25.03.2021 Top ring rethink.

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 Thursday 25th 39-52F, thick mist and overcast. Sunshine soon burned through.

A final [shorter] post was added at front right [SE] to the abbreviated post over the intended, new doorway. Some trimming was required. Then I shortened the cross brace to fit the SE octagon post. To tie it all together. It all helps!

This area will form a protective overhang for the new, inset door. Which means a canopy of some sort is needed. To stop rain running down my neck from above. As always occurred with rain dripping constantly from the veranda. As I paused to open or close the observatory door.

I now have a much better idea of the diameter of the new building. So the plywood, template arcs I made for checking the foundation block positions can be re-cut. To form a larger radius. The templates were always intended to be used on the new building's top ring. Or the dome's base ring. Nothing is wasted. Once I have cut them to the larger radius I can place them on top of the building's top cross braces to double check the radius and alignment.

Or [rather] not! I had laid and screwed several template arcs on top of the building to check what would work. It was immediately obvious that there is no room for a full, plywood top ring. Not if I want to clad the building right up to and beyond the dome skirt for better weather proofing. 

I certainly want to avoid another "bare midriff." Where the large, dome rotation rollers are exposed in a deep, open gap. Between the top of the building and the dome skirt. Which they are at present. Resulting in the need for an extended, aluminium flashing and heavy rubber skirt to throw the rain outside the building. 

Plus an inner, upstanding, stiff, plastic skirt. To stop the wind and rain from blowing straight into and through the large gap. The rubber skirt was never very successful. Despite being the heaviest pond liner I could obtain. 1.2mm from distant memory. The sheer weight of the minimum [off-cut] roll I bought online was unbelievable! It was still too floppy [and noisy] as it flapped constantly in the wind!

Which now means I may  need to reinforce the top of the building in some other way. Rather than using a broad plywood ring. There still has to be proper support for the roller metalwork, of course. A plywood ring could be trimmed back to the cross brace flats only on its outer edge. While continuing to be a normal [curved] ring inside the building. That would allow room for the rollers and still provide a fair [flange] stiffening effect on the building's structure. The very top of the building must miss the dome's reinforcing rib around the inner skirt. Though the difference in radius obviously helps here.

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