I found a nice example on YouTube of how to create a wire assembly that wraps around a torroid: http://www.youtube.com/watch?v=8GcovIbMRO0

I tried to copy this method for making my electrical transformer.

1. Create torroid.
2. Create a surface that is offset from the torroid.
3. Create spiralling swept surface that intersects the torroid.
4. Create a 3D sketch from the intersecting surfaces of the swept surface and the offset surface. This sketch will form the path.

Now... it looks simple, but the problem I'm having appears to be that when I attempt to create the swept surface in part 3 (seen at about 1:00 in the YouTube video).

Because my torroid is taller than it is wide, I can't create a spiralling swept surface that will intersect with the top of the torroid because I get an error when I try to create it. This is because it clashes with itself at the centre of the torroid if I make the sweep extend out further from its path.

I can think of several solutions, but I don't know how to perform them. I thought maybe I could somehow force the spiral to spiral along its own axis (I'm not sure how to explain that) so that it would intesect with both the top and the sides of the torroid. I'm not sure if I should bother with the method shown in the video any further, or try something completely different. Another solution could be to create a very small spiral path, create the 3D sketch, create the wire, and then create a circular pattern to create one spiralling wire from lots of small segments, but I'd like to learn a simpler method.

Can anyone help? I've attached some images to hopefully show my problem.

EDIT: I've attached the SolidWorks file to my first reply.