[ChrisM]

A few details on the turntable:

Diameter = 3.6 m
Lower ring (fixed to top of walls) = 100 x 50 mm ply
Upper ring (rotates) = 100 x 50 mm ply attached to a 75 x 75 x 6 mm steel ring rolled to 3.6 m dia.

In the photos, the plywood rings are blue, and the steel ring is red.

Eight plastic wheels are mounted on the lower fixed ring, and the steel ring sits on those wheels. Three additional wheels, spaced at 120 deg around the turntable, keep the two rings aligned.

The cross-section drawing also shows how the 5/8 geodesic dome was attached to the top plywood ring, and how the safety hooks (purple, & 13 off), that stop the dome lifting off the walls, were arranged. The brown-coloured C-section in which the safety hooks operate, was made from about 1.6 mm sheet formed and then rolled.

On the LHS of the sketch, the weather-shield can be seen. A neater and easier design would have had the turntable a fraction larger in diameter so that the weather shield did not require profiling.

Chris