Bolt Circle Pattern — PCD Coordinates & CNC Layout
Compute exact X,Y coordinates for holes arranged in a circular pattern. Essential for CNC machining, flange design, wheel mounting, and any fabrication requiring precise bolt circle layout. Exports coordinates for G-code and CAD.
Why This Construction Metric Matters
Why: Accurate bolt circle coordinates prevent misalignment, rework, and assembly failures. Wrong PCD causes wheels to wobble, flanges to leak, and parts to reject. CNC programs require exact coordinates for first-pass success.
How: Coordinates: X = (D/2)×cos(θ)+X₀, Y = (D/2)×sin(θ)+Y₀. Angular spacing = 360°/n. Chord = D×sin(π/n); Arc = πD/n. PCD (Pitch Circle Diameter) is the circle through bolt centers.
- ●Use center (0,0) or part datum for CNC programming.
- ●Verify hole count matches your pattern before machining.
- ●Check units (inches vs mm) before cutting.
- ●H7/H8 tolerance for general fabrication; H9 for field work.
Bolt Circle Calculator
Coordinates • PCD • Angular spacing • CNC ready
Quick Examples — Click to Load
4-Bolt Wheel Pattern
Standard 4-bolt wheel, 4.5" BCD
6-Hole Pipe Flange
Standard 6-hole flange, 6" BCD
8-Bolt Pressure Vessel
Large flange, 10" BCD
3-Hole Motor Mount
Small motor mount, 2.5" BCD
12-Bolt Large Flange
Very large flange, 12" BCD
Custom CNC Pattern
5-hole custom pattern, 3" BCD
🔧 Quick Pattern Selection
3-Hole Pattern
3 holes
4-Hole Pattern
4 holes
5-Hole Pattern
5 holes
6-Hole Pattern
6 holes
8-Hole Pattern
8 holes
10-Hole Pattern
10 holes
12-Hole Pattern
12 holes
📐 Input Parameters
Planning estimates only. Verify with a licensed engineer or contractor before construction.
📐 Construction Industry Facts
PCD = Pitch Circle Diameter (circle through bolt centers).
— ASME
4-bolt wheels commonly use 4.5 in. or 100 mm PCD.
— SAE
6-hole flanges are standard for pipe connections.
— ASME B16.5
Export coordinates for CNC G-code or DXF.
— Industry
📋 Key Takeaways
- • X = (D/2) × cos(θ) + X₀, Y = (D/2) × sin(θ) + Y₀
- • Angular spacing = 360° ÷ number of holes
- • Chord = D × sin(π/n); Arc = πD/n
- • PCD = Pitch Circle Diameter
What is a Bolt Circle Calculator?
A bolt circle calculator helps you determine the exact coordinates of holes arranged in a circular pattern. This is essential for CNC machining, drilling operations, flange design, wheel mounting, and any application requiring precise circular hole patterns. The calculator computes angular spacing, chord lengths, arc lengths, and provides coordinate tables for manufacturing.
Precise Coordinates
Calculate exact X,Y coordinates for each hole
Spacing Calculations
Angular spacing, chord length, and arc length
CNC Ready
Export coordinates for CNC machining
Visual Diagram
Visual representation of bolt pattern
How to Calculate Bolt Circle Coordinates
Calculation Formula
Y = (D/2) × sin(θ) + Y₀
Where D is bolt circle diameter, θ is angle, and (X₀, Y₀) is center point
Quick Reference
Common Bolt Circle Applications
3-Hole Pattern
Triangular pattern, 120° spacing
Motor mounts, Small flanges, Light fixtures
4-Hole Pattern
Square pattern, 90° spacing
Wheels, Flanges, Mounting plates
5-Hole Pattern
Pentagon pattern, 72° spacing
Custom flanges, Decorative patterns, Special mounts
6-Hole Pattern
Hexagon pattern, 60° spacing
Pipe flanges, Pressure vessels, Large wheels
8-Hole Pattern
Octagon pattern, 45° spacing
Large flanges, Heavy-duty mounts, Industrial equipment
10-Hole Pattern
Decagon pattern, 36° spacing
Large pressure vessels, Custom applications, High-load flanges
12-Hole Pattern
Dodecagon pattern, 30° spacing
Very large flanges, Heavy machinery, Special applications
Bolt Circle Formulas
Standard Bolt Circle Diameters
| Diameter | Inches | Millimeters | Common Uses |
|---|---|---|---|
| 1.5" BCD | 1.5" | 38.1 mm | Small wheels, Light fixtures |
| 2.0" BCD | 2" | 50.8 mm | Small flanges, Motor mounts |
| 2.5" BCD | 2.5" | 63.5 mm | Medium wheels, Pumps |
| 3.0" BCD | 3" | 76.2 mm | Standard flanges, Wheels |
| 3.5" BCD | 3.5" | 88.9 mm | Medium flanges |
| 4.0" BCD | 4" | 101.6 mm | Large wheels, Flanges |
| 4.5" BCD | 4.5" | 114.3 mm | Standard flanges |
| 5.0" BCD | 5" | 127 mm | Large flanges, Pressure vessels |
Common Applications
CNC machining, flanges, wheels, flywheels, pulleys, brake rotors.
Frequently Asked Questions
What is PCD?
Pitch Circle Diameter—the diameter of the circle through the bolt centers.
Clockwise or counterclockwise?
Depends on your coordinate system. Most CNC uses standard math convention (CCW positive).
Machining Tips
- • Use center (0,0) or part datum for CNC
- • Verify hole count matches your pattern
- • Check units (inches vs mm) before machining
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