Unrelated Measured Minimum Material Envelope vs. Unrelated Measured Mating Envelope, Y14.45

[Burunduk]

Either I'm the one confused, or there is some serious mess within the new ASME standard on Measurement Data Reporting, related to the use of the unrelated measured minimum material envelope versus the unrelated measured mating envelope, for the resolved geometry method of material condition modified form tolerances. It starts right from the defining paragraphs (section 3) and continues in specific case descriptions in section 6.

Example:

3.23 MEASURED MINIMUM MATERIAL LOCAL
LINE SEGMENT SIZE
measured minimum material local line segment size: the size (length) of a line segment that is normal to the center plane of the unrelated measured minimum material envelope and that has length based on the local width (from surface to surface) of the measured width feature.
The value is subject to measurement uncertainty.

NOTE: ASME Y14.5 specifies that a derived median plane is formed from the center points of all line segments bounded
by a width feature, and those line segments are normal to the center plane of the unrelated actual mating envelope. For derived median plane flatness specified at least material condition using the resolved geometry method, additional tolerance values must be determined for each location on the feature. The
additional tolerance values must be based on size values that are relevant for the applied material condition modifier and the particular location of the feature from which the center point was
found. The locations and associated orientations used to determine additional tolerance must be the same as the locations and associated orientations used to derive the median plane.
Measured minimum material local line segment size is defined in this Standard to provide the relevant size for additional tolerance calculations at each location. See para. 6.3.6.

The note essentially says that the orientations for the line segments used to determine the derived median plane need to be the same as the orientations of line segments measured as local sizes for "bonus" tolerance calculation. AND YET, the "measured minimum material local cross section sizes" are specified to be normal to the unrelated measured minimum material envelope, whereas the note reminds that per ASME Y14.5, the derived median plane is formed from center points of line segments normal to the unrelated actual mating envelope (unrelated measured mating envelope per Y14.45).
Despite the requirement for "sameness" it looks like two types of line segments are described, each type is normal to a different envelope.

Guys, what's going on? Are the bonus-providing and center point determining line segments supposed to be the same or not?

Edit: title and bolded text for use of the exact Y14.45 terms.

 

[3DDave]

Perhaps not - Y14.45 measured results include measurement error which Y14.5 does not address.
In 14.45, "actual" refers to the value if there is no measurement error, "measured" refers to the value that has measurement error.

 

[Burunduk]

3DDave,
I was concerned that if I used the exact terms from Y14.45 some users might not recognize them, so I used the Y14.5 terms with the addition of "measured". Nevertheless, I edited the post so that it is clear what the issue is (it's not related to measurement error or the word "actual").

 

[3DDave]

Instead of editing I'd suggest entirely rephrasing, perhaps with a diagram to show what you think is the difference/similarity.

 

[3DDave]

Also is "unrelated measured minimum material envelope" defined in Y14.45?

 

[Burunduk]

3DDave,
Do you have access to the ASME Y14.45 standard? I could point you to the definitions of both types of envelopes, and the two associated types of line segment sizes, each defined to be perpendicular to a different envelope.

There is also a discrepancy between the "derived median plane" as defined in ASME Y14.5 and the "measured derived median plane" as defined in ASME Y14.45. And in addition to that, another discrepancy between the "measured derived median plane" according to Y14.45 and "Flatness of a Derived Median Plane at LMC, Resolved Geometry Method" (6.3.6 in Y14.45), which describes something that is more on the same page with the Y14.5 definition than it is with the Y14.45 definition of a derived median plane (measured).

 

[Dean Watts]

Burunduk,

If I am correctly understanding the point you are making, I think the issue is that we should have been more clear about the intent of the note applied to 3.23. The intent of the note is to point out that Y14.5 's definition of derived median plane does not acknowledge the LMC, so the minimum material, possibility. The intent of the note is not to provide a reminder, but to instead point out the reason for the difference in the Y14.45 wording. In order for Y14.45 to describe how the measured value of any tolerance applied to a derived median plane at LMC, it was necessary to state that the Measured Minimum Material Local Line Segment Size must be measured with the line segment being normal to the measured minimum material envelope.

Regarding paragraph 6.3.6, you have pointed out an error. Instead of "Measured local line segment size", the term in this section should be "Measured minimum material local line segment size". I am guessing you already noticed that 6.3.6(a) and (b) use the correct terms, but the text of 6.3.6 uses the wrong term. Thank you for pointing this out. The error made it past quite a few reviewers. This will be corrected in the next release of Y14.45. You can also be proud (I think ) to be well versed of some of the more obscure (likely not often used) parts of Y14.45.

Our intent was to make it clear that the bonus providing and center determining line segments (or circles for establishment of a median line) must be the same. Unfortunately the error you have found in 6.3.6 slipped by. Hopefully, most users of the standard will go straight to 6.3.6(a) and (b) .

Best Regards,
Dean

 

[Burunduk]

Dean,
So, there is a deliberate difference between ASME Y14.45 and ASME Y14.5 in the derived median plane definition, if I understand you correctly.
While Y14.5 only states that the derived median plane is obtained from center points of individual point to point distances in the direction normal to the unrelated AME, regardless of material condition modifiers, according to Y14.45 it is different between the RFS/MMC case (which still corresponds with Y14.5), and the LMC case at which the point to point distances are taken normal to the unrelated minimum material measured envelope. 

If so, SEVERAL changes are required in paragraph 6.3.6, and correct me if I'm wrong.
It reads:

"6.3.6 Flatness of a Derived Median Plane at LMC, Resolved Geometry Method
There is a linear measured zone for each measured location on the feature. The linear measured zones are normal to and centered on a common flat plane that is parallel to the feature center plane but is not constrained in location."

