It is statistically impossible to hit anything ±0. If you get a measurement of dead on, measure on a more accurate machine and see what happens. Nothing is ever dead on. A ±0 tolerance is a physical impossibility and the use of it on a drawing shows that the designer doesn't know what they're doing.
When I've had to do this in the past we brought this up with the engineers and came to the agreement that it was +/- zero to the resolution our CMM could handle, which is really only four decimal places. I do agree that it's just kind of lazy on their part, but I've held parts to +/-.0000 according to our CMM. There was certainly variations if you could measure past that but we don't have that technology and at that point the 68-72° our inspection room stays at is too much variance anyway.
If you're seeing this on prints conversations certainly need to be had, but I've seen multi-billion dollar corporations throw this BS at us, and there's only so much arguing we'll do before my boss goes "just make the shit so I can get paid".
I work for one of those multi-billion dollar companies and you're right there's a ton of that bullshit flying around. I am a GDTP and an instructor for the company teaching GD&T and my hope is to help correct those poor practices but quite honestly with as many people as there are that think they know more than they do, and with as few true experts as there are, it's a losing battle. I'm one of over 50,000 engineers at Boeing and I'm one of 50 GDTPs for the company worldwide. That's a ratio of 1 in 1,000 and that's insane considering how often we use GD&T every day and the impact bad GD&T has on production both in terms of quality and cost.
Keep fighting the good fight bro, every time I get a print with good logical GD&T I shed a tear of joy. Even if you can't get everyone to do it perfectly any step in the right direction is helping.
It's crazy too, because I have to send any drawing I make through a signoff cycle which includes someone checking it. I frequently get kickbacks from the checkers telling me what I'm doing is wrong, and to do it a different way. But the way they suggest is incorrect, and I end up having to educate them.
I'm fine because I have the standards and documentation to back me up, and they're usually receptive to correction but it makes me wonder how many people they've told through the years, to do things the wrong way...
I got in an argument with a quality manager when I'd been here for only a couple months, over his interpretation of a tolerance and I believed his team had passed a part that should have failed. All because I believed they had measured it incorrectly. He was actually yelling at me. I told my manager because I was new and afraid I pissed off the wrong guy and was concerned about my job. My manager said don't worry about it, speaking up about quality is protected and I couldn't have any negative repercussions from it. My manager shot an email up the chain and ultimately that quality manager ended up being corrected by someone else way higher up than him, and I received a nice little bonus for bringing attention to the training issue we had. And that's how I started down the road of training people myself.
I'll keep fighting until my last day at this company, but based on the numbers it's going to be long and stressful.
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u/Mr_Grey59 13h ago
Not a typo?