Hi Burr, the singularity goes to be opposite of the first curve that was picked.

So for instance in your arrangement you probably would want the singularity/pole point to be at the very top, that would be most similar to a surface of revolution and make the 2 similar curves behave more symmetrical to one another:



So to do that, pick this curve first:



Now if you turn on surface control points, you will see that they kind of start at that first pick curve and collapse down to a single point opposite of it like this:



If you instead pick one like this:



Then if you turn on control points you can see that it will collapse down towards the opposite of it, but that gives a kind of asymmetry:




But really revolve or rail revolve is much better for something that pivots like this.

- Michael