Checking Clearance of diameter

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  • Checking Clearance of diameter

    I am having trouble coming up with a good way of measuring the clearance on 2 different parts. This is a valve and the diameter must be within .0002 of clearance. I would like to make a report showing the overlay of each but I have trouble getting there. Right now I just measure points around the diameter take the difference of the readings at each hit. Is there an easier way ?
    DEA MISTRAL
    PC DMIS CAD++
    Version 2013
    Windows 7 64bit
    DataPage+ 2011 MR1

  • #2
    I personally would not use a CMM to check that close of a diameter tolerance, too much error involved. I know this doesn't answer your question, but that's probably going to be the typical response.

    IMNSFHO
    Mark Farren

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    • #3
      I'm not exactly sure what you are trying to do but measuring a diameter with a tolerance of .0002 - I wouldn't use a CMM unless there is absolutely no other way to measure it.

      Edit - WMFS
      Last edited by #2#; 09-05-2006, 05:08 PM.

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      • #4
        I would be careful to measure the size.

        What you can do though is to mount a ring gauge of similar size on the machine, close to your part. Calibrate the probe your normal way. Then measure the ring gauge and measure the diameter you need to measure with the SAME speed, approach and retract and probe orientation. If you measure the ring gauge 0.000050" undersized, I found that you pretty much assured that you will measure your feature also 0.000050" undersized. So correct for the size by adding 0.000050" to the measured diameter.

        I do this many times, verifying size on a known artifact of similar size. Works good for me.


        Jan.
        ***************************
        PC-DMIS/NC 2010MR3; 15 December 2010; running on 18 machine tools.
        Romer Infinite; PC-DMIS 2010 MR3; 15 December 2010.

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        • #5
          I think it all depends on how intimate you are with your CMM. I feel very comfotable measuring a tolerance that invovles this little of clearence. I do it everyday and get good correlation with hard gages as well as customers. Its all about how well you know your machine.

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          • #6
            how large of a diameter are you checking? if its not that big you may want to try one of these bore gages they are extremely accurate and i think you can rent them.

            http://sunnen.net/gageit/pg-700e.jpg

            http://sunnen.net/gageit/form.jsp

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            • #7
              I have to agree with some of the others. The CMM is not a good tool for such a tight tolerance. Pins, air gages, bore gages are the way to go.
              When in doubt, post code. A second set of eyes might see something you missed.
              sigpic

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              • #8
                The 2 diameters are small. We are looking at anywhere from .250" to .750"
                We have been unsuccessful trying to verify the clearance. We use a DEA Mistral.
                Thanks for all your input.
                DEA MISTRAL
                PC DMIS CAD++
                Version 2013
                Windows 7 64bit
                DataPage+ 2011 MR1

                Comment


                • #9
                  You are suffering from tunneling. No doubt. See my reponse here:

                  http://www.pcdmisforum.com/showthread.php?t=2289

                  Suggestions:
                  - run the machine quite slow (make sure you calibrate at the same speed as you measure) because that usually improves the tunneling slightly (up to a point where you get bad effects from not going fast enough).
                  - as I suggested before, try to master on a ring gauge.


                  Jan.
                  ***************************
                  PC-DMIS/NC 2010MR3; 15 December 2010; running on 18 machine tools.
                  Romer Infinite; PC-DMIS 2010 MR3; 15 December 2010.

                  Comment

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