This took me a while to do, with a lot of tweaking and adjusting. Perhaps it was the use of rudimentary tools to make this (no CAD program) or my inability to focus (too many distractions elsewhere). Alas, here’s what a segment looks like:
I opted to build a threaded rod helix, thinking that it would be easiest to do (this being my very first helix build). I originally read about this specific design (7 segments per loop with 7 pairs of “ears”) from http://spcascade.com/Helix/helix_notes.html.
And, I suppose because it was 7 segments and not 8, aligning everything by hand was tedious. Fingers crossed that everything actually lines up once put together. The holes are made to be 1/8″ as pilots for a larger hole for the threaded rods. This was I can angle the drill to whatever minute value I need to, adjusting for a location of each rod in the loop.
This design makes for a 28″ outer and 25.5″ inner track radius, although it might be possible to squeeze 1/2″ more or so, depending on the clearances with the outer “ears.”
Finally, I’m including my helix_segment_final vector file for anyone else wishing to re-use this design. It was made from scratch as I couldn’t find any ready made on the web, so YMMV. One could probably scale this design up or down to get other radii, as desired.