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Possible illegal gd & t callout

Shane-o
I believe I've stumbled across an incorrect use of Runout to a Flat Datum-A-Plane.
Imagine a bolt with a flat head: this is called out as Dat -A-. It also has a Flatness callout to itself, which is fine. The threaded shaft has a Runout callout to Datum -A-. This I believe is incorrect. If the pitch diameter of the threaded shaft was described as Datum -A- with the flatened side of the bolt head having the Runout callout, this would be correct. Am I correct? I just want some verification.
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  • To be fair, what Nano said also has truth to it. The problem isn't that the screw head is the A datum, it just can't be the primary AND sole datum. If the flat head was Datum A and the OD of the head was B and the FCF was run-out of the pitch to A|B, it would be valid. I really hate ever having to deal with the pitch though, because it is almost impossible to actually use the pitch. The pitch almost always ends up being used indirectly, and run-out of a pitch is physically impossible, because the pitch is not a surface. So, I guess I would debate ever calling run-out of the pitch, for that reason. But ignoring that part of it, oohh, squirrel!

    Unless! Maybe it could be construed as a helical path along the thread at the pitch diameter?! But, then it wouldn't technically be a circular element anymore... Maybe that would be more appropriate for TIR? Interesting idea. Hmm.
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  • To be fair, what Nano said also has truth to it. The problem isn't that the screw head is the A datum, it just can't be the primary AND sole datum. If the flat head was Datum A and the OD of the head was B and the FCF was run-out of the pitch to A|B, it would be valid. I really hate ever having to deal with the pitch though, because it is almost impossible to actually use the pitch. The pitch almost always ends up being used indirectly, and run-out of a pitch is physically impossible, because the pitch is not a surface. So, I guess I would debate ever calling run-out of the pitch, for that reason. But ignoring that part of it, oohh, squirrel!

    Unless! Maybe it could be construed as a helical path along the thread at the pitch diameter?! But, then it wouldn't technically be a circular element anymore... Maybe that would be more appropriate for TIR? Interesting idea. Hmm.
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