Real-world application of ALL OVER profile tolerance

[Nescius]

The concept of an ALL OVER profile tolerance is easy to understand in cookie cutter examples, but I'm very interested to learn how the forum membership has used and seen this tool in the real world.

From the 2009 standard, 8.3.1.6:

"A profile tolerance may be applied all over the 3 dimensional profile of a part unless otherwise specified."

As always, the phrase "unless otherwise specified" is problematic. Specified how?

Let's consider a cube, fully defined with basic dimensions, with an ALL OVER profile tolerance. If I apply a refining, tighter profile tolerance or flatness tolerance to a single face of the cube, is it no longer located/oriented relative to all the other faces?

It would be easy to say that the ALL OVER tolerance still applies to all surfaces and the single face in question must simply meet both tolerances...however, what if I desire to allow one face of the cube to vary by more than the ALL OVER tolerance? Meeting both tolerances becomes meaningless, then. Furthermore, if the more generous tolerance qualifies as "otherwise specified", and the ALL OVER tolerance is trumped, is the face in question no longer located/oriented relative to the other faces at all?

Must the part be fully defined with basic dimensions, no +/- allowed? This is a much-debated topic itself, +/- dimensions and a profile tolerance applied to a closed outline...profile not controlling size.

In theory, the ALL OVER profile tolerance is a powerful tool...perfect for a part with some very complex aesthetic or ergonomic surfaces, but also a handful of more conventional features that must be controlled differently.

Is this a gray area with open interpretation or am I missing something?

 

[Belanger]

Interesting discussion. And I have a real-world application which came up recently, so let me bounce the attached graphic off of everyone...

The form of the cut-out is very important between W-X and Y-Z (the sharp radii). The form of the remaining surface is less important. And the location of the entire cutout is to be held within .010.

Is that being accomplished? Or does anyone (ahem, CH) think that the location between W-X and Y-Z is uncontrolled?

John-Paul Belanger

 

[3DDave]

Hard to imagine there's a reason for that sort of control; the smaller segments have available to them the full .010 variation from section to section in lumpiness; only discrete depths are constrained, but not against planar rotation.

If that represents a real design limitation, OK. Nothing missing or self-contradictory with this part.

 

[CheckerHater]

Don't see anything wrong with the part.

I guess Belanger has mistaken me with someone else.

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

 

[Belanger]

Apologies if I mis-read your earlier posts, CH. When discussing the cube with all-over profile, I thought you wrote that a flatness tolerance on one face would nullify the profile's entire duties for that face. Whereas I disagree: flatness would refine the form of that face, but profile would still control the orientation/location.
Thus the analogy to my situation.

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

 

[mkcski]

There seems to be something that everyone is overlooking with the profile being "refined". The shape of the profile is defined by BASIC dims and the tolerance zone "follows" it no matter what width of the zone. So as you go "around" (along) the profile tolerance changes from a default ALL OVER zone to a wider or narrower refined zone - as in John-Pauls' sketch. This is true even with a "refined" flatness tolerance. The flatness must lie within the larger default ALL OVER zone. But now I am thinking: what happens if the flatness tolerance is larger than the default profile tolerance? Is it even logical to consider this for a design standpoint. I think not.





Certified Sr. GD&T Professional

 

[pmarc]

So did we reach any consensus on UOS all over profile interpretation? To me J-P's example just supports the "theory" that when an all over (or all around) profile callout without UOS is used, the callout applies in addition to any other callout specified on the drawing.

 

[mkcski]

pmarc:

I am not sure we have consensus, but I agree with your statement if: by "in addition" I assume you mean the additions are "refinements" of the UOS profile tolerance?

Certified Sr. GD&T Professional

 

[Nescius]

pmarc,

I, for one, do agree. I started this thread because I'm not sure why "unless otherwise specified" is in this sentence in 8.3.1.6:

"A profile tolerance may be applied all over the 3 dimensional profile of a part unless otherwise specified."

I don't like the wording of that sentence, and I was afraid that UOS was an unspoken/default characteristic of the all over tolerance. Does the sentence mean...

"A profile tolerance may [only] be applied all over the 3 dimensional profile of a part [in an] unless otherwise specified [mode of operation]."

or...

"A profile tolerance may be applied all over the 3 dimensional profile of a part unless [the part is] otherwise specified."

I know, I'm off the deep end.

 

[pmarc]

mkcski,
Yes, the additional callouts must not be in conflict with the all over/all around callout. I am just not sure why you used the UOS term in conjuction with the profile tolerance ;-) That is not what I said.

 

[mkcski]

pmarc:

I did not use the best choice of words. Let me try again.

I assume that whenever an ALL OVER profile is applied, it effectively becomes the "UOS" criteria and overrides anything in the title block or other document (J-P used the word nullify in his Oct 7 post). Adding other GDT controls can only refine the "default" ALL OVER profile.

Certified Sr. GD&T Professional

 

[pmarc]

Hmmm...

Not sure how to comment on your last reply, mkcski, so allow me to put it this way. (I am afraid I can't be any clearer than this).

I will use J-P's example:

Case #1 - as is - all-around profile is specified WITHOUT extra 'UOS' note.
In this case profile of a surface controls entire contour all around and profile of a line controls line elements of the contour in zones W-X and Y-Z. In other words, profile of a line does not nullify all-around profile of a surface requirement in zones W-X and Y-Z. But this also means that profile of a line tolerance value can never be greater than profile of a surface tolerance value, otherwise there is a conflict. Just like there is a conflict when someone applies, for example, flatness tolerance of .010 to a surface that is already controlled by parallelism tolerance of .005.

Case #2 - all-around profile is specified WITH extra 'UOS' note.
In this case all-around profile of a surface applies only in zones X-Y and Z-W. It does not apply in zones W-X and Y-Z, because in these zones it is nullified by profile of a line requirement. This results in following:
1. Profile of a line tolerance can be of any value except .010.
2. 3D size and form of the contour in zones W-X and Z-W becomes totally uncontrolled. Additionally, orientation and location of the contour in zones W-X and Z-W relative to referenced datums is uncontrolled too. That is why some additional controls would be required to make the entire contour fully defined.

Does that clarify how I understand the 'UOS all-around/all-over profile' concept and how I see the difference between 'all-around/all-over' and 'UOS all-around/all-over' requirements?

 

[pmarc]

One correction to my last reply:

Case #2 - all-around profile is specified WITH extra 'UOS' note.
In this case all-around profile of a surface applies only in zones X-Y and Z-W. It does not apply in zones W-X and Y-Z, because in these zones it is nullified by profile of a line requirement. This results in following:
1. Profile of a line tolerance can be of any value except .010.
2. 3D size and form of the contour in zones W-X and Z-W becomes totally uncontrolled. Additionally, orientation and location of the contour in zones W-X and Z-W relative to referenced datums is uncontrolled too. That is why some additional controls would be required to make the entire contour fully defined.

 

[mkcski]

pmarc:

Sorry for the delay getting back to you - very busy today.

This is embarrassing, but following the posts I did not "see" the two cases and did not make a distinction between them. Sorry for wasting your time trying to get your point across to me.

Our drawings do NOT have a UOS note. By default our UOS condition is a "+/- and angles" title block - no default ALL OVER profile or any other GDT. So, I was not cognizant of the subtle difference between the two cases that you so clearly described. I think I agree with both. But bet me think about this and get back to the forum.

Certified Sr. GD&T Professional