Roundness & the Limits of Size - GD&T

M

Mr. Friend

Hi all, a very knowledgeable colleague of mine has made the claim that "when there is a diameter AND a roundness callout on a print, the average diameter and roundness must be within their respective tolerances in a free state" (see attached image).

He claims this is consistent with ANSI Y-14.5. I, however, disagree with this claim for the following reasons.

Section 2.7 of ASME Y14.5M-1994 deals with what the standard refers to as "Rule#1" whereby all form tolerancing takes place within the size limit boundaries. So circularity tolerancing would be a zone consisting of two concentric circles that cannot exceed the boundaries created by the size limits. The only exceptions would be if "notes" giving permission reside next to the feature or in the notes area of dwg. My understanding is that no element of the surface of a feature of size can violate the limits of size boundaries. The exceptions are stock, parts subject to free state variation in the unrestrained condition, or a straightness scenario which is described in section 6.4.1.1.2 when a feature control frame is "associated" with the size dimension (directly attached and not off to the side) of a straightness only. The Limits of size section directs the reader to this straightness section as the only form tolerancing allowed to violate the limits of size.


There is also a description of circularity in the standard that supports this, stating-" ....each circular element of the surface must be within the specified limits of size."(figure 6.8 section 6.4.3 -6.4.3.1).


I think that if the feature control frame has a note that states "AVG"(see section 6.8.3), or free state symbols, my colleague's claim is permissible. otherwise the claim violates the limits of size.

Is it possible that this claim is true? Is the claim not stating that if an average diameter measures at maximum size, and it contains an out-of-roundness condition, it still conforms as long as the out of roundness result does not exceed that listed in the roundness feature control frame? Am I reading this right?

-Mr. Friend
 

Attachments

  • Diameter and roundness callout.pdf
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Stijloor

Leader
Super Moderator
Rule 1 dictates that the boundary at MMC can not be exceeded. Form deviations are refinements WITHIN the limits of size.

The Standard also states when Rule 1 does not apply and when Rule 1 can be overridden.
 

Stijloor

Leader
Super Moderator
And what might be the exceptions?

To make a long story short, the best answer is in ASME Y14.5-2009. Pages 95-98. The text and graphics provided there make it very clear.

I have witnessed too many GD&T discussions here, where the posters do not provide adequate details such as the applicable GD&T standard and without correct references to the applicable paragraphs and drawings in the Standard.


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M

Mr. Friend

Thanks you for your response. 2009 actually shows a figure specifying circularity in a free state with average diameter in which it confirms what I had said concerning the requirement for disclaimers next to the diameter size or roundness feature control frame. So the word "AVG" would be required to reside next to the control information in order to consider average diameters.

Additionally, 2009 adds flatness as an additional exception (besides straightness, which was listed in 1994) but only if the "flatness tolerance is associated with the size dimension." (ASME Y14.5-2009 section 2.7.1). The Independency symbol is also introduced in this 2009 standard as well.
 

Stijloor

Leader
Super Moderator
Hi all, a very knowledgeable colleague of mine has made the claim that "when there is a diameter AND a roundness callout on a print, the average diameter and roundness must be within their respective tolerances in a free state" (see attached image).

He claims this is consistent with ANSI Y-14.5.

So, how are you going to heal your colleague from his misinterpretation(s)?

Another "good" one is concentricity. :popcorn:
 
M

Mr. Friend

Well, actually the argument I posted at the top of this thread was copied from the email I had sent him him in which he responded by stating that his claim is in conformance with the standard. He didn't provide any textual evidence, however, so wanted to double check myself with some outside opinions.

I'm not too sure I want to engage in a second approach with my Quality Manager. And your suggestion is.....
 
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