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DARYLREECE1-Visitor
1-Visitor
December 2, 2021
Question

Midplane GD&T datum in MBD

  • December 2, 2021
  • 3 replies
  • 4178 views
I am using Creo Parametric 4.0 M110

Is it possible to create a midplane GD&T datum in MBD? I cannot figure out a combination that will allow me to select the middle plane as a datum.

    3 replies

    tbraxton
    22-Sapphire II
    tbraxton22-Sapphire II
    22-Sapphire II
    December 2, 2021

    Once you have created a DTM plane feature you should be able to use it as a GD&T reference. Are you asking how to create a midplane DTM?

     

    How to create a midplane DTM Plane

    https://support.ptc.com/help/creo/creo_pma/usascii/index.html#page/part_modeling/part_modeling/part_four_sub/To_Create_a_Datum_Plane_Midplane_Between_Two_References.html 

     

     

      D
      DARYLREECE1-VisitorAuthor
      1-Visitor
      December 8, 2021
      Hi,

      That only creates the datum plane, but I can't attach the Datum Feature Symbol (e.g. -B-) in MBD to that plane.

      Thanks,
      Daryl
      tbraxton
      22-Sapphire II
      tbraxton22-Sapphire II
      22-Sapphire II
      December 9, 2021

      In Creo 4+. When using an annotation feature to create a datum feature symbol the only options for attachment are:

      Select a dimension, a gtol, a dimension witness line or a point on a surface.

       

      https://support.ptc.com/help/creo/creo_pma/usascii/index.html#page/model-based_definition/To_Create_a_Set_Datum_Tag_Annotation_Element.html 

       

      In a drawing you may be able to display what you are trying to do using a dtm plane.

       

      https://support.ptc.com/help/creo/creo_pma/usascii/index.html#page/detail%2FTo_Set_a_Datum_in_Drawing.html%23 

       

       

       

      Chris3
      Chris321-Topaz I
      21-Topaz I
      December 2, 2021

      Creo used to have what were called "set datums" which attached to datum plane features. Starting with Creo 4 they did away with these for MBD. It is not good practice to attach a Datum Feature Symbol to a datum plane because it begs the question what are the features that define that Datum Feature Symbol. If you have a dimension that defines the midplane then to attach the Datum Feature Symbol to that as shown below.

       

      It is also possible to "cheat" although I don't recommend this. If you create a small fill surface on a datum then you can then attach a Datum Feature Symbol to that fill surface.

       

      ss_gd-and-t_da_type_003_1809335.png

        T
        23-Emerald IV
        TomU23-Emerald IV
        23-Emerald IV
        December 9, 2021

        If the datum feature symbol is attached to the feature's dimension, then by definition the midplane of that feature is the datum.  It's not correct to attach datum feature symbols to datum planes.  Even though these planes are 'features' in the CAD software, they are not features in real life since you can't physically touch them on the actual part.  Datum features symbols are only supposed to be attached to actual features - something you can physically touch on the part.

         

        TomU_0-1639082819162.png

         

        Edit:  Good explanation of this here:  https://www.gdandtbasics.com/relating-secondary-datum-feature-to-primary-datums/

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