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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
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
