Tangent plane modifier (legal usage—not functional one in my shown case) 1

[aniiben]

Tangent plane modifier shown on the bead (the curved surface)-see attached file.

Designer decided to use T modifier with either profile or perpendicularity. My scheme is incomplete by intent and I would like to get your opinion about the validity of T modifier on curved surfaces in general. Leave alone that for the part shown the datum scheme is not depicted as a functional one, I am just trying to get the legality aspect of it (T modifier)

We know it is legal (per Y14.5-2009) to use T on profile and /or perpendicularity however we are not sure about using it on the shown surface (which is not a plane).
There is a statement in 2009 (6.5 Tangent Plane page 103 :” Where a tangent plane symbol is specified with a geometric tolerance, the flatness of the toleranced feature is not controlled by the geometric tolerance.” )

Is this enough to forbid usage on curved surfaces? Or engineer does not think so.

What is your opinion?

Monday = fun day

 

[semiond]

My immediate and first impression is that it doesn't make any sense (until someone will convince otherwise).

 

[aniiben]

So, it is illegal? Or does not make sense in the shown application, but might make sense on other CURVED SURFACES ?
If the latter, could you please provide an example where T on curved surfaces make sense.

Thank you
Ani

 

[semiond]

The later is correct.
The curved surface needs to allow a flat plane to touch on at least 2 extremities - think of a wavy curved shape. In that case - makes sense, but still not sure about legality

 

[drawoh]

aniiben,

In ASME Y14.5-2009, read paragraph 6.5 and see figure 6.18 (in ASME Y14.5M-1994, paragraph 6.6.13 and figure 6.43). In your drawing, a surface cannot be perpendicular to both datum features[ ]A and[ ]B.

I think you are showing a section view. If you were showing a non-section side view, and those round things were something like a weld bead, the tangent modifier would make sense.

--
JHG

 

[aniiben]

In your drawing, a surface cannot be perpendicular to both datum features A and B.

The intent is to constrain additional degree of freedom, similar to Fig 6-4 (2009)

But I guess at this point does not matter. What I am interested in, is the legality or the lack thereof.

The argument (for legality) has been: a plane defined by a circular element...

 

[semiond]

The argument (for legality) has been: a plane defined by a circular element...

A circular element "defines" (if you insist on calling it that way) an infinite amount of planes, tangent to it at an infinite amount of points (even if we analyze it only in two dimensions!). You will always find a plane that will comply to your orientation requirement - therefore the requirement is meaningless.

Perhaps if you treated the two arc shaped protrusions as a continuous feature and applied T on the CF, you could have something to work with.

 

[powerhound]

Sticking to your request of only whether or not this is legal, my position is that this is not a legal use of the tangent plane modifier based on the wording of 6.5 in the standard.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

 

[greenimi]

Why a plane cannot be created by this circular element and then modified with T modifier? Just asking.
3 points will create this plane....at least in theory.

 

[semiond]

greenimini, try to draw a straight line through 3 points that are coincident with an arc.

With that said, if the drawing shows a section view like drawoh suggested - the "circular element" aniiben mentioned might get a different meaning (perhaps this is how you interpret it too?). but i didn't see him confirm that, and there is no section lining in the drawing.

 

[aniiben]

Here it is an application similar with what I am dealing with.
Small beads on the right end of the assembly, as shown and I am trying to understand why someone would use T modifier and what would be the design intent.
See attachment for a close-up and the link for a visual.

https://www.lesker.com/newweb/flanges/adapters_fittings_vcr.cfm?pgid=cf

 

[CheckerHater]

I am trying to understand why someone would use T modifier and what would be the design intent.

That looks quite simple: functionally they care the most about the area of the part that contacts tangent surface, so they want it to be located / oriented correctly.

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

 

[aniiben]

CheckerHater,

So, do you agree that T modifier has been applied correctly for this application (on the curved surfaces)?
Not sure I understood it correctly and how T modifier would coarsen the profile requirement (or the perpendicularity requirement).... if it does. Suppose to "relax" the flatness at least according to the Y14.5-2009, but no flatness is applicable on shown surface, unless we are talking about the flatness of a circular element....

Back to T modifier and its scope to coarsen the profile.......I think it does, because otherwise the designer woudn't place a circularity requirement (within .004) with tolerance smaller than the profile (which circularity suppose to be a refinament, I guess).

 

[powerhound]

The argument (for legality) has been: a plane defined by a circular element...

The argument against legality is as follows:

6.5
Where it is desired to control a tangent plane established by the contacting points of a surface, the tangent plane symbol is added in the feature control frame after the stated tolerance.

On a spherical feature there are no contacting points, just a contacting point. Look at figure 6-18. This is what tangent plane means. Why does this issue keep lingering?

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

 

[chez311]

powerhound - see the attachment in the comments provided by the OP and below indicated feature, looks like its not just a spherical/round shape but a revolved feature. There would be a multitude of points to contact a tangent plane on this surface - indeed the contact region would be in the shape of a circle. I'm no expert in the use of the tangent plane modifier but this looks workable.

Edit: I should say that I don't mean to insult you to say that you didn't look at the attachments, I'm just confused by your talking about a purely round/spherical surface because it doesn't look like thats what it is. Theres more than a single point of contact in this example.

 

[powerhound]

You're right. I looked at the first attachment and it doesn't represent what you're showing here. The OP looks like two spherical bosses as it is lacking critical lines to depict otherwise. This changes my position. It still looks weird but I can't come up with a direct prohibition of it's use in the standard.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

 

[CheckerHater]

The OP sketch contains 2 profile requirements.
I think they should be joined together (composite?) to show that designer cares about cross-section of the profile, but cares even more about its ability to contact certain tangent surface.

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

 

[semiond]

aniiben,
Apparently IT IS a section view of a round part that you were showing in the first sketch. Why didn't you show section lines? Or a diameter symbol on the 3.82 size? and why didn't you approve it is indeed a section after drawoh implied it?
You confused a few people here including myself. You could spare yourself a few irrelevant replies on this thread.

 

[3DDave]

It makes no improvement as it does not refine the underlying contact - there can be multiple gaps as large as the profile tolerance allows. The correct callout to improve the condition would be runout.

 

[greenimi]

3DDave,
I guess the OP wants exactly the opposite of refinement....not to improve the surface condition but to accept more "functional" gpod parts.