Weariness of Cylinder Straightness [again]

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  • Weariness of Cylinder Straightness [again]

    Running PC-DMIS 2013MR1 SP5
    I've looked through sources that pointed to this thread:
    __________________________________________________ __________________________________________________ ___________

    The QM is asking me to measure the straightness of several cylindrical parts.
    The method he wants me to use involves:
    Constructing a cylinder from two circles, one on each end of the part, to Level/Origin to
    Then using Vision, measuring a couple-thousand-point line along 1 side of the part
    Dimensioning the straightness of that line.

    My problem is; We have a tallyrond, which is specifically designed to measure things like cylindricity, straightness, etc.
    The QM is trying to tell me "Oh this machine is super accurate we should be able to get those things better than the tallyrond";
    I'm trying to tell him "bollocks".

    Is the method described able to get true straightness, when he callout is 0.0010mm?

  • #2
    That method will measure a 2D segment of the cylinder for straightness but doesn't necessarily represent the entire cylinders form. For that you should check cylindricity.

    And yeah, the tallyrond sounds like the better choice over Vision. That's pretty much what it's made for.
    PC-DMIS 2015.1, SP10, CAD++
    Global 7/10/7, 5/5/5
    Renishaw PH10MQ, PH10M, TP200


    • InspectorJester
      InspectorJester commented
      Editing a comment
      That's what I said!
      But in 3 minutes I can tell you one small section of one side is potentially within .002mm...
      So it's accepted!...?

  • #3
    Depending on the model I guess, but most talyronds are great at discerning single millionths of an inch of form error for non-axial features (circular runout & roundness, for example).
    Does your talyrond have a z axis quill and motor to control moving indicator along Z? That's more like a formscan if that's the case. If your talyrond can traverse the indicator(s) in Z than I agree completely with ya, CMM can't compare to an industry standard tool, made specifically for that one job.


    • louisd
      louisd commented
      Editing a comment
      Oh wait. .001mm/.000039" tolerance?! How big is the part and what is it made of?
      A warm handprint might throw that out of spec!
      --I'm presuming your environment is very well controlled, you are wearing a couple layers of cotton gloves? If you have a TTL laser and can traverse the axis shooting the TTL laser normal to the surface, yeah that would be better than a talyrond...
      Maybe at highest mag zoom and normal to a sectioned edge, traversing X/Y maybe with vision.
      If with purely a vision sensor along Z axis using focus point as data?, no way.

    • UKCMM
      UKCMM commented
      Editing a comment
      Louisd Taylrond make many types of machines and you are right the one you linked to would not be any use but that is not the type being used. As has been said the Talyrond will run rings round any CMM / vision system when using the correct one a 0.001mm limit is no big deal.

    • InspectorJester
      InspectorJester commented
      Editing a comment
      Well I'm no expert, and I refuse to use it because it runs on Windows NT, but that looks like the one..
      I've got no lasers, but I do "traverse the edge" vision :P
      I've gotten results, but I don't believe, with a tolerance like that, it should completely replace the machine designed for it.
      You know?

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