General Tolerances

There has been a lot of discussion over the years between various suppliers of investment castings regarding tolerance that is appropriate for the process. While there continues to be some debate, what follows is meant to be a general guideline. An investment casting is meant to be a "near net-shape" part that offers the most value. If the buyer and producer maintain a high level of communication, the design requirements and cost efficiencies will be met by processing capabilities.

Radii
The general tolerance is +/- 1/64”, although if necessary we can reduce this to a span of 0.005”. For best results and lowest costs, allow a generous radius, and avoid sharp corners.

Straightness & Flatness
Castings are mechanically straightened when necessary.
Tolerances for flatness and straightness are .003” to .005” TIR per linear inch and depend on alloy and configuration of casting.

Roundness
The general linear tolerance of +/- .005” applies to diameters. On larger tubular castings, closer tolerances can be held through mechanical straightening.

Holes
Tolerances for holes are as follows:

Up to .250” diameter +/- .003”
Up to .500” diameter +/- .004”
Over .500” diameter +/- .0005” per inch

The following table gives you the amount of eccentricity you can expect in an investment casting.

Outside Diameter	Inside Diameter	TIR Eccentricity
1/4"	1/4"	.008
1"	1/2"	.010
1-1/2"	3/4"	.010
2"	1"	.016

Angles
The angular tolerance should not be closer than +/- 1/2 ”.

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