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I have had my order confirmed for a 4.3m Ø [13' diameter] grass green, domed, calf rearing "hutch" in GRP. Plus an extra top panel. The latter will provide the matching material for the bi-parting shutters for the observation slit. Delivery is expected in four to six weeks.
I had better get on with expanding the observatory building when the weather allows. Ice and light snow, followed by day long rain, have made everything very wet. Probably to my advantage because it softens the self-compacting gravel. Which has to be excavated in a ring for the twelve, concrete, foundation blocks.
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There will be an interesting exercise in fitting the shutters with their preformed, spherical curvature. I'm hoping to use straight, heavy duty drawer slides again. The shutters' own curvature will result in a much more streamlined arrangement than the traditional, flat, but vertically curved, "Palomar style" shutters.
Hopefully with much lower wind drag when closed, or open. My present [Palomar style] shutters have regularly been pushed closed from wind pressure on the outer ribs. Usually when the slit is at right angles to the wind. Early morning solar imaging is often accompanied by the prevailing, south-westerly breeze. I fitted siding, door bolts to stop the shutters from moving involuntarily. Spherical shutters will have much narrower, outer ribs.
One minor worry is the shutters having exactly the same curvature as the dome over their greater [vertical] length. They will, of course, be made [only] slightly over half half slit width. To meet in the middle but will open fully to expose the observation slit as normal.
The usual arrangement is that the centre, shutter ribs stop dead against the dome [slit] ribs when open. The shutter centre ribs stop against each other when they are fully closed. A weather strip, applied to only one shutter, overlaps both shutters when closed. To seal any, slight gap.
Will there be sufficient flex in this much narrower format [say 50cm wide?] to allow the shutters to clear the dome? Or will they drag somewhere as they close? They will, after all, have exactly the same radius as the dome over which they will have to fit. Opening the shutters will push them safely away from the dome. While closing brings them closer.
Another "interesting" detail is that the shutter ribs will be at an odd, but constantly changing angle to the shutters themselves. Which will mean complex curvature will have to be applied to the outer edges where they meet.
Assuming the tops of the shutters are tightly constrained, the shutters may prove to be too stiff for ample clearance at the bottom. Then I shall have to use the original, semicircular, animal "doorway" cut-out. To absorb any, inward projecting curvature. A waterproof shelf will then have to be provided to shed the rain outwards, clear of the dome's base ring.
This rain shelf could be attached to the bottom of both shutters. Much like a weather bar on a common, outside, house door. Tilting the shutters upwards and outwards at the bottom [as if hinged at the top slides] would reduce clearance issues at the bottom.
Though I don't foresee any major problems. The vertical shutter ribs will close against the dome's [slit] ribs. In exactly the same way as a normal pair would do. The depth of the ribs will dictate the clearance. It is fortunate that I intend to complete the shutters with the dome safely down on the ground. To be lifted onto its rotation rollers only after it is finished and has been fully tested.
It would be useful to find a rigid plastic ball. One which could be cut up. To confirm the geometric relationship between spherical shutters cut from the dome material itself. Perhaps I am overthinking the problem. The relative "narrowness" of the shutters should minimize any interference issues.
EDIT: After all that discussion of potential problems: The image [above right] shows that there should be no interference problems as a result of the matching radii. It just requires careful sizing and positioning of the shutters to meet the drawer slides at top and bottom. Plus, very careful attention to the [plywood] shutter and dome ribs.
The shutters must be made longer than the distance over the dome's surface. Because they have to cover slightly more than the circumference of the dome beneath them. This much is obvious from the drawing. The ends [top and bottom] must be treated as if they had a larger radius than the dome. The actual shape of the shutters between the slides is meaningless. It could even be a square shape or any other. The difference in radius at the ends, compared to the dome, is automatically increased at the circumference. By a factor of slightly over three. [Pi = 3.142 or roughly 22/7]
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