Alignment

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  • Alignment

    I am new to pc-dmis programming, I just finished the 101 course and I am now playing with my machine. The part that I have now has a central cylinder and a plane on the flange. No straight edges to create a line. Plane is datum A and Cylinder is datum B. I know its going to be an A/B alignment but how do I set it and why would it be that way? I want to understand the logic behind this. Thanks in advance

  • #2
    Any alignment is always relevant to your work plane, the direction the cmm is seeing from. This usually z+, like you would look at the main view of a print, or from above the part. If that is the case you are measuring vertically with your probe. When you measure the plane you would level it in z+ because this removes rotations about the y and x axes and stabilizes translation, or up and down movement in z. You now have restrained 3 of the six degrees of freedom, 2 in rotation, and 1 in translation. Now when you measure the cylinder you can set both x and y to the same location. This will stop rotation about z and limit movement back and forth along y and left to right along x. All six degrees of freedom are now constrained and the cmm knows exactly where the part is. Very important when you have other features to measure. Hope this helps your understanding.
    Last edited by Jim Poehler; 01-13-2016, 03:07 PM. Reason: changed 3 to 1 for translation, my mistake fast typing

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    • #3
      Meas plane
      Meas Cyl
      Construct a point (offset option - select the cylinder, and put in a 10mm / 1 inch offset in either X or Y - assuming the cylinder axis is in Z)

      Alignment..
      Level to plane in Z
      Rotate to cylinder and point in either Xplus or yplus depending on which way you constructed the offset point
      Origin x and y on cylinder
      origin z on plane
      Automettech - Automated Metrology Technology

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      • #4
        Yes it does. I wanted to be sure of my thought process

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        • #5
          According to Geometric Dimensioning and Tolerancing, the order of precedence (from left to right) in feature control frame is critical when setting up an alignment to check part. Datume A is primary and Cylinder B is secondary in that order and B must be simulated so that it's normal to A.

          The first thing you do is to measure plane A and then level to it.
          Measure B as a circle on one end and then measure B again on other end.
          Construct a best fit circle using points from 2 measured circles above, BF Recomp and set MAX_INSC for ID (MIN_CIRSC for OD), datum B is now simulated and is square to A

          There's no tertiary therefore no rotation is needed but some swears (including Hexagon people) that the nominal would change if the alignment is not completed.

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          • #6
            Originally posted by Londonjr View Post
            I am new to pc-dmis programming, I just finished the 101 course and I am now playing with my machine. The part that I have now has a central cylinder and a plane on the flange. No straight edges to create a line. Plane is datum A and Cylinder is datum B. I know its going to be an A/B alignment but how do I set it and why would it be that way? I want to understand the logic behind this. Thanks in advance
            Could you show an image of the cad model or part from the print? That would help.

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            • #7
              Originally posted by DungT View Post
              According to Geometric Dimensioning and Tolerancing, the order of precedence (from left to right) in feature control frame is critical when setting up an alignment to check part. Datume A is primary and Cylinder B is secondary in that order and B must be simulated so that it's normal to A.

              The first thing you do is to measure plane A and then level to it.
              Measure B as a circle on one end and then measure B again on other end.
              Construct a best fit circle using points from 2 measured circles above, BF Recomp and set MAX_INSC for ID (MIN_CIRSC for OD), datum B is now simulated and is square to A

              There's no tertiary therefore no rotation is needed but some swears (including Hexagon people) that the nominal would change if the alignment is not completed.
              The order is indeed important! Agree....the primary example leveling to a cylinder controls up to 4 degrees of freedom...however, if that same cylinder is made secondary then it only controls 3 degrees and of last one degree...if I am correct...so order matters ...

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              • #8
                It helps if you have datums called out..

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