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As I struggled to adorn the folded refractor OTA and mounting with several tarpaulins in a gale, I longed for a proper observatory. Just imagine never having to protect the equipment from the elements ever again. Just imagine being able to go out there, open the shutter and start observing or imaging. The often large investment in all the tools of amateur astronomy is often wasted. Simply from the mental inertia involved in getting all the kit set up outside. If polar alignment and optical collimation are also required then the desire to brave the cold and the wind may easily become an insurmountable obstacle in the mind of the would/be enthusiast.
The number of hours spent observing is inversely proportional to the number of hours wasted carrying and setting up heavy equipment. Why not put all the observing and imaging tools in an observatory-shaped toolbox?
The number of hours spent observing is inversely proportional to the number of hours wasted carrying and setting up heavy equipment. Why not put all the observing and imaging tools in an observatory-shaped toolbox?
For the umpteenth time I looked at the Pulsar observatory dome website. 2.2m is definitely too cramped but what about the 2.7m? I measured the straight refractor tube and then the 40cm long dewshield and fumbled with the focuser under the tarpaulin. Another 20cm? Yikes! There would leave only a bare few inches clearance for the straight OTA. Even if I made a larger box to carry the dome I'd be struggling to move around the telescope. Probably banging my head on the underside of the supporting ring too. Bøøger!
Enter the turret, barrel, or half cylinder dome, stage right. [Again!] A quick google for virgin aluminium sheeting showed 1.25 x 2.25m sheeting is readily available for only an arm and a leg per sheet. Throw a little-used kidney into the budget and you can even have pristine, white coated aluminium. With a RAL number and a protective film to boot. Only £150 a sheet plus delivery! Gulp. You wouldn't want to get the design and build wrong, would you?
None of your struggling with wrinkly hemispherical metal gores for me. As a two-dimensional sheet refuses to accommodate the usual three. Four flat, but gently curved sheets and you can have a flawless, finished, half cylinder roof. Two more sheets and the up-and-over shutter is in place! It can be very slightly bigger than 3m per side with only one neat seam as an epaulet at each shoulder. The half moon ends would obviously need closing off too but those are flat and undemanding of fighting with spherical geometry.
The square shoulders and wide opening provide plenty of room and no problem looking out the wide slit even with a typically offset GEM. Plenty of headroom right out to the gable ends. Or for equipment storage where it won't be interfered with in normal use.
The square shoulders and wide opening provide plenty of room and no problem looking out the wide slit even with a typically offset GEM. Plenty of headroom right out to the gable ends. Or for equipment storage where it won't be interfered with in normal use.
Previously my thoughts have centered around gently bending, thin plywood. Or even hardboard over a traditional curved, laminated plywood form. Probably followed by smelly fiberglass and hours of sanding and then painting for long term waterproofing and coolth. But why bother with all that extra work and weight if the job only needs doing once? Aluminium sheet is very long lasting if it is thick enough to be largely self-supporting in cylindrical forms. Though I have my doubts that it would get away with only edge support.
DIY dome ribs are traditionally of softwood or laminated plywood. But, what about gently curved angle profile aluminium? It might be a bit pricey if an engineering company was paid to curve the angle to a gentle 1.5m radius though. Why not make an angle profile rolling machine?
Metal profile benders [more actually rollers] are fairly simple affairs of three rollers. Grooved or multiple rollers with suitable spacing would do. Crank the aluminium profile through the rollers and, hey presto! You have a curve depending almost entirely on the pressure applied by the middle roller. Pop rivet the angle at the dome shoulder and it becomes largely self supporting. A stripe of silicone will ensure a tight seal. Well, it's a plan, of sorts. Not wishing to reinvent the wheel, I had better ask an expert. Astro forums are full of them.
DIY dome ribs are traditionally of softwood or laminated plywood. But, what about gently curved angle profile aluminium? It might be a bit pricey if an engineering company was paid to curve the angle to a gentle 1.5m radius though. Why not make an angle profile rolling machine?
Metal profile benders [more actually rollers] are fairly simple affairs of three rollers. Grooved or multiple rollers with suitable spacing would do. Crank the aluminium profile through the rollers and, hey presto! You have a curve depending almost entirely on the pressure applied by the middle roller. Pop rivet the angle at the dome shoulder and it becomes largely self supporting. A stripe of silicone will ensure a tight seal. Well, it's a plan, of sorts. Not wishing to reinvent the wheel, I had better ask an expert. Astro forums are full of them.
The square-shouldered "Nissen hut" just needs to be rotated on the spot of course. A well tried arrangement of a plywood base ring. With numerous, small rubber wheels with journal bearings to carry the weight and provide low friction. All without demanding a perfect rolling surface like steel wheels or naked journal bearings would do. No expensive, curved steel ring required to act as a rail for grooved wheels. No noise, late at night, either.
There is also the possibility of using rolled, corrugated sheets for the roof and sides. Farm stock, like goats, pigs and perhaps sheep, rely on small "tunnel" shaped buildings. Miniature Nissen huts if you will. I am still unsure how small a radius can be obtained from stock. Nor whether they would be available in sun reflective white. Most seem to opt for farmer's grass green.
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