[bojan]

Semi-rings are at the location finally.., waiting for assembly into one ring.
They will be assembled (welded) together once the 8 steel pipes (stomps that will support the dome and floor of the obs) are in place and levelled so the ring can rest on flat plane.

I was thinking about the rollers, attached picture illustrates one possible alternative.
Rollers could be made of metal or some hard plastic, shafts will be M10 ~ M12 screws (high tensile). I think there will be no need for ball bearings as the dome rotation is very slow and occasional.