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Thread: Runout or Concentricity

  1. #1
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    Runout or Concentricity

    If I mount the following object on a V block at point A and put a indicator at point B, what am I measuring? Basically I want to see if the two diameter's center lines are collinear.


    k1x4e0.jpg
    Last edited by Kelly Bramble; 03-07-2013 at 08:11 PM.

  2. #2
    Administrator Kelly Bramble's Avatar
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    Runout.... Assuming that you rotate the surface "A" on the v-block

    If the dial indicator is zeroed and remains at a single measuring location while rotating 360 degrees - Circular Runout

    If the the dial indicator is zeroed then moved from one end of the small diameter to the other while rotating on surface "A" and measuring all surface locations - Total Runout.

    Be aware that the v-block can introduce measurement error into either runout measurement method/definition.

  3. #3
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    Thank you for the response.
    One more question. If an object is in spec from runout, can it be assumed that the concentricity is also in spec?

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    Administrator Kelly Bramble's Avatar
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    No.... Depends on the engineering drawing standard and the concentricity specification...

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    Well, the drawing doesn't have any spec. I'm designing it and need to add one. Maybe you can suggest? Ill try to explain it the best I can!

    The diameter A fits inside of an object (red in the picture). There is another piece (blue in the picture) that pushes on the B diameter. I want to make sure that the B diameter is centered on the blue object.

    - I say it should be total runout, another guy says it should be concentricity. Which should it be? Should it be something else?

    p087-1-jpg.jpg
    Last edited by Kelly Bramble; 03-08-2013 at 12:52 PM.

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    When in doubt, use run out!
    I was always taught that run out automatically controls concentricity.

  7. #7
    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by Tactical14 View Post
    Well, the drawing doesn't have any spec. I'm designing it and need to add one. Maybe you can suggest? Ill try to explain it the best I can!

    The diameter A fits inside of an object (red in the picture). There is another piece (blue in the picture) that pushes on the B diameter. I want to make sure that the B diameter is centered on the blue object.

    - I say it should be total runout, another guy says it should be concentricity. Which should it be? Should it be something else?

    Quote Originally Posted by Kelly Bramble View Post
    No.... Depends on the engineering drawing standard and the concentricity specification...
    Well, if you are located in the USA you probably want to design to ANSI or ASME dimensioning and tolerancing standard, specifically, ASME Y14.5-2009.

    If outside of the US, you should consider ISO 1101 or one of the many country derivative standards.

    If the installation is static (not moving) I would probably use position tolerance, though runout is technically a more comprehensive tolerance control.

    Concentricity, when using ASME or ANSI standard is not what you think it is – at least from a classic dictionary definition point of view. Concentricity for ISO and derivative standards for coaxial cylinders is identical to position tolerance as defined by ANSI or ASME.

    Seriously, you’re asking relatively fundamental questions about dimensioning and tolerancing.

    You should consider at the least buying a book on the subject.

    There are many great books on the subject available, however mine are well liked, comprehensive and folks love them.

    See:

    Geometric Boundaries II – ASME Y14.5-2009 --> http://engineersedge.com/catalog/pro...roducts_id/124

    or

    Geometrical Boundaries – ISO 1101 --> http://engineersedge.com/catalog/pro...products_id/30
    Last edited by Kelly Bramble; 08-17-2013 at 01:51 PM.

  8. #8
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    To be determined accurately, you need to dispose of the V-block and use a toolroom lathe with a 5C (or similar) collet to grip the test piece. With a known hardened and ground piece of rod, check the runout of the collet. Then test the linearity of the collet and saddle movement left to right.

    Replace the rod with your part then do the run out tests Kelly described.

    It would be impossible to do the left to right test with a V-block and indicator as the paths must be parallel and there is no way to control that on a test table.

  9. #9
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    My book says that runout is a surface to axis control, concentricity is a median points to axis control, and position is an axis to axis control. I'm drawing a shaft which is supported by two different sized bearings. I need the two diameters to be located on the same axis to keep the shaft from wobbling. I think I will datum one and add position tolerance to the other. In hind-site I should have used the same diameter for both because the manufacturing now will take longer to ensure the two axis are aligned.

  10. #10
    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by surfmase View Post
    I think I will datum one and add position tolerance to the other. In hind-site I should have used the same diameter for both because the manufacturing now will take longer to ensure the two axis are aligned.
    I don't follow what your suggesting. Designing for the same diameters on a rotating shaft is not required for reducing manufacturing costs of the shaft feature. However there is advantages in the that assembly will then be allowed to use the bearing simplifying the assembly.


    When choosing between Runout (Circular or Total) and Position tolerances determine whether you need form control of the diameters as well.

    Total runout will control a surface form in terms of cylindricity, straightness and circularity in addition to control the position of the diameters where Circular runout will form control circularity in addition to position.

    Do your shaft diameters require consistent form controlled surface against the bearings?

  11. #11
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    I would say that regardless of whether the concentricity symbol uses the ASME or ISO interpretation, a part passing a runout check (circular or total) will automatically pass a position tolerance of the same value. However, if a part fails the runout check, you cannot say it's because of a position error; it might be another factor (circularity, parallelism, and others).

  12. #12
    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by Belanger View Post
    I would say that regardless of whether the concentricity symbol uses the ASME or ISO interpretation, a part passing a runout check (circular or total) will automatically pass a position tolerance of the same value. However, if a part fails the runout check, you cannot say it's because of a position error; it might be another factor (circularity, parallelism, and others).
    I agree - runout is way more comprehensive..

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