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Having finally decided on round, storm lift stops, I sawed out seven more, 10cm squares and then cut off the corners. Then I stacked them onto a length of M8 studding in the lathe. Turning octagons into circles is a noisy business. I used the lathe drive and small cuts which is time consuming on thick aluminium. The end of the temporary axle was drilled with a center drill and then supported on a running center in the tail stock. 
When it came to fitting the disks to the steering wheel axles I quickly discovered I had no spare M8 nuts. It required at least three nuts per axle plus the Nyloc nut on the bottom. My stock of longer M8 bolts was also rather limited. I needed something much longer than the existing stainless steel hex-socket heads. My lifetime collection of old coffee jars of fixings produced some black hex-socket head screws. These are bound to rust but at least I could assemble the disks to see how they performed.
Then rain stopped play. So I retreated back indoors for lunch. I still need to notch the base of the ribs to clear the disks as the dome rotates. I also need to modify the 2x8 plank at the base of the observation slit. The disks obviously can't pass through solid wood! The board needs to be slotted to an inner radius. Or raised off the base ring with a larger radius arc of solid spacer material. Leaving an inner track clear of the lift stop disks.
The images above show the sequence of steps required to cut eight 4" Ø disks out of scrap, 10mm, aluminium plate. The final result needs new stainless steel fixings. Longer screws with nuts as spacers will protect the skateboard wheel bearings from end loads. I had to use stacks of washers as spacers and this is not a stable solution as well as risking overloading the bearings.
Tomorrow's weather is another cloudburst warning from the DMI so I had better make what progress I can today despite today's light rain.
Click on any image for an enlargement.
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