Geodesic Domes

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	Control systems via observation then persuasion, never edict.


	If people know what you are trying to achieve, they will generally work with you.

First project was a requirement for a portable shade house for our orchids in a house we were renting. It had be light-weight, strong, reusable, easy to build and cheap. With a bit of research on the net, we found that geodesic domes filled all of these criterion. Initially they looked a bit tricky to design, but a visit to the desert domes web site took out all the difficulty. (Many thanks to Tara Landry for her calculator.)

Construction materials are wide and varied. Timber, metal or plastic. Solid, box or pipe.

If you are looking for maximum strength for weight, then pipe is the go. Material selection often comes down to what you are most comfortable with. Various web sites showed metal construction, but in the tropics I didn’t want the problem of corrosion protection of something that was going to be wet all the time, so I selected 20mm PVC electrical conduit. I figured it would be stiff enough as long as the struts didn’t get over 600mm in length. (determined through a bit of experimental bending.)

The length of each strut in Tara’s calculator is a center join to center join. Allowed an extra 40mm in length to the calculator values. Built a little gauge and used a conduit cutter to speed up the process. There are three different lengths in the 5/8 dome so coloured PVC tape was used to make sure they didn’t get mixed up. (Very handy at assembly time)

Experimented with flattening the ends of the conduit, so they could be bolted together and found that the plastic was pliable with just boiled water. (A paint stripping hot air gun was also suitable, but the hot water was easier.) The number of ends that had to be flattened, meant it was worth building a jig. Bit of scrap mild steel and a hinge did the trick. Setup to squash the end 40mm of pipe. Put six ends at a time in the hot water and then flattened them one at a time in the jig. Held the jig down for 10 seconds to allow the conduit to cool. Re-boiled the water and then did the next six. It was also important to keep the flattened ends in the same plane, so a smaller plane clamp was used when the second end was being flattened.

There are three different lengths to build the 3V dome. The plastic pipe is fairly forgiving, but it is better to get the distance between the holes as accurate as possible. Marking out every length accurately would have been a real pain. This meant building some drilling jigs. They made the job very quick. (see the photo gallery)

Assembly doesn’t take too long. For the joins, used 6x40mm stainless steel bolts for the 6 way joints and 6x35mm for the 4 and 5 way joints. On the plastic pipes washers are a must. Start at the bottom and build layer at a time. The pipes will have an angle of offset as they join. Put the joints together loosely at the start and then tighten up once you have the next row in place. There is enough flex in the pipes to allow for a bit of bend. Use a hair dryer or paint stripper to run over the joints once they are tightened up. Just heat them enough to take the stress out. Don’t melt them. The structure will be fairly flexible until all the struts are in place. Then it is amazing how stiff it becomes.


	The door was designed and built on the fly. Just took out one of the hexagons for an entrance and put a few cross bars to keep it stiff. These bits had fairly sharp angles on the end, a vice and heat gun was used in preference to do the shaping.

The shade cloth is cut out in 5 triangles. Measure the dome and allow some extra for the seam. Ours was sewn on a home machine with some sail thread from our local sail maker. It is a bit awkward to sew because shade cloth is so dam slippery. We used 6 meters of a 3.6 wide meter roll. Used a rule and some chalk to mark out before cutting. If you jiggle your triangles around you be able to use less shade cloth.


	What did it cost? Shop around and get the best price on conduit. Mine cost $90. Stainless steel bolts, nuts and washers $47. Shade cloth was about $100 worth. Fun building? Immeasurable.

	If you use a 6V dome the biggest you can go with plastic conduit is 2.8 meter radius. Still makes a comfortable shade house for plants.