Investment Castings Steel Castings Ferrous Castings Nonferrous Castings Machined Castings Casting Foundries

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
	Micro-inches
	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.

STRAIGHTNESS

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

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.

Casting Length	As-Cast	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
4.76-12.70 D upto 1.5d
12.70 D upto 2.0 d

CONCENTRICITY

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

ROUNDNESS

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.

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