I remixed the design to replace the central axis :
First, the rings and central rod did'nt fit together (didn't checked if it was the design, or my printer, or both)
Second, the rod broke at it's base

So I redesigned the base so I could mount a wood rod 14 mm Ø.
The rod should be mounted tight in the base, but in case there is too much play (the hole is designed at 14.5mm Ø. I got a tight fit on my printer), you can add a 4x16 mm wood screw at between the rod and the base (from the bottom)

After 2 days of play, the rod is still in place :).

I attached the f3d if you want to modify it.