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Concentricity and runout

pcdmisstudent
Hi So I got this part where an ID is datum A (measured as circle)
then i have an OD (also circle) which i evaluate runout and concentricity on.
The runout deviation of the OD is about 0.01mm but the concentricity deviation is around 0.07mm

How can this be?
Correct me if I'm wrong but i know both runout and concentricity is how an object deviates from a perfect circular shape or position.
so runout basically measures the wobble when rotating to an axis (so circularity and position)

And concentricity is how closely the object and the datums axis are aligned to each other (so circularity isn't involved)

How can the concentricity deviation be so much higher than the runout?

Ty all for the gdpt tips!
  • If "Datum A" is really just a 2D circle, maybe that has something to do with the axes of this circles.
    in this case, Its axis shouldn't actually be included in the calculation.
    What I'm trying to saying is that you should specify a reference vector that is not defined by the circle "A" vector.

    In other words: test if a plane "B" affects the result if you calculate the concentricity by B|A​,
    something like that

  • If I'm not mistaken runout is about surface control to the datum whereas concentricity is about location of median of points within circular zone to the datum. Two different things. Anyway I've been hearing newest ASME standard does it away with concentricity & symmetry altogether being replaced with position. This ain't surprising because concentricity is basically a position without feature MMC & LMC modifiers. I've seen that once before where for some reason conc was worse than runout and/or position but that was checked via the point to point probe head not scanning head maybe that is why such big difference. I heard from GD&T instructors that they recommended checking conc via roundness tester.
  • As Henniger123 says, above, it probably has to do with alignment or datums. It's also not beyond the realm of possibility that there's an undocumented enhancement in play; what version?
  • I agree with Kai, it sounds like an alignment issue. If the circles are measured at different heights and being projected to a wonky workplane, it may give you those sorts of problems.

  • in reply to MattR
    I'm curious. I also read concentricity is about location of median of opposed points.... So, given that, how would a roundness tester accurately report the nonzero result (concentricity) of a perfectly formed oval?
  • Concentricity boundary and tolerances EXCLUDE FORM ERROR. Concentricity is juged via AXIS LINE.
    (Circular) Runout INCLUDES FORM ERROR about the circle. It's boundary and tolerances are relative to the physical edge of the circle, not the axis line.
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