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Tangent Plane Modifier
4

Tangent Plane Modifier

RE: Tangent Plane Modifier

(OP)
May the tangency plane modifier be legitimately invoked as illustrated?

RE: Tangent Plane Modifier

I don't see the problem here.

You have curved (domed) feature so you control it with Profile.

The only thing that is (functionally) important is the contact with tangent mating part, so you use tangent modifier.

Using two round holes as RMB datum features may be not convenient, but still legal.

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

RE: Tangent Plane Modifier

No. You cannot use the tangent plane modifier on anything but nomially flat surfaces.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II

RE: Tangent Plane Modifier

(OP)
Can the profile apply just to the height, and just drop the modifier, John?

RE: Tangent Plane Modifier

Yes but you need to make the radius a basic dimension. The profile is applied to the surface of the radius, not to the height dimension.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II

RE: Tangent Plane Modifier

(OP)
By changing the radius to basic, and using the profile, isn't that requesting the radius to be checked too?

All that is really desired at this level in the assembly is to check the protrusion relative to the mounting scheme.

RE: Tangent Plane Modifier

Quote (powerhound)

You cannot use the tangent plane modifier on anything but nomially flat surfaces

Reference, please...?

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

RE: Tangent Plane Modifier

ASME Y14.5-2009

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II

RE: Tangent Plane Modifier

Paragraph?

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

RE: Tangent Plane Modifier

Can you really not look it up yourself?

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II

RE: Tangent Plane Modifier

CH,
One question or two actually. Assuming for a moment that you are allowed to apply tangent plane here, what is the length of that plane and how does the tolerance zone look like?

RE: Tangent Plane Modifier

Quote (powerhound)

Can you really not look it up yourself?

Looking...

Definition (from Para. 1.3.45)

plane, tangent: a plane that contacts the high points of the specified feature surface.

No mention of nominally flat surface.

Application (from Para. 6.5)

...The tangent plane symbol is illustrated with orientation tolerances; however, it may also have applications using other geometric characteristic symbols where the feature is related to a datum(s).

Interesting... The OTHER symbols using datums(s) are position, concentricity, symmetry, runout and profile.

Still, couldn't find where exactly use of tangent is limited to flat surfaces.

Anybody?

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

RE: Tangent Plane Modifier

You left a lot out of your condensed version of 6.5. It does mention that flatness is not controlled when a Tangent plane is specified. This would imply a nominally flat plane. If it applied to any type of surface then it would have said that FORM is not controlled by the geometric tolerance. It also says that the tangent plane would contact the high pointS of the surface.

Since you seem to think that Tangent plane can be used on any characteristic that uses datum references, how would you use it with concentricity?

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II

RE: Tangent Plane Modifier

CH,

Your question to pmarc demonstrates your lack of understanding of the tangent plane modifier.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II

RE: Tangent Plane Modifier

What if the pin from your drawing was not perfectly perpendicular to the datum plane A (which will most likely be the case in reality)? How would the line depicting plane tangent to the tip look like? How long would it be?

RE: Tangent Plane Modifier

powerhound, this is third insult in a row.

What exactly did I do to deserve it?

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

RE: Tangent Plane Modifier

pmarc,

I lost interest to this discussion. I am sorry.

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

RE: Tangent Plane Modifier

What can I say, CH?

I do not know you, but you definitely are not the person who says: "I was wrong" very often.

RE: Tangent Plane Modifier

Sorry. I don't see where I insulted you but since you feel that way, I apologize profusely. I am well aware that insults are the fastest way to turn a thread south and bring the progress to a grinding halt. I don't tend to be so direct with those who really don't know GD&T very well but you do know it, thus I just cut to the chase. Saying that you don't understand the tangent plane modifier is not an insult. An insult is where I would say something that you might find offensive, like calling you names or berating you.

I can't find a single thing that I consider insulting in any of my responses. What did I say?

I'm not trying to insult you, but you are wrong about the tangent plane modifier. Are you willing to address the points I made about para. 6.5? Maybe provide a reference that supports your position?

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II

RE: Tangent Plane Modifier

"Where the tangent plane rocks on a convex surface, see ASME Y14.5.1M for methods of verification."

