I saw this once and it was done with 3 parts. I cannot find the
brochure where it was explained with pictures, so I will try to
explain it by heart.
The principle is that there is a central flat band running under the
outer and center rings. This flat band (the inner ring) is sawn into
2 halves. One on each outer ring (soldered underneath it).
The total width of these two parts should be a little wider than the
width of the spinning ring. This to do the magic.
In one flat band you saw three half-harpoon-like spaces in
juxtaposition to the flat inner bands lining.
Then from the other half of the flat inner band you file down the
band to form 3 half-harpoon-like harpoons (confused?, so am I), so
the whole can twist and turn in each other without ever turning back
(principle of the harpoon).
No soldering is needed then, at least not for the join.
It's a lot of work, but it's worth it.
Hope this helps