Thanks Michael - That is the result I'm after. Of course I want to be able to do this myself for future projects, so I'll take your tips and experiment.

The quality of the sine-wave sweep rail seems to be one important issue. Here is how I made the sweep rails:

I drew a 2D sine-wave using your shortcut script. Duplicated and inverted to create two sine waves that cross over. Using Trim, selected points to get just a single cycle. The resulting drawing is two opposing curves that looks like a Cat's Eye.

Projected the two Cat's Eye curves onto the ring surface. Used Circular Array to repeat the Cat's Eye 6 time around the ring.

Here is where the issue starts: The six Cat's Eye curves had a very small gap between at the center line where they touch, so I grabbed each end point and dragged to snap to the next curve's end point. Then I selected each curve segment and joined. Then repeated for the opposite 6 sine sine wave segments. At this point in the process, I thought the six curve segments were fused because a single click would select the entire chain. What should I have done here to insure a clean rail? Would the Rebuild Curve shortcut have helped here?

Next I drew a small circle and used this as a profile to sweep the two sine wave rails, resulting in two solid tubes. Next I hoped to Boolean subtract each from the solid ring.

If I can get a clean sweep rail then I can experiment some more. Also, how much of difference in tube diameters would you suggest? 5%? 1%?

Thanks again Michael for your helpful explanations.

Ed