I'm having some trouble creating a spiraling ramp - that is, a feature that spirals around a central axis, and becoming taller (longer) centrally. My approach was this:

1. I created a helix to serve as a path for the base of the feature
2. I then created a pair of spirals to serve as guides for the top of the feature.
3. I created the feature with points interseting the helix at the bottom, and the sprirals at the top.
4. I applied "Swept" to create the ramp feature

The preview looks perfect (see image), increasing in height toward the middle, and it appears to have uniform finite thickness throughout the spiral. However, when I click the button to finalize the sweep, I get a "zero thickness" error.  I'm out of ideas on how to do this.  Thoughts anyone?