Dimensional variation in an investment casting may be caused by many factors. Most of these factors are closely controlled by the foundry, but minor “lot to lot” variations do occur which result in the tolerance bands defined in this section. While it is often true that maching tolerance on a given part may be closer than tolerance for an investment casting...it is also often true that critical review of a design will allow a slight backing off on tolerances, undercuts, blind holes, etc., for translation into higher production yields and lower initial piece costs...
The cost of any part increases in direct proportion to the maximum preciseness of its dimensional tolerance requirements. This is true of castings, as well as fabricated and machined parts. Investment castings are designed to minimize the cost of producing close tolerance parts.
Linear Tolerances
|
Dimension
|
Normal |
|
Up to ½" |
± .007" |
|
Up to 1" |
± .010" |
|
Up to 2" |
± .013" |
|
Up to 3" |
± .016" |
|
Up to 4" |
± .019" |
|
Up to 5" |
± .022" |
|
Up to 6" |
± .025" |
|
Up to 7" |
± .028" |
|
Up to 8" |
± .031" |
|
Up to 9" |
± .034" |
|
Up to 10" |
± .037" |
|
|
