Fusion
The issue is not the curves as those are fine.
The top surface should not loft into a singularity (point), as that often creates problems. In this case, that is very easy to avoid.
The next issue is a double-whammy. The bottom surface is not only a loft into a singularity but also transitions from a sharp crease into a tangent surface. Likely, Fusion encounters a near tangency condition, which makes it difficult to shell.
I separate the bottom surface into two lofts to isolate the problem into a smaller area and gain a little better control.
That object then shell fine.
@kjoellesdal wrote:
So it was a user error by me and not the application to blame 🙈
While that's true sometimes, I would not use the term "error" here.
Some shapes are deceptively simple but not so easy to model.
Sometimes, lofting into a singularity cannot be avoided, such as with the bottom surface. I was not sure whether or not breaking this into two lofts to provide more control and avoid the near tangency issue was going to work. I got lucky 😉
Often modeling such shapes takes a bit of experimentation.
