6 Replies Latest reply on Jan 19, 2017 11:04 AM by Jim Steinmeyer


    Luca Fiorio

      I am trying to adopt top down design for my work, but I am facing some issues with the coding (naming) of the parts and assemblies and with the management of the dependencies between the skeletons and parts. In the following I present a simplified (few parts and assemblies) version of a problem that we experienced while trying to adopt top down design for the first time.




      With reference to the left top-level_assembly in the attached figure, what I understood is that in the top-level_assembly we have a top-level_skeleton that defines the interfaces and the placement of each sub_assembly. Each sub_assembly, depending on its complexity, can have its own sub_assembly_skeleton that inherits the geometries published from the top-level_skeleton. Eventually inside each sub_assembly we can have other sub-sub_assemblies and parts that inherit the geometries published from the sub_assembly_skeleton (in the diagram only the SUB_ASSEMBLY_3 is exploded).


      During the design of our system, at a certain point, we wanted to improve the SUB_ASSEMBLY_3 and this improvement was radical (enough) to require a complete new sub_assembly. But at the same time there were few parts and sub-sub_assemblies that could have been re-used from the old sub_assembly (this means that we used the same files, not a copy of the old files).

      In the following, the modified or new assemblies and parts will be named with the "NEW_" prefix (so are different files from the old ones).


      Here is what we did:

      - create a new_top-level_assembly that has the same (old) skeleton because we don't change any interface between the sub-assemblies

      - create the NEW_SUB_ASSEMBLY_3 with its new SUB_ASSEMBLY_3_SKELETON

      - create the NEW_SUB-SUB_ASSEMBLY_1, NEW_SUB-SUB_ASSEMBLY_2 and the NEW_PART_1

      - inside of the the NEW_SUB_ASSEMBLY_3 assemble the old PART_2 and the old SUB-SUB_ASSEMBLY_3


      As you can see from the picture, the problem that we are now facing is that some elements (parts and assemblies) of the NEW_TOP_LEVEL_ASSEMBLY depend from the old TOP_LEVEL_ASSEMBLY. Obviously we did a mistake, but the lack of time and the complexity of the sub-sub_assemblies and parts guided our decision to re-use the old elements.



      - how would you have managed the improvement of the SUB_ASSEMBLY_3? Is it correct to create a new top-level_assembly? Please consider that we should always have a complete assembly of our system ready for production, and that we can not produce something that has not been tested at least once.

      - can you suggest me a good guide/book to learn top-down design? So far I only found some internet videos and articles.

      - how do you define how many nested skeleton there should be? Theoretically we could have a skeleton in each sub-...-sub assembly.

      - which information are usually stored in the skeletons?

      - considering the issue with the naming convention (keep the same name for parts and assembly re-used) do you have some suggestion to improve the coding of the files? Can you suggest me a book or guide? I would like to understand how large assemblies are managed, like for example in car industry.


      I heard that probably a PLM could solve some of my issues, but for the moment in my company we don't want to buy it because we are a small group. However, I am interested in knowing how a PLM could solve my problems.

          John Stoltzfus

          Wow most interesting - can't wait to see where this will go...


          Personally I use a Skeleton Sketch to control all aspects of the the design and right at the moment is bad timing for me to go into a long reply, but attached is a pdf of my workflow and also a model - take in consideration that the model is very simple and is basically setup to show the feature tree, not the design complexity or design simplicity, it is all about feature tree management etc..


          For me it's not how you approach design or what features you use, for me it's all about being able to take "Any" item in the feature tree and delete it, without having the entire assembly breakdown and melt....


          Design intent is the biggest hurdle for any designers, how what and where......  How do I start, begins with where do I want to end up at, what are the chance for quick changes, it wouldn't work for me to do bottom up design, it would take way to long to make a simple change, I want one or two dimensions that change the overall sizes and how they are controlled depends on the sketches, planes etc....


          Think Zones - from point A to point B, what is the carrier. a sketch line or a plane, or both, what get's you from point B to point C.......etc  these all need a common connection and that in my case is always sub-assemblies and each of those sub-assemblies has the same Skeleton Sketch as the first part in the feature tree..


          edited - updated and bumped (where's everybody at)??  Just me an Luca, someone asks for a free design and he get's like a thousand replies, this post just two.......

            Rick McDonald

            I'm still in early learning mode on Top Down.

            The culture at my company has always been Bottom Up and we (the designers) are still trying to show the importance of assembly drawings.

            Most are designed by parts first, make an assembly and make and assemble the parts.

            Detail drawing and assembly drawings last (so they never get done).

            We are trying to show the importance of fully documenting the designs - it's a struggle.

            Were still on Excel 2003 so we can't even use features like Design tables or anything that requires Excel 2007+.

              K. V.

              Bookmarked it! I'm not used to the top down methode (Learned the bottem up and never took the time to sort out the top down) and i really want to learn it! Might be quite usefull for me on my internships and school projects