2 Replies Latest reply on Jun 9, 2014 4:02 PM by Jerry Steiger

    EPDM and Skeleton-driven assemblies

    Tim Culbertson

      I’ve run into a puzzler regarding EPDM and “skeleton” parts used for top-down design.


      At our company, we’ve proposed a top-down design assembly structure incorporating a “skeleton” part which contains sketches and critical dimensions. This part is used to drive several “real” parts in the assembly in terms of geometry and part location. The coordinate systems for all parts are coincident in the assembly, then geometry is created in each part based off the reference geometry in the skeleton part. For purposes of discussion, suppose our assembly consists of Component A which sits on top of Component B.


      Suppose we have Assembly1 containing skeleton1 which drives components A1 and B1. We design, validate, and then move these files to a read-only/locked state in EPDM upon their release to production.


      Suppose now that we need to design a derivative Assembly2, slightly different from but existing in parallel to Assembly1. Assembly2 has a new skeleton (skeleton2) since it’s driving slightly different geometry for component B2 (let’s say it got an inch taller). Assemby2, however, re-uses component A1 in its original geometry.


      Since A1 is locked, it cannot be updated to reference skeleton2 without an unnecessary/artificial revision cycle.


      The geometry of A1 itself remains unchanged. However, in Assembly2 component A would have to sit 1 inch higher, so its skeleton-driven location has changed. As a result, Assembly2 has B2 driven by skeleton2 and A1 driven by skeleton1. The geometry for A1 is fine, but it appears 1 inch too low in the assembly.


      I’m not even entirely sure we want to update A1 to reference skeleton2, because then the component will be positioned too high in Assembly1.


      I’ve thought about trying to divorce the location of the part from the skeleton (i.e., have the skeleton only drive part shape, not its location, and then position the part in the assembly using normal assembly constraints rather than just having all components share coincident coordinate systems). This feels like it’s breaking from a top-down design approach however?


      Surely other companies out there have solved this issue. Other people’s experiences?

        • Re: EPDM and Skeleton-driven assemblies
          Craig Schultz

          I use copy tree and use "tranform-->rename"  or "transform-->replace with serial number"


          How I do top down for our welded assemblies is create a multibody sheet metal weldment.  Then I break it of into the piece parts by inserting the "base" part into the piece part, and deleting bodies.  Then reassemble into an assembly.


          So for example:

          ABCD - Base (weldment multibody)

               Drives - ABCD - Top, ABCD - Bottom, etc

          ABCD (top level assembly) includes all parts


          So you can replace "ABCD" with your new part number.  Or you can replace with serial numbers.  That way each skeleton or ABCD - Base part drives the appropriate assembly.

          • Re: EPDM and Skeleton-driven assemblies
            Jerry Steiger



            I would use the approach you suggest in your next to the last paragraph. It is not breaking the top-down design approach, it is just using it in a way that better fits your situation. I would build every part from its own origin and then keep the location and orientation information of that part in a particular assembly in the skeleton part for that assembly.


            Jerry S.