How to set hole pattern as datum for True Pos.

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  • How to set hole pattern as datum for True Pos.

    Print calls a plane Datum A , Datum B is a rectangular 2x4 pattern of holes thru plane A.
    then there are a bunch of other features that call TP to A and B.


    Searching the forum I figured out how to do a best fit alignment.
    I'm stuck on how to set holes as B with DATDEF for use in a true position dimension (using Xactmeasure, PCDMIS 2016).


    HolePattern.jpg

  • #2
    Measure the holes, create a set of all eight, do FCF TP on the set, DATDEF the set as B
    AndersI
    SW support - Hexagon Metrology Nordic AB

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    • #3
      used Constructed Feature Set, selected all 8 holes
      assigned set to B with DatDef
      made a TP dimension, FCF to A and B for one of the other hole's call out (these aren't shown in above sketch).

      the FCF's tetrahedron is rotated about Z from the best fit alignment...it should be the same, i'm programming offline with CAD

      Do I need to select the holes in a certain order for the Set to work?
      Is these one of the those things that doesn't work offline, but works when you actually run it?
      or am I doing something else wrong?

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      • #4
        Which bestfit alignment? The FCF fits the set internally, and keeps that fit result for use by the datum B.
        AndersI
        SW support - Hexagon Metrology Nordic AB

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        • TK_Fire
          TK_Fire commented
          Editing a comment
          I'm working offline with CAD so everything should be perfect, but when I move the cursor to FCFLOC1 the blue tetrahedron for the FCF is not square to the part, it's off by ~12 degrees CW about Z which seems random

      • #5
        How can those 8 holes be a datum? I can see a bolt hole circle being a datum. And what they really are looking for is perpendicularity. But you have to give them a true position for both the top and bottom of those holes back to -A-
        sigpicSummer Time. Gotta Love it!

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        • TK_Fire
          TK_Fire commented
          Editing a comment
          not worried about the one shown in the sketch. there are other holes not shown in the sketch that are true positioned to A and B.
          Last edited by TK_Fire; 05-31-2019, 11:22 AM.

        • vpt.se
          vpt.se commented
          Editing a comment
          The callout is looking for the position between all holes (location and direction) not just perpendicularity.

      • #6
        When I construct a feature set from a hole pattern measured as cylinders, the resulting datum B has location but no orientation or rotational control. When I attempt to use both datum A and B with a position dimension there's a error saying that "Primary and secondary axes are coincident." Is there another way to define a pattern as a datum in PC-DMIS?

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        • #7
          If I construct a set of four circles, do a FCF TP on that and then use the set as a datum, I see PC-DMIS show two coordinates and three directions lockable by that datum:

          dof.PNG
          AndersI
          SW support - Hexagon Metrology Nordic AB

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          • #8
            Originally posted by Paul Sarrach View Post
            How can those 8 holes be a datum? I can see a bolt hole circle being a datum. And what they really are looking for is perpendicularity. But you have to give them a true position for both the top and bottom of those holes back to -A-
            Er, why?

            Why do you imagine a bolt circle be a datum, and not any other pattern of holes?

            If the mating part has a flat face which sits against A and eight studs which locate through those holes it's perfectly valid.


            Also it's not just checking perpendicularity, it's checking the relationship of the holes to each other.

            Imagine an assembly with various electrical components in which are connected by wires. You need to ensure the mounting holes for each component are right to each other (so the component can be affixed) but the relationship between each component isn't that critical, because the wires take up any slack/misalignment.

            Automettech - Automated Metrology Technology

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            • #9
              After you made your best fit alignment over the 8 holes you select a workplane , for example Xplus.
              Open Constructed feature and select plane. Don't select an element only select Alignment and create it.
              This plane you made you select for the DATDEF in X direction.
              Same for Y and Z direction.
              Attached Files

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              • AndersI
                AndersI commented
                Editing a comment
                Why make it complicated when XactMeasure does it for you? Creating datums from the alignment is OK if the drawing says so (mostly by using [ XYZ ] in ISO-land), but be careful with other datum combinations...

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