Did circularity change?

[Burunduk]

In figure 5-10 of the ASME Y14.5-2009 standard, in the tolerance description for circularity of a cylindrical or conical feature, it is explained that the tolerance applies to circular sections at planes perpendicular to "an axis" which reasonably corresponds to that edition's definition of circularity (5.4.3), which mentions "an axis or spine" normal to which the tolerance applies. I always understood this to suggest that the axis is not necessarily the "feature axis" (unrelated AME axis), and it can be optimized for the best circularity measurement result.

In the 2018 version, the definition of circularity, now to be found in the definitions section in para. 3.6 mentions "the axis or spine" and the description in fig. 8-10 mentions the axis of the unrelated AME as the element normal to which circular elements are examined. I am no longer sure what the intent is. Is there an error in the tolerance description in the figure, or does "the axis" mean "feature axis" - which is essentially the axis of unrelated AME? Was there a deliberate change that means no more fitting/optimization for circularity to obtain the best result?

 

[greenimi]

I think we have talked about it before and Evan J. concluded that figure 8-10 has the error of calling the UAME

 

[3DDave]

So now implied datums are OK? What's the tolerance on that perpendicularity?

 

[greenimi]

https://www.eng-tips.com/viewthread.cfm?qid=451995

Here is the discussion I was thinking and talking about

 

[axym]

Hi All,

As far as I'm concerned, the definition of Circularity didn't change. The 2018 figure references the UAME, but it shouldn't have. The way ASME Y14.5 works, the definitions are in the text and the figures are for illustration only and technically don't define anything. So the "axis or spine" wording in the text takes precedence. You can use the UAME axis as the reference geometry for the circularity zones, but you don't have to.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[Burunduk]

Then I guess it is another questionable modification in the latest edition of standard. I realize that the definition is the text and the figures are intended only to aid understanding, but the change of wording in the text from "an axis or spine" to "the axis or spine" had me suspecting that something was done by the intention to alter the meaning... maybe not. Thanks all.