12 Replies Latest reply on Apr 4, 2017 10:30 AM by Adam Worsham

    Adding thickness to knitted surfaces

    Craig Williams

      Hello,

       

      So I have researched this topic and can't seem to find the solution to my answer.

       

      I have created two surface lofts, trimmed the surfaces where they intersect, knitted the two surfaces together and then when I attempt to add a thickness it fails.

       

      I have attached the file.

       

      Any help on this would be very much appreciated.

       

      Craig

        • Re: Adding thickness to knitted surfaces
          John Stoltzfus

          This takes Paul Salvador - he'll be on later

          • Re: Adding thickness to knitted surfaces
            Ingvar Magnusson

            What is the thickness you are after ? Inwards/Outwards ?

             

            thicken.jpg

            • Re: Adding thickness to knitted surfaces
              Chris Dordoni

              Craig, what is your desired thickness?

               

              It fails for me if I attempt to increase thickness beyond 0.5mm or so. The likely cause is that the thickness you want is exceeding the minimum radius of curvature.

               

              Using check entity can sometimes help in determining where you have some tight areas. Its moderately useful as way to determine where the problem lies and in this case I can easily get 0.25mm radius although the value reported is far lower.

               

              I would start by trying to find the tightest areas. Its also relevant which direction you want for the thicken .. I offset to the inside (or Side1 using the Thicken feature). Using your Plane 10 to to create a section, I added some circles to show the ridges where the thicken is likely failing. You could reduce or smoothen the curvature in these areas as a starting point; however, if you want a greater thickness you would likely have to modify most of the others.

               

              An alternative would be to generate the second surface with a different loft (reduced curvature)  instead of using Thicken. This would produce a varying wall thickness, which may or may not work for your application.

                • Re: Adding thickness to knitted surfaces
                  Craig Williams

                  Hi Chris,

                   

                  I am looking to 3D print the part and i'm looking to ultimately create a part which is suitable for injection moulding.

                   

                  The purpose for all this is for me to learn design for manufacture. I know it would be wise to start on something more simple but I have chosen to pursue this and intend on continuing.

                   

                  I think I understand what you are saying, so ultimately the sine wave crescent needs to have a smaller amplitude to stop self-intersecting geometry when a thickness is added?

                    • Re: Adding thickness to knitted surfaces
                      Chris Dordoni

                      It might be possible to maintain the overall appearance, using the section sketch you have already created, with additional sections. A new section with a smaller amplitude could be located nearer to the narrow end. Otherwise, if keeping the one section only, you might have to reduce the amplitude significantly to achieve the 2mm thickness, and this would make a significant visual change to the overall appearance of the part.

                       

                      The Check entity function can help to locate a problem area by putting an arrow in the display as shown below when the entry in the results list is clicked. In this case its not very clear exactly what you would have to do to increase the minimum curvature in the area that is referenced.

                      The problem is in the red area I circled. Just by moving the spline points a bit might change the curvature.

                       

                      The curve cross section at that area looks very shallow and I would not expect there to be an issue here. However, the way the surface is stretching along the loft, it is causing the minimum curvature to be a lot smaller than might be expected. It would be a bit of trial and error to resolve it. Multiple iteration of using Check entity and modifying sketches might be needed. Eventually the progression would move on to the other rippled areas.

                       

                      For this form I would say you would need 4 cross sections to get something that will look the way you want and give enough flexibility to make some small corrections that will not significantly change the overall appearance. Note that cross sections and other curves can be 3D sketches as well, though they can be more difficult to work with. As you gain experience you will better understand when to use one over the other.

                  • Re: Adding thickness to knitted surfaces
                    Adam Worsham

                    I may be coming to the party late... but looking at the thicken command or even surface offset, you can see where there are some issues with the surfaces. This is where your sketches are connecting and causing some discontinuous sections. You may want to try a fit spline and look at the relations. After I cut those sections out of the surface, I was able to get it to thicken to 2mm.

                    shell_4.jpg