Conflit between Run out and position tolerance 1

[roberto1brazil]

Hi everybody.
Please, could someone say me if the configuration shown in the drawing attached would be legal? The tolerance position frame of 0,02 mm would be conflicting with the run out of 0,05 mm? Thanks for any clarification.
Roberto

 

[pmarc]

There is indeed a conflict.
Or to be more precise, if the actual part meets 0.05 circular runout requirement, it will always meet dia. 0.2 postion requirement. Thus the position tolerance adds no value to the print.

 

[CheckerHater]

pmarc,

May I ask you a question:

Given the fact that position symbol is applied to what appears to be common axis, how do you know exactly what feature position applies to?

 

[pmarc]

CH,
Of course, the way the position FCF has been shown is incorrect (assuming we are following ASME Y14.5 or 2004+ editions of ISO 1101), but since we only see two features of size on the sketch, and one of them is datum feature, I simply assumed it applies to the smaller cylinder.

Out of curiosity, what do you think about placement of datum feature symbol B? If this print was in accordance to ASME Y14.5 (1994 or 2009), and knowing that datum was the axis, would you accept its location?

 

[CheckerHater]

First of all, neither of datum symbols is actually a datum symbol, per ISO, or ASME, 1982, OR 1994, or whatever.

It was discussed on this forum forever and decided that placement of datum symbol B will have only one meaning, so it is not illegal per ASME, but is still questionable per ISO. But you are right: position tolerance could mean position of the 25 DIA axis in relation to 25 DIA OD surface

Exactly for the reason that axis could be applied to anything, position tolerance could also mean anything, including relation between datums A and B (I’ve seen worse)

Runout tolerance is properly applied to outside surface of the feature, buy is it really runout tolerance?
Runout, by definition, is related to axis, not to flat surface; I’ve never seen runout with secondary datum.

So the correct answer to OP question would be no, there is no conflict; all GD&T on the drawing is complete and utter creative drafting without actual meaning.

 

[pmarc]

Runout tolerance is properly applied to outside surface of the feature, buy is it really runout tolerance?
Runout, by definition, is related to axis, not to flat surface; I’ve never seen runout with secondary datum.

In that case I recommend looking at figure 9-5 from Y14.5-2009. Quite common practice when datum feature cylinder is not long enough to derive datum axis in repeatable way.

It was discussed on this forum forever and decided that placement of datum symbol B will have only one meaning, so it is not illegal per ASME, but is still questionable per ISO

My question was rather about the meaning of such datum feature symbol placement per ASME, not about its legality. Does this method, in your opinion, indicate that the datum axis should be derived from the entire cylinder, or from a single line on the cylinder surface?

 

[pmarc]

The last sentence should be:
My question was rather about the meaning of such datum feature symbol placement per ASME, not about its legality. Does this method, in your opinion, indicate that the datum axis should be derived from the entire cylinder, or that the datum is derived from a single line on the cylinder surface?

 

[CheckerHater]

Thank you for reminding me about Fig. 9-5.

About placement of the datum symbol.
According to ASME Y14.5-2009 Para. 4.3 (d) “a cylindrical datum feature establishes datum feature simulator that creates a datum axis” No other option is given.

It was discussed on this forum and generally agreed, that because there is no other interpretation, Para. 4.3 overrides Fig.3-4. and datum derived from cylindrical FOS is always an axis, regardless of where the datum symbol is placed.

I personally do not completely agree and believe that datum symbol should be placed where it creates less confusion, because people familiar with ISO standards are avare of the following interpretation:

 

[CheckerHater]

Not to say that datum symbol on OP drawing cannot be shown aligned with the dimension properly, because it looks like neither ’82 or ’94 symbol (did I mention that before?)

 

[roberto1brazil]

Thanks all of you for the comments and explanations. For sure I am learning each day a little more about GD&T. I would have just one more question: If the value of the position tolerance were 0,02 instead of 0,2; the runout in this case would not have meaning and so could it be suppressed?
Anyway, as far as I have understanding, the best way to control the geometric dimension of the smaller diameter would be keeping the runout information and removing the position tolerance. Isn’t it?

 

[CheckerHater]

If position was specified as 0.02, runout would still have meaning.
Runout also indirectly controls form; so imagine that axis of your small diameter has perfect position, but the cylinder itself has an oval cross-section. Checking runout will catch that oval.

 

[pmarc]

My vote is that if position tolerance was 0.02, circular runout tolerance 0.05 would not have any meaning in this particular case. Here is why:

Normally circular runout tolerance, when applied to surfaces of revolution, is a composite control that deals with location of toleranced feature relative to datum axis and with form of the feature in each cross section, that is circularity. Parallelism of toleranced feature to datum axis can be added to this list too.

But in this case, when position tolerance = 0.02 is tighter than 0.05, AND total size tolerance for dia. 15 = 0.04 is also tighter than the circular runout tolerance value, it is the position FCF that controls location of the cylinder and it is the size tolerance that controls form of the cylinder, including ovality.

In my opinion circular runout tolerance would have a meaning if its value was smaller than size tolerance for dia. 15.

Regardless of these considerations, both callouts applied simultaneously to the single diameter look at least oddly.

 

[CheckerHater]

In this case probably yes.

Doesn't mean position and runout should never ever be used together.

roberto1brazil, if you got confused by our bickering, start with simpler things. There is good reading about controlling coaxiality in this newsletter:

http://www.mechsigma.com/newsletters/2003_10_Newsletter.pdf

 

[roberto1brazil]

Thanks pmarc and CH for the comments.
CH, I have read the newsletter that you had attached. The information enclosed will be useful for me.
Best regards
Roberto

 

[TheTick]

The original tolerances are not in conflict, as meeting one does not mean missing the other. However, it is hard to imagine a way in which meeting the runout will not automatically lead to meeting the position.

 

[powerhound]

Actually, you can meet one and miss the other. Assuming the position tolerance applies to the axis of the smaller diameter, the diameter can have coaxial error of 0.15 and meet the position tolerance but it will fail the circular runout requirement. This is a conflict. Your second sentence is spot on though.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[TheTick]

You miss the point. Meeting one does not force you to miss the other.

 

[powerhound]

I guess I am missing the point. Meeting the positional tolerance at 0.15 does, in fact, force you to miss the runout tolerance. What point did I miss?

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[TheTick]

You're missing the fact that it is possible to make the part in such a way that all requirements are met. It's not a situation where if you meet one requirement you are forced to miss the other.