Prints have a design language to them which allows you to express fully constrained geometric designs on a napkin if you need to. Dimensions, radii, diameters, angles, datums, positions, projections, sections, GD&T. None of this is obvious in a 3D model. You don’t know what the driving dimensions are, what can be inferred from other dimensions, if it is a coincidence or a requirement that two features line up, etc.

This is so critical. In architecture and structural engineering, you can add to this that you don’t actually know a lot of the real dimensions - you’re laying out the important ones from the structural grid or from survey points, and whatever is left doesn’t matter.

Even markup, at least in a design environment, can be done in 3D (or at least on a computer), but the communication of constraints, that is, what dimensions are important and which are irrelevant or unknowable has not yet been developed in 3D models, and I suspect it will be some time before any useful language for that purpose stabilizes.

Can you come to my job and explain how tolerances work to these engineers?

I never thought about any of that before but it totally makes sense.

When learning skills that are depicted visually, I’ve found it’s better to get a book that’s old enough to have illustrations or diagrams if possible. 2d line drawings in black and white, or with judicious use of 1 or 2 other colors. A skilled illustrator can show exactly what you need to see but photographs necessarily have various other stuff in view. Illustrations can clearly depict motion, hidden parts, or changes over time in ways that photos can’t hope to.

And that’s without the benefit of assuming a lot of knowledge on the part of the reader the way you can do within a profession like you are describing.

You can say ‘it’s an operating expense’ but that isn’t the problem. The problem is that the shit breaks when you need it to work, especially if you are welding or sizing or just have machinists or welders being fucking idiots on the floor as they often are (because it is hard to not be a fucking idiot in a place that you spend 40-60 hours a week). Let alone fumes, grease, and dust. It’s an idea that sounds good but just doesn’t work imo. Paper just works better, and I’m not even a geezer.

You can have a computer on the shop floor (I recommend at least three within walking distance for layout design), but having a computer (or even screen) in every booth to run CAD through is dumb as hell. I knew this from working in a shop and I know it from experience when I was overruled by management because they got it into their heads from some networking guru that every booth needed a screen, half of which now no longer work after three months and aren’t going to be replaced. I still haven’t had the balls to say I told you so, but it’s annoying as shit to see stuff coming from a mile away. Maybe it works for the Germans and Finns, but our shops just aren’t nearly as clean as theirs are.

Sometimes it is nice to see the 3-D, but the print should tell you everything you need to know, and if it doesn’t then you have to talk to an engineer about it because someone fucked up. And if they aren’t making prints, it is totally up to the machinist’s discretion. Idk, I can’t even imagine not making a fully speced print for a design, it’s such an anathema to the kinds of products I work with. Even a small run has to have tolerances or the welders will literally have to feel out good parts from bad parts, which they do not appreciate.

You never dimension a feature when it can be inferred from other dimensioned features. Dimensions are added until nothing is ambiguous, without constraining any feature more than once.

Tbf engineering 3d models should also be this. They’re usually not, but

They are out there, but they are usually stuck running basic processes that are essential to products but can’t be trusted with incoming hires to maintain quality. Ironically, incoming hires usually work on more bespoke projects because they aren’t as essential to the business being successful (unless the process has been highly automated, and then no one gets any real machining experience). Shops are weird like that.

I ask this because if I need something machined, I just send an onshape link to a friend with a shaepoko or run a fabworks order, neither of which need 2ds. I can’t do half depth through fabworks because it’s just lasered, although I’ve had significantly fewer issues with fabworks than with shaepoko guy.

“If it fits, it ships”

“We can inspect the parts when they send them back”

“Fuck it, It’s [that one consumer goods company which sends purchase orders to an ISO 13485 (medical device manufacturing) facility for some reason]”

All jokes aside, tight tolerances DO NOT indicate good engineering. Anybody can add a bunch of extra zeros to a fucking blueprint. A well engineered part / assembly will have things toleranced as loosely as permissible, with the exception of a handful of critical dimensions, and a good design will ensure that even those critical dimensions don’t need to keep the machinist running back and forth between the grinder and the laser micrometer.

Excessively tight tolerances will cause a lot of perfectly functional parts to be scrapped, require additional machining operations, more expensive tooling, more frequent tool changes, increased rework, increased machine operator skill, increased inspection frequency, etc. etc. etc. When some fuckstick like Elon Musk comes around and says they’re tightening the tolerances to make the fucking door panels line up correctly, they’re telling you they have no idea what they’re doing.

Holding tight tolerances is a matter of workmanship. Engineers are supposed to be the ones figuring out where that effort makes the most impact and where it makes no difference whatsoever.

Lol. Woops. *Jatco

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Tolerates