CNC Machining Tolerances: A Practical Guide
2026-08-14 · Guide
Tolerances define how closely a machined part matches its nominal dimensions. Tighter tolerances improve fit and function but increase cost dramatically beyond certain points.
Standard tolerances
For most machined features, ISO 2768-m (roughly +/-0.1 mm) is achievable at no extra cost. Fine tolerances of +/-0.05 mm require controlled processes, and anything within +/-0.01 mm requires precision equipment, stable temperature and careful measurement.
When tight tolerances matter
Only features that mate with other parts or affect sealing and balance usually need tight control. Specifying +/-0.01 mm across every surface is the most common and most expensive drawing mistake.
How to specify
- Apply tight tolerances only to functional features
- Use general tolerances for everything else
- Discuss critical dimensions with your supplier before production
At KS-Dewoz every critical dimension is inspected and reported, so you receive measurable quality, not promises.