 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 |
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