Available Metals: Designing Your Casting:

The following descriptions demonstrate the high level of precision we can achieve in your casting. Use these descriptions when designing your casting. Please call if you need assistance.

1. Standard Linear Tolerances

As a general rule, normal linear tolerance on investment castings can be as follows; Up to 1 inch ± 0.010 inch. For each additional inch thereafter, ±0.003 inch. Following is a chart indicating expected normal and premium tolerances. An exception to the Standard Linear Tolerance exists on thin wall thickness where the tolerance must be a minimum of ± .020 inch.

2. Linear Tolerances
 
Dimensions
Normal
Premium
Up to 1/2 inch ±.007 inch ±.003 inch
Up to 1 inch ±.010 inch ±.005 inch
Up to 2 inches ±.013 inch ±.008 inch
Up to 3 inches ±.016 inch ±.010 inch
Up to 4 inches ±.019 inch ±.012 inch
Up to 5 inches ±.022 inch ±.014 inch
Up to 6 inches ±.025 inch ±.015 inch
Up to 7 inches ±.028 inch ±.016 inch
Up to 8 inches ±.031 inch ±.017 inch
Up to 9 inches ±.034 inch ±.018 inch
Up to 10 inches ±.037 inch ±.019 inch
Maximum Variation ±.040 inch
3. Normal Tolerances

Normal tolerances are tolerances that can be expected for production repeatability of all casting dimensions.

4. Premium Tolerances

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 chart above. It will depend on the alloy and configuration and should be determined in close cooperation with your investment casting supplier.

5. Flatness

Flatness refers to a single plane surface; in investment casting, usually a function of the volumetric shrinkage of the part. The following table serves as a rough guide in areas under 6 square inches:
 
Section Thickness
Possible Dish for Face of Casting
Up to 1/4 inch Not Significant
1/4 inch to 1/2 inch .004 inch TIR
1/2 inch to 1 inch .008 inch TIR
1 inch to 2 inches .016 inch TIR
6. Radii

A general tolerance is ± 1/64 inch.

7. Concentricity

Concentricity between I.D. and O.D. will usually fall within the diameter dimensional tolerances. A general rule is that component diameters will be concentric within .005 per inch of separation.

8. Gate Areas

Removal of gate or gates with a witness of .010 inch to .020 inch can easily be accomplished. Flush removal or removal to a contour requires additional labor and expense.

9. Parallel Sections

A general tolerance is .010 TIR per inch as cast. The proper combination of configuration, alloy, and hardness may result in .005 TIR through straightening.

10. Fillets

A minimum of 1/32 inch is recommended. As generous a fillet as can be permitted is desirable.

11. Angles

Angular tolerance is dependent on the configuration forming the angle. A general rule of thumb is ± 1/20 for well supported sections. Sections where inherent distortion could be expected may range up to ± 20. Many sections can be mechanically straightened.

12. Straightness

A general design guide for Axial straightness is ± .005 inch/inch. Some castings can be mechanically straightened to closer tolerances.

13. Surface Finish

Ferrous 90 to 125 RMS Average Surface finish can be improved by secondary operations.

14. Minimum Section Thickness

Under normal circumstances, walls thinner than .050 ± .010 are not practical although they may be feasible in certain designs. In most instances, walls of .090 ± .010 are desirable.

15. Holes

Holes can be cast to size if their diameter and locations are dimensioned with attainable tolerances. As a rule, through holes should be no longer than six (6) times their diameter; blind holes two (2) times their diameter.