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dgallup:

I think hate is to soft of a word. We need more powerful 4-letter words. hahaha.



Certified Sr. GD&T Professional
 
If we eliminate the "emotional effect of ISO 8015"[bigsmile] what would then be the "correct" answers for the OP questions in ISO and also in ASME? [santa]
 
I do not have a copy of 8015 to review.

Certified Sr. GD&T Professional
 
Greenimi -- I believe that everything you wrote in your earlier email today (the longer, earlier one) is correct. If ISO is used (with the 8015 independency assumption) or if ASME is used with the circled I, then the answers would be the same for all of these questions.

And your explanation for why parallelism isn't a factor sounds good, in my opinion.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
 
greenimi said:
I am not sure how can I explain why (would not be added), but I would say because the orientation (parallelism in our case) never locates only orients and the extreme boundaries are already determined by the flatness and the size tolerance. Am I correct?

It's not that parallelism never matters. It's the relative size of the parallelism and flatness tolerances. Consider what would happen if the parallelism tolerance was very small.
 
Nescius,
Well now I am confused. Why the relative size of the parallelism and flatness matters? Parallelism is for one side and flatness for the opposite one (which is the datum feature).
Not sure I understand how the provided answers will change if parallelism would be for example 0.01 instead of currently shown value of 0.2?

Could you please explain? Is your case/scenario affecting both ISO and ASME or just one of them?

Thanks
 
In the sketch that John-Paul posted, imagine if the right edge was very flat/parallel. If the local size were to remain at 38.2 across the middle of the part, it would fail the local size requirement at the top and bottom.

I have no experience with ISO tolerancing, but I don't perceive any difference from ASME when it comes to the original question of this thread.

I have a question for the ISO folks. Is there an ISO standard that gives a rigorous definition of "local size" or "2 point measurement"?
 
Nescius said:
Is there an ISO standard that gives a rigorous definition of "local size" or "2 point measurement"?

ISO 14405-1:2016

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 
After I spent some time yesterday and go over the material posted by mkcski from ISO (Alex K) my understanding is that ISO and ASME differs on how the maximum and minimum envelopes are calculated.

Capture_ISO_book_Alex_K_vn4gt9.png



ASME :as shown by J-P Belanger: 38.4 maximum envelope and 37.6 minimum envelope.

ISO: I would add/remove 0.2 for parallelism (from J-P Belanger) calculated values and consequently the values will be 38.6 for maximum and 37.4 for minimum.

Reason: I would say that the two tolerances (flatness and parallelism) cannot see each other due to the Independency principles. Alex K book states also: size and orientation are independent requirements and affect (or define) the extreme boundary of the feature of size.

Mkcski,

That concept you had in mind when you said:” I am pretty sure ISO allows the GDT tol to be additive to the size when "I" is applied. And I assumed the Y14.5 did NOT have this interpretation” ?
 
gabimot -- If we say that ISO allows the max envelope to be 38.6, is it possible to meet the still-required max local size of 38.2?

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

I made the distinction b/w ISO and ASME because unlike ASME, "I" is the default in ISO. From my understanding, when independency is in effect, the interpretation is the same for ASME and ISO.

Certified Sr. GD&T Professional
 
Belanger said:
gabimot -- If we say that ISO allows the max envelope to be 38.6, is it possible to meet the still-required max local size of 38.2

Hmm...ISO stuff..... Good question: I was thinking about it a little bit before, but maybe I am not thinking this correctly.
Follow me:
Actual local sizes are all at 38.2--perfect tab or rectangle, but bend--
For the orientation/parallelism we need the extracted median line to be within 0.2 (and not the entire surface of the opposite face of datum feature C). Now, I know the surface will control the median line but not vice-versa, so I concluded (maybe wrongfully[bigears]) the parallelism is additive....[ponder]...when the OP envelopes (maximum and minimum) "non-violation" condition.


 
According to the graphic given in the first post, the GD&T is all surface stuff, so there is no median line to be considered. You are probably thinking of a "feature of size" geometric tolerance.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
 
Belanger said:
According to the graphic given in the first post, the GD&T is all surface stuff, so there is no median line to be considered. You are probably thinking of a "feature of size" geometric tolerance.

Okay. So, If the OP case would be a cylinder and not a rectangle then your answer (38.2/ 37.2) will be different in ISO versus ASME? (since it is a rectangle the answer is the same)


 
I guess if the part is a cylinder then no parallelism to be applied
 
I assume, based on what we have discussed so far, we have concluded that 38.4 (maximum) and 37.6 (minimum) are the envelopes / answers for the OP questions on both systems: ISO GPS and ASME.

Now, I am challenging myself to find a case or cases where these two envelopes (maximum and minimum envelopes that a particular feature of size dimensions would never violate) are NOT the same in both systems (ISO GPS and ASME). I am just getting my feet wet in the ISO system (so to speak) therefore, sometimes I might not be on the right track.

Any good examples, of those kind of differences, would be greatly appreciated---just to “keep my brain alive” during the Holidays.
 
greenimi:

From my understanding I wouldn't waste my time chasing differences in this area.

In general -in most cases differences between ASME and ISO don't exist. Hey...parts are physical and the geomantic characteristics of part features are the same no matter if they are defined in accordance with ASME or ISO standards. It just that the symbology to communicate the characteristics is different. Its like reading a foreign language. You need an interpreter to convert it to so you understand OR you learn how to read both and do the conversion in you head. In the end, the "words" (symbols) are different but the meaning is the same.

Certified Sr. GD&T Professional
 
There would be different answers between the two systems if one (and only one) of these two things happened:

1) In the ASME example that the OP proposed, his extra note is removed

2) If the OP's note is retained in the ASME example, but the ISO example added a circled E for that width dimension

Then you'd be comparing an example of envelope-contained-by-size with an example of independency.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
 
I am wondering if there are ANY cases where the parallelism gets added to the form control and MMS in order to obtain the maximum envelope and how those cases would look like?
Cylinders/rectangular forms/ random shape
 
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