Hi Colin,

You're welcome.

If you mean by a "straight forward sweep", a two rail sweep, it will
work that way as well. It would also work the same way in Rhino.

It wasn't so much the tightly curved section that caused it to break,
your curve has a kink where it transitioned over the shoulder towards
the side of the ring. I just tried it again with your curves as a two rail sweep.

I <separated> your curve and replaced the kinky section with a <blend> line that
makes a smoother transition (with tangency) and the 2 rail sweep works better,
but the surface still has a little bump in it that you could easily fix with a hand file in the wax.

If you drew the curve completely over, you could get it to be smooth as a 2 rail sweep. (see 2nd file)

If the design was a more complicated free form shape, perhaps you'd have more
control over it with a two rail sweep, but for this one, a one rail sweep worked OK.

Since everything was in place after I did the trims, I just swept the two sections
as one rail sweeps and joined them, but if you did it as a two rail sweep
it would take about the same amount of steps and accomplish the same thing.

The thing to always remember is, good construction lines make good surfaces. :-)
The key to making good construction lines is to let MoI "draw" the hard stuff
with blends or tangency or whatever other feature that seems most useful and appropriate.

-Jesse