Dome build: New insights.

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The weight of the dome and overcoming its inertia is an important factor in its use. Rolling resistance is really quite low once it is moving. The deliberately large, dome supporting wheels have nicely low friction and massive overcapacity for any likely loading.

The thin, plywood, covering panels weigh 35kg in total. The shutters will probably add another 50kg. While I could load the dome to test the changes in effort to rotate it there doesn't seem much point. Because I really can't do much about it.

A sturdy handle, extending downwards to a more comfortable working height, will ease the pushing load as age takes its toll.  It is not normal to have to push anything above head height as I had to do with the ribs for the video.

I had a new insight into stiffening the octagon building. I had been dreading having to add heavy timbers to "triangulate" the structure. It might end up looking like an old water or windmill inside the octagon. Instead, I can add slender, stranded steel cables, tensioned by turnbuckles, to minimize any obstruction. This will also avoid having weak, load bearing, compound miter angles on the ends of struts. There are no very sensible joining angles in an octagon.

The freedom to simply run I-bolts through joists and join tensioned cables between them would be a vast improvement over lengthy 2x4s or larger timbers. Cables tension, while solid struts are usually working in compression. Both bracing systems are usually crossed, or arranged in series, to manage loads in both directions.

The cables can be run well above head height in dead [unused] spaces. Moreover the cables can be optimized for 45 x 45 x 90 degree triangles for maximum stiffness.  This will allow plenty of clearance for storage or carrying long instruments "upstairs" to the observatory. Being of such small diameter there is considerable freedom to site cables without interfering with the independent, pyramidal pier. Which, itself, almost fills the lower building. Making storage options, at ground level, rather limited.

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I also had a new idea about the upper tier of the dome covering panels. I'm tired of endlessly struggling with long, narrow and flimsy triangles of thin plywood and awkwardly angled struts. So why not use much thicker plywood? The heavier plywood becomes the structural material. The struts merely backup for joining and weather sealing the panels and minor stiffening.

Shaped plywood strips can be added to the slit frame to widen the supporting surfaces at these vital junctions. The upper struts of the dome skeleton will need to be thinned to match the increased thickness of the plywood. This can be done with the router using a trimming bit.

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