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

 

[aniiben]

semiond,

[/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?

Semiond,
I am very sorry for the confusion. I appologise for any inconvenience that may have cause.

Because I cannot post a complete drawing and also because I am interested to find out the correct CONCEPT, USAGE and its LEGALITY (on the curved surfaces), I drew my sketch in 3D CAD model (not drawing). Some 3D CAD platforms do not have hatches on the sketch level in the model and that’s is why the sections lines are not shown (technical difficulties)
Diameter on 3.82 it is just an oversight.
Also I have too many irons in the fire and probably that’s why I haven’t approved (or disapproved) drawoh implied comment about the section view.

Again, I apologize and thank you for your input.

And back to the main discussion: is this T modifier (in the profile or the perpendicularity) correct usage (legal or functional just to extent a bit) for this application?
At this point I will assume no since there is no flatness (as per the standard requirement). Can a flatness be applied to a circular element (and make this callout legal)?

 

[semiond]

aniiben,
It's ok, don't worry about it.
I personally think you raise a good question and now that i understand what you mean by "circular element" i think that the tangent line control scheme makes sense, and i am intrgued myself about it's legality. At first, i thought the "circular element" was the arc-shaped outline showed in your sketch, and hence my (and other repliers) initial confusion. After understanding your intent better, i thought it would be a waste if a good question doesn't get the right treatment because of misunderstandings. Sorry if my previous post sounded too critical.

 

[greenimi]

I am not even sure that perpendiculaity applied on a non-plannar feature is a legit callout, let alone applied with T modifier. Can someone confirm or disapprove my statement above, please?

Did you see some examples or applications (in the standards or elsewhere) where perpendicularity has been applied on a non plannar surface?

 

[chez311]

And back to the main discussion: is this T modifier (in the profile or the perpendicularity) correct usage (legal or functional just to extent a bit) for this application?
At this point I will assume no since there is no flatness (as per the standard requirement). Can a flatness be applied to a circular element (and make this callout legal)?

Is it the correct usage? I think 3DDave/CH have already answered you there. You need to address the form/orientation of the entire surface to ensure proper function - the tangent plane (if we agree its legal in this instance) ONLY contacts the high points and does nothing to address gaps/deviations in the surface itself. That being said I could see possibly utilizing the tangent plane as a datum (if thats allowed??) to reference other features on the part, but does little to actually control the surface in question.

As far as I can tell there is no requirement to use flatness with tangent plane, I think the consensus here is that your proposed usage is not explicitly prohibited by the standard but might not do everything you want it to do - the form of the surface itself, not just the tangent plane, needs to be addressed per the above.

 

[3DDave]

greenimi,

The perpendicularity is applied to the tangent plane, not the non-planar surface. The tangent plane is fit through the top extremes of the surface, so it doesn't apply to the profile control. In any case, it doesn't act as a useful control and I have no idea why it was added to the standard beyond being a pet project. The figure showing it is contrived to show the best case; if the surface is convex it can be set as either perfect or uninspectable by failing the 14.5.1 criteria for not being in the middle third.

 

[mkcski]

Given the revelation about the surface-of-revolution geometry of the part: I think there is confusion when placing the T in the profile FCF. This creates a "questionable" link between the "curved" (non-planer) shape of the profile and the planer concept of Tangent Plane. In a section view, I recommend a separate phantom line be placed across the "high" contacting "circle of points" and a FCF with the T symbol in it added to the line. This would uncouple the profiled shape from the Tangent Plane requirement.

Certified Sr. GD&T Professional

 

[greenimi]

Mkcski,
Just make sure your proposed separate phantom line to not be confused with unilateral profile.
I understood that unilateral profile requires a basic dimension to be shown, but the basic dimension shown or missing should not change the callout definition......

 

[mkcski]

greenimi: Yes, there needs to a clear delineation between the profile tolerance zone and the TP tolerance zone. From what I can determine from the OP, the tangent plane would only be oriented to the datums and not linked to any BCS or +/- dimensions associated the profile tolerance.

Certified Sr. GD&T Professional

 

[aniiben]

May I ask what we have concluded in this discussion (if anything)?
Is it legal per Y14.5 to use T modifier on curved surfaces as shown?

I am just a little bit confused now.

 

[drawoh]

...

Also I have too many irons in the fire and probably that’s why I haven’t approved (or disapproved) drawoh implied comment about the section view.

If my comment is correct, you probably have a valid and practical application for a tangent plane modifier. Otherwise, you probably don't.

--
JHG

 

[powerhound]

May I ask what we have concluded in this discussion (if anything)?
Is it legal per Y14.5 to use T modifier on curved surfaces as shown?

My opinion is that since this situation isn't directly addressed then it is probably okay. The interface of the bead and a surface plate is a plane established by the points which will be in the shape of a circle. If the intent is to only control the perp of that tangent plane and leave the rest of the points uncontrolled, then this will probably work.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

 

[mkcski]

I think there is confusion when placing the T in the profile FCF. This creates a "questionable" link between the "curved" (non-planer) shape of the profile and the planer concept of Tangent Plane. In a section view, I recommend a separate phantom line be placed across the "high" contacting "circle of points" and a FCF with the T symbol in it added to the line. This would uncouple the profiled shape from the Tangent Plane requirement.

I think is "legal". But additional clarifying dimensions and symbols need to be added to separate the profile and the Tangent Plane tolerance zones.

Certified Sr. GD&T Professional

 

[greenimi]

I checked the new draft and is no mention to other surfaces other than plannar ones. I think curved surfaces is a no-no per the intended standard.
Looks like I am alone in this "boat"?
Anyone else joining me?

New per draft tangent plane has been added to total runout along with existing orientation and profile callouts.

Am I really alone in this "barn"? Or am I too conservative and closed minded?

 

[mkcski]

greenimi: I with ya man - planar only.

Certified Sr. GD&T Professional

 

[DeanD3W]

aliiben,
I agree with the others that say that the tangent plane modifier will not work for this application.

What I think would work fine is to show an end view of the feature (so the feature appears as two full circles, with the highest portion of the ring projecting towards us), with a phantom line circle at the as-designed high point, that is specifically not shown with a basic radius dimension. Then add a profile of a surface, if needed a perpendicularity, and if needed a flatness tolerance with a leader that ends with a dot on that phantom line circle, and a note below the feature control frame(s) that says something like "HIGH POINTS ALL AROUND THIS RIB". My intention is that this apply to a measured set of high points all around the raised rib. At each measured location I think a series of points should be measured along a radial line, with the highest point found being put in a group that need to be within the tolerance zone(s). Maybe a more descriptive note than the one in quotes above would be needed to make this clear?

Dean

http://www.validate-3d.com