10 Replies Latest reply on Jan 30, 2008 4:07 PM by 1-6TXHTM

    Ellipse length

      I do alot of work with ellipses (aluminum tanks). We build these out of aluminum sheets and they are cut to length,
      and then rolled around an elliptical head (two sheets to completly wrap and not half and half).
      The problem is there is no way to set the length of an ellipse.
      Does anyone have a work around or something I am missing?

      Thanks
      Lorne
        • Ellipse length
          Deepak Gupta
          Hi Lorne,

          Are you trying get the flat pattern of the elipse..
          • Ellipse length
            Kelvin Lamport
            Given the perimeter and size of one axis, you could use a DT to calculate the other axis.

            http://www.efunda.com/math/areas/EllipseGen.cfm
            • Ellipse length
              Pedro Nunes
              yeah kelvin, you are right... but i try to use that formula and the result becomes with ~10% of error, wich i think in cad/cam is a very bad approximation
                • Ellipse length
                  What I am looking for is to be able to call up the length in a cutlist or BOM and to be able to drive the shape of the ellipse based on length (like the dimension around arc function). We have a number of different head sizes but the bottom sheet is always the same length (84"). Right now I have to model the ellispe, dimension the X and Y axises and then trim the partial ellispe to length by trial and error and dimension the end points (which change if the head size changes). What I would like is to be able to dimension the axises and the length of the partial ellipse.

                  I hope that made sense. I don't need a flat pattern for this application.
                • Ellipse length
                  Roland Schwarz
                  Believe it or not, modern mathematics has not come up with a way to calculate the exact perimeter of an ellipse or partial ellipse. Any formulae you find are approximate.
                  • Ellipse length
                    Mahir Abrahim
                    If you try Google, many other more exact approximations can be found.
                      • Ellipse length
                        Just an update. I have figured out a work around that seems to work for my application.

                        What I did was first sketch a full ellipse to the dimensions I want.
                        Second I added arcs to the bottom of the ellipse (where I needed the partial ellipse) I added references of coincident of both end points of the arcs to the ellipse and created a point at the mid-point of each arc. I also added a reference from this point to be coincident to the ellipse.
                        I then added length dimensions to the arcs (all of them adding up to the value I need), and sketched a line that crossed the ellipse and was coincident with the two outermost points of the arcs.
                        I then trimed the ellipse with this line making a partial ellipse with a driveable length (it won't be 100% accurate but close enough for my application), and a driveable ellipse size.

                        Lorne