Dimensions & Tolerance

Tolerance level is something that calculates and figures out the exact and correct values for which an investment cast according to the given specification, reaches a maximum point without getting damaged by any means. The tolerance can be specified in many dimensions and in many suitable industrial ways, by which a buyer can deduce and co relate according to the required specification and be assured about the maximum ratings or tolerance accordingly.

We are MRK Steel Cast, an ISO certified 9001:2008 company dealing and manufacturing quality investment casting and metallic shaped instruments according to the given specifications. We have a set of lists, from which a person or a company can correlate the charts so as to match their requirements. The levels and different specified tolerances and its variants are listed below as follows:

Surface Finish

As-cast finishes will vary with alloy specified but generally fall within the range quoted. For a ground finish an allowance of 0.010 in. (0.25mm) should be made.

Metal C.I.A. value
As-cast Machined
Stainless Steels 90-126 60-125
Cobalt Chrome Alloys 80-100 50-100
Carbon Steels 90-125 60-125

General Tolerances

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

Dimension Tolerance
Upto 25 mm ±0.25mm
Above 25 mm ±0.25mm/25mm

Closer tolerance may be held on selected dimensions following design evaluation.


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

Casting Length As-cost Corrected
25 mm ±0.50 mm ±0.25 mm
50-100 mm ±0.75 mm ±0.50 mm
100-150 mm ±1.00 mm ±0.50 mm
150 mm ±1.50 mm ±0.62 mm


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

Casting Length As-cost Corrected
25 mm ±0.20 mm ±0.10 mm
50 mm ±0.37 mm ±0.15 mm
75 mm ±0.50 mm ±0.20 mm
100 mm ±0.62 mm ±0.25mm

Cast Holes

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 tobe exceeded, although usually at increased cost.

Through holes
Diameter (d) mm Maximum Depth (D) mm
3.17-6.35 D upto 1.5 d
6.35-12.70 D upto 3.0 d
12.70  D upto 5.0 d
Blind Holes
Diameter (d) mm Maximum Depth (D) mm
Diameter (d) mm Maximum Depth (D) mm
4.76-12.70 D upto 1.5d
12.70  D upto 2.0 d


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.

O.D.(mm) I.D. (mm) Eccentricity (mm)
As-cast Corrected
18.75 6.25 ±0.100 ±0.100
25.00  12.50  ±0.125 ±0.125
37.50  18.45 ±0.200 ±0.200
50.00  25.00  ±0.250  ±0.200


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.

O.D. (mm) Tolerance (mm) I.D. (mm) Tolerance (mm)
12.50 ±0.25 upto 6.25 ±0.30
25.00 ±0.50 6.25-12.50 ±0.40
37.50 ±0.60 12.50-25.00 ±0.50
50.00 ±0.75 above 25.00 ±0.50 (per 25 mm)

Minimum Section Thickness

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

Material Minimun wall thickness obtainable
18/8 stainless steels 1.62 mm
25/12 stainless steels 1.50 mm
Carbon steels 2.25 mm
Cobalt-Chrome alloy 1.12 mm

Parallel Sections

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

Gap (mm) Tolerance(mm) As-cast Corrected
6.25 ±0.075 ±0.075
12.50 ±0.125 ±0.100
18.65 ±0.150 ±0.100
25.00 ±0.175 ±0.125

Other Features

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.