THE DOME

 

I spent quite a bit of time sourcing foam sheeting for the dome at the right price. I was quoted $65 for a single sheet of 2.4meter x 1.2meter x 50mm from one joint but they would deliver any quantity anywhere in Brisbane for $50, yeah right. It ended up costing me $22 a sheet and I picked them up with my trusty astro trailer. I converted the original plans to metric and reduced the size by 30% as I could really only fit a 2 meter obs in the back yard.

I needed to build the dome first to ensure it would work and to see what the final diameter of the dome would be. There was some confusion as the plans show you building hexagons and polygons to construct the dome however the plans do not show the triangles for the hexagons as equilateral triangles as true hexagon triangles should be. This had me stumped for a while but as the whole show is curved in the end, the sides of the triangles need to be longer to afford the required curve.

NiChrome wire is used to cut the foam and is available from JayCar and Dick Smiths in 4meter lengths which is plenty. Dick Smiths wire is thicker than the JayCar wire so requires more go juice to get it hot enough to cut but itís Ĺ the price. The jaycar is the one to use, itís thinner uses less juice and has a better cut.

I built a cutting bench on top of the patio table, with a guillotine cutter on the end and it worked fine. I had to run 24v to the cutting wire to get it hot enough over the 1.3meter cut distance. I ended up with 110 triangles and marked each one with a P (pentagon) or an H (Hexagon) with an arrow pointing to the base of the triangle.To cut the tapers on each edge of the triangles I screwed together a wooden L bracket reinforced with a $2 metal L bracket from Bunnings, and attached it to the side of the cutting bench. I drilled a hole in the bench and ran a cutting wire through the hole via a metal collet to the L bracket and set the angles for the tapers.

I found it a lot easier to build the dome upside down and flip it once complete and the glue had dried, it wasnít that big and was very light. Thank god for a couple of sunny days at the end of the build which dried the glue in a hurry and made the final build a lot easier.

I used Bostik ĎNo More Nailsí to glue the triangles into shapes and the shapes into the dome and I used a lot of it J , around 24 tubes. It filled any gaps quite well but while the weather was cold and wet, it could take up to 3 days for the glue to go off while gluing the triangles into shapes. But finally we had a dome and it measured about 2.1 meters on the outside diameter and about 1.2meters tall.

In retrospect, I should have used selleys no nails, this product does not eat the foam, is waterproof and stronger than the bostik product. However it is very sticky so attaches to everything and requires a mineral turps clean up, which definitely eats foam. As the build takes so long, Iíd go the selleys product next time.

Once completed and the shutter track and ring was fitted, I rendered the dome with Acrylic render. I used Taulbmans ArmaWall Roll On Render and Top Coat Texture. I got these off ebay for around $100. The Acrylic render gives a tough hard finish yet is elastic.

 

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