Bolt Circle Calculator
Calculate bolt hole coordinates for circular bolt patterns online free. Enter number of holes, radius, and angle to get precise XY coordinates for CNC, CAD, and drilling.
About This Calculator
The Bolt Circle Calculator determines the precise XY coordinates for each hole in a circular bolt pattern. Engineers, machinists, and DIY enthusiasts use bolt circles to design bolted joints for machinery, flanges, wheels, and structural connections. This tool is essential for CNC programming, CAD modeling, and manual drilling layout.
The bolt hole coordinates are calculated using the standard bolt pattern equations: for each hole i, the x-coordinate is cos((i-1) × B + A) × R + xc and the y-coordinate is sin((i-1) × B + A) × R + yc, where B = 360°/n is the angular spacing between holes, A is the offset angle of the first hole, R is the bolt circle radius, and (xc, yc) is the center offset. The chord length between adjacent holes is 2 × R × sin(180°/n), and the bolt circle diameter is simply 2 × R.
Regional Notes
Global: Bolt circle patterns follow the same geometric principles worldwide. Metric units (mm) are the standard for engineering drawings and CNC machining, but the same formulas work with any unit of measurement. The calculator outputs in millimeters for coordinates.
US/UK: Imperial units (inches) can be used by entering radius values in inches. The coordinate output will then be in inches as well. Common US bolt patterns include 4-lug (4×100mm, 4×4.5") and 5-lug (5×4.5", 5×5") for automotive wheels.
India/Europe: Metric units are standard. Common automotive bolt patterns include 4×100mm, 5×112mm, and 5×114.3mm for passenger vehicles. Industrial flanges follow ISO and DIN standards for bolt patterns.
Frequently Asked Questions
What is a bolt circle?
A bolt circle is the imaginary curve that passes through the centers of all bolt holes arranged in a circular pattern. It is used in bolted joints to temporarily join two pieces of material together using bolts and nuts inserted through prefabricated holes.
How do you calculate bolt hole coordinates?
Bolt hole coordinates are calculated using the formulas: xi = cos((i-1) × B + A) × R + xc and yi = sin((i-1) × B + A) × R + yc, where B = 360°/n is the angle between holes, A is the angle of the first hole, R is the bolt circle radius, and (xc, yc) is the center offset.
What is the angle between holes in a bolt circle?
The angle between consecutive holes in a bolt circle is calculated as 360° divided by the number of holes. For example, a 4-hole pattern has 90° between holes, a 5-hole pattern has 72°, and a 6-hole pattern has 60°.
Can I use this for CNC machining?
Yes, the XY coordinates generated by this calculator can be used for CNC machining, automated drilling, 3D printing, or imported into CAD software. The coordinates represent the exact center positions for each bolt hole in millimeters.
What is the chord length between bolt holes?
The chord length between adjacent bolt holes is calculated as 2 × R × sin(180°/n), where R is the bolt circle radius and n is the number of holes. This is the straight-line distance between the centers of two neighboring holes.
What is the minimum number of holes for a bolt circle?
A bolt circle requires at least 2 holes to define a circular pattern, though practical bolted joints typically use 3 or more holes for stability. Common bolt patterns use 4, 5, 6, or 8 holes depending on the application.
How do I prepare bolt hole coordinates for g-code?
After calculating the XY coordinates from this calculator, format them in g-code as G81 X{x} Y{y} R2 Z-5 F100 for each hole position, where X and Y are the coordinates from the calculator output table.