|
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.
Go Top
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.
Go Top
STRAIGHTNESS
There are practical limits to straightness which can be achieved
but mechanical straightning can reduce variations.
Go Top
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.
Go Top
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 to be exceeded, although
usually at increased cost.
|
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.
Go Top
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.
Go Top
MINIMUM SECTION THICKNESS
Wall thickness will depend upon area of casting and alloy selected.
The following values are of guide from general experience.
|
|
Minimum
wall thickness obtainable
|
|
|
|
|
|
|
|
|
|
|
|
|
Go Top
PARALLEL
SECTIONS
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.
Go Top
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. |