How to Accurately Calculate Hole Spacing in Machined Parts
A Practical Guide for Engineers, Designers, and Manufacturers
A Practical Guide for Engineers, Designers, and Manufacturers
To calculate hole spacing:
Formula:
Spacing = (Total Length - 2 × Edge Distance) ÷ (Number of Holes - 1)
Example:
For 5 holes on a 120 mm plate with 10 mm edge margin:
(120 - 20) ÷ (5 - 1) = 100 ÷ 4 = 25 mm
🔧 Try it instantly: Hole Spacing Calculator
Accurate hole spacing ensures:
Proper assembly fit
Even load distribution
No structural failures
Compatibility with CNC production tolerances
Missteps can lead to:
Bolt misalignment
Stress fractures
Poor aesthetics
Costly redesigns
Step 1 – Measure Total Length:
Determine the total distance over which the holes will be placed.
Step 2 – Define Edge Margins:
Establish the space to leave on both ends (usually ≥1.5× hole diameter).
Step 3 – Apply the Formula:
Use: Spacing = (Length - 2×Edge) ÷ (Holes - 1)
Step 4 – Validate Using Calculator:
Use EKINSUN’s Hole Spacing Tool for quick verification.
Part Length: 210 mm
Edge Margin: 15 mm
Holes: 7
Material: 7075-T6 Aluminum
Result:
(210 - 30) ÷ (7 - 1) = 180 ÷ 6 = 30 mm spacing between holes.
✔ Leave Tolerances – Allow ±0.1 mm for most materials; tighter for hardened steel.
✔ Follow Minimum Spacing – Center-to-center spacing ≥2× diameter to avoid cracking.
✔ Allow for Fastener Heads – Ensure enough clearance for washers or heads.
✔ Material Matters – Plastics deform easily; stainless steel requires lower speeds.
Some designs may require irregular spacing:
Acoustic or vibration optimization
Aesthetic layouts
FEA-based stress zones
Tip: Follow the function—not just symmetry.
Pitch: Distance from hole center to next center
Edge Margin: Distance from first/last hole to part edge
Bolt Circle: Circular pattern of holes (use separate calculator)
CNC Tolerance: Precision typically ±0.05–0.1 mm
Mechanical engineers designing multi-fastener parts
Product designers working in CAD or Fusion360
CNC machinists creating drill paths
Educators teaching mechanical drafting
Q: What's the minimum hole spacing in aluminum?
A: Minimum is 2× hole diameter, but 2.5× is safer for structural integrity.
Q: Can I use the same formula for curved parts?
A: No. Use a Bolt Hole Circle Calculator for circular layouts.
Q: What’s the ideal edge margin?
A: At least 1.5× hole diameter; 2× or more for critical components.
Q: Does the calculator support inch and metric units?
A: Yes. EKINSUN’s tool supports both systems.
Q: How accurate is CNC hole spacing?
A: Tolerance is typically ±0.05 to 0.1 mm with proper calibration.
Alex Liao is the lead engineer at EKINSUN, with over 10 years of experience in CNC machining, materials engineering, and product design. He specializes in simplifying technical workflows for global engineers and manufacturers. His team has delivered precision parts for aerospace, robotics, and medical sectors across 12+ countries.
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📧 For technical inquiries: support@ekinsun.ltd
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