Hi…,
I have tried Sweep1 with this ellipse and curve, and get this kinky result.
sweep1_ellipse_trouble.3dm (128.2 KB)
Thanks
Michael
www.flexiCAD.com
Aha.
I recently fiddled with trim problems on Sweep1 surfaces.
Perhaps this is the main reason.
I didn’t notice the bad result.
@Michael_Meyer If you check the box “Refit rail”, you will get the V5 style single surface. However, you are right, without that we should still have a valid result, I would think much like an ellipsoid with fully multiple knots at the quadrants…
–Mitch
Hi Mitch,
good point. I haven’t seen this new button, perhaps I need soon glasses. 
I hope all other Rhino users will see this.
Thanks
Michael
This is what we should be getting…
sweep1_ellipse_trouble_msh.3dm (203.0 KB)
Edit: looks like something similar to this has been filed as a bug almost a year ago, but did not make it to the fix list for 6.0, still listed as 6.x… @lowell ?
https://mcneel.myjetbrains.com/youtrack/issue/RH-37564
(I added a comment to the bug report referencing this post)
Done how?
Can you guess? 
By hand?
Yeah, sorta. I made a circle the size of the smaller ellipse radius and centered on the ellipse; moved the profile over to the circle; Sweep1 the profile on the circle (no refit). The result does not have kinks. Then I used Scale1D to scale the surface back to the original ellipse. QED.
–Mitch
1 Like
This is also in V5, but never showed a visible effect.
No wonder we didn’t try in V6.
That’s because I think pretty much everything was already refit automatically except in certain “special” situations - I don’t recall which though.
Hi Mitch, all - we got quite a bit flack, back then, for ‘rounded rectangle’ type sweeps - straights and tangent arcs, a common thing - being single complex surfaces and not polysurfaces with simpler faces:
-Pascal
Makes sense.
Good to have this argument.