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I tried 150mm [6"] spacers between the dome and the shutters and it was too much. 120mm was better and still ensured 60mm clearance for the slides at the top of the dome.
What I should do is cut some more plywood arcs to the new outer radius but the showers were becoming a real nuisance. Setting up the router trammel system would almost guarantee everything got very wet. I can always reduce the radius later to use the arcs for the base rings. Or even the slit ribs, without any loss of material. Making arcs longer in radius uses up no plywood.
I've stopped for lunch after much fussing with the shutters. Adding and removing packing and swinging a radius bar pivoted on the ground and up on blocks. The edges of the bare shutters just don't align with those of the slit cut-out on the dome whatever I try.
Why should a mark on a radius bar nicely match the dome radius when the bar is pivoted on the ground? But not when raised on blocks? Makes no sense when the dome is carefully levelled despite being raised off the sloping ground. It ought to need the base of the radius bar to be lifted to the skirt level. I even tensioned a ratchet strap across the dome skirt to confirm the expected level in the middle of the dome. Then stacked blocks to just go under the webbing.
It should measure 2.15m high from a line across the skirts. Which is the radius to which I have been cutting the arcs. If it is short on height then that explains the radius bar needing to be longer than theory dictates. It needed a mark on the radius bar at 237mm to follow the edge of the slit cut-out on the dome roof. Which is crackers!
Perhaps my understanding of spherical geometry is simply inadequate? I may not be following a great circle of know radius. I went to such trouble to make the cut-out and shutters straight edges. Only adding straight ribs to the shutters will confirm that the edges really are straight. The shutters lay flat on their edges when laid on their sides. How can they be anything else if the ribs follow the edges? Now stop messing about and get on with it! 🙄
The images show the 120mm spacers and the result of trimming five arcs to 227mm radius. It needs six arcs per shutter to have staggered joints on two laminations. The shutter is laid on its side on a reasonably flat area. I have no outside ground which is really flat. Though I could lay some plywood sheets on the ground and pack them up to be flat. Only if the sheets were flat to begin with. I have spaced the brackets at 40cm. The dome seams are bolted at 20cm centres. 20cm seems like overkill for the shutters but more brackets could always be added later.
I cut one more arc to 227cm radius and screwed them all together into a double thickness arc with staggered joints. I also trimmed the skewed bottom off the shutter. Its exact angle will remain a mystery until it is resting on the dome's plywood base ring. The completed shutter leans laterally and spherically. I made the shutters over long to ensure I could cover the slit with some to spare.
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