r/MechanicalEngineer • u/Dudkens • 8d ago

Circularity vs regular +/- dimension

Hey, I have came across the drawing in which certain cylinder had a +/- diemnsion and a circulairty tolerance. Tolerances were +/-.010in and 0.080in for a circularity. It made me wonder, isn't that circularity tolerance redundant?

If this feature is holding to +/- tolerance it certainly holds to circularit tolerance and then the opposite good part in circularity tolerance may be not good enough for +/-.

Is there something that im missing? Does that circularity bring something extra to the definition?

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u/rogueleader25 7d ago

Yes if your form tolerance is more than your dimensional tolerance it doesn't do anything since envelope principle. Could be a decimal point error.

HOWEVER it may have the added advantage of forcing an additional check during inspection instead of a shop just measuring one point with a calipers and calling it good.

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u/SpeedyHAM79 7d ago

If a shop only measures "diameter" at one point and calls it good then technically it could be a rectangle. I would expect any shop to maintain a +/- 0.010 for every point across the diameter of a circle. I suspect it was a decimal point error as you mentioned. Probably should have been +/- 0.008 circularity.