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Monday 15th. Just in case anyone is still wondering why I rabbit on an on about this project:
A summary: The poor man's observatory dome? Poverty is relative. Think in terms of four 55" flat screen TVs. The same price as a 2.2m domed observatory in the range of popular, British, commercial observatories. Or the price of their 2.7m dome not including delivery.
I am "borrowing" a brand new, commercial, agricultural building as a donor. Which means I will soon have a cosmetically attractive, fully functional, 14' or 4.3m Ø dome. Green or white to taste.
It isn't quite that simple of course. Nothing ever is. This certainly isn't a turn key, oven-ready observatory. This dome "kit of parts" will require some manageable DIY but nothing too difficult.
Those with friends or contacts can get help in handling the considerable [160lbs] weight of the individual segments. A lot more friends will be required to lift the completed dome onto a low, observatory building. You may need to have a whip round for crane hire. Or rent a telescopic loader. Or borrow a tame farmer for an hour. High stacks of big bales in a barn are a sure sign of an experienced telescopic loader driver at work.
This would make an ideal project for an astro club or educational facility. WITHOUT any of the usual complications of building an observatory dome completely from scratch. Been there. Done that. Didn't like it.
Along with my 3-part, dome "kit" I have ordered an extra "roof" segment. To give me the perfectly matching, curved, GRP material I need to make the bi-parting shutters. Though an up-and-over shutter is equally valid for those who prefer them. I just don't trust one to ignore gravity in the hands of a forgetful old fart. Your mileage may vary.
A long rectangle will be cut out of the original top/roof segment of three. About a meter wide and just beyond the zenith will do nicely. The missing area will become the open, observation slit.
The bi-parting shutters will be cut from the "extra" roof segment I have ordered. These will require some curved arc, plywood ribs, for edge support and sealing. The plywood will normally be invisible and sheltered from the weather inside the GRP shutters.
The shutters will be mounted on standard, industrial drawer slides. The sort of thing they use on mechanic's tool cabinets. I can vouch for the fact that they work very well for at least three years. Without any maintenance on my part.
The resulting domed observatory must be mounted on rotation rollers on top of a suitable building. In my case it must be raised to see [the sky] over an absent neighbour's hedges. Where your ground level does offer unobstructed views. Then the dome can be mounted on low walls to personal taste and height. Though I'd avoid naked bricks as a likely heat trap. Or paint them white.
My rotation rollers will be solid plastic, industrial wheels used on mobile, industrial, workshop containers. These come in a range of sizes at fairly modest cost. I shall have twelve, nylon wheels in 160mm diameter. Eight of these have worked well on my present 3m dome. They come with free, pressed steel, forked housings to fix them to the top of your building. These rollers have needle roller bearings for low friction and a huge load capacity. 350kg each! Probably about the same weight as the completed dome.
Dome rotation is strictly in the hands of the dome builder. I shall have a simple, chain driven, bicycle crank. Rotating a 4" [100mm] loaded lever, friction drive roller on the underside of the dome's plywood, base ring. This has worked very well when the base ring was dry. It slips when the base ring is wet from rain leaking in through my plywood dome. GRP should keep the roller track, bone dry.
If you want auto-rotation or tracking to follow your telescope[s] movements then you are on your own. I missed that lesson.
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