Work out general tolerances
Find the tolerance that applies and type it, mixed with missing view questions. Get 10 right to finish.
A dimension on this drawing reads 5.6 with no tolerance next to it. What tolerance applies?
Where the tolerance comes from
- US drawings (ASME). The title block has a row per number of decimal places. A dimension of 2.50 has two places, so it takes the .XX row, for example ±.01. Type
.01. - European drawings (ISO). The title block names a class of ISO 2768, often m (medium). Look up the size in the table: 40 mm falls in "over 30 up to 120", which is ±0.3 mm in class m. Type
0.3.
ISO 2768 linear tolerances
| Size (mm) | f (fine) | m (medium) |
|---|---|---|
| 0.5 up to 3 | ±0.05 | ±0.1 |
| over 3 up to 6 | ±0.05 | ±0.1 |
| over 6 up to 30 | ±0.1 | ±0.2 |
| over 30 up to 120 | ±0.15 | ±0.3 |
| over 120 up to 400 | ±0.2 | ±0.5 |
| over 400 up to 1000 | ±0.3 | ±0.8 |
Type only the number. The ± sign and the unit are optional.
Questions
- What tolerance applies to a dimension with no tolerance on it?
- The general tolerance from the title block. US drawings give a tolerance per number of decimal places. European drawings usually refer to ISO 2768, where the tolerance depends on the size.
- What is ISO 2768-m for a 40 mm dimension?
- Class m (medium) gives ±0.3 mm for sizes over 30 up to 120 mm.
Explained in our own words and checked against several textbooks. For the full rules, see ASME Y14.2, ASME Y14.3, ISO 128, ISO 5456-2, ISO 7200 and ISO 2768-1.