Casting / Forging Tolerances
Machining allowances are usually in the order of 0.5mm – 2.5mm depending on casting size.
Symbols, Lettering, Numbers etc., can be cast in relief or inset.
All of the following information is for the as cast condition, unless otherwise stated.
General Tolerances: Steel
Section Thickness: Steel
The minimum section thickness that can be cast under normal situations is 1.5mm.
Under certain conditions this can be reduced to 1.15mm
Nb a section thickness over 5mm may require a special technique during
the manufacture of the pattern to counteract wax shrinkage.
Wall Thickness Tolerances
As a general rule 125 micro inches, this can be improved
to 64 micro inches in some circumstances.
Holes should be kept as short as possible, in relation to the diameter.
Blind holes are more difficult to cast.
Tolerances are as per general tolerances
All tolerances are for as cast roundness on O/D’s and I/D’s
Tighter tolerances can be supplied by Machining
As a general rule, the larger the O/D the closer to concentricity the I/D can be cast.
Tighter tolerances can be supplied by machining.
All of the above information is an aid to a designer by giving an indication of what
an Investment Casting is capable of.
Consultation with the foundry at the earliest possible stage will enable the optimum tolerances
and finish to the casting to be gained.ing