CMM 'stutters' when moving in Z

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  • CMM 'stutters' when moving in Z

    CMM is a Global Image 7-7-7 (2005)
    When manually moving up in Z minus the machine 'stutters'. But only in the lowest area near the granite (about 1/4 of the Z travel)
    When in DCC the machine moves in this area without 'stuttering' but emits a weird 'hollow bowl' or 'windy growl' sound, again only when moving in Z minus (in same lower area).
    Sorry for the description, but my creative writing skills are a bit lacking.
    I should add that it doesn't happen when moving upward slowly..... at less than about 1/3 speed. Anything above slow movement guarantees it will occur.
    I've pulled off the cover, looking for the obvious... loose belt, dirty this or that, perhaps counterbalance. The machine gets wiped down daily with Septihol (we've always used this stuff) and lint-free Kimwipes.
    After looking with cover off, I'm thinking this is beyond my pay-grade to diagnose. Figured I'd ask here for any insight to the problem, but I'm convinced we need to call in a Tech.
    Boss (as usually the case) wants to save department budget $$, and dump the fix on me.
    I've searched similar threads, but nothing seems to match the exact problem I'm seeing.
    Any help is appreciated.
    Last edited by sealevel; 04-06-2016, 08:55 AM. Reason: add speed condition

  • #2
    You could check the air bearings (maybe one of them is too screwed, or not enough), and look at the track on the Z if there are some stripes (not sure of the vocabulary !!!!!).
    If you have the cover pulled of, you can check the air bearings, with a comparator (lifting pad : press the pipe, and look at the displacement of the pad).

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    • #3
      Only thing I would suggest to add to this is touch on connectors where air line go into air bearings
      A tech had me do this on one of our older machines
      If tubing is deteriorating you will hear air rushing by, the tubing becomes more brittle and back pressure will cause noise; tube is losing it's ability to expand and contract to change in pressure.

      Had the air line redone on that machine.

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      • #4
        Your bearings are going bad. Schedule a service visit now.

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        • #5
          If it's "howling", it sounds like a bearing. Our Z axis bearing went out in our Optiv, which made a grinding/howling sound.

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          • #6
            does it have an air-cylinder counter-balance? this could be part of the issue.
            sigpic
            Originally posted by AndersI
            I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

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            • #7
              make sure your air pressure is correct, you do have a small range for the air pressure for the air bearings. I had the same issue and was told by service to turn the air up one bar. Worked great. You should also be getting an error from the controller if the air bearings are losing pressure. Double check that their is no water or oil in your airline. Capture.jpg
              sigpicTAU ALPHA PI INDIANA DELTA CHAPTER
              "Due to the highly confidential nature of my job, I am not allowed to know what I am doing" - author unknown

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              • #8
                thanks for all replies!
                @ Jefman.... no visible 'stripes' on Z rail. (if I'm thinking the same as what you mean)
                @ Rich i wiggled the air hoses. no noise, but will re-check.
                For those voting its the bearing, seems entirely possible, but why only at full extension (lowest point of Z travel)? And why only in manual mode does it shudder/stutter?
                @ Matt am thinking this is case, but how to tell if its an air-cylinder CB? is there a way to check?
                @ Benedict No controller errors, and the PSI reads right around 58. AFAIK for a Global of this type/build.... this is correct. BTW, very clean, dry air. no moisture visible in the lines.

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                • #9
                  could be an electrical issue with your jog box...movement wheel or stick could be going...?
                  sigpicTAU ALPHA PI INDIANA DELTA CHAPTER
                  "Due to the highly confidential nature of my job, I am not allowed to know what I am doing" - author unknown

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                  • #10
                    I worked a machine once that developed a squeak, It was an armoured cable rubbing on the horizontal. I heard a few years after leaving there that the squeak developed again and someone coated the slides in oil :-o

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                    • #11
                      Make sure the bearing ways are clean from top to bottom.
                      sigpic

                      Brain- Pinky, are you pondering what I'm pondering?
                      Pinky- I think so, but where will we find an open tattoo parlor at this time of night?

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                      • #12
                        Sealevel,

                        We just had Hexagon in this week for our Xcel 9 15 9 with the exact same issues and turned out to be two physical bearings in the Z column and the Z axis motor. Ours had started making the "howling noise" and "windy growl" for a few weeks and we were told to try and get it to last until June when the machine came due for calibration (didn't quite make it...)

                        The Tech also noted on our Global that we were starting to have the same issue with our 9 12 8 Global and merely adjusted the belt on the Z axis drive and it works great now.

                        Would definitely recommend getting someone in soon


                        4/1/96

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                        • #13
                          thank you all for your input. This thread has convinced the boss to get a tech in here.
                          I'll post the results once they diagnose the problem..........

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                          • #14
                            Great job guys, we've convinced management!!!!
                            sigpicTAU ALPHA PI INDIANA DELTA CHAPTER
                            "Due to the highly confidential nature of my job, I am not allowed to know what I am doing" - author unknown

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                            • #15
                              We had the issue with the machine "stuttering" but it was actually the reader head that needed to be replaced. Doesn't seem to be the same issue because of your howling noises, but who knows.

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