Odd All-Around Profile Application

[Nescius]

Putting this question into words is awkward at best, so please do see the attachment. What is the interpretation of an all-around profile tolerance that controls a part outline where one of the controlled faces is partially represented by a hidden line in the drawing view in which the profile tolerance is applied?

 

[Nescius]

mkcski, just to clarify, I may be the reigning GD&T champion under our roof, but it's not because I'm particularly good at GD&T. I'm new at my company, and their GD&T usage up to this point has been only occasional and almost always full of errors. It's a steep hill to climb.

djhurayt, if I'm understanding you, I would disagree. I don't think the fact that the lines are hidden is the deciding factor.

CheckerHater, if I am following you, you'd still advocate that the "hidden" (whether or not they're actually hidden, depending on the view the tolerance is applied in) portions of the partially "visible" FEATURE are controlled.

Is the cylinder in my attached example a single feature in the sense that matters in your analysis? Would you advocate that the entire circumference of the cylinder be subject to the profile tolerance?

I think this latest example distills the issue even more.

 

[mkcski]

Nescius:

I understand completely. From my "teaching" travels at companies in my region, your situation seems pretty normal, which I assume, is why this Forum is so active. My experience: In 1999, after studying for a year, I took the GDT exam and passed with fly-colors. But working "alone" at my company I still had this confidence problem with knowing the material. In 2010 I was fortunate enough to attend a Y14.5 committee meeting where the persons who "evolve" the standard gathered - there names are in the front of the book. Talk about intimidation! After listening to the various topics for three days, I realized I understood everything they were discussing and even had a "opinion" to add (but only Committee members could talk - guests are observers). This really gave me confidence that I know the material. I still buy every GDT book that comes out and read it to get a different perspective. I am now beginning to study the differences between ISO 1101 and Y14.5. Wish me luck.

 

[djhurayt]

Nescius:
My reasoning was not because they are hidden lines. But I thought the profile is the outline that is seen on the plane that the view is taken from. Using you most resent example(the one with the cylinder) in the view you have your gtol shown the profile would apply to the two horizontal lines, the vertical lines, and 360° of the cylinder. Where as if the gtol was applied to the view that would be the back side of the one the gtol is currently attached to, then the gtol would be applied to both horizontal line (same), the vertical lines (same), but in this case only 180° of the cylinder.

 

[CheckerHater]

if I am following you, you'd still advocate that the "hidden" (whether or not they're actually hidden, depending on the view the tolerance is applied in) portions of the partially "visible" FEATURE are controlled

I say, yes, for better or for worse, the entire cylinder will be controlled. BTW, how would you separate part of cylinder being controlled from part of cylinder being not controlled?

I also say, that if, in your opinion, it is not clear what is controlled and what is not, it is YOUR job to add symbolic or verbal note to clarify your intent.

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

 

[Nescius]

djhurayt, I think I'm following your reasoning. However, I still don't necessarily believe that applying the tolerance in one view vs the other makes any difference. If the "hidden" (maybe "interior" is a better word now?) surfaces are controlled at all, I believe they'd be controlled in either case.

CH, I don't disagree, and could absolutely accept that interpretation as long as the drawing made it clear. It would be a great way to define shapes like this, assuming you actually wanted the control to apply to the interior surfaces.

As far as separating the halves of the cylinder, that's tricky. Why separate it at all? Can two profile tolerances overlap? One to control only the perimeter, another to control only the cylinder. The outside half of the cylinder would be subject to both. I don't see anything glaringly wrong with this, but I'd have to ponder it a bit more.

 

[CheckerHater]

This is tricky area.

Yes, we can have two profile tolerances applied to the feature and they should be applied at the same time.

BUT even within one profile tolerance the surface may have sharp corners or steps and still comply.

Something to consider

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

 

[mkcski]

No one has mentioned composite profile as a possibility. This separates control the location of the surface from the "accuracy" of the surface, which may solve the problem.

 

[Tarator]

Let's change the angle of view a little bit? Would you guys agree that with an all-around profile call-out, the feature(s) you want to control should be a closed loop/path? And shouldn't this loop/path be only one? I think it should, and for that reason, I think OP's drawings are illegal. What do you guys think?

 

[patdh1028]

My interpretation is that features of the part don't come into play. Surface profile all-around controls a continuous "true" profile, not a feature or collection of features, or even a surface. So I would say from original post, the non-visible surface is not controlled by the all-around profile. I think the only reason we may expect that it would be is because it seems odd to have a contiguous surface with different tolerances applied to separate parts of it, and manufacturing processes to produce a part like this may produce those surfaces all at the same (tighter) tolerance. But partial surface tolerancing is perfectly legal. I would say the drawing is legal and that the profile all-around control results in a partial-surface control of the partially-hidden surfaces.

If to the very same view a non-all-around profile of a surface control was added to each of the two partially-hidden surfaces, those controls would apply to the entire respective surface. It's the all-around specification that throws a wrench into the "normal" works.

 

[Nescius]

patdh1028,

I tend to agree, on all points, especially this:

Surface profile all-around controls a continuous "true" profile, not a feature or collection of features, or even a surface.

I like to think of it as a "silhouette control", and believe this interpretation is the most robust, meaning the least likely to be turned on its head by a thus far unimagined part geometry.