Profile applied to something other than a surface

[Belanger]

In paragraph 8.5 of the 2009 ASME standard (or 11.5 if you're looking at the 2018 standard), they mention in passing that "profile control is used primarily as a surface control."
The word "primarily" intrigues me, because what else could it be applied to? I'm thinking that that word should have been deleted when they revised it last year.

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

 

[CheckerHater]

Wasn't it yourself explaining "profile of a line" just couple of days ago?

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

 

[Belanger]

So you're saying that profile of a line doesn't control a surface? I suppose it controls a FOS then...


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

 

[TheTick]

I usually use it on sections.

 

[CheckerHater]

Profile of a line doesn't control all the aspects of a surface, just like circularity does not control cylindricity.

It is also possible, that committee reserved "non-surface" profile for something like derived centroid, but never really developed it.

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

 

[Belanger]

CH -- I should give you the full sentence from that paragraph so you can understand my question better:
"Since profile control is used primarily as a surface control, 'regardless of feature size' is the default condition on a size feature application. MMB and LMB application (modifiers) is only permissible on the datum feature references."

As you can see, the profile-of-a-line versus profile-of-a-surface idea has nothing to do with the question. (I think the centroid idea isn't really possible because it distorts the intrinsic meaning of profile.)

But that sentence does say something about a "size feature application." Other thoughts?

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

 

[chez311]

I think the paragraph would do well without the statement* at all, perhaps its an example of leaving something open ended instead of saying "profile is a surface control" to prevent questions about whether profile can be applied because "is it a surface? is it a FOS? is a portion of a surface or control of 2D elements still a surface control?"

Note that in 2018 they did change the statement with the questionable inclusion of the word default "Since profile control is used primarily as a surface control, 'regardless of feature size' is the default condition on a size feature application." to something a bit more definitive "Since profile control is used primarily as a surface control, MMC and LMC modifiers shall not be applied to the tolerance value."

*Edit: I should say I mean to remove the first part of the statement. Remove the part about "primarily a surface control" and leave the part about "MMC and LMC modifiers shall not be applied to the tolerance value." in 2018

 

[Belanger]

Good catch on the 2018 stuff, chez311. But you all see my point -- the word "primarily" gets us to think that profile can legitimately be applied to something other than a surface.
The only other thing I can think of is dynamic profile, where there is some variation in the feature's size. (That didn't exist in 2009, but there was a precursor to that idea in Fig. 8-18.)

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

 

[axym]

J-P,

In the runout section of Y14.5-2018, total runout and profile of a surface are applied to tangent planes. This may be what they're referring to with "primarily".

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[axym]

J-P,

I just re-read Section 8.5 in 2009. When they say that profile is used "primarily as a surface control", this may have meant that profile is usually applied to surfaces that are not features of size. Rather than saying that the default condition is RFS, it probably would have been better to say that material condition modifiers to not apply to profile tolerances. Really, the whole paragraph is very confusing. Applying profile to a FOS would mean that profile is being applied to a feature that has a directly toleranced (i.e. non-basic) dimension, which is a questionable practice in the first place.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[chez311]

When they say that profile is used "primarily as a surface control", this may have meant that profile is usually applied to surfaces that are not features of size.

Agreed, though its stated in a less than optimal manner. Your note about the tangent plane modifier is interesting though.

Rather than saying that the default condition is RFS, it probably would have been better to say that material condition modifiers to not apply to profile tolerances.

Again agreed, see my previous post - they changed this in 2018.

 

[Belanger]

In the runout section of Y14.5-2018, total runout and profile of a surface are applied to tangent planes. This may be what they're referring to with "primarily".

That could be the case, but that still doesn't set up the sentence which is getting at the application of MMC and LMC modifiers, because even with tangent planes MMC and LMC would make no sense.

...this may have meant that profile is usually applied to surfaces that are not features of size.

I then ask: When is a surface a feature of size?

Sorry to be contrarian on everything, but it just seems to be a case where the addition of one word causes more confusion than any strange inference which someone might have come up with if the word hadn't been used.

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