Yes I have wound coils by hand on both toilet paper rolls and paper towel rolls. Using melted wax to cover windings and seal tube from moisture.
PVC pipe would be easier though. And you can get that in very nice sizes.
Have you thought about using wiffle balls for your variometers?
If you put a limit on the rotation then you wouldn't have to make bushings for the connections.
The ball style is going to be hard to keep the windings symmetrical and in place. Maybe super glue in segments as you wind?
I've seen some old ones that were grooved for the windings, which I'm sure made winding them easier.
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