2 Replies Latest reply on Apr 5, 2010 10:45 AM by 1-FZQ2NU

    Revision Rolling?

    Barry Cavanaugh

      Are you familiar with the concept of "Revision Rolling"? This is the scenario in which a change of a revision to a child part, way down at the bottom of the multi-level assy, causes the child's immediate parent's revision to change, and the parent's immediate parents' revs to change, and so on and so forth upward thru the hierarchy until you reach the top level.

       

      In the literature, this is a bad thing to do, and the application of "interchangeability" rules allows you to decide when you need to roll the revision on upper level assys vs. when you can keep them at their existing rev (such as when a change is "interchangeable")

       

      specific question:

       

      you have a bracket, with no holes in it, released at Rev A. It is a child part of an assy, and this assy is used in several upper level assy's. Drawings for these assy's exist, and there are views that show the bracket as a member of the assy. The drawings of the assys are also released at rev A.

      If you then add a hole to the bracket, but this change is interchangeable with the bracket version without the hole, one simply changes the rev of the bracket to B and releases it. No need to roll the revision on upper level assy's, at least according to the rules I've read. BUT - what about the drawings of the intermediate assys? You released them at rev A and they remain at A, and those dwgs have views that include the bracket, now if you send the drawings and models to a supplier, they are going to open up of those same rev A drawings, only this time they will show the bracket with the hole in it? Will the suppliers freak out and say "hey! you sent us a rev A of this assy last week, and in this view the bracket is shown and there is no hole in it, but this week you send us models and files and I open up rev A of the same dwg and the bracket has a hole in it?"

       

      sorry for the long msg ,but we are struggling with this issue and any comments and advice is appreciated.

       

      Barry Cavanaugh

      MIT Lincoln Laboratory

        • Re: Revision Rolling?
          John Burrill

          I think every CAD job I've ever had came with this issue.

          On one hand you want your drawing package to be up to date (that's one of the things you tell people about Solidworks right?-that you can update a part and every assembly where it's used will update too?)  On the other, there's the very real cost of preparing documentation, distributing it and superseding versions that are already out in the ether.  If every minor change to a component prompts a complete document package revision, well you'll go nuts.

          In this case, I'd say the shortest answer to is to explain the situation and let proper document controls determine how your suppliers handle it.

          Your fabricator is going to make the bracket from the detail drawing according to the revision you've supplied.  Your assemblers are going to build the unit according to the partnumbers in the BOM.  If both are aware of the doctrine that revisions must maintain interchangeability of parts then this situation won't cause more than a minor curiosity.

          At my company, the assembler spotting a difference between the part in an assembly and a physical part would check the detail drawing for a revision and the effectivity date for the revision to make sure it had gone into effect and the disposition for existing inventory to determine if an old part could be used in place of a new one.  That's why we have those controls, otherwise, subtle differences int he assembly drawing like material thickness would get missed.

          m2c

          John

          • Re: Revision Rolling?

            What are you using for revision control . . . are you using revision traps within the PDM process or are you manually entering them in the file properties etc.?  Do you move drawings around the workflow process the same as you do parts and assemblies?  How are you building the 'Sub Assembly' used in the many 'Assemblies' into the tree / BOM, are you pasting it as reference to all the assemblies that use it or is it being built into the CAD everytime?

             

            I think I undersatand what your issue is and probably have some answers since I have been working through a very similar issues for the last 6 months while getting our Rev Scheme under control, I just want to make sure that we are talking about the same thing before I give you the long answer