Simple newbie question - 1 rail not working as expected

Hi A really simple one but I am struggling with a simple issue. I create 2 ellipses make a rail curve between them, but whatever I do the surface produced goes down from the lower ellipse then reverses and twist u to the top ellipse producing a weird shape. Rotating the ellipse 180 degrees and reversing the point does nothing. Really frustrating as should be simple!

Any help appreciated!

In a simple test here, I cannot reproduce this. Could you post the curves?
Also, perhaps a loft between the ellipses will do the trick in this case?

certainly can. it seem really simple so I don’t know what I am doing wrong,. How do I post the curves? there is no file attach?


Just drag and drop the file into the message window… --Mitch


sweep.3dm (521.1 KB)

Yeah, that’s a tough one to understand. Sweeps - especially 1 rail sweeps - try to turn the profile to keep a constant orientation relative to the rail. The result is that the large ellipses get twisted up as they go into the sharper bends of the rail.

A couple of possible workarounds:

  1. Sweep2 and use the 2 ellipses as rails and the wiggly vertical profile as the profile.
  2. Add a vertical line between the two ellipse “centers” and again use Sweep2 with the wiggly profile and the line as rails and the ellipses as profiles.

I’m not sure if they will get you the results you want, as there are a number of shapes that one might expect from these 3 input curves.

HTH, --Mitch

thanks I will try a two rail

in the end used a loft successfully thanks