Chicago Vacuum Casting
Precision Investment Castings from miniature to 50 pounds
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quick question?Linear 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.

Linear Tolerance

The general rule-of-thumb for linear tolerance of investment castings is usually expressed as +/-.005 per inch of length. As with any such rule, there are always exceptions required by process capabilities. The chart below can be used for most applications. Premium tolerances can be made available for a few selected design characteristics such as holes and slots. One should keep in mind however that tighter tolerances sometimes require special procedures and/or secondary operations which can increase the cost of the casting and increase the need for longer production times.

Inches

Millimeters

Dimension Normal Premium Dimension Normal Premium
up to 1/2" ±.007 ±.003 up to 12.7 ±.18 ±.08
1/2" to 1" ±.010 ±.005 12.7 to 25.4 ±.25 ±.13
1" to 2" ±.015 ±.010 25.4 to 50.8 ±.38 ±.25
2" to 3" ±.020 ±.015 50.8 to 76.2 ±.51 ±.38
3" to 4" ±.025 ±.018 76.2 to 101.6 ±.64 ±.46
4" to 5" ±.030 ±.020 101.6 to 127.0 ±.76 ±.51
5" to 6" ±.032 ±.022 127.0 to 152.4 ±.81 ±.56
6" to 7" ±.035 ±.025 152.4 to 177.8 ±.89 ±.64
7" to 8" ±.038 ±.028 177.8 to 203.2 ±.96 ±.71