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 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.