Almira Observatory

ALMIRA

OBSERVATORY

A suburban observatory in Worcestershire, UK based on a metal garden shed

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Construction 9 - Roof Skirts and Roof Lockdown Mechanism.

	In order to prevent the weather getting into the observatory, the roll off roof is surrounded by a skirt. The skirt is attached to the roof carriage on the front and sides, but has to attached to the shed frame at the back. This back section is hinged to allow the overhang of the roof to clear it when the roof is opened and to maximise the northern horizon.

	The skirts were made from lengths of 150 mm x 12 mm (6 inch x ½ inch) planking which were screwed to the roof carriage. (This picture was taken some time later in the build after the doors had been installed)	The front skirt was cut to provide a few millimetres clearance over the roof rails. The front skirt was screwed to the side skirts and the 50 mm x 50 mm (2 inch x 2 inch) strenghtener at the front of the roof carriage.


	The back skirt in the open position. The skirt is hinged on two brass hinges and a brass piano hinge in the middle. Note the eyes with string attached which stops the skirt from opening too far and allow it to be closed from the inside.	Here is the back skirt in the closed position from inside the finished observatory. The large wooden block screwed to the inside of the skirt supports the sagging back section of the roof carriage.




	With the roof open, I found that the light from some of my thoughtful neighbours' security lights reflected off the white edge strip on the roof and was surprisingly bright. I painted the roof edge strip matt black (see picture above) and this solved the problem. By the way, the structure that looks like a mini bird box is in fact a rain hood for the external temperature sensor on my weather station.

	For security and to stop the roof being blown away in a storm, it is important that that roof carriage is held very firmly against the main roof when in the closed position. This was achieved by using four heavy duty (12 mm) wire tensioners, called turnbuckles (Screwfix item #58991). I called these completed mechanisms 'lockdown bolts'.

	Each lockdown bolt consists of two M10 coach bolts, one going through the roof rail and the other through a large wooden block screwed and glued to the underside of the roof carriage. The eye on the turnbuckle is secured to the lower (roof rail) bolt. To lockdown the roof, the hook on the turnbuckle is simply hooked over the bolt connected to the roof carriage and the turnbuckle gently tightened. Once open, the turnbuckle simple hangs free from the lower bolt	In operation, I found that hook scrapped across the thread of the upper bolt whilst is was being tightened, making a right racket! In this later photograph you will see that mechanism has been modified with each bolt being fitted with a piece of plastic pond pump hose slipped over the bolt and held in place with two penny washers, these in turn held in place by two locking nuts. This made operation of the mechanism much easier and quieter.


	In use, one has to be careful not to over tightening the lockdown bolts as this could distort the roof carriage and/or split the wood blocks on the roof carriage. Once tightened, the roof is going absolutely nowhere! I later had to plane out a scoop of wood at the top of each roof rail to prevent my knuckles from being scrapped whilst tightening the turnbuckles. I also found that the hook tended to hit the thin metal roof when being hooked over the upper bolt. To prevent damage I glued a thin piece of MDF to the inside of the roof above each upper bolt. You can see this in the right hand photograph.

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Last updated - 13th July 2007