Thoughts on circular runout

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  • #16
    Form, Fit, and lets not forget the most important Function. A feature that calls back to a datum with the callout "RUNOUT" Is intended for that feature to run uniform to the datum, If they run relatively uniform together, then it would be less wear on the material itself. Also back to what I stated before "WOBBLE" For A centerline to represent the form and condition of the actual material that is controlling other features?, sorry not going to trust that on such a tight tolerance .0002 ? Jim Poehler I'll state it again, 2 Indicators
    (In Memory of my Loving wife, "Ronda" who I lost March 7, 2016. I love you baby.)
    They say "Nobody's Perfect." I must be Nobody.

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    • AndersI
      AndersI commented
      Editing a comment
      That may be an important measure, but it isn't "runout" as defined by the standards, it's something else...
      A bit like measuring material thickness instead of form of the surfaces.

  • #17
    FWIW I agree with KIRBSTER269

    I work with steering shaft components which include tubes that vary in size and form.

    We had to do a capability study with runout for a customer and we asked which way they wanted us to do it so we could get comparable results. They instructed us to use two indicators with roller v-blocks to account for the wobble and form error. We proposed using a chuck with a single indicator, but they said that wouldn't be representative of the function of the part.

    Nevertheless, I like threads like this to help broaden my knowledge base from other's interpretations/perspectives.

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    • #18
      I love how that GD&T has eliminated the ambiguity of print interpretation, so that anyone, anywhere can clearly understand the intended gobbledygook.

      B&S CHAMELEON/PCDMIS CAD++ V2011

      There are no bugs, only "UNDOCUMENTED ENHANCEMENTS!"

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      • AndersI
        AndersI commented
        Editing a comment
        Well, the interpretation of a correct drawing should be 'easy', the problem is getting a drawing that correctly shows the *intent* of the constructor...

    • #19
      I still think using 2 dials and cancelling out error from the datum feature on the controlled feature will cause you to accept bad parts.. What you are trying to do is remove the wobble inherent when you rotate around an axis.

      When you put a dial gage on the datum feature you are seeing that wobble error plus the form error. For example, if you have a lobed datum feature that also wobbles and you put a dial gage against it you are seeing both types of error, and you really cant separate them out.

      Even if you knew all you had was wobble error, you would have to use 2 dials, one on each side of the datum feature to see if one wobbled more than the other.

      If they did, what would the angular displacement be at the very end of your controlled feature? It could be even more than the value you are getting. Or maybe less.

      My point is that just subtracting runout error from the datum feature off the runout of the controlled feature is not correct. It may work for you in most instances, but it really isn't correct.

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      • KIRBSTER269
        KIRBSTER269 commented
        Editing a comment
        As I was helping someone else with this issue. I noticed I left something out, First, one indicator for the Datum To get it as true as possible. I noticed your misinterpreting runout with circularity. If the Datum is as out of whack as I showed in the Pictures, Part would be bad non the less. But when a cylinder is controlled by another, and the engineer calls a runout, If it don't run together, from force of the feature to the other, then technically it would put pressure on the weakest spot, In the end material would wear faster. I always check circularity first anyways, my pictures will always look like it's blown out of proportion. It's to help others get a better picture of the difference.

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