Changing program to take 'point' from part, to hard stop.

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  • Changing program to take 'point' from part, to hard stop.

    Hi all,

    Just starting out with CMM programming. We have a program already set up that we have run into issues running in the past.
    We have a plane-line-point alignment for it, that used to be based off the part entirely.
    We believe it to be more accurate if we check from a hard stop, to more accurately mimic how the part is produced.

    I have set the 'point' to re-learn, and retaught the CMM where to take it's hit for the point (in both manual and DCC alignments).
    However, after doing so the data is showing that the part is shifted further than what we had before.
    Trying to troubleshoot and figure out why this is. I found that the numbers have shifted away from the hard stop by half of the diameter of the tip.

    What am I doing wrong here?
    Not sure why this would happen, or the best way to correct it.


  • #2
    It’s best in my opinion to alignment to the part using the part.


    • #3
      When using relearn the THEO vector will not have been updated but the HIT vector will this will cause a compensation error. In your example the THEO before vector will have been 1,0,0 and the after needs to be -1,0,0 .


      • #4
        Is the surface that that you are touch or pushing up against perp to the // that cartoon is drawn on?
        just as drawn on before hard stop is at bottom of part, after full surface so you will get high points on this surface only and if out of square to bottom surface there will be a draft or slope of form error that you may not see depending on where the CMM actual points are measured.
        there are a ton of possibilities here but this is where I would start looking at the part mechanically / physically


        • #5
          Darrel, under most circumstances I would agree. This part is giving us difficulties though, that we think can be alleviated by mimicking how it is machined.

          UKCMM, I tried your suggestion & changed the vectors from + to - on the 'point' and it changes the distance of the features on top of the part from being -.020" to over by +.020"
          My tip is .040" in diameter.. not sure if this is a coincidence or not.

          Rich, the hard stop surface is perpendicular to the part. it is a 90 degree angle block. The part itself rests on a set of pegs on the bottom of the Rayco Plate.
          The parts do vary in terms of squareness, but when checking with calipers, we will always grab the highest point (wherever that may be; It fluctuates)
          Our tip is not long enough to grab the entire height of the fluctuating feature, but calipers will.


          • #6
            Correcting the vector needed to be done but appears not to be the problem.

            Has probe compensation been turned off.

            If you go into Parameter settings ( F10 ) then under Probing ( Tab ) you will see an option Compensation Options with a tick box if NO tick then compensation is OFF, tick to turn ON hope this helps.


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