Why this using sweep1?

Rhino
1

The break happens no matter the diameter.

HOW
HOW1296×771 240 KB

WHY.3dm (980.1 KB)

2

there is a slight kink (G0) transition there, is it needed? if you can make it G1 it will probably work correctly

3

I can see the kink when I zoom in close to the original curve I rotated. I’m not certain I’ve completely wrapped my head around the G labels, but I’m getting there. How/where do I find that info about an object, and then change it?

4

exploded the curves and use GCon

you could replace marked curves with tangent blendcurves, since these curves are G0 at both ends:

image
image1224×816 43.8 KB

5

Thanks. BlendCrv and trimming with the created blend worked.