5 Replies Latest reply on Jan 20, 2014 4:12 PM by Eric Irwin

    Swept surface discrepancy between 2012 and 2013

    Jason Swackhamer

      Solidworks doesn't maintain surface consistency across versions. I don't understand why they can't keep a versioning system within the model to keep the part's topology the same across updates. I haven't seen this in a while and thought that they'd addressed the problem (it was a problem particulary with lofted surfaces early on) and am surprised to see it with a swept surface. It doesn't necessarily bother me that the surface would deviate from the centerline spline, although .0003" seems like a lot. The problem is the discrepancy between versions. We prototyped this a year and a half ago, and are now cutting the production tooling. The prototypes were created in swx2012, but we've since transitioned to swx2013 and that's where the production tooling was created. So now we have a discrepancy between our production and prototype drawings (we're still cutting to the original prototype of course).

       

      We created the model using a  swept surface in swx 2012. It uses a spline as a centerline. The resulting surface intersects the spline 100% in 2012, but deviates by .0003 in Solidworks 2013:

       

      Before Rebuild.JPG

       

      After a cntrl Q(!) in deviates by .0002:

       

      After Rebuild.JPG

       

      Kind of a terrible situation since all the solutions are messy...

       

      -Jason S.

        • Re: Swept surface discrepancy between 2012 and 2013
          Eric Irwin

          Wow, what kind of tolerances are you producing your parts to?  I agree that this is somewhat of an issue, but how much difference does 1/10,000 make to your final product?

            • Re: Swept surface discrepancy between 2012 and 2013
              Jason Swackhamer

              Eric-

               

              This for an injection mold so relatively close tolerance work. Admittedly, in this case, not so much of a problem in terms of the actual part in the end for a few reasons (the surface is offset to form the other side of the part, so the distance between them stayed the same, just shifted). It's more having to track the problem down. When we notice something that doesn't make sense, we investigate until we have an explanation because sometimes a small discrepancy is a sign of a larger problem, say like using an out of date model. Fortunately we caught the problem before cutting to the wrong number, but still had to shut the job down until we figured it out.

               

              I kind of have the attitude that it makes sense to get the modeling precise since precision is cheap on the computer. It's more expensive in the steel! We hold a ±.0002 on our molding (these are multi cavity tools) so this would have pushed us out of our tolerance range. And if we're holding that kind of tolerance in steel, solidworks should be able to hold it in the computer.

               

              Hope this makes it clearer (reading it through—not so sure...but no more time to spend!).

               

              Thanks,

               

              -Jason S.

                • Re: Swept surface discrepancy between 2012 and 2013
                  Eric Irwin

                  Jason,

                   

                  Thanks for the explanation.  I guess the real question is, if you cut the steel to the new geometry, does is truly affect the end result?  I know you are holding your steel tolerances that tight, but what is the affect on the plastic parts and what are their tolerances?  I'm sure the plastic tolerances are not .0002.

                   

                  On the other side, I understand the frustration with changes in geometry as the software moves forward.  I think there are much bigger issues with geometry happening between software revisions, at least we have seen them.  I do understand that with every revision there is pressure to make the software faster and/or more robust.  I am sure that means that the math used to create complex surfaces goes through some changes and their are probably heated debates internally at SW over how much legacy to carry forward.  Point being that decisions have been made and I'm sure they are not taken lightly.

                   

                  This does suck that you had to figure it out, but at the same time, it was also a learning experience.  The next time this happens, you might be better prepared?  I guess you still had the option of using the model from the previous version, but maybe someday you won't.

              • Re: Swept surface discrepancy between 2012 and 2013
                Roland Schwarz

                Interesting.  Very arcane knowledge that most people don't really care about, but could affect hard-core surfacers.  This is the first time I've seen someone lodge a cmplaint about it.

                 

                Waaayyy back (2001?), SW actually noted this in the API help.  Every new version has a revamped algorithm for interpolating lofted surfaces (and swseeps, too, apparently).  SW even acconted for this in the API, tagging loft features with a version so that SW would know which algorithm was used.

                  • Re: Swept surface discrepancy between 2012 and 2013
                    Jason Swackhamer

                    Roland-

                     

                    Thanks—I wasn't aware that version tracking actually is a swx policy. Like I mentioned, I had noticed that the problem with lofts seem to disappear some time ago (around 2001 sounds about right). In all fairness, while this is a sweep, it's somewhat loftish, having guide curves.

                     

                    I'll submit it as a bug (not too hopeful, but what the heck)...maybe they just messed up on the versioning.

                     

                    -Jason S.