Calibration of calibration sphere

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  • Calibration of calibration sphere

    Hi all,

    We have an Optiv 321 GL and decided to send the "sphere+ring" calibration tool for calibration every 5 years, and here it is, we have to send it for calibration this next month for the first time !
    The problem is that this is the only one we have, and need to use the CMM during that time...
    So i'm wondering: how you, guys, manage that at your work ?

    I called the Hexagon guy today to know if a loan was possible for that kind of tool but they don't have anything for me :/


  • #2
    It's usefull to have 2 spheres and 2 rings, and it's not very expensive.
    However, is it usefull to send a sphere and a ring for calibration, if there's no crash on them ?
    I just ask it because the uncertainty of calibration is often bigger than the deviation, so changing the value is close to a nonsense.

    If you have 2 artifacts, calibrate with the "master" and check the second can prove that they don't change.

    I have kept the sphere of my old "Chameleon", I'd never send it in calibration, and I use it for all calibrations without any problem. I can check the calibration with another sphere (Global), with the first step of a KOBA gauge, and never have any deviation coming from the calibration.

    Those thoughts are valid for ceramic spheres only, steel spheres can rust.

    For the ring gage, the problem is a little different : does the deviation coming from a new calibration perceptible by the optics ?

    Maybe I will hurt some of guys here, but I'm convinced that, it the artifacts are used carefully, their re-calibration isn't usefull.


    • #3

      5 years LOL. What the heck do you do if it fails certification? Recall all the product you shipped for half a decade and re-measure it, looking for when the artifact went bad?

      JEFMAN makes a very valid point: the normal usage of the machine's calibration artifact does not wear it, except for the rusting of uncoated steep spheres.

      The thing that kills these things is damage - ceramic shatters, steel spheres dent and steel rings go egg-shaped upon impact.

      Better to label these as Not Requiring Periodic Calibration, and keep a pair of them in case damage is suspected.


      • #4
        First, sorry for that topic, i didn't found anything about sphere calibration whith the search box and now that i have that topic open i see there's already some questions (and even a poll !) about it in the related topics
        Second, thanks for the answers guys, because that's exactly what i think, and the answers i wanted to comfort my thoughts
        But you know, we are in Medical Devices here and managers never think about the real need of something, they just want things to be calibrated to be able to show beautiful papers to auditors...

        We have a metal sphere, sure we could have 2, but it's not just a standard one as this includes the ring, and it's not so cheap: 3500€ according to Hexagon (yes, all is relative...).
        Maybe i'll have to purchase a little ceramic sphere (thanks for the link JEFMAN) to be able to calibrate the probes during this period of time.



        • #5
          My spheres are not in the qms system at all, maybe one day an auditor will push it but that's what it will take for me to do anything with that.


          • Pariah
            Pariah commented
            Editing a comment
            They should be. They should also have a sticker showing when they're due for re-cert like all other quality tools.
            ...even if it's 5 years up the road.

        • #6
          To be honest our spheres are supposed to be calibrated every 5 years too. IDK who that knucklehead was that decided it has to be done like that but the fact is that we have to do it.
          So when that time came (last year) we spoke to our Hex Rep and it turned out that if we purchase new spheres it comes a tiny little bit cheaper than shipping our spheres, paying for the calibration and shipping them back to us. Difference mainly came from the transport to be fair. So we actually purchased 4 new spheres and solved the problem for the next 5 years.
          My point is that this might be an option for you too pab39 mainly because you get to use your current spheres while you wait on the new ones and it will probably cost you less than re-calibrating the old ones.


          • #7
            We've recently had an independent auditor come in for a surveillance audit, and while it never came up, that doesn't mean it won't in the future. It seems like they look until they can find SOMETHING.

            We've got a nice ceramic sphere, but only the one, and a good outside Calibration service. I'm sure if we needed it back in a day, that could be arranged, but at significant cost.

            This whole topic raised a question in my mind: How should my cal sphere be stored? Kept in a foam lined box? Temp controlled? Laying on a shelf?


            • vlmitkov
              vlmitkov commented
              Editing a comment
              Foam lined box, out of reach of children.

            • mckenzie
              mckenzie commented
              Editing a comment
              ive got ours in a pelican case. its safety orange so if the children walk off with it its glaringly obvious

          • #8
            We have 4 machines, so 4 spheres that get calibrated yearly. We bought one extra sphere that I keep locked away so when a sphere goes out for cal, the spare gets assigned to that machine. No big deal at all. I do know of a reputable company that has very fast turn around on these as well if anyone is interested.


            • #9
              Our spheres are not in our QMS but we do have a super mic that could get the diameter of the sphere or the ID of the ring. We calibrate mics and threaded gages in house as well.

              Like some of you have said, its never been brought up in an audit.


              • Peter Fuller
                Peter Fuller commented
                Editing a comment
                Sphericity is a major concern with spheres, a roundness tester might be something you should look into.

            • #10
              I work in the aerospace industry. We have 2 CMMs and 3 calibration balls. We stagger when the cal balls get calibrated so we never have 2 out at the same time. They are calibrated annually. We HAVE been audited on this issue. We had to pull out calibration reports, etc from our vendor to prove that this year's calibration could be traced back to NIST artifacts. The boss now sees this 'exorbitant' (sp?) expense as simply the cost of doing business. A necessary evil, if you will. Yes a few $1000 (no Euro sign) sounds like a lot, and it probably is to any one of us, but to a business that has probably invested $100,000's (and that is probably quite LOW) on a CMM and associated space, personnel, etc, it is quite a minor expense. Now if only I could get them to spend 5c on a more powerful computer!!


              • JEFMAN
                JEFMAN commented
                Editing a comment
                € : ALT + 0128 works in Europ...What about US keyboards ?

              • Schrocknroll
                Schrocknroll commented
                Editing a comment
                € works for me.

              • mckenzie
                mckenzie commented
                Editing a comment
                € works on the west coast too!

            • #11
              Oh, long time i didn't logged in here, i'm late, just see your answers

              The thing is that we use a CMM with both camera / probes, so we have a special tool, not only a sphere:


              @vlmitkov: Yes that's also an idea which become more and more realistic here !

              But as we have to calibrate also the shift between camera and probes, i'm wondering about ordering just a sphere and then use a simple calibrated ring gage for the shift calibration, after all, no need to have these 2 items on the same tool.

              What do you think ?


              • #12
                Originally posted by Ego Murphy View Post
                5 years LOL. What the heck do you do if it fails certification? Recall all the product you shipped for half a decade and re-measure it, looking for when the artifact went bad?
                What this man said, be the company that generates reliable numbers, not the company the generates random numbers!
                Systems Integrator
                Hexagon Manufacturing Intelligence


                • pab39
                  pab39 commented
                  Editing a comment
                  Heh, yes, if i would be the manager...

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