle is converted from degrees to radians for the trigonometric functions. Radius times cosine is the X offset and radius times sine is the Y offset. Adding the entered center coordinates translates the pattern without changing its size, spacing or orientation.

Angles are normalized to a readable 0-to-360-degree range and coordinates are rounded only for output. The input model permits any finite center and start angle, requires positive PCD and restricts the whole hole count to 1–360 to keep the displayed table practical.

Four holes on 20 mm PCD: At center X10 Y20 and start angle 0 degrees, radius is 10 mm and spacing is 90 degrees. Counterclockwise coordinates are (20,20), (10,30), (0,20) and (10,10).

Six holes on 100 mm PCD: Radius is 50 mm and spacing is 60 degrees. With a 30-degree start, the first offset is approximately X43.3013 Y25. Subsequent counterclockwise points advance by 60 degrees around the same center.

Clockwise ordering: For four holes centered at zero with a zero-degree start, the second clockwise hole lies at negative Y rather than positive Y. The physical set of four points is identical; only their listed order changes.

Confirm whether the drawing specifies pitch-circle diameter, bolt-circle diameter or radius, and ensure it passes through hole centers. Identify the start-angle reference and viewing direction. A mirrored setup can reverse apparent rotation, so relate +X and +Y to the actual work coordinate system.

Round only after comparing required coordinate precision with drawing tolerance and control resolution. Check fixture orientation, work offsets, units and absolute/incremental state in the real program. Simulate the pattern and verify the first hole and center before running the full cycle.

Keep the calculator record with the drawing revision, units, input source and rounding rule. Recheck the result after any change to the tool, stock, setup, work offset, CAM strategy or inspection method. A correct equation can still be applied to the wrong reference feature, so identify the physical planes, axes and dimensions before transferring a number to a setup sheet.

Before machining, review workholding, rigidity, holder projection, runout, tool condition, coolant or lubrication, chip evacuation, machine travel and control behavior where they affect the operation. Prove out through the shop’s approved process and inspect the resulting feature. The calculator documents nominal arithmetic; it cannot observe the machine, material, tool or part.