Guide to Designing and Buying Investment Castings
These tolerances can be expected as a general "Rule of Thumb" and closer tolerances may be obtained by use of additional controls or secondary operations.
Linear Tolerances:
Up to .250" ± .004" per inch
.251" to .500" ± .005" per inch
Over .501" ± .005" per inch
Straightness:
Axial straightness + .005" per inch. Some castings may be mechanically straightened to closer tolerances.
Flatness:
Flatness refers to a single plane surface. In investment castings, it is usually a result of the volumetric shrinkage within the part.
| Thickness |
Flatness |
| up to 1/4" |
004" T.I.R |
| 1/4" to 1/2" |
008" T.I.R. |
| 1/2" to 1" |
012" T.I.R. |
| 1" to 2" |
016" T.I.R. |
|
Concentricity: Casting diameters will be concentric within .005" per inch of spearation.
Fillets:
1/32" minimum is recommended. The larger the more desirable.
Gate areas:
A gate witness of .010" to .020" is normal. Flush removal requires additional labor and expenses.
Surface Finish:
80 to 120 RMS are average.
Hole Positioning:
± .004" per inch from any single reference point.
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