I have been humbled.

[Pablo]

Took a 4 hour GD&T test today. My brain is pretty much fried.

The thing is - I froze up. I know the 1994 and later stuff because that's all I've used since, well 1994. But there were 1973 and 1982 version questions as well. I choked. Well OK I passed, but putooey.......

 

[1sttruck]

Is this for a 'tolerancing engineer' test ?

I found that being 'feature' based, GD&T wasn't intuitive for a lot of people, and that by trying to develop feature based xyz datum frames as much as possible it made it easier for a lot of people to understand. Consider that in school people tend to use xy (and sometimes z or other) axes, the machine tools in shops tend to use xyz (and additional) axes, and the measuring equipment uses xyz (and additional) axes; but the GD&T standard ends up creating lots of 'non-xyz' references.

 

[Pablo]

No it's a QE refresher type test. I don't mind thinking in 3-D while I calculate bonus tolerances for max material condition or figuring the symbology out and the like - but throw problems out with no context of what year they where drawn and by just the style used in problem, ascertain the version of Y14.5 and figure it all out? It's simply not real world - if I'm handed a rare GD&T 1980 drawing, hey I can figure it out because I can read the date.

 

[sprintman]

GD&T??

 

[Pablo]

Geometric Dimensioning and Tolerancing

 

[NJC]

MMM-mmm, GD&T! I took a 3 day course a few yrs back and remember ... well, almost nothing. Fair enough since I work in an R&D environment and it's much more focused no MFG.

But I DID remember one (2?) useful thing: the difference between flatness and parallelism.

 

[Pablo]

Easy one.

Flatness is simply an imaginary zone a surface must fall within as specified in the feature control box, it is not controlled by any datum or any other feature.

Parallelism is controlled by a datum/feature and as the name implies the feature indicated must by parallel to specified datum with the tolerance in the feature control box.

 

[1sttruck]

GD&T is great stuff provided one embraces the idea that one takes the time to dimension, tolerance, and measure parts to determine function, as opposed to just making it easy to measure. To do this might require developing 'tolerancng' experts who work with design, parts/assembly manufacuting, and production to make it happen.

When troubleshooting some product problems I can recall asking why such a suspect part was measured the way that it was, and I was told because it was easy to do. So they ended up with parts that were easy to measure, that looked like good parts, but since the measurements had literally nothing to do with how the part was used they ended up with a product that didn't work, had lots of good looking but unusable parts, and a design that was broke as their only solution was trial assembly to see if it worked.