Tolerances

Shape and alloy selected will influence accuracies achieved but values given are normally accepted through out the investment casting industry.

There are practical limits to straightness which can be achieved but mechanical straightning can reduce variations.

Flatness is also affected by dimensions of casting. Addition of ribs will minimize bowing, twisting and distortion and mechanical straightning will reduce variations where necessary.

Depth (D) and Diameter(d) of hole must allow for adequate penetration of investment material.

Values given show usual limits for cast holes but pre-formed ceramic cores allow this restrictions to be exceeded, although usually at increased cost.

The larger the outside diameter becomes, the closer to concentric an inside diameter can be cast.

Mechanical correction can normally be made where wall thickness is thin enough to allow plastic deformation.

For solid bars roundness is affected by solidification stresses and tolerance required increases nearly in proportion to diameter, inline with usual ‘Lost Wax’ tolerances.

Values shown are for as-cost roundness on inside and outside diameters of tubes of varying sizes. Wall thickness is important and tighten tolerance can be obtained by mechanical correction if desired.

Wall thickness will depend upon area of casting and alloy selected. The following values are of guide from general experience.

Parallelism can be maintain by adding fire-bars to minimize distortions. Values shown are typical tolerances for various gap-widths between parallel sections per inch cost.

Angles : Angular tolerance to ±1/2° (Closer by mechanical corrections).
Symbols : Latters, Numbers, etc., can be reproduce in relief or inset.
Serrations, Splines and Gear Teeth may be cast in certain instances subject to prior agreement.