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.

 

[AndrewTT]

Since the perp. callout is at MMC don't you have to consider the related actual mating envelope (outside of the material) and not the actual minimum material envelope (inside the material)? The smallest value the RAME could have is 151.5 which would be the feature made at its smallest size with perfect orientation to A. Is this perhaps why the question writer had 16.65 as the correct answer?

 

[Belanger]

pylfrm and pmarc (and AndrewTT, mkcski et al.) -- Thanks for the input. One other thing to think about though: the perpendicularity is only of concern if we are looking for the thinnest wall at one particular cross-section (depth-wise). The thinnest wall as a complete wall (throughout the depth) would be based only on the RAME. Thoughts?

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[mkcski]

I am beginning to think there are two correct answers depending on your interpretation of the phrase "minimum permissible distance" from the question. Maybe??

Certified Sr. GD&T Professional

 

[greenimi]

The definition of the "minimum permissible distance", "minimum wall thickness" is subject to multiple interpretations. This is not the first example where we have seen that. GDTP preparation book from Robert H. Nickolaisen had a couple of these calculations and the answers are not the same amoung the experts.

So, UOS "unless otherwise specified" the definition is.......................
And yes, I know, you guys like to use the UOS note...

 

[pmarc]

One other thing to think about though: the perpendicularity is only of concern if we are looking for the thinnest wall at one particular cross-section (depth-wise). The thinnest wall as a complete wall (throughout the depth) would be based only on the RAME. Thoughts?

Well, not really, J-P. You may get uniform wall thickness of 16.15 throughout the entire depth. Take pylfrm's example again and imagine that the flat spot on the OD goes from the top to the bottom of the part. If the toleranced hole is produced at its LMC size and perpendicular to datum plane A, this will produce the uniform wall thickness.

I am beginning to think there are two correct answers depending on your interpretation of the phrase "minimum permissible distance" from the question. Maybe??

As greenimi said, it is not the first time on the forum when discussion like this ends up with conclusion that the answer may depend on what someone understands by "minimum permissible distance".

 

[3DDave]

I'd be looking at the smallest distance from any point on the surface of the hole to any point on the surface of the outer diameter.

 

[AndrewTT]

If I have ~60 seconds on a test to give an answer to this question then I probably land on the 16.65 answer because I don't know that I could arrive at the 16.15 answer without 2D cad or more time to lay out a drawing manually.

Maybe they should have worded it "Assuming the part is made perfectly cylindrical...".

 

[mkcski]

AndrewTT: Since the 16.15 answer is not on the answer-list, by default I would choose 16.65 answer.

All: I really appreciate these discussions!!! They really allow me to "see" other approaches to what I thought was the "only way" Thanks.



Certified Sr. GD&T Professional

 

[pmarc]

Andrew,
Don't worry. I would not really expect this kind of questions on the Technologist level exam.

 

[pylfrm]

One other thing to think about though: the perpendicularity is only of concern if we are looking for the thinnest wall at one particular cross-section (depth-wise). The thinnest wall as a complete wall (throughout the depth) would be based only on the RAME. Thoughts?

Well, not really, J-P. You may get uniform wall thickness of 16.15 throughout the entire depth. Take pylfrm's example again and imagine that the flat spot on the OD goes from the top to the bottom of the part. If the toleranced hole is produced at its LMC size and perpendicular to datum plane A, this will produce the uniform wall thickness.

Agreed. I chose that example because it works for all interpretations I could imagine for "minimum permissible distance between the outside of the part and the edge of a hole".

Additionally, the case where datum feature B is a perfect cylinder with diameter 151.5 and maximum perpendicularity error only yields a local wall thickness of 16.15 in the limit as the plate thickness approaches infinity.

I too would have chosen 16.65 from the options provided.


pylfrm

 

[Belanger]

Then the simple answer is to drop it from the batch of questions I posted there. No use making the question itself confusing. Thanks again all...

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[pylfrm]

Belanger,

I don't think the question itself is confusing in its current state, just the answer choices provided.

Maybe they should have worded it "Assuming the part is made perfectly cylindrical...".

This would actually make it worse I think. The answer would then depend on the interpretation of "minimum permissible distance between the outside of the part and the edge of a hole". If you go with "smallest distance from any point on the surface of the hole to any point on the surface of the outer diameter", then you'd have to use a perpendicularity error, but that depends on the plate thickness. Assuming a thickness of 12, which looks pretty close visually, the answer would be about 16.43. I wouldn't consider that very practical to calculate in a test without CAD software though.


pylfrm

 

[3DDave]

pylfrm - have you a sketch that shows that thickness affects the minimum distance? I don't envision perpendicularity as a consideration.

pylfrm - nevermind - I got it. It's what I would have done in making this calculation. It just needs a square root key on the calculator, not CAD.

This is easier when the fixture to check the part is the primary consideration and then allowable variation is superimposed over it.

 

[Belanger]

I'm actually fine with the notion of an indentation around the circumference (thus the answer does need to be changed), but my main concern is whether the wall thickness is to be found at only one spot, or throughout the thickness of the part. That's why it's not a good question for a test.

Attached is a quick sketch showing this dilemma. (You all can discuss it as much as you want, but I'm gonna yank the question.)

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[pylfrm]

Belanger,

I now realize that various combinations form and orientation errors can result in a local (point to point) wall thickness of less than 16.15, so I guess it does make sense to remove the question. Alternately, perhaps it could be modified to state that perfect form and orientation shall be assumed for all features.

This (along with thread1103-419878) is a good example of how a characteristic that might appear to be indirectly controlled is often not really controlled at all.


pylfrm

 

[Belanger]

I like your suggestion, pylfrm. I've kept the question but modified it to assume perfect form and orientation.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[3DDave]

JP - I've thought for a long time that the standard should just adopt the perfect form /orientation explanation. Based on the number of people I have worked with who refuse to consider errors in form or orientation in their selection of datum references and analysis of tolerances it seems useful to simply be done with it and codify it. Plus it makes the math so much easier. As a practical matter, when asked about variations in form or orientation I'm always rebuffed with the same argument - 'they' wouldn't make it that way/it would be rejected for workmanship.

 

[pylfrm]

Belanger,

Glad it could be saved. It certainly was an interesting question.


3DDave,

What do you mean by "the standard should just adopt the perfect form /orientation explanation"? Just as a simplifying assumption for some of calculations in the examples?


pylfrm

 

[3DDave]

Pylfrm,

Accepting as a general principal that orientation effects on positional tolerances not be considered, only such variations as parallel axis translations. The standard already ignores orientation contributions in Fig 4-16 (c) because it makes the math easier to manage. Perhaps the analysis of the figure is repaired in the 20xx public draft.

Looking at the desire to change the example problem suggests that this is the way the problem is typically analyzed. It isn't an example of a restriction on most drawings, but it is the typical.

 

[pmarc]

I like your suggestion, pylfrm. I've kept the question but modified it to assume perfect form and orientation.

And now the perpendicularity callout you added at the beginning of the thread has become useless

I've thought for a long time that the standard should just adopt the perfect form /orientation explanation.

If done (which seems like is not going to happen in the 20xx version), it would have to be done very cautiously. I agree it helps to perform "hand" math, but unfortunately it may also lead to false conclusions in certain situations. In J-P's example, if the composite position callout applied to pattern of 5 holes was specified at RFS, the perfect-form-and-orientation assumption would lead to a different minimum distance between the outside of the part and the hole surface than possible without the assumption.