Building the walls

This can be quite an expensive part of the project if you don't have access to a plentiful supply of good and cheap wood. I think you need to build this part as sturdy and rigid as possible and do the BEST job you can. A nice dome can look terrible if it has a rickety old building underneath it. You can use 4" x 2" treated pine if you want the wood to last longer, or hardwood if you can get your hands on it. I priced a 2.4 meter length of treated pine at $22.80 at the local hardware store. This is too expensive for me so I approached my next door neighbor who happens to be a carpenter and he gave me lots of good left over stuff. Bless him again. That's got to be worth a carton of beer. The wall frame is supported on metal post supports concreted into the ground and clad in Color-bond fencing. The Color-bond really needs to be bought new as second hand stuff is rarely in good condition and this is the external part that everyone sees. You need to make sure that the diameter of the building including the cladding, does not exceed the outside perimeter of the dome ring. You must allow a small space for freedom of movement and a weather strip around the outside. The pictures I will add later will illustrate this better.

I built two more rings for the top and bottom of the walls. These need to have an external diameter less than the dome ring, as you need to allow for the profile for the Color-bond cladding. In my case the profile is 25mm. To the rings, attach 4" x 2" support joists underneath, using an off-cut to space them. The space is to allow for the 4" x 2" upright timbers that will support the whole structure.

I attached metal post supports to the horizontal timbers of the wall's bottom ring. This ring will support the entire observatory so spend some time leveling it and getting it right. Lay the ring on the ground and mark where to dig your holes. Remove the ring, dig the holes about 400 millimeters deep. Replace the ring then use a spirit level and straight edge or a string line and spirit level to level the whole ring over the holes. Mix concrete so that it is just workable. This makes it stronger. Too much water causes segregation and you end up with a weak concrete. With the post supports attached and hanging in the holes, fill them up with concrete and leave to set for a day or two.

If you have a look at the photos you will see that I have placed a brick under each upright support  with a little bit of cement. This is just to support the plywood ring temporarily until all the timber is joined and the tin goes on. You can leave them there of remove them later. After fitting the supports in the slots, secure each one with a bracket, making sure you hold a spirit level on the side to keep them vertical until secured. My brother and my neighbors came over to help lift and position the top ring onto the upright supports. Then it was just a matter of securing them with brackets again.

Tack some insulation sheeting around the outside of the walls before you put tin on. If you don't want your instruments cooked in summer, I suggest using silver side out. Before you get all excited and start screwing the tin on, position the tin all around, lightly tacking it in place with overlaps. This is not only to make sure you have enough, but to ensure that it lines up vertically all around before you screw it on permanently.

For the inside walls I used some Perspex sheeting salvaged from the scrap heap. Thin plywood would be a good alternative as well. If it doesn't meet the carpet perfectly, don't worry. Make sure it is neat along the top of the wall first. You can dress off any gaps on the bottom later with a flexible skirting board.

The door was built from recycled material also. Square tube steel frame for the door itself, double skinned with an old steel cabinet door lining the inside and colourbond for the outside. The whole thing is hinged on solid bar-in-pipe welded hinges, onto a steel angle iron frame, recessed into the timber.