Inspecting a targeted point

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  • Inspecting a targeted point

    I am trying to inspect the Z position of a Point at X.500Y.500 When I dimension the Point X and Y are not at X.500 or Y.500 How do I Inspect the Z position of a Targeted Point?

  • #2
    You do the exact same as with the X and Y dimension, but select Z instead. LOCation, select your point, uncheck "auto" and select the axes you want reported.

    If it is a point you have taken (not a point created by other features) in the XY-plane, the difference between X-actual (and Y-actual) and X-nom (and Y-nom) could be the positional accuracy of your machine. The machine simply reports where it took the point (if the assumption is correct). In other words, the only distance you can call "measured" with some confidence is in this case (if the above is correct) the Z-coordinate.
    PC-DMIS CAD++ 2o19 R1 SP4

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    • #3
      This is a copy of the point in my Program How do I make it take a hit where I want? Thanks for your response!
      TARGET POINT=FEAT/POINT,CARTESIAN
      THEO/<0.5,0.5,0.0001>,<0,0,1>
      ACTL/<0.5113,0.5057,0>,<0,0,1>
      MEAS/POINT,1,WORKPLANE
      HIT/BASIC,NORMAL,<0.5,0.5,0.0001>,<0,0,1>,<0.5113,0.50 57,0>,USE THEO=YES
      ENDMEAS/
      DIM LOC5= LOCATION OF POINT TARGET POINT UNITS=IN ,$
      GRAPH=OFF TEXT=OFF MULT=10.00 OUTPUT=BOTH HALF ANGLE=NO
      AX NOMINAL +TOL -TOL MEAS DEV OUTTOL
      X 0.5000 0.0010 0.0010 0.5113 0.0113 0.0103 -------->
      Y 0.5000 0.0010 0.0010 0.5057 0.0057 0.0047 -------->
      Z 0.0001 0.0010 0.0010 0.0000 -0.0001 0.0000 ---#-----
      END OF DIMENSION LOC5

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      • UKCMM
        UKCMM commented
        Editing a comment
        The X,Y hit position is governed by the type of CMM and what limit you have set for positioning accuracy. The errors you are seeing are outside of what you would normally expect. So unless you have a bad drive or very large target limit I would discount them as the cause.

        It is more likely that the surface you are probing is not at vectors 0,0,1 but at an angle and what you are seeing is cosine error of that point.

      • NinjaBadger
        NinjaBadger commented
        Editing a comment
        Not the case UKCMM - for a single point in the z direction like that there won't be cosine error as such. The point is compensated at 0,0,1. That's not to say there might not be some slight cosine error on the point but it won't show itself like that, and especially not by that amount.

      • Douglas
        Douglas commented
        Editing a comment
        is it good practice to use that point as a workplane? unless it is on a plane that is used for leveling I'm not sure I like that idea, any error from theo to actual values could be offering a bit of error no?

    • #4
      I am guessing you haven't done an actually DDC alignment to your current 0.0 / 0.0. Its a guess because no-one can answer this question with only a screen shot of a "point" that isn't taken exactly where you want it.

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      • #5
        Thank You for your responses. I did a DCC alignment. The target point is just a point on my level plane. I am using these points as an example. I expected the X and Y positions to be a lot better. I will have my CMM checked out to see if there is a problem or if there is a large target limit set. Thanks Again

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        • #6
          there's two settings under your F10 Opt.Probe "Positioning accuracy" & "Probing accuracy" that you can fiddle with, to increase your ability to lock down the location of your measured point. These settings are program specific, and you can even insert the command mid-routine and revert it.
          Fiddle at your own risk. You might dramatically increase inspection time as the CMM will take longer to locate more accurately.

          You can also increase the accuracy by adding a couple movepoints to 0.5 x 0.5 y before taking the hit.

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          • #7
            I questioned our local CMM Calibration service about this. He said CMMs are not like a CNC, It might not go to the exact spot you call out like a CNC will. I checked that by giving it a Move to point and actually checking to see what point it went to. My CMM was definitely not perfect. Please respond back as to how accurate your CMM goes to a Move to point. Thanks

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            • #8
              You can always put Snap on for the vector point, then it will always show correct in x and y - but I'd prefer to get to the bottom of why you've got so much drift.
              Automettech - Automated Metrology Technology

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              • #9
                Thank You!!!! Putting Snap on Targets my point Exactly. X and Y were exactly in the correct position. Thank You for your help. I will check into the drift issue.

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                • NinjaBadger
                  NinjaBadger commented
                  Editing a comment
                  It doesn't - it just doesn't report / show any deviation in those directions. i.e. the point will not strictly have been measured at 0.5,0.5

                • vpt.se
                  vpt.se commented
                  Editing a comment
                  This^^

                  It reports them as perfect, but they're not. The "actual" values for the X and Y are more like your previous values.

              • #10
                snap on Bump.. however be sure to turn snap off for non planar points

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