In combination with profile as a boundary tolerance MMC is OK - go figure.

On its own, in the tolerance portion of a profile tolerance, it is senseless. There is already a boundary established - so making that boundary vary based on the size of the feature it is intended to control is not a useable concept.

That said, as a datum, MMC applied to a datum feature that happens to be controlled by a profile control can be a real-life application, so it should not have much trouble unless a CMM with non-supportive software is brought into the process.

1. If profile is used on a datum feature then the datum reference needs to be treated as a feature NOT a feature of size. This is beacuse of the current definition of how we are to use profile. " It is used to control Form..." as with all other form controls they are applied to features not features of size.

2. While there is an exeption made for the combining of Profile of a surface and Tolerance of position, the exeption is to the rule of applying Tolerance of Position only to features of size. This combined usage Dave mentioned is still an application of Profile with the addition of Tolerance of Position @ MMC for the purpose of allowing a bonus tolerance on Profile applications. The instructions for doing this are clear. the Tolerance of Position must be at MMC and with the BOUNDARY statement included. The inclusion of the BOUNDARY statement is what allows for these two controls to be combined this way. The interpretation of BOUNDARY is explained under Chapter 5, Tolerance of Position.

1. If profile is used on a datum feature then the datum reference needs to be treated as a feature NOT a feature of size. This is beacuse of the current definition of how we are to use profile. " It is used to control Form..." as with all other form controls they are applied to features not features of size.

2. While there is an exeption made for the combining of Profile of a surface and Tolerance of position, the exeption is to the rule of applying Tolerance of Position only to features of size. This combined usage Dave mentioned is still an application of Profile with the addition of Tolerance of Position @ MMC for the purpose of allowing a bonus tolerance on Profile applications. The instructions for doing this are clear. the Tolerance of Position must be at MMC and with the BOUNDARY statement included. The inclusion of the BOUNDARY statement is what allows for these two controls to be combined this way. The interpretation of BOUNDARY is explained under Chapter 5, Tolerance of Position.

Not sure what you take issue with. Spelling?

The portion of Casey's answer you refer to is valid if a material condition modifier is used in conjunction with the datum reference, without which there is no datum shift.

There are three material condition modifiers - RFS, which does not allow datum shift, LMC, and MMC.

Of LMC and MMC, 2.11.3 - Datum Features at Virtual Condition - only relates to a datum feature of size and then only for LMC and MMC.

However, in figure 6-19, 'Y14.5M' clearly identifies the MMC boundary of a feature with a profile control.

Therefore, one can use a feature controlled by a profile tolerance as a datum reference with the MMC modifier, seemingly in conflict with the limitations of 2.11.3.

Perhaps you've misread the standard - profile can control combinations of size, form, orientation, and location. See 6.5.1. Profile controls can also be used as a refinement of size. Same paragraph.

My current definitions come from ASME Y14.5M-1994.

Where are yours from?

Also refer to 4.5.4 and 4.5.4.2 and 4.5.4.3.

According to 2.11.3 "A virtual condition exists for a datum feature of size.......". A surface controlled by a profile tolerance does not meet the definition of a Feature of Size, see 1.3.17. Therefore how can 2.11.3 be applied? What figure in the standard gives an example of datum shift allowed by placing mmc with a datum feature which is itself controlled by a profile tolerance?

(b) A maximum material condition boundary (MMC concept);

As I wrote, the standard provides that a feature controlled by a profile control has an MMC - virtual- condition - see figure 6-19.

Hence it it possible to determine the true geometric counterpart for the feature and use that as the basis for a datum simulator.

Also, since 1.3.20 indicates that MMC is a condition of a feature of size, the profile boundary must be a feature of size, since figure 6-19 identifies its MMC and LMC boundaries.

<soapbox>

Yours is a good question and the next question might be - Why isn't the answer more obvious?

Answer - various parts of the standard are written in clumsy or misleading ways.

I won't identify those parts as I have done so in the past and received the comment that I just did not understand the language of "GD&T."

Perhaps I don't understand any of the half-dozen programming languages I've successfully written in either. Maybe compilers and interpreters are more forgiving of not understanding than people are.

For me, ASME-Y14.5 is just another programming language, but with less refined rules than any other I've read or used.

Who are you asking "What is the advantage to using profile on a "simple" feature of size and wanting to allow for mmc when there is already a very simple straight forward and well understood symbolism for doing so?"

VSA is still around? I got to use it for a year and it's a great teaching tool. I understand why they would have a hard time including datum features controlled by profile tolerances.