11 Replies Latest reply on Feb 5, 2017 9:54 AM by Chris Dordoni

    How to avoid twisted surfaces

    Ole Gjerde



      I am making a model of a traditional norwegian hardanger fiddle, and it has som challenges. The geometry is quite complex, and to achieve a model with both outside and inside geometry I have made some profiles and 3d-sketches and used a lot of lofted surface. Then I extrude material to the outer surface, and try to remove with a cut to the inner surface.

      See the attached files

      The model is almost perfect and quite sofisticated . It works well parametric, and will be a fantastic tool for me and my cnc-mill.


      But my problems is to achieve nice surfaces ecspesially around the F-holes, which are quite complex on this type of fiddle, This gives my problems with making the last extruded cuts which goes in to the inside of the plate.


      Any of you guys who can give me som good advice about defining the surfaces in this geometry? Is the main idea about sketch structure wrong?


      Best regards

        • Re: How to avoid twisted surfaces
          Bjorn Hulman

          Hi Ole,

          Looks like you've been busy there!

          What I would suggest is to try not to acheive all your detail at once. Get the overall surface done first using as few guide curves as possible. I would suggest you should be able to get the top surface done in 2 or 3 features.

          Once you have a nice shape, you can trim the details off.

          • Re: How to avoid twisted surfaces
            John Stoltzfus

            The best guy that I know to ask would be Paul Salvador the surfacing guru

            • Re: How to avoid twisted surfaces
              Ole Gjerde

              Hi guys!

              Thanks for helping me, it means a lot for me and my project!


              I cant see the jpgs I added here now, but I  guess you have seen it and not just ansvering out of what I wrote.

              You see the main thing here is that this is not i violin. Then I would be good to go months ago. I you making a violin, you basically can make it as a bottom, and just doing the F-holes afterwards. So the outer surface have a contunious geometry. But I am a hardangerfiddle-maker, and that is a bit difference. The F holes has to be a 3d-sketch, and the geometry is not continuous.

              So if you still mean the same, I wonder how I should divide the surface, and maybe were? The surface has to stop on the 3-d sketched f-hole, and if it should be cutted, the surface has still to be on the line.

              The biggest problems are especially around the 2 circles in the ends of the F-holes where I get sharpened surfaces neccesarily.


              Put in a picture of a real hardangerfiddle (which I have made by hand myself)




                • Re: How to avoid twisted surfaces
                  Chris Dordoni

                  The picture helps a lot Ole. Nice work, you are a craftsman.


                  The f hole configuration complicates this. I think you might consider the top as 2 major surfaces with transition areas. I do believe that trimming the surfaces is the best way to generate the hole rather than using a 3D sketch as the boundary of the hole.


                  It is difficult to explain the specific steps without constructing an example model ... can you share your SolidWorks file?

                • Re: How to avoid twisted surfaces
                  Ole Gjerde

                  Here is the geometry again

                  outside.JPGsketches.JPGsurfaces.JPGtwisted surfaces.JPG

                  • Re: How to avoid twisted surfaces
                    Christian Chu

                    "extrude material to the outer surface, and try to remove with a cut to the inner surface.

                    See the attached files"


                    Please correct me if I'm wrong - if  yes, then ignore my response.

                    Seems to me as you are doing surfacing and solid at the same time. It'd be confused and hard to control the shape of the model. I think you should use surfacing only to get what shape you want then convert your final surfaces to solid (using thicken for open surfaces or shell for closed surfaces)

                    I'd prefer using boundary over loft feature for better curvature control

                      • Re: How to avoid twisted surfaces
                        Ole Gjerde

                        It is not the main problem that I am doong solids/surfaces at the same time AS I can see. But I want in the end to end up with a solid where I can define in first place the outer geometri and secondarily the thickness of the plate.

                        problem is that the outer surfaces (just in som instances) dont can be used for making solids (extruded boss/cut -up to surface) or thicken -because of that they get a bit twisted in some corners