Tight tolerances look good on a drawing, but every extra decimal place adds machining time, inspection time and cost. Knowing where precision really matters can cut your part price significantly.
Standard vs. Tight Tolerances
If a drawing has no tolerance, most machine shops apply ISO 2768-m, about ±0.1 mm for typical dimensions. Tolerances of ±0.01 mm or tighter need slower cutting, more careful set-ups and CMM inspection.
Where to Specify Tight Tolerances
- Bearing fits and shaft diameters
- Mating surfaces and alignment features
- Sealing faces and O-ring grooves
- Threads and precision bores
How Tolerances Affect Cost
As a rule of thumb, going from ±0.1 mm to ±0.01 mm can double the machining cost of a feature. Applying tight tolerances only to functional features keeps the rest of the part economical.
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