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Sunday 9th 45-60F and climbing. Bright sunshine with a little, high, bobbly cloud. It reached 70F for several hours in the afternoon.
Picturing the complex geometry of spherical shutters in my mind is a struggle. The inner edges are level [laterally horizontal] and follow a straight line in plan view. The outer edges are lower and leaning downwards towards the dome. Though still straight. The shutters rest flat on the ground on either edge.
I think the outer shutter rib is going to be quite a problem. Both in shape and angle to the shutter. The rib needs to be vertical. Fortunately I can bend the steel brackets to match whatever angle is required. Provided, of course, that I can cut the ribs to size. Both in radius and depth.
The other interesting part of the puzzle is that the shutters move horizontally on their slides. So the outer [plywood] ribs approach the dome surface as they close. Suggesting that they will be quite shallow in depth. They need to seal flat against the slit ribs like any other bi-parting shutters.
First, I need to fit one, inner rib [upright] and its shutter, in the closed position. To be able to measure downwards on the outer edge to the dome's surface. Just reaching this area higher on the dome is a struggle. I can use my mitre gauge to asses the angles required between the shutter and the outer rib. Whether this is possible without fixing the inner rib to the shutter remains to be seen. The whole lot will probably want to slide sideways off the dome! I have to keep clamping them with G-cramps.
I placed a vertical board in the centre of the dome to support the shutter rib. Unfortunately there were several factors denying me the ability to place the shutter on top. The arched steel reinforcing tube at the doorway prevents the rib from settling to the correct height. I'd have to cut a huge notch in the rib. Or remove the tube and support the doorway on made to measure trestles. Something which would give me the freedom to make and fit the slit ribs to the dome without hindrance.
This is the option I am taking now. It is obvious that I cannot proceed without removal of the arched tube. I have tried various geometries but the supports must be inside the dome. If it were outside it would have to be right out at the edges of the doorway. Otherwise the shutters would hit the supports when opened.
Vertical posts would be clamped to the dome using steel, angle brackets. Would this stop the posts from collapsing inwards as the weight of the dome falls on them? I am trying to come up with something which does not hinder access until the slit ribs can be installed to support the dome. A crossbar could be temporary. Provided I wear a hard hat.
The cross bar just needs to avoid intruding into the rib space. Which, as can be seen the image, places it rather low for elderly limbo dancers like myself. Which explains the fringe of hanging cords designed to remind me to duck.
The dome did not move when the weight fell on the angle iron supports. I'm afraid the inside of the dome is littered with offcuts of wood. Used for initial leverage and levelling of the dome. I really ought to tidy up!
I had a sudden insight into the outer shutter ribs. The shutters lie perfectly flat on the top of the dome before the ribs are added. So raising the shutter by Xcm, at the centre, will do exactly the same at the edges. I still don't know the radius required on the outer ribs. Though I could easily set up the shutter, on its centre edge, on the ground and measure it there. Provided the shutter is not distorted out of shape it will be exactly same as if it were in place on the dome. I just need to ensure the ground is flat.
A thunder storm is heading north from Holland. So I had to replace the shutters and tidy everything away.
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