Tolerance is the amount a dimension may vary and still function. Tighter tolerances cost more—more measurement, slower feeds, more scrap—so the goal is to specify only what the part actually needs.
Standard stock tolerances
Most shops hold ±0.05 mm (±0.002 in) on typical features at no extra charge. That covers the vast majority of structural and enclosure parts.
When to go tighter
- ±0.02 mm for press fits, bearing seats, and locating features.
- ±0.01 mm for precision pins, gauge surfaces, and optical mounts.
- ±0.005 mm and below only when functionally required—expect significant cost.
Position, not just size
A hole at the right diameter but in the wrong place is useless. GD&T (Geometric Dimensioning and Tolerancing) lets you control position, flatness, and perpendicularity independently. Use a position tolerance with a datum reference rather than stacking plus/minus on X and Y.
Communicate intent
Call out tight tolerances only where function demands them, and reference datums consistently. Over-tolerancing the whole drawing is the fastest way to inflate cost without improving the part. Our quality process covers how inspection is planned around your critical features.
FAQ
What tolerance can CNC hold reliably? ±0.01 mm is routine on well-fixtured features; tighter is possible with measurement and process control.
Should I tolerance every dimension? No—default to stock tolerance and flag only critical ones.
