Assignment Question

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  • Assignment Question

    I never use assignments simply because I do not know how, I am supposed to get more training in January,...That said, I work with heavy steel parts, formed and welded, and the company never has fixtures (or are they willing to pay for them for the CMM). I often take a plane off the top plane in Z plus and take a plane off the table for part thickness. I then manually create a generic feature offset the thickness of the part and parallel to it, because the bottom is often a datum. I have done a search and still having a hard time w this, I want to be able to have the software assign the thickness I got from one measurement into a generic feature automatically, If I'm too vague I apoligize, any input would be appreciated. thanks

  • #2
    Not sure if this helps

    It sounds like you're wanting to offset based on the distance measured between the two planes. You can assign the measurement as a variable -

    You would select dimensions when assigning variable - locate the nomenclature of your dimension and end with ".MEAS".

    ASSIGN/V1 = DISTANCE_A.MEAS.

    From there i think you can create a generic point.

    Hope that helps
    Brown & Sharpe / PC-DMIS 3.7
    Eph 2:8-9 / 1 Thes 5:21 - Who or What are you living for?

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    • #3
      If I'm understanding correctly;I'd level to that and use that for Z zero. Then you could just create a generic point from the Z measurement of the part plane.

      TABLE_PLN =FEAT/CONTACT/PLANE,CARTESIAN,TRIANGLE
      THEO/<0,0,0>,<0,0,1>
      ACTL/<0,0,0>,<0,0,1>
      TARG/<0,0,0>,<0,0,1>
      ANGLE VEC=<1,0,0>,RADIAL
      SHOW FEATURE PARAMETERS=NO
      SHOW CONTACT PARAMETERS=NO
      TABLE_PLN_AL=ALIGNMENT/START,RECALL:STARTUP,LIST=YES
      ALIGNMENT/LEVEL,ZPLUS,TABLE_PLN
      ALIGNMENT/TRANS,ZAXIS,TABLE_PLN
      ALIGNMENT/END
      PART_PLN =FEAT/CONTACT/PLANE,CARTESIAN,TRIANGLE
      THEO/<0,0,3>,<0,0,1>
      ACTL/<0,0,3>,<0,0,1>
      TARG/<0,0,3>,<0,0,1>
      ANGLE VEC=<1,0,0>,RADIAL
      SHOW FEATURE PARAMETERS=NO
      SHOW CONTACT PARAMETERS=NO
      PART_TOP_PNT=GENERIC/POINT,DEPENDENT,CARTESIAN,$
      NOM/XYZ,<0,0,3>,$
      MEAS/XYZ,<PART_PLN.X,PART_PLN.Y,PART_PLN.Z>,$
      NOM/IJK,<0,0,1>,$
      MEAS/IJK,<0,0,1>

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      • #4
        Thanks, I'll give that a try!

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        • #5
          Excuse me if I am missunderstanding the question. This doesn't sound like something that requires assignments and generic features. Why not place the part on the table upside down, measure the "bottom" (which is now facing up), and report out the flatness. Now you know everything you're going to need to know about that surface so you can take the part off the table, measure the table, level and z zero on the table, and then place the part bottom side down back on the table. Now you have actual measured data about the quality of the bottom surface and have then used a datum feature simulator (the CMM table) to represent that surface for future measurement. This should be equivalent to using a high point plane (tangent plane in GD&T terminology) to represent the bottom surface. If you need an average plane instead of a high point plane you can gather the information you need to calculate what the difference would be when you are measuring the bottom surface at the beginning. In this later case you would need to use an assignment to transfer that extra offset to get from high point to average.

          Another thing you can do if you don't want to flip the part over is to place it on 6" shuttle blocks and then use a 1-2-3 block or other flat surface and just hold it against the bottom of the part while the CMM comes down and takes the hit right next to the part on the 1-2-3 block. Sounds a bit crude, I know, but its effective and saves a ton of time in some situations.
          2013MR1 SP6
          Global Frames, Tesastar-M Heads, LSP-X1M/H Probes

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          • #6
            Thanks for the response DaSalo, I often do place parts on blocks to fixture, ( it's pretty much all I have to fixture). Sorry I cant post any print to better explain what I want to do, (Gov't), alot of times I can get thickness of the steel, but for certain dimensions I cannot reach the other side on occasion, or do not have enough room on the other side of the metal to get a decent plane on others. If I flipped the part over, it may mean more Operator interaction, which is not good where I work. I try to make it as simple as I can to run. I basically want to take a measurement for my metal thickness, then be able to either have that number offset an alignment, and/or it would be nice to know how to have that number automatically changed in my generic feature. I currently manually go in and place the numbers in every part, after I get my thickness w mics.

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            • #7
              ASSIGN/V1=DIST2.MEAS

              This should set V1 as what I measured, correct? Now what I want to do is create a generic parallel plane at - V1 in my Z axis, so every part as Dist2 changes, I want it to change V1 and therefore, make my generic plane always the correct distance from the top plane. How do I, or is it possible, to create a plane parallel to(we'll just call it pln1) PLN1 but minus my value in V1 to the Z axis? What I'm wanting to do, is construct a line at the intersection of the generic plane and an auto plane, to get the distance I am looking for.

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              • #8
                I am completely lost in this. I know, crappy drawing.., but maybe this will help, there are reasons I cant get to the bottom side, that aren't drawn in, but this is a simple version, I need a step by step, if someone is willing to help, It would be greatly appreciated.
                Last edited by JThomas; 12-15-2011, 02:05 PM.

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                • #9
                  I have another option but it's more work, note that all I use is iterative alignments. There is a way to flip a part in the middle of a program called equating. Basically in short version: align, measure, measure features accessable to both sides for equal alignments (create iterative), flip part over and measure same features (man, iterative then equate). Once equate is done side 1 measurements will be moved to accomidate newly equated alignment. It works for me as I have to flip fixtures around to capture measurements on two opposite sides. Just an option.
                  Horizontals - Dual Arm 40-17-21 / Single Arm 30-14-16 - PCD 2013MR1 (64bit)

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                  • #10
                    Thanks Russd, I understand how to flip the parts in the program, the problem is that this is just an example of what I want to learn how to do. We run many parts that are 500+ lbs that I simply cannot flip over.

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