6 Replies Latest reply on Sep 19, 2007 1:25 PM by Charles Culp

    Fully constrained splines

    Rhyc Sandberg

       

      I'm using more spline curves these days in sketches. What I'venoticed is that they are more difficult to fully constrain than theusual suspects (lines, arcs, etc.). I'm wondering if this is reallysomething to be concerned about or not?

      I've been taught since my earliest SolidWorks training days(from VARs using the SolidWorks training manuals) that we wantfully constrained sketches. But what are the consequences ofleaving a spline that isn't fully constrained? And is theretechnique to it? For instance, can we reasonably leave some splinepoints undimensioned in the middle of the spline somewhere as longas the end points are dimensioned/merged/coincident/tangent/etc.constrained?

      By the way - I am 'constrained' to using SW 2006 until our headoffice in Japan upgrades.

       

      Rhyc Sandberg

        • Fully constrained splines
          Matt Lombard
          I typically leave internal spline points unconstrained, but you could use the "fully define sketch" tool to dimension it arbitrarily, which is as good as anything. If you get into it, there is far too much to constrain, with all of the handle angles and magnitudes, in addition to spline point locations. I treat spline endpoints like anything else, though. They should be constrained. If you're worried about things moving around, you might set the spline to "proportional", or simply fix it.
            • Fully constrained splines
              Rhyc Sandberg

              Matt,

               

              Thanks for the input. I thought perhaps I could leave somespline points undefined without having problems, but wasn't sure.I'm just so programmed to have fully constrained sketches...

               

              Rhyc

               

                • Fully constrained splines
                  Kevin Quigley
                  Depends what you are modelling. I tend to tie down the splinepoints where the surface meets  a boundary, but I generallytry to keep the spline unconstrained through the early designprocess, perhaps moving to a more fully constrained solution as thedesign is finalised.

                  To be frank though, if I find I can't get the precise curves I needusing the SW splines (and they are a bit clunky) I export therelevant data to other apps (I use Ashlar-Vellum Cobalt and VX forthis) and generate the curves there then re-import back to SW tocreate the surfaces or in some cases import surfaces generated inthe other apps. You loose the parametrics for the surface (well youcan tweak with the free form features) but sometimes it is justquicker and easier elsewhere.

                  Of course if SW had better spline tools and conics......
                    • Fully constrained splines
                      Mark Matthews
                      I have never used Ashlar Cobalt, but if it's splines are any thing like Aslhar's Graphite I don't see how they compare to SW. I find them the clunkiest splines ever. They add edit points to a spline as you modify it.
                        • Fully constrained splines
                          Kevin Quigley
                          The good old adding points to spline bug Mark

                          Yes that was true in older versions of Graphite but that wassorted.

                          Cobalt's splines are vastly superior to Graphites, very fluid andeasy to manipulate. SW's splines are quite robust but they aredifficult to manipulate and fine tune. Cobalt's and others (likeRhino for example) have many more ways of creating and editing. Ifind that for fine tuning and subtle adjustments it is easier tohave more than one spline type.
                      • Fully constrained splines
                        Charles Culp
                        Rhyc,

                        I know this is a constraint that Matt doesn't use, but these areoften instances where I like to use the "FIX" constraint. When I create a spline, and don't want to bother withdimensioning the internal points, (I just eyeballed them when Icreated them, anyway), I will just use the FIX constraint. This way I know that the point isn't ambiguous, and when Imove or change other points, it will not move on me.  

                        Thus  you can have a fully constrained sketch ( no (-) next tothe sketch), and be certain that things won't just change on theirown when you move other points on the sketch.  I find it isespecially important with 3D sketches, where things like to movearound quite a bit based on other changes in the sketch.