6 Replies Latest reply on May 17, 2017 11:56 PM by Paul Salvador

    Spiral offset uniformity

    Dmitriy C.

      Hi all,

      I've encountered an issue that seems like a bug. When creating an offset of a spiral in a sketch, the distance from the source line varies along its length. In the case of a bi-directional offset (see screenshot), the original line doesn't run along the center, although the distance between the two offset lines seems to stay constant. I've attached a file with this drawing as an example. This is not the behavior I expect -- perhaps this is a known bug? If not, are there suggestions for centering the offset? I think this is a problem with splines in general, but I haven't seen it with arcs where the radius is fixed. Thanks!

      How to Create Uniform Spiral Offset.png

        • Re: Spiral offset uniformity
          Dan Pihlaja

          I haven't opened your part (I am using SW 2015 and I am assuming you are using something newer

           

          Anyway, can you run this test?

           

          In the spot that I have boxed below (it looks like it is not centered there)

           

          Draw 2 horizontal lines and then measure the length of the lines.

           

          If they are different, then I would report this to your VAR and see what they say.

           

          If they are the same, then this is only a graphical error and it might look better with higher image quality....

            • Re: Spiral offset uniformity
              Dmitriy C.

              Hi Dan,

              I can confirm that this isn't just a display error. For example, the measurement tool reports unequal distances, and if I were to extrude the spiral shape, the solid would also be uneven. However, by adding lines that span the two offsets, the spacing is adjusted/corrected locally.

              For example:

              1a.png1b.png1c.png1d.png

              I've used this method to recenter the offsets around a spline spiral before, but I basically have to add at least 8 lines per revolution to get a reasonable fit.

               

              I've recreated the drawing in SW2014 and attached the file in case you want to take a further look. I use SW through a university license, so I'm not sure who our VAR is. Thanks for the input.

               

              ----------------------

              Edit: a word

            • Re: Spiral offset uniformity
              Vladimir Urazhdin

              The construction (center) curve is the spiral. Offset curves are just splines created by SW "black box". Distance between splines looks like correct, but distances between center curve and pseudo offset curves are just a rough approximation.

              Capture1.JPG

              Capture2.JPG

              • Re: Spiral offset uniformity
                Paul Salvador

                if I recall,..that type of sketch offset has never worked accurately,.. so, the workaround is to do a thicken and use the edges for the offset. (image attached)

                thinoff.png