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Best fit alignment, MMC and positional tolerance.

WM321
Hello.

I'm trying to tolerance the 4x Ø4.49 holes on this part to datums [A][F], and have the following questions.



1. How do I create a best fit rotation as required for datum -F- (through the 4x R5.5)?

I have went ahead and completed the rest of the program and used a rotation between the left and right R5.5 in place of the best fit, and I am having issues with the reporting of the position and MMC.

2. How do I properly add MMB to the positional tolerance?

I have used the MMCADD evaluation within POSITNXY, and evaluated the diameter directly before this. See evaluations suffixed _LEFT, MMCADD should say 0.094, not 0.090, and it is not affecting the positional tolerance calculation. Where am I going wrong?





Thanks.
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  • Are you 100% sure about the "F" datum being all 4 of the R5.5? I think if it was all , then the "F" callout would be WITH the 5.5TYP callout.
    Are you 100% sure that the "F" datum IS the R5.5 and not the entire outer profile?
    IF the "F" is NOT all of the R5.5 and is only the one it is pointing to, then there is no best-fit for the holes as the center bore and the single R5.5 make a rotation line for the alignment.
  • in reply to Matthew D. Hoedeman
    If the teeth of the spline are constraining the rotation about "A", then anything you do with a best fit for the holes invalidates that rotation about "A" and the "F" is useless in that case as the teeth would control rotation about "A", and "A" controls the other 2 rotational DOF as well as 2 axial DOF (for a total of 5).
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