pass rate for ASME Y14.5 certification test 2

[AndrewTT]

I just read on the Tec Ease web site that the pass rate for the senior level test is only 15%. Does anyone know what the pass rate for the technician level test is? I am planning on taking the 2009 technician level test as soon as it is available (~end of January). If the pass rate for the technician test is anywhere near as low as the senior test I will adjust my studying accordingly.

 

[3DDave]

pmarc,

I was going after only orientation; even so the result would be different values. But I think it would fit better with the incomplete understanding of the geometry that most users seem to have of what the allowances of variation can have on acceptable parts.

I've mentioned before my 3 buds who took the test, 2 passed, 1 failed. The one who failed didn't understand offhand why the projected tolerance zone formula in the 1982 version multiplied the base position tolerance by 2 in the portion relating to the projection zone ratio. Simple geometry, and he was contracted as a D&T expert. As long as he didn't have any problems that involved orientation, the answers were OK, but where orientation of the resulting feature could affect things? Not so good. I don't know about the other two because the question didn't come up for them.

I think it is rare for current machining technology to get parts that are sufficiently out-of-square to notice the allowable orientation errors. There was an entire military program that had been worked for years for TACOM that had no default angle tolerances and didn't use FCFs to control them. Parts would not have been rejectable per the drawing even if nominally 90º angles were 5º off, but no one noticed and parts fit. I mention TACOM specifically because they had developed a rule that there should be no default tolerances on angles. So the project team just eliminated that section from the title block. (The entire rule was that no dimensions should depend on a default tolerance and that all directly applied tolerances should be applied to the individual dimensions.)

So if a major military contract with deliverable drawings and customer sign-offs misses a critical orientation tolerance is missing entirely and the production of parts to that contract are delivered and used without noticing, then it seems like a good chunk of industry in insensitive to orientation requirements because the variation of the parts is smaller than a value that matters.

If true, and it seems to be true, then there isn't any point in including mention of orientation sensitivities, except as an appendix item for special applications. It would certainly simplify the test questions and fit within the limited mental model most users seem to have while not violating the performance expectations for actual parts.

 

[SeasonLee]

I always follow Al Neumann’s method when making min/max wall calculations, good guide and reference, snapshot from his textbook page 16-12.

Season

 

[3DDave]

That's an excellent example of what I wrote earlier. The OB is held perpendicular, though there is no such limitation in the standards to do so.

 

[pmarc]

So if a major military contract with deliverable drawings and customer sign-offs misses a critical orientation tolerance is missing entirely and the production of parts to that contract are delivered and used without noticing, then it seems like a good chunk of industry in insensitive to orientation requirements because the variation of the parts is smaller than a value that matters.

So how did they calculate correct sizes of MMBs for secondary datum features of size relative to primary datum planes? Unless you want to say that they did not have to do it because they never specified secondary datum features at MMB and they never used hard gages to simulate datums. Is it really what the rest of the world do or should do?

 

[3DDave]

They didn't use datums for most of the features - straight-up conventional dimensioning and tolerancing. A rectangular plate could have been out of perpendicular by 5 degrees and not violated any drawing requirement, which had no limitation on the implied non-basic 90 degree angles.

I don't know about the rest of the world. Just the US DoD and our suppliers and our QA/QC never noticed or cared about the omission.

I have since worked at an FDA regulated company. While they did have angle tolerances, parts made to those limits could not be assembled, but they had no interest in changing them, because they just assumed the supplier would make usable parts regardless of the tolerance.