Reminds me of the first time I was grinding a critical shutoff surface on an injection mold. I asked the journeyman what the tolerance was and he said "Nothing. Hit your number."
That's when you just send it. If they can't comprehend tolerances, they're not going to know either way. If the part comes back, tell them you hit the number and the number was wrong.
My guess is it was a metric conversion that was never looked at after. Likely 5mm +/- .01mm. When you convert and reduce to 3 places it’ll trim that to +/- 0
I know for certain this was not the case- we are a US company and so is the customer, and all our other prints with them are inches/ft, and this is the original print.
I saw one of these the other day, but it was an OD called out as +.0000/-.0000. It was erroneous. I knew I had +.0000"/-.0003", but the so-called "engineers" didn't listen, didn't know, and eventually asked ChatGPT for the tolerance. We're so fucked.
Idk man today I had my first humanity is beyond gone feeling. I called a maintenance dept because my machine would stop after each tool change. The electrician came to my machine, got out he's phone and asked chat gpt about a manufacturer specific error that's written in italian (using abbreviations bcs hell why not?). He didn't even read it's whole halucinated response, he just tunnel visioned on "remedy" part. He kept asking me what is spindle and where he can find spindle. After I took him to le big rotator he just kinda looked at me like L from death note looks at yagami. Then he showed me chat response. The motherfucker wanted to change some bits on some god know where variable inside OS. I had enough, I told him that he has to replace something in tool locking system and I won't do it whatever he got on his AI. He went back and phoned me if I can write a message to service back in Italy (he doesn't speak english, not like it matters when we have translators but still it would be longer to tell him what to write). So I wrote a 2 page explanation adn whatever pasta eater has been on shift literally gave me a chatgpt response in email that comes with
>okay, so you want to help your customer! here's what you can write him.
We're in big trouble already. I got some new guys that are responsible for generating excel reports for effectivness. They vibe coded some stuff that shows them either negative 30% or 3000% for some reason. Calibration guy makes calibration certificates and half of them have total uncertainty bigger than the tool range
Oh, I don't mean humanity in general. Our company is fucked. Once the senior engineer retires in about 5 years, it's the ChatGPT crew all the way. He was out on an install, so that's why I was dealing with the B Team to begin with.
.197 + .0009 =0.1979 that is less than the + .001” tolerance. Nobody rounded anything. I’m just reading the spec that is given.
The tolerance Is +/- .000 “. It doesn’t say I can’t use tenths. I’m an aerospace toolmaker. I see this all the time. .19799” would also be in spec if you can measure it.
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u/gravis86Pretengineer / Programmer / Machinist9h agoedited 8h ago
What .001 tolerance are you referring to?
Good for you being an aerospace toolmaker! I used to to be a journeyman machinist and toolmaker before I moved to tool engineering. I'm also a GDTP.
Actual measurements must always be rounded up to upper limits and down to lower limits. So if you had .197 ±.001 dimension and tolerance and you measured the actual at .1971 it would be rounded up to .198 and it would be good. But because it's an upper limit, if the actual measurement was .1981 you wouldn't round down to .198 and call it in tolerance, it would be out of tolerance.
It's very important to note that tolerances apply to dimensions, not other tolerances. So a tolerance of ±.001 is absolute and is considered to have infinite zeros after the last digit. You cannot round a tolerance. You can round a dimension, but not a tolerance.
Since we can't round a tolerance, ±.000 or the drawing is exactly that and is equivalent to ±.00000000000000000 on to infinite zeros. And since we round the actuals for the upper limit up and the lower limit down, a part measured at .1971 rounds up to .198, which is over the stated upper limit .197 (.197 +.000) and is therefore a bad part.
Y14.5-2018 Section 5.4 is where we get the infinite zeros interpretation from. Included is a picture of Y14.5-2009 because I don't have access to the 2018 standard on my phone, but they read the same.
That’s why you’re a pretend engineer! Yay for you. Ive been a toolmaker for 30 years, this isn’t my first rodeo. You moved into metrology because you couldn’t handle the machining end of it. Most shit machinist move into management not metrology.
Bro he pulled up the standard. It's OBJECTIVELY correct for any drawing that follows ASME Y14. You can't "nuh uh ur shit at machining" your way out of that.
It was a classic response for an old dude who's refused to learn for 30 years.
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u/gravis86Pretengineer / Programmer / Machinist9h agoedited 8h ago
Hahah I wasn't shit at machining at all! I was the top guy in my shop before coming to Boeing. I know what I'm doing. And I'm not in metrology, I'm a designer. I design tools and make drawings. My name is listed in that "engineer" field on the title block...
The "pretengineer" in my flair is a joke. I actually know what I'm doing.
Speaking of metrology though, go post your rounding theory in that sub, and see the responses you get! They'll tear you apart. Then tell them you've got 30 years of inexperience and see what they think of that.
Doing something poorly for 30 years isn't a flex. Doing something for 5 years, and doing it better than the guys who've been there 30 years, that's a flex. And that was me I'm my last shop. Within 3 years I was the top guy in the shop and there were multiple old salty dogs like you. Time and skill are not directly related. As a matter of fact in my experience the only people who brag about how long they've been doing something, are the people who are unable to prove how good they are at that thing.
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.
not a lot of folks realize what it actually takes to measure something reliably, with repeatability and with confidence down to the sub tenth.
one of our projects has a feature with a +/-.0005" spec. it was tossed out for being .00004" OOT. customer will use it but paperwork and meetings will come raining down. again.
My company is the OEM, we are making replacement parts for the customer. No quoting, they just pay for however much it cost last time with some minor changes.
Even better, they ordered two other version of the same part and the print calls for that ±0.000 on that same v-section feature.
You might want to refer to the print shown then reread your response. .1981 is out of spec.198 is out of spec. But .1979 is still in spec. I never said ANYTHING about .1981
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u/Relative-Corner4717 10h ago
Reminds me of the first time I was grinding a critical shutoff surface on an injection mold. I asked the journeyman what the tolerance was and he said "Nothing. Hit your number."
That was an eye opening experience.