problem with fixture plate

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  • problem with fixture plate

    Hello everybody

    So we have this fixture plate on our cmm with some pins on it.
    and all parts we measure are put in a fixture and slided against the pins, so no manual alignment requierment.

    problem is that every year when hex comes to calibrate our CMM, he has to take off the fixtureplate
    and when he puts it on again, the plate is in a slight different position.

    This kinda screws up for alot of our parts because we have to run the manual alignment again.

    Has anyone any idea for either
    1. A good setup for the plate so its precicily in the same position everytime we remove it and put i back. (Currenctly we put it with 3 bolts in the graphite plate)

    2. Work with a zero point system so that we align on our fixture plate and all other manual alignments are based on that. so if we remove /put back our fixture plate all we have to do is do a 3/2/1 alignment on fixtureplate. (instead of running manual alignment on every part)

    ty guys!

  • #2
    There are "rails" you can either manufacture or buy and bolt to the granite that will aid you in placing the fixture plate somewhat in the same place each time.
    PC-DMIS CAD++ 2o22.2 SP2


    • pcdmisstudent
      pcdmisstudent commented
      Editing a comment
      Could you send me a picture of what those rails look like?

  • #3
    There are others like Renishaw too.

    "Today's CMM inspections no longer require the use of expensive, precise clamps, plates and complex fixtures," according to Kay-Jay co-owner, Catherine Phill...
    PC-DMIS CAD++ 2o22.2 SP2


    • #4
      ah ok.
      But wont calibration tech need to remove those too?


      • zhicks
        zhicks commented
        Editing a comment
        We have the inspection arsenal rail system on all our CMM's. The plates snap into the rail using magnets and do not need to be fastened. The only thing bolted down is the rail and we've never had issues with leaving it bolted to the table during Hexagon's calibration.

    • #5
      The correct procedure should be to create a routine that aligns your fixture plate and saves the alignment externally. Then, in all of your other routines, you would start by recalling the external fixture alignment. Whenever the fixture plate gets moved, you simply re-run the fixture alignment routine.

      Example FIxture Alignment Routine Code...
                      HIT/BASIC,NORMAL,<20.398,51.307,0>,<0,0,1>,<20.398,51.307,0>,USE THEO=YES
                      HIT/BASIC,NORMAL,<65.04,50.715,0>,<0,0,1>,<65.04,50.715,0>,USE THEO=YES
                      HIT/BASIC,NORMAL,<65.456,9.262,0>,<0,0,1>,<65.456,9.262,0>,USE THEO=YES
                      HIT/BASIC,NORMAL,<29.084,0,-2.672>,<0,-1,0>,<29.084,0,-2.672>,USE THEO=YES
                      HIT/BASIC,NORMAL,<71.956,0,-1.563>,<0,-1,0>,<71.956,0,-1.563>,USE THEO=YES
                      HIT/BASIC,NORMAL,<0,6.726,-4.011>,<-1,0,0>,<0,6.726,-4.011>,USE THEO=YES
      Example of how to recall the fixture alignment in your other routines...
      PART NAME  : test
      REV NUMBER :
      SER NUMBER :
      STATS COUNT : 1
                  TIP/T1A0B0, SHANKIJK=0, 0, 1, ANGLE=0​
      rest of routine
      Neil Challinor
      PC-DMIS Product Owner

      T: +44 870 446 2667 (Hexagon UK office)
      E: [email protected]


      • #6
        I would create an external alignment program just for the plate and then recall the alignment in each program. Had this setup at a facility I used to work at.
        Horizontals - Dual Arm 40-17-21 / Single Arm 30-14-16 - PCD 2013MR1 (64bit)


        • #7
          so i would just create alignment on plate, save it, and recall that alignment in the beginning of each program, and then do the manual alignment?
          can i implement that to our current programs or would i have to redo them


          • neil.challinor
            neil.challinor commented
            Editing a comment
            It depends how your routines are set up. |It sounds like you have everything coming from STARTUP which is the CMM co-ordinate system (home position), and you are doing a manual alignment for each part. Once executed, do you then unmark the manual alignment and follow it with a DCC alignment? Doing things this way, you are purely relying on the fixture plate not moving and the ability of your parts to locate repeatably on the fixture plate.

            Essentially, if this is the method you are following, executing the manual alignment once and then unmarking it for subsequent runs is doing the same job as recalling an external fixture alignment, it just falls over if the fixture plate moves because you have to re-execute all of your manual alignments again. With a little careful editing, it should be possible to do away with the manual alignments and just recall your external fixture alignment, maybe followed by a few additional translations / rotations to make everything match what your previous, manual alignments were doing.

        • #8
          Grab a cold chisel and smack in some alignment lines on the table....... (OK, that's a joke).

          BEFORE removing the plate, grab some duct tape and put the tape on the table at the edges of the plate. When the tech is done, put the plate back up against the tape.
          Originally posted by AndersI
          I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.


          • #9
            Use shoulder bolts if possible to locate rails and save location to external alignment.


            • #10
              If you saved programs (already run with measurements) with an external alignment on a computer that doesn't have the external alignment on it, it's extremely hard to work on the program.

              I had programs saved with measurement results that had an external alignment on the production floor comp but not my offline seat, and it was terrible to work with since the hits didn't match the CAD any more.
              Last edited by Paperback Rocker; 12-02-2022, 10:38 AM.


              • #11
                The plate should have it's own external alignment program..if plate ever moves just re-run that program and all of your other measurement routines will work just fine


                • #12
                  We have 2 external alignment programs for our part fixtures. The first one is measured manually. Then the second one is an iterative DCC alignment that references the manual alignment. I make the prehits and retracts larger to account for slight variations in the position of the fixtures. Then, the actual part programs reference the DCC alignment. As long as the fixtures have only moved a little, the second alignment can “find” them and we’re good to go. I remove and reinstall our fixtures all the time and I never have to rerun the manual alignment.


                  • #13
                    I highly recommend the external alignment method neil.challinor outlined. It has the additional advantage that if you ever get a second CMM, you can put a second identical fixture plate on it, define the same external alignment, and put the same tips and angles on it all your routines done this way will automagically run on both machines without any additional effort. It blew my mind the first time I got it to work on our setup.

                    One thing I do differently from what he said is that I still start with a manual alignment after I recall my fixture alignment. Programming that offline finds the necessary offset from the fixture alignment. And if the fixturing ever changes somehow, you can just mark and run the manual alignment and you'll be good to go. You should be able to use this to convert your existing programs - put the recall command above your existing manual alignment, then run it through including the manual alignment. The CAD may end up in a goofy spot, but your program will be properly using the fixture alignment.

                    Regarding offline programming, I just copied one of the .aln files to my offline workstation. I haven't had any issues with that.


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