It was considered cautious to reinforce the top wooden doughnut ring that would carry the dome, with an outer ring of steel that would provide a strong belt around its periphery helping to maintain structural integrity especially during rotation.
The mating beam underneath required no such support as it was firmly bolted to the roof frame of the observatory square chamber.
…time to bend metal…again
Now up until this point I had planned to build the frame for support of the galvanized shell out of a circular row of 15mm width flat bars arrayed vertically around and rising up from the metal band on the periphery of the doughnut
…a giant bird-cage
These would bend inwards as they rose, to form a sort of giant bird cage of twenty risers to which the sheets of metal would be riveted.
For this reason a series of equally spaced 15 mm wide angles were welded to the top of the metal ring belt and a metal ‘spider’ was hooked on to a length of pipe to provide for temporary anchorage of the ribbing to allow their eventual welding together at the top.
The ‘Crown’ was made from a ring of flat bar to which were welded 20 radial horizontal lags. These were intended to anchor the vertical ribs of the cage, arising from the base ring…. a cunning plan, as Blackadder would say, but…