There are two major problems with Fusion here.
First Fusion does not allow T-Splines to create self intersecting surface.
I suggested that ability often particularly to make geometry like in this case that intersects and later can be trimmed by the user.

The second problem seems that Fusion is unable to loft between two end profiles along a center rail which is pretty embarrassing.
But even when adjusting the position of the end sketch (not being below the top profile) the rail function fails.


I whipped this one up with Blender's path tools in few seconds.
It allows you to smoothly flow a profile alone a path even when closed (cyclic) and then scale the profile along the path CVs.


The only work around might be to use T-Splines and build each half alone with horizontal tangent extensions along each end
so you can later snip the extensions off and join the two parts.
Blender is my go to sculpting tool as I find T-Splines lacking many modeling abilities and transformation controls I need for efficient work.
T-Splines I mainly only use for importing OBJ data to turn into NURBS in Fusion and that combo I feel is combining the best of both worlds
as both apps Fusion and Blender have ups and downs and T-Spline or Mesh2BREP is the perfect bridge tool.
Claas Kuhnen
Faculty Industrial Design – Wayne State Universit
Chair Interior Design – Wayne State University
Owner studioKuhnen – product : interface : design
