General tolerance ISO 2768 does not specify where to use these tolerances. You should define tolerance class as per design requirements and manufacturing capability. For example, the manufacturer recommends ISO 2768-mk for sheet metal parts and ISO 2768-fh for machined components. In the above example, “m” and “k” have defined the tolerance class.
You can calculate the critical dimension tolerance using tolerance stack-up analysis. You can also use a tolerance stack-up calculator for this purpose.
It is not possible to define engineering tolerances against each dimension. Therefore engineers define general tolerances in engineering drawings to define the variation. ISO 2768 standard defines general tolerance for:
- Linear Dimensions
- Angular Dimension
- External Radius and Chamfer height
- Geometric tolerance such as straightness, flatness, perpendicularity, symmetry, and runout.
General Tolerance : ISO 2768
| External Radius and Chamfer Heights | ||||
|---|---|---|---|---|
| Nominal Length Range in mm | Tolerance Class | |||
| f (fine) |
m (Medium) |
c (coarse) |
v (very coarse) |
|
| 0.5 up to 3 | ±0.2 | ±0.2 | ±0.4 | ±0.4 |
| over 3 up to 6 | ±0.5 | ±0.5 | ±1.0 | ±1.0 |
| over 6 | ±1.0 | ±1.0 | ±2.0 | ±2.0 |
| Angular Dimensions | ||||
|---|---|---|---|---|
| Nominal Length Range in mm | Tolerance Class | |||
| f (fine) |
m (Medium) |
c (coarse) |
v (very coarse) |
|
| up to 10 | ±1° | ±1° | ±1°30' | ±3° |
| over 10 up to 50 | ±0°30' | ±0°30' | ±1° | ±2° |
| over 50 up to 120 | ±0°20' | ±0°20' | ±0°30' | ±1° |
| over 120 up to 400 | ±0°10' | ±0°10' | ±0°15' | ±0°30' |
| over 400 | ±0°50' | ±0°50' | ±0°10' | ±0°20' |
| Straightness and Flatness | ||||
|---|---|---|---|---|
| Nominal Length Range in mm | Tolerance Class | |||
| H | K | L | ||
| up to 10 | 0.02 | 0.05 | 0.1 | |
| over 10 up to 30 | 0.05 | 0.1 | 0.2 | |
| over 30 up to 100 | 0.1 | 0.2 | 0.4 | |
| over 100 up to 300 | 0.2 | 0.4 | 0.8 | |
| over 300 up to 1000 | 0.3 | 0.6 | 1.2 | |
| over 1000 up to 3000 | 0.4 | 0.8 | 1.6 | |
| Perpendicularity | ||||
|---|---|---|---|---|
| Nominal Length Range in mm | Tolerance Class | |||
| H | K | L | ||
| up to 100 | 0.2 | 0.4 | 0.6 | |
| over 100 up to 300 | 0.3 | 0.6 | 1 | |
| over 300 up to 1000 | 0.4 | 0.8 | 1.5 | |
| over 1000 up to 3000 | 0.5 | 0.8 | 2 | |
| Symmetry | ||||
|---|---|---|---|---|
| Nominal Length Range in mm | Tolerance Class | |||
| H | K | L | ||
| up to 100 | 0.5 | 0.6 | 0.6 | |
| over 100 up to 300 | 0.5 | 0.6 | 1 | |
| over 300 up to 1000 | 0.5 | 0.8 | 1.5 | |
| over 1000 up to 3000 | 0.5 | 1 | 2 | |
| Runout | ||
|---|---|---|
| H | K | L |
| 0.1 | 0.2 | 0.5 |
To sum up, Engineering tolerance is a critical part of product design. And ISO-2768 standard defines the values of general tolerance. Experts always recommend performing tolerance stack-up analysis before design finalization.
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i want to know,,,according ISO 2768 -M. Can you tell me tolarance for welding follow standard iso 2768.thanks