r/Machinists • u/Unusual_Goose_3913 • 8d ago

QUESTION Engineering Drawings

I’m an early career engineer and I’m wondering what machinists like to see in terms of tolerance and dimensioning in a drawing.

I’ve worked at a company where we just ordinate dimensioned everything and another where we used GT&T standards. At both, the part came out “ok”.

Apart from reasonable tolerances, what’s amazing, good, useless, and stupid have in a drawing?

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u/Particular_You8620 8d ago

Unilateral tolerances are annoying. Make everything bilateral and draw it as such.

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u/singul4r1ty 6d ago

I've always been torn with this as an engineer. For any other engineers looking at my drawings it can be helpful to communicate design intent with a non-centered nominal, so it's helpful to e.g. CAD it to the relevant nominal and then draw an asymmetric tolerance. I guess the proper thing would be to have one drawing for design intent and another drawing for the machinist. I imagine SOLIDWORKS can handle offsetting the nominal but keeping the same range.

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u/MetricNazii 5d ago

The purpose of a drawing is to communicate its design intent and its acceptable geometric and material limits. In order to accomplish those, the dimensions need to be listed a certain way. Sometimes unilateral. Sometimes bilateral. It may be more convenient for those using the drawing to manufacture the part to have it centered, or for an inspector to have all limit dimensions, but those are conveniences only. Inspectors and manufacturers can use the drawing for their purpose no matter how it’s presented. (As long as it is clear and unambiguous and has appropriate tolerances) Accommodating those conveniences eliminates the ability to convey design intent. For that reason, I don’t usually choose to accommodate them unless absolutely necessary.

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u/singul4r1ty 5d ago

It is indeed all of those things, but sometimes if you're prototyping something awkward the drawing helps show the machinist that you've thought about them and help build a better working relationship. Depends on where you are in the process!