Thanks guys for your comments.
Well where do I start
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I guess what attracted me to the water tank idea was the shape, it looks like a real observatory and has a sealed floor (To keep out bugs).
Door area:
I knew that the tank would lose strength when it was cut. So I used 80 x 6mm aluminium flat bar for the door areas (in and out) and top of tank rim. I also used a 40 x 25 rhs steel tube for both sides of the door for added strength. For me this was enough strength and it kept the price down as well. My first cut (door area) was with a jigsaw it was not ideal for cutting this material very shaky. I made the door first while the tank strength was still was intact. The aluminium was bent by hand on a metal frame (kids climbing frame) not perfect but close. Rollers would be nicer!. The end part of curved sections was bent with a large hammer between 2 points (blocks). The door making went ok but to hang it I had some movement even with supports under the door. two persons would be better.
Roof:
Now the roof section had to be cut. Not liking the shaky cutting of the jig saw made me purchase a mini rotorazer saw for $50 a bit like a grinder with saw blades. This made cutting the top section very easy. I chose to cut along the seam plus 50mm giving me as much wall height as possible. This was a mistake for 2 reasons. Firstly I should have made the cut at 100mm from the seam, my scope is a little low because of the wall height. Lucky I have extra room on the puck and I will get bigger longer bolts to compensate. Secondly the roof section would have been less wobbly. When the side hoist lifts the roof aprox 20kg it flexes and 2 sides sag about 200mm. This is because of the thin rim on top my 50mm cut not 100mm this would have made it more stable. To compensate I use a second lifting rope placed over the lifting arm with a hook on the sagging sides to support the roof keeping it flush (level) all round. Its not hard but could have been avoided.
The top rim:
The aluminium flat bar was made in 2 sections for the top section where the roof sits on. It made attaching much easier. It has made a lot of difference in the wall strength. When the roof is off the wall has some flex but for me no extra strength was needed. I guess one could add another aluminium bar further down.
The lifting hoist:
The longer larger diameter hoist pipe is attached to the wall in 3 places with cut flatbar washers it seems to hold ok. And is around 600mm above the tank. The second shorter smaller diameter hoist pipe fits inside the other longer pipe and is resting on the top support bolt giving about 1m height for the metal cables to be attached to. The arm that extends out across the tank is made of aluminium pool cover roller pipe (second hand). It was drilled with a hole saw to fit over the smaller diameter pipe resting on a aluminium plate which was hole saw cut as well.
One thing I found frustrating is the coloured silicon does not stick well on the poly tank so I used a clear silicon ( Selleys all clear ).
More to come!.
Den
