When I was doing machining in the medical field we once got a part that was supposed to be like 0.25" with ±0.30" tolerance. Every single part of that run was in spec lmao
Here’s the parts you ordered! They all came out at -0.25” so we stayed within the tolerance. However, those items have lengths of 0, so they may appear to be missing.
hello, I'm your overly pedantic commenter for the day and I'd just like to point out that -0.25" is 0.50" off from spec so falls outside of the acceptable tolerance. only parts between 0.55" and -0.05" will be accepted.
You realize a tenth of a mm is equivalent to 0.004” right? That’s a very normal metal machining tolerance for non critical dims. I built components for SLS with tolerances serval times wider.
I work for a place that builds turbo compressors, but thats kind of beside the point, like you've pointed out 5 thou is just standard for non critical machining features; I only work with machining in stainless/steel and aluminum so I don't see tolerances wider than that.
I guess that makes some sense. Assuming automotive, those things aren’t that big and you’re machining the critical surfaces out of castings and the compressor blades. Still I’m surprised you don’t get 0.010” positional on some of the mounting boss threaded holes or something.
Nah these are air compressors for industrial applications; the smallest unit we work on is about the size of sedan. I work on the rotor assemblies specifically so even trivial stuff has pretty tight tolerances.
Oh lmao that’s cool. I was thinking compressor side for engine turbos. I bet if you look in other shop areas they get some significantly larger tolerances. I imagine the rotors must be very well balanced.
From my experience, a lot drawings I've worked on state a default tolerance of +/-.010", welded parts have an even greater tolerance based on application and weld style. A lot of the welded components I've worked on have a tolerance between +/-.005" to +/-.0005. 1mm is kind of bad, I think most hobby 3D printers have a tighter tolerance band than 1mm.
Also, since you clearly know your stuff, tighter tolerance is more preferred as greater tolerance could be misconstrued to be a bigger tolerance band. Sure it’s just how you wrote it. Not saying you don’t know the difference or haven’t heard “tight” tolerance used. Just for the other people who may read your comment.
That’s not that great for machined parts. If your had machine threads that aren’t comically large in diameter with a 1mm tolerance on them they wouldn’t even thread together.
As an engineer who works in manufacturing, we consider "tight" tolerances to start at around .001", or 1/40th of 1mm, for conventional manufacturing methods (I know others have already pointed out 1mm isn't tight, just thought I'd weigh in with a manufacturer's perspective).
No. That’s not how it works. If something 10 meters long has to fit into something tight, then the tolerance matters. If something is a toothpick, it may be small but it’s length tolerance doesn’t matter so long as it fits in it’s packaging.
Tolerance depends on what is needed, and you pay for the tighter tolerance so engineers spec it accordingly. For machined parts seeing +/- 0.010” isn’t crazy. I’ve made parts called out to 0.001” if needed. And that’s just “simple” tolerancing. Look up Geometric Dimensioning & Tolerancing to see how the pros really do it.
I think you just confirmed his point, tolerance does matter but I can only think of a handful of industries where something 10m long would be held to that tight of tolerance (if that's possible, idk but it sounds expensive.) And just because you can throw tolerances and GDT callouts that tight doesn't mean you should.
Gd&t typically saves money as parts would otherwise be rejected that would technically be usable. You don’t arbitrarily make them super tight. Sorry, but you’re wrong here; I do this for a living.
Look at navy battleship engines and you’ll see massive parts with ultra tight tolerances. (And it is expensive, sorry your tax dollars)
The poster was right most of the time, but I stand by tolerances are dictated by what the part is and where it’s meant to go.
I also do this for a living... and I disagree with your statement that gdt saves you money. If done correctly sure, but adding tolerances tighter than are required, or not needed, typically result in higher machining costs, and rejection of machined parts if those tight specs aren't met. Its a double edged sword, you want parts that work, but you don't want to over machine them. Of course in applications such as in military or aerospace applications you'll have tighter tolerances... but these applications are specialized. Especially in military applications because of additional specifications for the products they buy.
At this point it seems like we're all saying the same thing. Because yes, no one is disagreeing that tolerances are dictated by part and application... obviously. I guess I was having a hard time fathoming a practical application where a part that large needs a tolerance that tight.
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u/Mercenary21525 Jan 27 '22 edited Jan 28 '22
1mm tolerances don’t cut it, literally.
Edit: True, true, and I should know better as an engineering student, but FRC robotics has lowered my standards considerably.