Reporting A Unilateral Surface Profile Tolerance

[DJ Nelson]

We have a surface with a profile of .008 U .000 to ABC.
we measured the surface with a scanner after aligning to the Datums.
We ended up with a MIN of .0072 and a max of .0121 the software calculated the measured Profile as .0322
I am not sure if I do not understand how this is calculated and reported but it seems questionable see Attachment
If correct or incorrect were can I find were it is that explains how to record this.

 

[greenimi]

All my references are based on the replay where the color sketch is shown --from J-Hendry--- (not from the OP)

So again based on this quote

I think this covers everything I'm seeing my side.(Symbol is current being updated from design team - This should read as UZ) If you need any more info let me know.

I am considering that shown U is actually UZ, then consequently the callout is an ISO callout so I had to translate it to ASME. The only way that I know to make it an ASME callout is |2 U 3|A|B|C|

 

[pmarc]

So my main point is that the tolerance zone shown in the sketch does not represent the |2 UZ 2|A|B|C| requirement.

And it definitely does not show a tolerance zone corresponding to |2 U 3|A|B|C| (assuming such a notation is even allowed in ASME).

 

[greenimi]

pmarc,
If I understand your replay correctly you are saying that |2 UZ 2|A|B|C| is not |2 U 3|A|B|C|.
So how are you translating |2 UZ 2|A|B|C| in ASME, then?

Or if I am asking you other related question: is |2 UZ 2|A|B|C| even allowed in ISO?

 

[pmarc]

pmarc,
If I understand your replay correctly you are saying that |2 UZ 2|A|B|C| is not |2 U 3|A|B|C|.

No, that's not what I'm saying.

Or if I am asking you other related question: is |2 UZ 2|A|B|C| even allowed in ISO?

I don't think ISO explicitly prohibits that.

 

[3DDave]

Anything not prohibited is allowed, especially for anyone claiming "by extension," where the rules don't say it cannot be extended.

"(c) Unequally Disposed Tolerance. When an unequally
disposed profile tolerance is 0.3 and 0.1 applies from the
true profile in the direction that adds material and 0.2
applies from the true profile in the direction that
removes material, the feature control frame would
read “0.3,” “unequally disposed” symbol, “0.1.”

What word salad.

When an unequally disposed zone is to extend 0.1 out
of the material and also extend 0.2 into the material
from the true profile, then the feature control frame
would read "0.3 (U) 0.1"

My notation |+.01/-.02| but that makes it too obvious and would highlight |+.03/+.01| for a zone that doesn't include the true profile.

I see that ISO 1101:2017 supports dynamic profile by using |x.xxx (0Z)| and no offset limit. Very clever.

 

[greenimi]

Quote (greenimi)
pmarc,
If I understand your replay correctly you are saying that |2 UZ 2|A|B|C| is not |2 U 3|A|B|C|.
No, that's not what I'm saying.

Quote (greenimi)
Or if I am asking you other related question: is |2 UZ 2|A|B|C| even allowed in ISO?
I don't think ISO explicitly prohibits that.

So then which ASME callout this calculation

2(tol value) + 2x1.686(max dev) = 5.372 per ASME

[2(number after UZ) + 1.686(max dev)]×2 = 7.372 per ISO

is pertaining to?

I think I confused myself therefore I am asking for clarification. Also, I think I understand all the values and calculations from the tables of figures 9-2 and 9-4 / Y14.45-2021, but those calulations are a little different than the ones proposed by the OP and J-Handry in this discussion

 

[greenimi]

pmarc,

And one additional question:
In ASME should I conclude that for example
profile |2|A|B|C| is exaclty the same as profile|2 U 1|A}|B|C|
or in more general terms
Profile|t|A|B|C| is the same as profile |t U t/2|A|B|C|
where t is tolerance zone value

 

[pmarc]

greenimi,
My reply containing two actual values (one for ASME and one for ISO) is purely based on what I think I am seeing on the picture provided by J-Hendry and how I understand some of his/her statements.

What I am seeing is:
-- a thick black line representing the theoretically exact feature (TEF), called the "nominal surface" by J-Hendry,
-- 4 blue dots, representing 4 measured points, that lie on the "material" side of the TEF,
-- a yellow tolerance zone which in ASME corresponds to |2(U)2|A|B|C|, but does not correspond to |2 UZ 2|A|B|C| in ISO (a corresponding ISO requirement would be |2 UZ 1|A|B|C|),
-- a table in which the second column from the right seems to provide the actual Y deviations of the 4 points relative to the TEF*.

