It rebuilds the curve a little strangely, and I can no longer check the “subd creases” command.
In this case I can work around by just using the SetPt command.
What I see is that If you draw the ring profile as periodic curve, that curve will be natively SubD Friendly.
Then you have a chance to not face the described behaviour when using Sweep 1 ( Right on the picture )
Ring profiles; depending on the drawing strategy applied, are often composed of a set of curves of varying degree ( left on the picture - 2 lines of D1 + 2 curves of D2 or 3 )
Converting these curves without impacting the shape sometimes leads to a compromise.
In my humble opinion, in some situations, I find more relevant to draw a ring profile in a specific way that better correspond to the needs instead of trying to convert an object to match the needs.
…which often leads to unwanted complexities or extra modelling steps.
I think it would be useful to have an option allowing to better manage the resulting curve structure while running the command MakeSubDFriendly.
In this case the profile was pretty simple to fix, but had I not checked that it could have been messy when it went off to the client as a fatter ring.
This profile was fairly basic, had it been more complex this could be a problem. I’ll be much more aware in the future of how this behaves.
Thank you for the detailed explanation and your help.
Thanks to pascal also.