16 Replies Latest reply on Nov 3, 2017 12:18 PM by Christian Chu

    Strange curves on lofted boss

    Matthew Good

      I'm modelling a hardware lug where the outside is purely aesthetic and going for an Art Deco sort of feel. You can see the overall model here (ignore loft 3, I was just experimenting).

      However I'm not happy with the ends of the lug which is modelled as a lofted boss. I've used sketch6 (which just follows the edges of half of the end face of boss extrude 3), and sketch13 and a guide curve sketch14 shown below.

      The lofted boss results in some strange surface with curves that I don't like. In certain places the loft sort of goes inwards (see below) and I can't figure out how to get a smooth rounded loft.

      I'm currently trawling through some literature/tutorials but any help from people with more experience would be greatly appreciated!

      Thanks,

      Matthew

        • Re: Strange curves on lofted boss
          John Stoltzfus

          You need an additional guide curve/s

          • Re: Strange curves on lofted boss
            Bjorn Hulman

            Hi Matthew,

            you using start / end tangency?

            • Re: Strange curves on lofted boss
              J. Mather

              My initial thought is, "Why are you using Loft?"

               

              My second thought is,"Why is there an unconstrained sketch, why are you up to Sketch20 for simple geometry, why are you up to Mirror10 and Shell9?"

               

              The reason these thoughts enter my mind is that I consider my initial attempts as merely exercises in understanding the geometry and then I start over from scratch using what I learned from my initial attempt(s).  My thoughts are that when I see a feature tree like this is, "Whack and Hack Technique." In my years of observation of hundreds of CAD users - that technique is not very productive.

               

              Just thinking out loud. You can ignore my thinking.

                • Re: Strange curves on lofted boss
                  Stephen Bittner

                  I used to be this particular, but I got over it.  :-)  As long as the end result is useful, nobody (but you) will care that the "first" sketch is actually "Sketch 4". 

                  • Re: Strange curves on lofted boss
                    Matthew Good

                    The reason I used a loft is I can't think of another way to get the geometry I require?

                     

                    Also as I'm just getting used to Solidworks and playing around with this model, I'm chopping and changing things in the model all the time to see if I like the effect. The unconstrained sketch is a guidance curve for a previous loft, since the sketch in the right plan has been altered, it is no longer coincident to points on that sketch, but its suppressed and I'm not using it at the moment. Equally if I delete a previous sketch and add another the sketch number goes up, I'm not actually using 20 sketches to define the model, simply deleting and adding and so the numbers go up.

                     

                    I certainly won't ignore the thoughts regarding the feature tree as I know that this is messy but I'm just using the model at the moment to experiment with.

                     

                    If you do know how I would achieve the same geometry at the ends without a loft though I'd be very interested if you could elaborate.

                     

                    Thanks,

                    Matthew

                      • Re: Strange curves on lofted boss
                        J. Mather

                        Matthew Good wrote:

                        If you do know how I would achieve the same geometry at the ends without a loft though I'd be very interested if you could elaborate.

                        Add Reply to this response and click the Use advanced editor link in upper right corner of reply.

                        Attach your *.sldprt file here for better guidance and elaboration on modeling technique.

                        I can tell you - that I will examine your geometry, then start from scratch.

                         

                        Oops, I see that you attached it in another response.

                        You should always do this in initial post if possible.

                        If the geometry is proprietary you should create a dummy example file.

                    • Re: Strange curves on lofted boss
                      Dustin Perreault

                      I am not sure if this is the shape you are going for or not. I cannot upload the file since you have an older version of SolidWorks but I can give my best advice if this is indeed the shape you are going for. I have found that lofts work best when you have an equal amount of line segments in each sketch. I'm not sure if it is the appropriate way to model but I created the geometry in two separate lofts. I have found guide curves to be my friend when using lofts. I rarely get a loft feature to come out exactly how I want without multiple guide curves. From my experience creating lofts that suit you best requires some trial and error as far as guide curve creation. My modeling techniques could quite possibly be considered "Whack and Hack" and I am working on improving that. Here is the geometry I came up with and the guide curves I used.

                      concept 1.png

                      concept 2.png

                      concept 3.png

                       

                      concept 4.png

                       

                      concept 5.png

                       

                      concept 6.png

                      I don't think Lofts are an inappropriate method for geometry construction for this part, however, you could possibly use surfacing tools, such as boundary surfaces. Just make sure you convert the surfaces to solid bodies when you are done, which (from my experience) can sometimes be tricky. I am still learning myself so take everything I say with a grain of salt. My best advice is to force your geometry to create the shape you want with guide curves.

                      • Re: Strange curves on lofted boss
                        Christian Chu

                        Matther,

                        I'm not against using loft feature at all, but I'd prefer using boundary for better curvature control