Hi Lordfox, Blend in general, whether planar sections or not is just not going to work very well on a case like you have there because you've got such differently shaped things you are trying to blend between.

Planar sections will especially have problems if one of the curves does "back tracking" and does not form a convex shape, and also if the surfaces being blended between have surface normals pointing nearly opposite from one another.

I've attached here an example for where planar sections will help, choose the "up" direction for the planar sections to be along the tubular surface's direction, which is the world z axis direction.

But basically in order to get a good result your objects can't just be wildly dissimilar like your case is, they need to be somewhat more reasonably similarly structured.

- Michael