Bolt Circle Calculator
Calculate X/Y coordinates for equally spaced holes with G-code output
Bolt Circle Parameters
Center Offset (Optional) X=0 Y=0
G-code Parameters
Calculation Results
Hole Pattern Preview
Red dot indicates the first hole (start hole)
Math coordinate system: X+ right / Y+ up
Hole Coordinate Table
| Hole # | X (mm) | Y (mm) | Angle (°) |
|---|
G-code Output
( Click "Generate G-code" button )
About Bolt Circle Calculator
The Bolt Circle Calculator is a free online tool designed for machining applications. It automatically calculates precise X/Y coordinates for equally spaced holes on flanges, gears, pulleys, and other circular parts. It also supports G-code output for direct use on CNC milling machines and machining centers.
How to Use
- Enter the Pitch Circle Diameter (PCD): the diameter of the circle on which all hole centers lie
- Select the number of holes: how many holes to drill on the circle
- Set the start angle: the angle of the first hole relative to the positive X-axis (counterclockwise is positive)
- Choose rotation direction: clockwise or counterclockwise for subsequent holes
- (Optional) Enter center offset: if the workpiece center is not at machine origin
- View the coordinate table or generate G-code for machining
Formula Explanation
This calculator uses basic trigonometric functions to calculate points on a circle:
- X = (PCD/2) × cos(θ)
- Y = (PCD/2) × sin(θ)
- Where θ = start angle + hole index × (360°/number of holes)
Applications
- Flange bolt hole machining
- Gear mounting hole positioning
- Pulley mounting hole drilling
- Circular cover plate screw layout
- Manual mill X/Y axis positioning reference
FAQ
Q: What is PCD (Pitch Circle Diameter)?
A: PCD is the diameter of the circle on which all bolt hole centers lie. For example, a 4-hole 100mm PCD means 4 holes evenly distributed on a circle with 100mm diameter.
Q: What direction does 0° start angle point to?
A: A 0° start angle points toward the positive X-axis (usually right). Angles increase counterclockwise, so 90° points toward the positive Y-axis (up).
Q: Which machines is the G-code compatible with?
A: The G-code generated uses standard Fanuc format, compatible with most CNC mills and machining centers. Please verify your machine supports G81 drilling cycle before use.
Q: What is the coordinate precision?
A: This calculator provides 3 decimal places precision (0.001mm), meeting general machining requirements.
