Sorry the 20 +/- .002 was purely an example. The actual case is a much larger frame, with a very thick paint process, that can cause the parts to run oot. The problems it's causing now mean lots of rework and re-engineering a number of parts.
I have a query - do engineering drawings include the paint thickness within the dimensions and tolerancing of a drawing?
IE if a drawing specified a dimension as 20mm +/- 0.002 but also called for a paint process should you make the part small to build in an allowance for the paint?