Should have been "parallel to the center plane of the measured minimum material envelope".

"The flatness measured value for each location is the length of the linear measured zone that is just large enough to contain the center point of the measured local line segment size. The location of the set of linear measured zones shall be optimized relative to the center points of the measured local line segment sizes such that the method B reported value is minimized."

Both bolded portions should have been: measured minimum material local line segment size/s.

 

[Dean Watts]

Good Morning Burunduk,

Yes, there is a deliberate difference between Y14.5's median line and median plane material and the more complete and more specific information in Y14.45. The job for Y14 SC45 was to write a standard to provide guidelines for the data content associated with GD&T specifications that Y14.5 provides. I believe the only way this can be done correctly and completely for the resolved geometry method for derived median line straightness or derived median plane flatness, especially when specified at LMC, was to have this difference. Thankfully we were able to release the standard in this manner, rather than delay its release additional years to wait for the needed improvements to Y14.5 to be made.

Yes, in the two places in paragraph 6.3.6 where "measured local line segment size(s)" appears, it should instead be "measured minimum material local line segment size(s)". As I mentioned yesterday, thank you for finding this error. It bothers me, and I'm sure the other SC45 members, but we will just need to fix this for the next release. I hope all users, if they do need to implement this particular (luckily seldom used) section, I hope the inclusion of the correct terms in items (a) and (b) puts them on the right path.

Please see paragraph 3.17 for the definition of "Measured Feature Center Plane". For tolerances specified at LMC, it states that it is based on the unrelated measured minimum material envelope.

Dean

http://www.validate-3d.com

 

[3DDave]

Why didn't 14.5 adopt this for 2018?

 

[Burunduk]

Dean,
Thank you for the clarification about "feature center plane" and paragraph 3.17- seems like this is an additional difference from ASME Y14.5.

Overall, I think it functionally makes sense to base the evaluation on the minimum material envelope when LMC tolerances are applied. The state of the mating envelope may not indicate a part that should be rejected when violation of the LMC VC boundary occurs, whereas the minimum material envelope is what should be considered. So introducing the difference was a positive move, but now ASME Y14.5 will need to catch up with that, and it will surely take a while until it happens. May be about a decade?
I wonder - wasn't there an overlapping period of the development time of both Y14.5-2018 (published 2019) and Y14.45-2021 when things like that could be coordinated between the committees?

Also, notice the wording in paragraph 6.2.6, dealing with DML straightness at LMC. Same problem, but this time the error is only at one place rather than two:

"The location of the set of circular measured zones shall be optimized relative to the center points of the measured local cross section sizes such that the method B reported value is minimized."

I suppose that it should be the "measured minimum material local cross section sizes".

When is the next update of the Y14.45 expected? Not soon, I guess.

On the positive side, I think it's a very important and helpful new standard, seems very well thought through, and it should achieve its goals.

 

[Dean Watts]

3DDave - In a perfect world Y14.5 would have incorporated the terminology we are discussing here that would make it consistent with its own intent in 2018. I will work towards ensuring this happens for the next release of Y14.5, and I hope all members, support group, visitors at meetings and public reviewers do the same. The volunteer membership of all of the Y14 subcommittees is good in some ways, and not so good in other ways. Imperfections included, I still think ASME Y14 standards are the best set of standards.

Burunduk - Thank you for pointing out the similar error in in 6.2.6 >:-| . I would personally be happy if a Y14.45 revision could be released as soon as we're comfortable that close enough to all the errors that slipped through have been found and addressed, but the decision to release that revision will be up to ASME. To do our job, we (subcommittee 45) will get to work getting a revised draft ready, then see what can be done. If you would like to participate, please let me know (contact me via email by adding dean@ to the URL of the website link below) and I will add you to our email distribution.

The invitation to attend SC45 meetings is open to all. Please send me an email and I will add you to our "visitors included" distribution. We do our work mostly using online meetings, and anyone that wants to contribute is welcome. My apologies for some lack of attention to my own website. I am amazed to find that I didn't include my email address on the site when it was revised recently and then a geographic move and some other life events and taking a full time contract job for the past year have taken my attention away for a while now. In addition to getting the SC45 meetings going again it seems that I have other work to do . If you would like to be added to the distribution for Y14.45 meeting notices please send an email to dean@validate-3d.com .

-Dean

http://www.validate-3d.com

 

[3DDave]

Many publishers manage with errata sheets. It's not as profitable for the publisher as selling entirely new versions, but it is what it is.

Other than CMM software developers who is the target audience to use Y14.45? I cannot imagine anyone with a height gauge and a granite table figuring out the unrelated minimum material measured envelope for a part feature. For the most part it doesn't look like feedback that would help engineering analysis of product performance, though some factors like median plane flatness are just transferred from Y14.5. OTOH there's no allowance in either for helpful considerations like measured moment of inertia or measured section modulus.

I'll say that the opacity for anyone not in from day 1 on the meetings means missing out on how such usability topics are introduced or addressed. It's a shame there is no companion volume of meeting minutes and submitted exhibits that were used to justify the contents, particularly of topics that were rejected; this applies to Y14.5 much more than Y14.45.

 

[Burunduk]

Other than CMM software developers who is the target audience to use Y14.45? I cannot imagine anyone with a height gauge and a granite table figuring out the unrelated minimum material measured envelope for a part feature.

I take that you haven't yet encountered a bad inspection report  not automatically generated by a CMM program?

Do you believe everyone with a height gage and a granite plate knows how to report a profile tolerance that references the datum feature face they rest on the granite plate? Wait till they get to an unequally disposed one.