4 Replies Latest reply on Jun 13, 2011 7:14 PM by Brent Zartman

    Tangency with Splines

    Brent Zartman

      Maybe this is my inexperience, but this seems inconsistant and just plain weird.

      Is there a way to create tangency with a spline between other sketch entities? Here's the situation. I want to create a 3 point spline with a spiral attached tangent to each endpoint. So, I opened a sketch, draw a 3 pt spline with the center coincident to the origin then continue to fully define the sketch. Exit the sketch, start a new one... since that is how you have to draw a helix/spiral... I put in a simple circle and it wont allow me to apply tangency to the spline. I called the VAR and their solution was to open the original sketch and offset the spline at a distance of the radius of the circle of the other sketch, then make the circle center coincident to the offset spline. This works. OK great. But heres the weirdness. I found that I can make lines, arcs, circles, and new splines tangent to the offset spline...  WHAT?? but not the original? Is this a bug? Can anyone explain this, or at least justify the peculiar behavior? I have included an example for reference (SW2011 sp03). As a watch out warning with splines, tangency, in this case, seems to be anchored to where you click, and not the entire curve.

       

      Thanks,

      Brent

        • Re: Tangency with Splines
          Roland Schwarz

          Spline tangency constraints can get flaky.  Sometimes it helps to add a construction line.  Make the construction line tangent to the spline and make the other entity also tangent to the line (instead of directly tangent to the spline).

            • Re: Tangency with Splines
              Brent Zartman

              Thank you. I had not thought of using a Tangent line. It is, however, very strange to me that you cant make the circle tangent to the original spline, but you can to the offset spline. Shouldnt the behavior be the same for both? They are both splines, right?... So if you can create tangency with an offset spline, why not the original?

            • Re: Tangency with Splines
              Jerry Steiger

              Brent,

               

              Spline tangency is trickier than other tangencies. For a spline to be tangent to another curve, it has to be close enough to tangent to decide how to move to achieve tangency. For this reason, it is best to have the other curves laid down first, then add the spline. As you already learned from Roland's post, it is often helpful to add construction lines tangent to your spline, so that you can move them around to get the spline approximately aligned.

               

              Jerry Steiger