Here is an example to show how to create a blend curve on a surface (in fact, it is just a 3d spline). Besides, you can try to fill a hole with 2 edges by using “Blend”, “Fill” and “Multi-sections surface” respectively. You will then see their difference, especially when the two edges are nearly perpendicular to each other. (workbench: GSD) More description can be found on the comment b…