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The glass fibre and resin I ordered should be delivered to a local parcel pick-up point today.
EDIT: I collected the parcel. The only problem is the small size of the laminating brushes. The largest they do is 16mm. I ordered 10mm by default without checking the size.
This was the only image worth sharing from late this afternoon. The seeing was poor.
I have been experimenting with the gaps between the slit ribs and slit cut-out. There is still considerable flexibility in the dome. Pulling the doorway supporting posts together lifts the top of the dome.
This gives me options before I start glassing over the rib/slit joint. I can adjust the tension between the posts using a ratchet strap around them. Just as I have done from the beginning. The cut-out was bound to weaken the dome. So I used posts, stuck in the ground, to fix the location of the top edges of the open doorway. I couldn't use the supplied, arched steel, reinforcing tube. Because it would have to literally pass though the slit ribs. An oversized hole could be plugged later but I hit my head on that arched tube enough times to need aversion therapy.
The shutters, together with the slit ribs are becoming very heavy. I am wondering if I should use jacks to lift two supporting posts under the tops of the slit ribs. I have one fixed post supporting a cross bar at the zenith but it gives me no adjustment. This post supports only the slit ribs.
The shutter ribs have 50mm packing pieces to lift them clear of the top of the dome. Not an ideal situation. The dome is a unknown variable unless stiffened or relieved of the weight it is supporting. The thick, zenith board will help to distribute the loads but is fixed only to the slit ribs. The shutter's top boards are, in turn, supported by the zenith board via the heavy duty drawer slides.
If I were to remove the central support post then all the weight falls on the top of the dome. I need to relieve that weight until the added glass fibre can do its job. I could even over-compensate slightly for sag.
This new glass fibre will ensure that the slit ribs become an integral part of the GRP dome. Providing the missing rigidity only once it fully hardens. Until then, the dome must be treated as a flexible mould for the additional fibreglass. Far more of a deformable balloon than a rigid structure.
There is really no point in glassing over a badly deformed dome. Similarly, if I remove the support too soon then the fresh glass fibre may delaminate or even tear. Which is why I am now going to glass the slit ribs to the dome inside and out. Allowing the slit ribs to form a reinforcing flange. It might be an idea to glass in the zenith board. This would provide vital depth. Stiffness being the square of the depth. As well as the glass fibre sealing the zenith board against wind blown rain.
I could use screw jacks with two, supporting posts. Each directly fixed to the slit ribs with perforated roofing plates. This would give me fine adjustment of the individual, slit rib heights. I can use a level across the ribs to ensure they really are level. If they are not, then the supported shutters will become uneven. Perhaps not sealing well against the slit ribs.
The slit ribs are rigidly spaced with 2x4s. The slit cut-out gives a clear indication of dome flexibility. The gaps on either side ought to be parallel. They are now wider at the bottom. So are a clear indicator that the sides need to be pulled back in.
EDIT: Pulling in the sides of the doorway was easy The gaps are now tight and parallel all the way. I fitted two upright posts with screw jacks. The slit rib crossbar is now level and easily height adjustable..
From the very start I have ensured the dome skirt is level and has remained so. This gives me a fixed geometric base or reference from which to measure my plywood additions. Without involving unnecessary guesswork. One can but hope that the skirt edge was cut accurately straight and level during manufacture. Though I have only myself to blame if my additions are not accurate.
As an animal shelter the dome would be placed directly on the ground. Which might be anything from a rough field to a perfectly finished, slab of concrete. If the latter, then it ought to sit nicely. Without any ugly gaps around the edges.
That said, this is not a precision moulding. It is not a fuel tank for a rocket. Its origins lie with agricultural, GRP, silo and animal shelter manufacture. I saw the opportunity to build a much larger than average, observatory dome. At a small fraction of the price of a much smaller, but highly finished, fully functional, turn-key, commercial product.
A fully functional, weatherproof housing for my long refractors needed to be affordable. There is no commercial, dome option remotely within my budget. Not by many times my intended budget.
So I am making one for myself from a donor, calf-rearing shelter. If you should feel the desperate need to copy me then do make yours white. They are available from the same source. Green is all but invisible in our landscape but absorbs the sun's heat. This can be mitigated but is not ideal for astronomical use. The small, extra price I am willing to pay for being allowed to erect this thing so visibly in our rural garden.
Large, round objects are as rare as UFOs in the rural landscape. Had I chosen white it would have been highly visible from half a mile away. It is just possible that a driver would become fixated on the huge white blob and crash! I know from personal experience how well a 2m Ø parabolic dish stands out against the dark trees behind it. A white dome, more than twice the size, would stand out like a beacon from afar!
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