Symmetry in PC DMIS 2020 R2

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Symmetry in PC DMIS 2020 R2

    I have this part with a symmetry callout. I have tried to use what knowledge was available from previous forum posts and the help center on PC DMIS itself, but no results.

    Does anyone have success using symmetry in PC DMIS? I have a part that has a requirement and its back to a spherical center, which to me is more of a true position rather than symmetry. I am attaching a copy of the drawing so you can understand my dilemma.
    Attached Files

  • #2
    That is a pretty funky callout.

    I agree with you, looks like those widths should be T.P.-s back to -B- and if they really wanted to they could control symmetry from one wall of the width to the other.
    SF7107(PCD), SF454(PCD), 152614(Quindos), 9159(Quindos), 7107(Quindos), B&S Manual, M&M Gear Checker

    Comment


    • #3
      Originally posted by DAN_M View Post
      That is a pretty funky callout.

      I agree with you, looks like those widths should be T.P.-s back to -B- and if they really wanted to they could control symmetry from one wall of the width to the other.
      Right? I understand that symmetry is looking for opposed points from what I read so I tried dimensioning it this way;

      2- auto planes on the outside flat surfaces, and 2 on inside flat surfaces (4.500'' and 2.500'' linear's) and then I constructed a midplane for the separate entities. When in xact-measure It wouldn't allow me to use Datum B as a feature for the dimension, so as suggested I switched to legacy and altered my alignment, but still no result on the measurement.

      I also tried midpoints for each point on the plane (10 per surface) and then tried to do them individually but still no result.

      I gave it a true position just so the machinist had SOMETHING to relate to, but I really don't think the engineer knew that wasn't the appropriate callout.

      My understanding is that the only real way to get symmetry is to have 2 flats that are being related to, sorta like a notch symmetry comparative to another notch, at least thats how I interpret PC DMIS help diagram.

      Comment


      • #4
        Yeah, for symm, try constructing an alignment plane from that sphere.
        Make sure you are in the correct workplane and that your XYZ origins are set to the sphere then construct the BPLANE to the alignment, then recall the normal alignment, and use the plane for the symmetry.

        Maybe that will work
        sigpic
        Originally posted by AndersI
        I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

        Comment


        • AverageInspector
          AverageInspector commented
          Editing a comment
          Tried this exact thing, couldn't execute because; "specification requires a fully constrained tolerance zone"

      • #5
        https://docs.hexagonmi.com/pcdmis/2019.1/en/helpcenter/mergedProjects/core/19_dimen_topics/19_dimen_files/image084.gif

        This is what the help diagram shows, which to me is accurate. It's requiring for the symmetry between the inside flat 7.8mm-8.2mm width surfaces back to the outside flat surfaces, which is sort of profile but with more constraint on the fact that they're opposed points/have to be on flat surfaces for both Datum and Dimension requirement.

        To dimension flat surfaces back to a center point is really either profile, or true position as agreed with above. Why do we as inspectors always get these awfully drawn prints?

        Comment


        • KIRBSTER269
          KIRBSTER269 commented
          Editing a comment
          Engineers nowadays are taught the software, and are told they don't need to know GD&T it's imbedded in the software. If you think I'm kidding I am not. The true Engineer is a dying breed.

        • AverageInspector
          AverageInspector commented
          Editing a comment
          I am seeing that more and more. I also tend to see the same name under "drafter" and "Checker" on the design label of the print, so these people are drawing their own stuff and checking it. That'd be like a writer being his own editor, bound to be riddled with mistakes since a 2nd set of eyes aren't there.

      • #6
        Originally posted by Matthew D. Hoedeman View Post
        Yeah, for symm, try constructing an alignment plane from that sphere.
        Make sure you are in the correct workplane and that your XYZ origins are set to the sphere then construct the BPLANE to the alignment, then recall the normal alignment, and use the plane for the symmetry.

        Maybe that will work
        Wouldn't I need more points than just the center point of the sphere to make a plane? I tried constructing 3 circle features from the levels I took on the sphere, and making a plane with their 3 center points but it wouldn't allow me to relate that as a Datum when working inside the feature control frame. Only relatable Datums were Planes (A and C)

        Comment


        • KIRBSTER269
          KIRBSTER269 commented
          Editing a comment
          Try lines.

        • Matthew D. Hoedeman
          Matthew D. Hoedeman commented
          Editing a comment
          If you have your XYZ origins set to the sphere, and are in the correct workplane, you then INSERT ~ FEATURE ~ CONSTRUCTED ~ PLANE, the mark the ALIGNMENT box and DO NOT select any feature(s). It makes a plane through your XYZ origin (thus the need for the sphere to be XYZ zero) and it will construct it in the current workplane.

        • AverageInspector
          AverageInspector commented
          Editing a comment
          Tried Matt's suggestion and have no results still. I am definitely in the correct workplane, and I am showing a constructed alignment plane without features selected, just alignment checked. Tried to dimension both the constructed midplane and the separate planes that are used to construct said midplane, still no results populating.

      • #7
        So ladies and gents, the vendor agrees that this is an arbitrary callout and have changed it to profile of the flats separately rather than mid-plane. Thank you immensely for all your help!

        Comment


        • neil.challinor
          neil.challinor commented
          Editing a comment
          Surface profile of constructed 3D widths back to datum B would be the correct way to go. As others have pointed out, symmetry to a singular, spherical datum is not valid under ASME because the sphere would not constrain enough degrees of freedom.

      • #8
        For clarification, the ASME Y14.5-2009 standard seems to call the datum to be an axis or centerplane, which the sphere cannot offer. Because of that, I recommended discussing this with the design engineer to see if a position callout, or another type of GD&T, would evaluate the function.

        Comment


        • #9
          As beech332 alludes to, a sphere does not constrain any rotational degrees of freedom so there is no defined coordinate plane from which to measure symmetry.

          Comment

          Related Topics

          Collapse

          Working...
          X