Standard Linear Tolerances


As a general rule . . . normal linear tolerance or investment castings can be as follows :


Up to l" ± .010". For each additional inch thereafter, ± .003".


Following is a chart indicating expected normal and premium tolerances : NORMAL TOLERANCES are tolerances that can be expected for production repeatability of all dimensions of the casting.


PREMIUM TOLERANCES are those which require added operations at extra cost, and provide for closer tolerances on selected


dimensions. In the case of premium tolerances, you can obtain even tighter tolerances than those shown on the following chart. It will depend on the alloy and configuration . .. and should be


determined in close cooperation with your investment casting supplier. LINEAR TOLERANCE


DIMENSION up to lh"


up to l" up to 2" up to 3" up to 4" up to 5" up to 6" up to 7" up to 8" up to 9" up to 10"


NORMAL ± .007" ± .010" ± .013" ± .016" ± .019" ± .022" ± .025" ± .028" ± .031" ± .034" ± .037"


maximum variation ± .040"


An exception to the General Tolerance Rule exists on thin wall th ickness where the tolerance must be a minimum of ± .020"'.


Flatness (dish) It will be seen that flatness and straightness are so


closely related that confusion may arise unless the foundry and the purchaser reach definite agreement prior to production.


Mil Std. 8 states that "a flatness tolerance is the total deviation permitted from a plane and consists of the distance between two parallel planes between which the entire surface so toleranced must lie". In measuring, the parallel planes must be the minimum distance apart.


Para11e1 distance apart. not at min. pl=e~J- _ - -----------


PREMIUM ± .003" ± .005" ± .008" ± .010" ± .012" ± .014" ± .015" ± .016" ± .017" ± .018" ± .019"


The degree of flatness exhibited in an investment casting is almost always determined by the amount of volumetric shrinkage that the wax and metal undergo during cooling. This shrinkage is usually in the center of the mass and is referred to as "dish" (shrinkage, dip, or "out of flat"). This dish can


be controlled (premium) by specialized techniques, but will always be present to some extent. General flatness tolerances cannot be quoted as they vary with configuration and alloy used. The following serves as a rough guide in areas under 6 square inches.


4


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24