Tolerances and fits
A size on a drawing can carry its tolerance: plus or minus, two deviations, its limits, an ISO 286 class such as H7 with the deviations read from the standard's tables at the measured size, or mark it as a basic or a reference size. Sizes without a tolerance of their own take the sheet's general tolerances, stated above the title block.
Access: select a dimension, then Tolerance in its properties. General tolerances: the sheet's properties, with nothing selected.
Add a tolerance to a size
- Select a length, radius or diameter dimension.
- Under Tolerance, pick the kind:
| Kind | Writes | Set |
|---|---|---|
| ± | 12 ±0.10 | The value, mm |
| Dev. | 12 with +0.10 over -0.05 | Upper and lower deviation, mm |
| Limits | The largest size over the smallest: 12.10 over 11.95 | Upper and lower deviation, mm |
| Fit | Ø12 H7 and its deviations from ISO 286 | Hole class, shaft class, what to show |
| Basic | The size in a frame, for GD&T | |
| Ref. | (12): a size given for information only |
ASME drawings write the same in their notation: .500 ±.010 in inches.
Fits
For a fit, pick the hole's class (H7, G7, K7, P7...) or the shaft's (g6, h6, k6, p6...). Show writes the class, the deviations or both; the deviations come from ISO 286 at the size the dimension measures, so they change when the size does. With both a hole and a shaft class the dimension writes the fit, H7/g6, and the properties say whether it is a clearance, transition or interference fit and by how much.
The tables cover sizes up to 500 mm and the classes in the lists.
General tolerances
New ISO drawings state ISO 2768-m; new ASME drawings state a tolerance block by decimals (.X ±.1 .XX ±.01 .XXX ±.005 ANGLES ±0.5° in inches). Pick another class or type your own text under General tolerances in the sheet's properties; None takes it off.