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ISO 2768 is a good pointer towards tolerances on lengths, angles and some geometric tolerance things. Engineers Edge have bits of it tabulated here. It's only valid for machined parts but it's a good start. There's an equivalent standard for welded parts, castings and presumably polymers. Generally aim for 'medium', I'm yet to find a machine shop that doesn'...


3rd edition Marks HandBook circa 1923 is what I use. When the local library re-opens, check out the modern versions in the reference section.


There are standards. But that's really putting the cart before the horse. Imagine you're designing ..anything. By default the tolerance is whatever you can expect from the fabrication process if everything is done very poorly, and carelessly. Is the part still acceptable? If so then you're done, no tolerance needed (practically speaking). Most of the time ...

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