My actual value for ASME (5.372) is for |2(U)2|A|B|C|.
My actual value for ISO (7.372) is for |2 UZ 2|A|B|C|.

* I said I didn't fully understand the picture mainly because the distances of the 4 measured points from the TEF on the sketch do not seem to be in scale with the values given in the table (for example, the point that seems to be the farthest away from the black thick line, which should correspond to 1.686 for point 1 in the table, is definitely not 1.686 away from the TEF on the sketch, otherwise the tolerance zone of 2 should be approximately twice as narrow as it is now).

 

[pmarc]

And one additional question:
In ASME should I conclude that for example
profile |2|A|B|C| is exaclty the same as profile|2 U 1|A}|B|C|
or in more general terms
Profile|t|A|B|C| is the same as profile |t U t/2|A|B|C|
where t is tolerance zone value

Yes.

 

[greenimi]

pmarc,

Regarding "|2(U)2|A|B|C|"

Per ASME Y14.45-2021 should I understand that in your opinion g value is 1.686? I am basing by statements on "2(tol value) + 2x1.686(max dev) = 5.372 per ASME"
If yes, I would like to ask you: why is not +.314 because 1.686 is closer to the "2" MMB boundary?
Again, I understand those two examples from the reporting standard (tables 9-2 and 9-4), but "adapting" it to "|2(U)2|A|B|C|" is harder to comprehend for my limited level of knowledge.

 

[pmarc]

Notice that all 4 points are outside the tolerance zone on the side that removes material from the part, so you have to pick the Y deviation that is farthest away from the LMB to obtain the g value.

The unfortunate thing in this example is that the Y devs are with + sign in the table despite that they represent so called under-min condition (again, assuming I am reading this whole illustration correctly).

J-Hendry could you please confirm if this is what the illustration is showing?

 

[3DDave]

I don't know what those numbers are about. Y+ is along the curve, X+ is across the curve, there is no label for what the red curve is (maybe the infamous green line,) the four dots aren't individually labeled, and the columns in the chart are not labeled.

I think there is no way to read this correctly.

---

With offset zones the reporting should at least be the maximum deviation between min and max (encompassing zone width) and the centering offset value between them, rather than a single number. This would tell if the process was able to follow the profile correctly or if it was a problem with the cutting edge path, as from tool wear.

Alternatively, report the max and min deviation directly, which would be too clear, I guess, and let the various users figure out what it means to them.

 

[greenimi]

pmarc

Notice that all 4 points are outside the tolerance zone on the side that removes material from the part, so you have to pick the Y deviation that is farthest away from the LMB to obtain the g value.
The unfortunate thing in this example is that the Y devs are with + sign in the table despite that they represent so called under-min condition (again, assuming I am reading this whole illustration correctly).

So, when g is to be calculated, its value is ALWAYS from LMB? I was thinking is either from LMB or MMB whichever is closer to the point you are reporting.....
What I know is if the point is within the tolerance zone then the g value is negative, if the point is outisde the tolerance zone then the g value is positive.

 

[pmarc]

greenimi,
No, g is not always calculated from LMB. It is calculated from LMB in this case.

For conforming features, when g is negative, it is calculated from the point that is the closest to either of the boundaries.

For non-conforming features, when g is positive, it is calculated from the point that is the farthest from either of the boundaries.

 

[3DDave]

In all cases the measurement that is farthest from the middle of the profile tolerance zone is used and that measurement is doubled and reported.

The boundaries are determined from the middle, so the middle is already known.

No need for calculating "g" or flipping the logic of which point is closest vs. farthest or conforms or is non-conforming.

I wonder how "g" got into the discussion for the Y14.45 rules.

 

[Burunduk]

3DDave:
"In all cases the measurement that is farthest from the middle of the profile tolerance zone is used and that measurement is doubled and reported."

For an unequally disposed profile, this method would require generating the middle first. "g" in that case may be more effective.

 

[3DDave]

It "may" be, but computationally it isn't. To do so requires generating curves for both limits and then comparing each point to both curves and then performing a logic test to see if it is between the curves or outside that area.

Using "g" is an inefficient algorithm that takes extra steps to produce the same solution.

If you know, by participation in the process, how "g" came to be, I'd ask for an explanation.

 

[Burunduk]

So the idea is no longer to satisfy the interests of the CMM manufacturers?

 

[3DDave]

Which idea?

 

[Burunduk]

For a comparator overlay I would prefer "g".