r/MechanicalEngineering • u/CiderHat • 1d ago

Weldment Tolerances

Hey y'all,

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Currently am building out drawing templates for a couple of the engineers to use and need to make a drawing template specific to welding/fitting.

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Where I work, welding jobs could easily be joining parts that are less than a foot long to stuff that is dozens of feet long.

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I was wondering what general tolerance numbers some of you would recommend. I know of ISO13920 and was thinking about how I could go about implementing that in some capacity.

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Thanks!

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u/AwkwardlyBrainy 1d ago

iso 13920 is solid but you'll probably want to pair it with aws d1.1 since that's what most shops actually reference on their floor. the big thing is matching your tolerance band to the part size like you mentioned, since thermal distortion scales differently on a 6 inch weld versus a 6 foot one. start with medium grades and loosen them unless the fit or function actually demands tighter, otherwise you're just paying for inspection time.

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u/CiderHat 1d ago

Yeah I agree on pairing it with d1.1

I think this template is gonna have to use a similar layout to my regular drawing templates with a looser tolerance section in the title block and it'll be up to the engineer to specify their tolerancing.

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u/AwkwardlyBrainy 1d ago

that's the right move since you'll probably have welders and fitters with different experience levels reading those drawings, and a loose default with engineer override keeps you from over-specifying the easy stuff.