CNC Machining Tolerance Chart for Prototype Parts
Use this CNC machining tolerance chart to decide which dimensions need standard machining tolerances and which need tighter inspection before requesting a quote.
A practical CNC machining tolerance chart should separate general tolerances from critical-to-function features. Tight tolerances increase setup, machining time, inspection effort, scrap risk, and cost.
How to use this chart
Do not apply tight tolerance to every dimension. Use standard tolerance for non-critical geometry and reserve tight callouts for interfaces that affect function.
- ✓Critical holes and bearing seats.
- ✓Mating faces and alignment features.
- ✓Sealing surfaces and press fits.
Why tolerance changes price
Tighter tolerance can require better fixturing, slower cutting, extra inspection, more scrap allowance, and sometimes a different process route.
- ✓More setups increase stack-up risk.
- ✓Hard materials may need slower machining.
- ✓Inspection scope affects lead time.
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FAQ
Is ±0.01mm always possible?
No. It depends on geometry, material, setup, tool access, and measurement method. Use it only for critical features.
Do I need a 2D drawing?
Yes, if any dimension is critical. The drawing tells the supplier which features require inspection.
What if I do not know the tolerance?
Explain the function of the part and ask for DFM feedback before quoting.