Rules of Thumb for Investment Casting Design
To get the most from your investment, it's important to understand investment casting design & purchasing guidelines. Investment casting design and production is a precise activity and understanding the process can help buyers avoid problems and bumps in the road to obtaining great investment casting results.
When it comes to investment casting design, the tolerances listed on this page can be expected as a general "Rule of Thumb." Additionally, closer tolerances may be obtained by use of additional controls or secondary operations within the investment casting design process.
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
- up to 1/4"
- 1/4" to 1/2"
- 1/2" to 1"
- 1" to 2"
- Flatness
- 004" T.I.R
- 008" T.I.R.
- 012" T.I.R.
- 016" T.I.R.
Concentricity:
Casting diameters will be concentric within .005" per inch of separation.
Fillets:
1/32" minimum is recommended. Larger is more desirable.
Gate areas:
A gate width 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.