Casting Tolerances
Tolerances depend on the geometry of each part, but the following tolerances are suggested as a guide to designers.
Lengths including hole diameters, held to:
| mm | inch | ||
|---|---|---|---|
| Section | Tolerance | Section | Tolerance |
| 0 - 15 | ±0.08 | 0.0 - 0.6 | ±0.003 |
| 15 - 25 | ±0.13 | 0.6 - 1.0 | ±0.003 |
| 25 - 50 | ±0.25 | 1.0 - 2.0 | ±0.010 |
| 50 - 75 | ±0.37 | 2.0 - 3.0 | ±0.015 |
| 75 - 100 | ±0.50 | 3.0 - 4.0 | ±0.020 |
| 100 - 125 | ±0.60 | 4.0 - 5.0 | ±0.025 |
| 125 - 250 | ±1.00 | 5.0 - 10.0 | ±0.040 |
Flatness
Generally held to ±0.13mm (0.005") per 25mm (1.00") square.
Straightness
Generally held to ±0.1mm (0.004") max per linear 25mm (1.00").
Squareness and Angularity
±0.5 degree
Note: Angular tolerances are affected by irregular geometries.
When tolerancing, use of a central feature as a datum may allow detail to be cast that would otherwise carry too large a tolerance. Where a mechanical interface feature is required on a surface, it helps to use the centre of the feature as a datum.
Wall Sections
Constant section thin walls are preferred but large changes of section can be accommodated through critical analysis of the component design and special tooling design features.
| Size (cubed) | Suggested Wall Thickness |
|---|---|
| up to 10mm (0.4") | 0.2mm - 1.0mm (0.008" - 0.04") |
| 25mm (1.0") | 0.5mm - 1.5mm (0.02" - 0.06") |
| 75mm (3.0") | 1.0mm - 3.0mm (0.04" - 0.12") |
| 100mm (4.0") | 1.5mm - 3.0mm (0.06" - 0.12") |
| above 100mm (4.0") | 2.0mm (0.08") upwards |
Wall thickness and flatness over large surfaces are better controlled if through-holes and ribs are incorporated in the design.
Wall Section Tolerances
| mm | inch | ||
|---|---|---|---|
| Section | Tolerance | Section | Tolerance |
| up to 0.5 | ±0.10 | up to 0.020 | ±0.004 |
| 0.5 - 1.0 | ±0.15 | 0.020 - 0.040 | ±0.006 |
| 1.0 - 2.0 | ±0.20 | 0.040 - 0.080 | ±0.008 |
| 2.0 - 4.0 | ±0.25 | 0.080 - 0.160 | ±0.010 |
| 4.0 - 8.0 | ±0.30 | 0.160 - 0.320 | ±0.012 |
