Cyldiner measurements using 180°

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  • Cyldiner measurements using 180°

    Hi
    I searched and could not find any prior threads on this.

    measuring as much of a cylindrical surface as possible is preferred for Total Runout, form, etc...
    In regards to cylindrical shafts, I understand that if the part was machined on a lathe, one perception might be to not measure 360°, but 180° might be preferred. I have suppliers that have push for measuring only 180° , but mostly for saving cmm part run time.
    I personally have used some different sized shaft parts ( and more than one part ) and measured the cylinders with 360°and 180° and checked form, TIR, etc... and the cg values, pt values, etc... did not show that one method ( 360° ) was better/worse than the other. ( 180°)
    Many years ago, we sent some cylindrical shaft parts to Hexagon for measurement to settle the differences between us and our supplier. Hexagon's results were extremely identical to ours. However, we had used 360° method and Hexagon used 180° method. And, Hexagon took less points and covered less surface area than we did.
    My thoughts have been that I will test each program I create for a cylindrical shaft part for use of 360° method and 180° method, using a type 1 study with one part, and if the results show no bias, then I will go with the 180° method.

    I just want to know other's thoughts on measuring cylindrical shaft features with 360° or 180°.

    thanks


  • #2
    It depends also on the algorithm.
    If you use a min circ or a max inscr diameter, you must measure more than 180°.
    If the cylinder is horizontal, you must use two tips, so the accuracy can be less than using a large ball with a little stem which allow measuring more than 180° (but much less than 360 !)


    The title is "Cyldiner". I thought it was "seal diner" ()
    Last edited by JEFMAN; 01-09-2019, 02:20 AM.

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    • Jim Poehler
      Jim Poehler commented
      Editing a comment
      That's sooo funny Jefman. Made my morning reading that. Reminds me of a recipe review for French Onion Soup once that called for dry sherry and the poster claimed she couldn't find any dried cherries in the market so she used raisins in the soup instead.

    • JEFMAN
      JEFMAN commented
      Editing a comment
      Jim Poehler : thanks for this story, that's very funny !

  • #3
    First time I'm hearing 180 deg is preferred method over 360 on cylinders.
    sigpicIt's corona time!
    737 Xcel Cad++ v2009MR1....SE HABLA ESPAÑOL

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    • #4
      Hi

      We use LSQ mostly as MI and MC are not the most repeatable in most cases. Typically test all three methods for GRR and use MI or MC if it is repeatable for each part.

      2014, we sent parts to Hexagon and asked for programs and results. Their programs, they measured 180°, not 360°.

      My thought is that 180° is not the preferred method. I would not state it is in adequate because there are times when a fixture impedes the ability to measure a full 360°.

      when I have parts horizontal, I can fixture the parts so that I can approach and measure from Y- and Y+ with A90B180 / A90B0, or X- and X+ A90B90 / A90B-90..... and enough clearance around the part so that I can typically utilize circle scans of 180°, one on both sides at the same location, for a full 360 coverage and construct a cylinder with all the circles.

      With supplier pressuring purchasing on length of inspection time and pressing for us to use 180° to match what they do, it has been difficult to discuss with little support.



      thanks


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      • #5
        My parts are entirely cylindrical, measured on a horizontal rotary table facing Y-.
        I measure said parts entirely in 180 degree increments, but here's why:

        The tolerance for the diameter of most of our parts is beyond the scope of the CMM; we have another gage for that (a tallyrond or some such machine; an upgrade from our previous version)
        The only thing I need to measure the OD of a cylinder for would be for an alignment; maybe for verification of straightness or form, simply because the measurements are good enough, and tilt compensation (because we don't have much in the way of fixtures due to the rotary table)

        Taking measurements with 180° or 360° have given me the same results for the data I need, but it really depends on the tolerances you're working with.
        If you're chasing microns, you'll probably want as much coverage as you need. If your tolerance is in thousandths, 180° would probably be fine; just be sure to test both ways before you decide to save some time.

        Comment


        • InspectorJester
          InspectorJester commented
          Editing a comment
          How do you feel about this process?

        • baseballfan
          baseballfan commented
          Editing a comment
          feel better if we had in and out of tolerance parts and performed a type 2 study. I know we will get around to a type 2 study.

          I am ok with 180°. I don't think it is fair to say it is inadequate or inappropriate method. I think it is fair to say that it may be not the preferred method or repeatable method and that there is risk by omitting that much surface area.

        • InspectorJester
          InspectorJester commented
          Editing a comment
          I agree 100%; given thorough enough analysis, and being able to see the measurable difference between, if they're close enough, it's good enough.
          I do also, however, agree that there is a risk in not measuring it all the way around.
          If I'm just getting a location, or a straightness, 180° is fine.
          A diameter, a form, etc, and I would feel better doing things all the way around; however, in my tests, I haven't discovered a noticeable difference, but I DO feel better measuring the whole cylinder, versus just a section.

          All the matter of the QM, more or less

      • #6
        In my experience, turned components will eventually start to exhibit lobing error in parallel with the frequency of the motor driving the lathe. The typical wear pattern of a motor's bearings running at 60hz is a tri-lobe. If you measure only 180 degrees of a cylinder exhibiting a tri-lobe pattern of cylindricity error, you could only end up capturing 1 of the 3 lobes. This might impact your ability to capture the true mating envelope of the component, which is entirely the point of our jobs.
        Also if the part is thin material, it will avert any chances of capturing dents or dings or other surface anomalies affecting the form.

        Cutting this corner (or half in this instance) would never be something I put my stamp upon.
        Last edited by louisd; 01-09-2019, 01:24 PM.

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        • baseballfan
          baseballfan commented
          Editing a comment
          I agree. thank you.

        • InspectorJester
          InspectorJester commented
          Editing a comment
          Now that makes sense

        • mckenzie
          mckenzie commented
          Editing a comment
          Ive also seen lobing in thin or soft material from jaw pressure especially when using 3 jaws. we usually see it here with aluminum and plastics

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