A Garden Shed Observatory



Contributed by Don Dillinger

Having discovered the joys of CCD astronomy, I also discovered that by the time I had my scope and camera set up and well aligned, it was time for bed. Or the clouds had rolled in. Something had to be done!

Living in the Pacific Northwest, in a small suburban community, I needed a place to keep the scope safe, dry, and accessible; it also had to fit in with our garden and landscape, and be acceptable to the Neighborhood Association's aesthetic censor.

I decided against a dome, although tempted by the tried and true, ready-made units available, primarily because the appearance would clash with the surroundings, draw attention, and require a larger size than I could easily afford to provide enough working space for me, my computer table and scope.

A roll-off roof design based on a garden shed kit began to appeal to me. I lack experience and time for such projects, however, and despite some significant cost advantages, I figured I'd have to build it twice due to my own goofs, and then it would not be such a good deal after all. Besides, it would take me months to build it, even if we had unusually good weather, and I wanted immediate gratification.

I finally started calling local contractors, and found one that specialized in garden shed type buildings who was willing to experiment and help adapt a routine structure to a somewhat altered destiny. He was actually quite interested in the plan, and seemed to have a good time helping me work out the details.

The Design

The basic design is an 8x10 cedar shed with a pitched roof, which rolls on tracks onto 6x6 inch outriggers, extending 10ft from the building. The pier is a 5 foot concrete cylinder set in a 2' x 3' x 3' concrete deadman buried in the local clay. The scope is attached to the pier via a custom-built aluminum wedge, sitting on a steel plate at the top of the pier. The floor is completely isolated from the pier.

The most entertaining part of the design phase was the roof track design, for which I drew on a number of sources, deciding on a "track" style rather than a "channel" style. I was concerned that a wheel running in a channel carrying a 500 lb roof would come to a sudden halt if it encountered any debris in the channel, while an inverted "T" shaped track would shed water and leaves and twigs, and allow greater ease of movement. I drew up some sketches and went down to a local smithy, who advised me what materials he had readily available, and ended up with track made of stainless steel angle-iron, and wheels made from pulley wheels purchased at Eagle Hardware and welded to a 3/8" thick steel support plate 4" wide, which in turn was bolted onto the underside of the roof.

The top plate of the wall is a 2x4 rectangle, with the track bolted to it; the roof has a similar 2x4 rectangle on the underside, to which the wheel support plate is bolted. Suitable fascia board was added at the ends and sides to hide the track assembly; octagonal vents on each end of the roof, with a faux-stucco finish around, to match the stucco and vents on our home.

The roof is held down by 4 steel hasps, one at each interior corner, which are unlatched to roll off the roof. There are five wheels on each side of the roof, so arranged to allow the roof to overhang the end of the track by a foot or so, to extend the range of movement of the roof without adding to the length of outriggers, an important consideration from the aesthetic viewpoint.

2.5 inch conduit runs from an inside corner of the building, down into the deadman, up into the pier to the top, to allow for various cables to the scope.

Construction

Went smoothly, since I didn't have to do it myself! The only challenge for the crew was the roll-off roof, which they built by making the upper and lower plates, attaching the hardware, then putting it up on on the wall and blocking it with scrap wood while the roof was constructed on top of the whole thing.

Surprises/Regrets

The only surprise so far was when I attached the scope to the pier, expecting a completely immobile mount, and instead finding that the image seemed to chatter continuously when the drive motor ran! It turns out that the mount seemed to be too rigid, and failed to dampen the natural resonance vibrations of the fork arms. A little rubber padding between the mount and the pier solved the problem.

As for regrets, I think I would make the outriggers even longer, if I were to build this at another site; in the "off" position at my site, the roofline strategically blocks some streetlights, but at another site, I would want a foot or two longer tracks to allow the scope a lower horizon in that direction.

Don Dillinger
6121 76th DR SE
Snohomish, WA 98290

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