Seems not to be restricted to flat surfaces. The note about not restricting flatness is applicable when it is applied to nominally flat surfaces, not as a limitation of applicability to flat surfaces.

RE: Tangent Plane Modifier

Dave,

Are you playing devil's advocate or are you serious? Think about what that sentence is saying. If the intent was to imply that tangent plane could be used on curved surfaces then why does it only refer to a convex surface? I'll tell you why. Because a nominally flat surface that happens to be concave will easily render it's high points with regards to a flat plane thus that scenario is not even addressed.

Now stop the madness. This is getting crazy.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II

RE: Tangent Plane Modifier

3
Question: could you guys have a civilized dialog or conversation ?

RE: Tangent Plane Modifier

Sorry PH. I really can't explain the ability of the committee to muddy the waters by simultaneously adding an example explanation while apparently restricting the applicability; the '94 version the explanation was cleaner by not pandering.


The better argument is that the profile tolerance, in this case, cannot be affected by the tangent modifier. The zone is already defined and the tangent modifier doesn't refine the description. In the case of parallelism the tangent modifier reduces the tolerance zone from applying to all the points on the surface to only the high points on the surface (though any convexity guarantees a pass, at least for parallelism, 14.5.1's lengthy explanations aside.)

I also think the (R) should be (SR) and the spherical radius should have a basic dimension somewhere on the drawing.

If the OP is looking to have some random shape at the top of the pin and not a tightly controlled radius, then use that as a datum and locate the holes relative to the tangent plane established by the datum reference and whatever other surfaces are needed to keep material around the holes.

RE: Tangent Plane Modifier

I actually see that addition as a clarification. Verifying a tangent plane requirement on a concave surface really poses no problem while verifying it on a convex surface isn't as forthcoming. I can see why it would need to be explained in the math standard. I suppose I'll ask about it in Florida later on this month.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II

RE: Tangent Plane Modifier

(OP)
Yes, (SR) should have been the designation.

The application is an assembly. The spherically tipped rod has a retracted and an extended condition. Presumably, the radius is confirmed prior to assembly, thus the desire only to state how far it protrudes.

This question has provided me with a new appreciation for what the tangent plane modifer is, and a degree of frustration for trying to express what I would have thought should be confirmable with just a height gage.

RE: Tangent Plane Modifier

WD,

Backdriving the holes is the best bet. Because a datum plane is, practically by definition, tangent to a part, there is no question of its location on the part.

Thinking more on it, I'd go with datum A as-is, add a width datum to the diameter of the rod, and add a datum (nominally tangent) to the end of the rod. With these three datums immobilizing the part, control the position of the holes in the direction perpendicular perpendicular to the tangent plane. An alternative is the width of the block instead of the rod as the secondary datum. The width datums can be referenced RFS or MMC.

The basic explanation is you want the end of the rod at a particular location and you want the holes to line up with the matching holes in another part when the end of the rod is in the correct position. The end of the rod is the functional interface and should be a datum reference.

If you were to create a fixture to assemble this part, it would make sense to push the end of the rod against a stop and then set the depth of the block until the holes were positioned over pins. The alternative is to adjust and measure, which is inefficient.

RE: Tangent Plane Modifier

Hi All,

I would say that this is not a legitimate application of the tangent plane modifier. I don't think that there is any text that specifically forbids it, but I don't think it's a logical extension of principle either.

Unless otherwise specified, Profile of a Surface applies to the entire surface. There is no mention in the standard of controlling other geometry derived from the surface. The derived geometry in this case is not just a tangent plane, it would need to be a tangent plane that is constrained in orientation to the ABC datum reference frame (the spherical end cap has many possible tangent planes).

There might be another way to get something close to the required control without the use of a tangent plane. Another way of looking at it is that the extremity of the spherical surface needs to be at certain distance from the B and C holes. Perhaps specify a surface profile tolerance on a limited area of the spherical surface. The limited area would be graphically indicated with a hatched area with a certain (small) diameter, in the "middle" of the spherical tip. This would require that the horizontal location of the pin be quite accurate relative to ABC - there would probably have to be a position tolerance for the pin axis. If the form of the pin is reasonably good, then the extremity of the spherical tip should be reasonably in line with the axis of the pin.

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

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