Geometric dimensioning and tolerancing

Elliott_t · Sep 27, 2018

Hi all,

I'm new to the forum and a new mechanical engineer. I'm needing to design parts and create dimensioned drawings and am trying to teach myself GD&T, and I figured the best people to ask questions of were probably the people interpreting the drawings.

Can anybody tell me if they are familiar with GD&T and this is the correct sub-forum to post questions in relation to it?

Thanks,
Elliott

gregormarwick · Sep 28, 2018

This sub is as correct as any other.

Be aware that there are two principal standards of GD&T in use globally, ISO and ASME. There is a lot of overlap, but there are some critical differences. ASME is rarely referenced outside of America, but being that most of the members of this site are American, most answers to your questions will have an ASME bias, so take care of that.

If you haven't already, you should get some good reference material. This one lives on my desk and sets everything out in an easy to understand manner.

billmac · Sep 28, 2018

gregormarwick said:
This one[/URL] lives on my desk and sets everything out in an easy to understand manner.

That is a good book and I also use it. Having said that, you might be best served by finding a training course somewhere. There are a number of areas where a deeper understanding of what and why is helpful. If you have a search through old posts on this site you will find a few discussions that should point some of these out.

DDoug · Sep 28, 2018

How much did you pay for your degree ?

You didn't have a single class dealing with GD&T ?

Please name said college.

gregormarwick · Sep 28, 2018

digger doug said:
How much did you pay for your degree ?

You didn't have a single class dealing with GD&T ?

Please name said college.

I have crossed paths with a lot of young mech. engineers over the last 10 years or so.

Not a single one that I can recall has had the first clue about how to apply GD&T.

It's fair enough. On the scale of important things to learn in a mechanical engineering degree it's pretty near the bottom. If it's covered at all I expect it's very cursory.

Larry Dickman · Sep 28, 2018

gregormarwick said:
I have crossed paths with a lot of young mech. engineers over the last 10 years or so.

Not a single one that I can recall has had the first clue about how to apply GD&T.

It's fair enough. On the scale of important things to learn in a mechanical engineering degree it's pretty near the bottom. If it's covered at all I expect it's very cursory.

That's because, on the engineer's side it's easy. Just call out all true positions .001. See how easy it is.

NRDock · Sep 28, 2018

digger doug said:
How much did you pay for your degree ?

You didn't have a single class dealing with GD&T ?

Please name said college.

Pitt used to offer a BT (technology) degree in Johnstown. I would hope they taught GD&T, but didn't choose that path, so don't know.
I'd like to know if any engineering school's BS (science) curriculum includes GD&T as a requirement.
Apparently, smart manufacturing isn't considered "science".

plastikdreams · Sep 28, 2018

NRDock said:
Pitt used to offer a BT (technology) degree in Johnstown. I would hope they taught GD&T, but didn't choose that path, so don't know.
I'd like to know if any engineering school's BS (science) curriculum includes GD&T as a requirement.
Apparently, smart manufacturing isn't considered "science".

I would think it would be in a drafting course...which I would imagine engineering would have in the curriculum. Irresponsible application of go&t causes problems that compund more than bonus tolerance.

nicholasnbailey · Sep 28, 2018

As a recent mechanical engineering graduate I can say that we never covered anything on GD&T, everything I know is self taught

Sent from my A577VL using Tapatalk

DDoug · Sep 28, 2018

gregormarwick said:
I have crossed paths with a lot of young mech. engineers over the last 10 years or so.

Not a single one that I can recall has had the first clue about how to apply GD&T.

It's fair enough. On the scale of important things to learn in a mechanical engineering degree it's pretty near the bottom. If it's covered at all I expect it's very cursory.

So what is ranking higher ?

4 years (8 semesters) and they can't squeeze it in ?

Must be too many classes on how to "hide your mistakes",
and "cover your arse with paperwork"
And "dealing with Laywers".

plastikdreams · Sep 28, 2018

digger doug said:
So what is ranking higher ?

4 years (8 semesters) and they can't squeeze it in ?

Must be too many classes on how to "hide your mistakes",
and "cover your arse with paperwork"
And "dealing with Laywers".

And how to be a liberal

Rudd · Sep 28, 2018

Fer cryin out loud guys, the man is coming in here asking the shop how to do something. That indicates a good engineer to me. He's willing to learn how it's done by those that deal with it. And all y'all can do is beat up on him because he's an engineer. Pretty pathetic.

DDoug · Sep 28, 2018

plastikdreams said:
And how to be a liberal

...and how to farm out work to low cost overseas operations, and how to screw suppliers.

Oh, and the biggie "Delegating Responsibility".

DDoug · Sep 28, 2018

Rudd said:
Fer cryin out loud guys, the man is coming in here asking the shop how to do something. That indicates a good engineer to me. He's willing to learn how it's done by those that deal with it. And all y'all can do is beat up on him because he's an engineer. Pretty pathetic.

I am an engineer, I am not beating him up on anything.
I am asking why his college (name is still unknown) does not offer it.

A drawing is the language used to talk with a machine shop.
Part of that language is GD&T. And how does the engineer figure tolerance
stack ups ?

strokersix · Sep 28, 2018

Tolerance stack is nearly impossible or mostly meaningless without GD&T for anything but very simple geometries.

Properly used GD&T is very effective. Improperly used GD&T is worse than none.

Not taught in engineering school. Learned on the job.

FWIW I am a retired engineer with significant machine shop experience. My last role before retirement was to lead the organization toward full and effective GD&T usage. I am a big fan of GD&T.

plastikdreams · Sep 28, 2018

It's very useful when used properly, I wish it was used more often lol.

DDoug · Sep 28, 2018

strokersix said:
Tolerance stack is nearly impossible or mostly meaningless without GD&T for anything but very simple geometries.

Properly used GD&T is very effective. Improperly used GD&T is worse than none.

Not taught in engineering school. Learned on the job.

FWIW I am a retired engineer with significant machine shop experience. My last role before retirement was to lead the organization toward full and effective GD&T usage. I am a big fan of GD&T.

And it should be taught as a "core competency" for the degree.

I'm sure "Industrial basketweaving", "Religious studies", or a host
of other "electives" could be dropped...... :eek:

plastikdreams · Sep 28, 2018

digger doug said:
And it should be taught as a "core competency" for the degree.

I'm sure "Industrial basketweaving", "Religious studies", or a host
of other "electives" could be dropped......

Why do you keep ragging on the guy jeeze

boslab · Sep 28, 2018

Machinists moan about engineers, engineers moan about machinists, so it is, was and shall be, plus nil minus 0.001
Mark

Upnorth4 · Sep 28, 2018

boslab said:
Machinists moan about engineers, engineers moan about machinists, so it is, was and shall be, plus nil minus 0.001
Mark

And Millwrights whine about them all

I'm a Canadian Millwright and we spend a good portion of time on GD&T in third year.

But hey if the Engineer's design if off and the Machinist is at the outside of limits the Millwright just uses a bigger hammer to assembly it, or welds it as appropriate.

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