ASME concentricity passes inspection, what can we say about its position?

[Crvasu]

New here. My first post. My English is bad.
ASME 2009, just got the book.

The question I have: if a feature controlled with concentricity passes the inspection (two opposite indicators 180 degrees apart- I watched some youtube videos) then is it guaranteed that will pass the position to the same tolerance?

I am enquiring about American concentricity, not about European concentricity.

 

[CheckerHater]

Generally, yes.
For more detail, I really like this newsletter:

http://mechsigma.com/wp-content/uploads/2017/11/2003_10_Newsletter.pdf

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

 

[greenimi]

CH,
You said, generally, Yes.
Are there any exceptions you can think of?
Cases or scenarios where this “yes” is no longer actually valid?

I cannot find a valid case in your attachment where "yes" is a "no".

I assume "yes" = If a feature controlled with concentricity passes the inspection, then is it guaranteed that will pass the position to the same tolerance?

 

[CheckerHater]

@greenimi:
"Concentricity" is a weird control that (arguably) may be applied to shapes other that normally associated with "Position"
By "generally" I mean there is no equal sign between the two.
This is also why I reference the newsletter: on one hand it creates hierarchy showing what other controls will be satisfied if one is satisfied, and on the other hand creates an example which control is good for what, all backed by clear illustrations, etc.

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

 

[powerhound]

I cannot find a valid case in your attachment where "yes" is a "no".

The reason it is not equal is because concentricity controls the derived median line, whereas position controls the axis. I suppose it is possible for a part to fail concentricity but pass position. I don't think you could pass concentricity and fail position though.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

 

[greenimi]

I suppose it is possible for a part to fail concentricity but pass position.

Yes, and that is shown in CH's attachment in case IV (one from the last)

.I don't think you could pass concentricity and fail position though.

That is my thinking/question too. Is it possible? How? Not sure it is possible, but you never know what cases might be there.

 

[pylfrm]

The question I have: if a feature controlled with concentricity passes the inspection (two opposite indicators 180 degrees apart- I watched some youtube videos) then is it guaranteed that will pass the position to the same tolerance?

No, this is not guaranteed. The attached image shows a cross section of a feature with RFS position error of diameter 1.000 and concentricity error of diameter 0.243 (approximately).


pylfrm

 

[CheckerHater]

@pylfrm:
Sorry, it is not very clear what your diagram represents. Could you please provide further explanation?

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

 

[pylfrm]

CheckerHater,

That was a bit of a half-baked proof, wasn't it?

Attached is a new image which I hope will be more clear. The region bounded by the white outline represents possible as-produced geometry for ASME Y14.5-2009 Fig. 7-60. The concentricity error is 0.100, but the RFS position error is approximately 0.324.

Let me know if additional explanation is desired.


pylfrm

 

[powerhound]

If we are talking about the only difference being position vs concentricity then I don't know if I see this. The feature being controlled should rotate around the exact same axis for both callouts. Is that what you're showing here? It looks like the axis of rotation is different. Can you show where the axis of rotation is?

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

 

[pylfrm]

powerhound,

I'm not sure what you mean about rotation. If you're wondering about the datum axis, it's at the common center of the two tolerance zones. I didn't label it because I took that as a given.


pylfrm

 

[powerhound]

What I mean is that it looks like the datum axis for your position scenario is actually different from the datum axis for your concentricity scenario.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

 

[pylfrm]

powerhound,

Do you agree that the two circles representing the tolerance zones are concentric in the image? If so, why would the datum axis for either tolerance be anywhere other than at the common center of those circles?


pylfrm

 

[powerhound]

So I thought this was actually going well until that last response. Thanks for the lesson.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

 

[pylfrm]

powerhound,

I probably phrased that poorly. I'd like to understand why it appears to you that the two tolerances have different datum axes. Hopefully I can provide either an improved example or a better explanation.


pylfrm