Dome Prototype: Phase 2

Project begins: December 2019

My idea for the next project is a partial dome, sort of like an overturned satellite dish. I needed something for the garden to diffuse sunlight that was burning the vegetables during summer. After Project Sunburn failed to do this, I knew that I needed something far sturdier for a shade structure. Here is a rendering that I put together with Blender with what I had in mind.

dome penta

The all wooden construction of the prototype turned out to be much too fragile to support the weight of the dome and survive the weather. This was likely due to the use of 1x1/2 strips with glue and screws, which evidently is woefully inadequate for the structural support that domes require. The weakest points were the hubs where panel corners connected. Therefore, I designed a hub jig from which to fabricate steel joints, then connect the hubs with 2x3 struts. The horizontal angles are all 120 to allow formation of hexagonal shapes. The vertical angle is 15 to allow for a 2V frequency. This allows fewer hub joints but forms a blockier-appearing dome.

Dome hub first attempt

This is the first hub joint fabricated. Turned out to be extremely sturdy, allowing me to stand on the top of the joint without collapsing.

home hub completed prototype

There were several problems with this design. The first and most fatal to the design was the 120 angles. I mistakenly assumed that 120 made sense for what appeared to be interlocking hexagons. The truth is that this dome design consists of interlocking pentagons, which didn't appear obvious until I completed several hubs and nothing fit correctly. Therefore, I needed to change the hub horizontal angles to 108 with two 126 angles. This meant cutting all of the
120 hubs apart to reuse in the updated angle design. The updated hub hub jig allowed me to use the pieces salvaged from the previous design to use the correct angles.

updated hub angles

The second problem was the 2V frequency.

garden pentacenter mockup

I pretty much terminated Phase 2 at this point because of all the problems. I have some possible solutions, which I will apply for Phase 3 (in progress).