Dimension tolerances for investment casting are significantly tighter than those of sand casting, typically falling within the ±0.003 to ±0.005 inches per inch range (±0.08 to ±0.13 mm per 25 mm).
The industry refers to several international standards to define these limits, most notably ISO 8062-3 and the German VDG P690.
For general dimensions, a rule of thumb is ±0.5% of the nominal dimension. However, for smaller features, higher precision is often achieved.
| Nominal Dimension (mm) | Standard (CT5/D1) | Precision (CT4/D2) |
| Up to 6 mm | ± 0.15 mm | ± 0.12 mm |
| 10 to 18 mm | ± 0.22 mm | ± 0.17 mm |
| 30 to 50 mm | ± 0.40 mm | ± 0.31 mm |
| 80 to 120 mm | ± 0.55 mm | ± 0.44 mm |
| 180 to 250 mm | ± 1.20 mm | ± 0.95 mm |
Beyond simple length and width, investment casting is known for its ability to hold tight geometric forms:
Generally 0.005" per inch (0.127 mm per 25 mm). Larger flat surfaces may experience "dish" (concavity) due to volumetric shrinkage.
Standard is ±0.005" per inch. Long, thin sections are prone to bowing and may require mechanical straightening post-casting.
Typically within 0.005" per inch of separation between diameters.
The minimum recommended wall thickness is usually 0.030" (0.76 mm) for small areas, with a tolerance of ±0.020" (0.5 mm)
Several variables can influence whether a part stays within the "Normal" or "Premium" tolerance bands:
High-alloy steels and superalloys shrink more aggressively than aluminum, making tight tolerances harder to maintain.
Large, heavy sections adjacent to thin walls cause uneven cooling, leading to distortion.
Variations in the ceramic shell temperature during pouring can cause minute dimensional shifts
Heat treatment can cause parts to "grow" or warp, often requiring a final straightening or machining step.
Different industries use different "Casting Tolerance" (CT) grades from the ISO 8062 system:
Standard for high-precision Investment Casting
Standard for Shell Molding
Standard for Sand Casting
