Tolerancing
It is not possible in practice to manufacture products to the exact figures displayed on an engineering drawing. The accuracy depends largely on the manufacturing process used and the care taken to manufacture a product. A tolerance value shows the manufacturing department the maximum permissible variation from the dimension.
Each dimension on a drawing must include a tolerance value. This can appear either as:
- a general tolerance value applicable to several dimensions. i.e. a note specifying that the General Tolerance +/- 0.5 mm.
- or a tolerance specific to that dimension
The method of expressing a tolerance on a dimension as recommended by the British standards is shown below:
Note the larger size limit is placed above the lower limit.
All tolerances should be expressed to the appropriate number to the decimal points for the degree of accuracy intended from manufacturing, even if the value is limit is a zero for example.
| 45.25 | should not be expressed as | 45.25 |
| 44.80 | 44.8 |
Page last updated by Paul Hudson
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