ISO 8062 ISO 8062 geometrical tolerances for castings
ISO 8062 geometrical tolerances for castings · Fundición (ISO 10135) · ISO 1101
Example in plan
How to interpret it
On the drawing, “ISO 8062-3 CT10 + ⌖ on machined holes only” states a iso 8062 geometrical tolerances for castings requirement.
What controls
Standards framework that, in addition to the CT dimensional tolerance grades, sets out the general geometrical requirements applicable to castings: what deviations of form, orientation and location are permitted in the as-cast geometry when the drawing does not state otherwise, and how they relate to the machining allowance. Its role is the same as that of a general machining tolerance: to cover what the drawing does not explicitly specify, without replacing explicit GD&T feature control frames.
How to verify
As-cast geometrical deviations are verified like any other geometric tolerance, but with instruments suited to rough surfaces and large parts: portable measuring arm, 3D scanner aligned to the model, or surface plate with dial indicator and defined supports. The essential thing is to first establish how the part is supported, because on a cast surface the result changes radically depending on the chosen support points; if the drawing defines supports or datum targets, those are used.
Common mistakes when interpreting it
- Applying machining geometric tolerances to as-cast surfaces that are covered only by the general casting criterion.
- Measuring geometry on a casting without defining the supports and getting different results at each inspection.
- Assuming that a GD&T frame drawn on a face automatically means there is machining allowance to machine it: the drawing must state that.
How to get it in the workshop / if it comes out of tolerance
Use it to answer the question “this as-cast face is warped; is it rejectable?”: if there is no GD&T frame on it, the criterion is the general casting one, not the machining one. When the drawing does place a geometric feature control frame, that frame governs and normally implies the surface is machined. Mixing both worlds on the same dimension is the main source of disputes between the machine shop and the foundry.
If a part fails an as-cast geometrical requirement, first check how it was supported for measurement: with castings, more than half of geometry rejections are measurement setup problems. If the deviation is real and systematic, the correction lies in the molding tooling. If it only affects subsequent machining, it can often be solved with more machining allowance and a well-distributed work offset rather than a mold change.
Related symbols
Other symbols in Foundry (ISO 10135)
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