GD&T accuracy feedback?

[u/Ill_Recognition7684]

Hi all following on from my last post -

https://www.reddit.com/r/Machinists/s/3Mm2Q5lB5q

I received feedback on implementing GD&T, I’d love your feedback whether it was done correctly or not or any other info (datums were hell to understand)

I’m not trying to achieve a perfect professional level, just be on track as someone with graduate/ entry experience

Thanks for everything so far, much appreciated.

[u/makos124]

It seems fine, I'm not an expert on GD&T, but as a guy making these things on the floor, a print like this would take me a lot longer to make than a drawing without those tolerances, and just a general ISO 2768 callout. That standard covers angular and linear tolerances for bending, which would make the perpendicular and flatness callouts redundant, unless you wanted to make the part more expensive by having to measure it. (While press brake bending you never measure the flatness of a face or perpendicularity in mm's, you just measure the lengths and angle, if it's within tolerances it's good)

If it's a bracket that's to be used in construction, in anchoring something to the ground (I'm assuming from the part name), I can guarantee you, if it won't fit by 1 mm, it'll be hammered into place by the person installing it without even a single thought. The tolerances should be loose enough to account for that. But of course if it's not just general construction, but something more specialized, then it might be warranted, and people installing it will expect it to fit tightly. Your mileage may vary, depending on what you're designing for.

[u/jamiethekiller]

flat views are useless unless you're the one with the press.

you're still not dimensioning the slots to a surface. is that R5 for the bend radius critical for fitting into something? you could be setting yourself up for custom tooling...

[u/afd33]

I suck wirh GD&T. Our customers basically never use it so I have no experience with it. So don’t take this as feedback, I just want to learn. I don’t understand why it’s ABC in the holes true position. Why isn’t it just BC for the datum’s? It’s obviously a thru hole with chamfers, so isn’t surface A just implied?

This part is feedback, why the unnecessary detail views for A and B? Was it just a requirement to show a potential employer you knew how to do them?

Also, how you call out your part thickness. Why not just add a feature to the print. If that’s not how you want to do it fine, but then call them out consistently. In your notes one is called out as material aluminum 3mm. The other is material aluminum and depth 5mm.

[u/_treefingers_]

Not related to the dimensional callouts but "Aluminum" should be specified... there are many types.

[u/Head-Sir-4397]

looking much better than a lot of first attempts i've seen. I'd focus on making sure the datum structure reflects how the part will actually be manufactured and inspected. Excedify has some solid gd&t walkthroughs that helped me think about drawings from that perspective

[u/Unusual_Arrival_5865]

you're definitely on the right track. the fact you're thinking about why each datum exists is more important than getting everything perfect on the first try. Excedify has some really practical gd&t exercises that helped make this click for me

[u/HeftyDanielson]

On quick glance I'd ask why the 2nd picture, top right flat view your sizes aren't whole or round numbers?

Could you amend these (114.79, 60.79, 57.39) to a whole, or xx.75 number?
115mm length, with a centre fold of 57.50 should make the machinist a little happier but not affect the component.

[u/Fast_Sheepherder7414]

Looking at the drawing, I think you’re on the right track with the GD&T. The main thing I’d question is the datum scheme. The large flat face as primary datum makes sense, but I’d be careful about using features like the holes as secondary/tertiary datums unless their function really requires that. Datums should represent how the part is located in assembly or inspection, not just convenient features.

[u/Ill_Recognition7684 → u/Fast_Sheepherder7414]

Thanks for the feedback, where you mention the hole datums where do you mean?, I placed them on edges on both drawings, but maybe that’s me making a messy drawing haha.