?I'd trying to construct a 6 foot vertical pole, where a horizontal bar (3 foot wide) will fall due to gravity and spin around the pole on its way down
a bit like this toy works here.
Scale up the example illustrated. Keep the "screw thread" small in diameter, thus keeping the helix angle steep and avoiding sticking.
You probably need to make this by bending a helix in tube. This is often done by bending several helices in parallel, and so self-spacing them. You might be able to bend three 1/3rd lengths, then joining them end to end, thus giving three times the pitch of a close-spaced helix.
I wouldn't assume the helical rod will stay as a rod, but will probably need to have intermittent mounts from the back. So your carrier bar needs to have a ring around the upright and just rest on the helix, rather than having a hole that fits over the helix.
Another way would be to machine it from plastic tube, using a home constructed "router lathe" (search for that). This is a constructed square gutter, with a router sliding across the top on a carriage. The router carriage is driven on 1/2" threaded rod, which is driven by Meccano chains & gears from the rotating workpiece.
If it's for long term public art, just pay the money and have one machine bent in stainless tube.
How heavy will the horizontal bar be? Unless it's really heavy, I imagine copying the toy will work - use a form made from wood with protruding nails at regular intervals and wind a thick bit of steel wire around it (heating as you go). I think there should be enough tension in the wire once it's cooled that you can transfer it to a 'fresh' pole and use it as a guide for the horizontal bar.
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