Here's the first hexagon that I put together. I originally planned to build from the bottom up, but now I'm thinking it might make more sense to build from the top down. Fastening the strut ends is difficult to do high in the air.
My DW took an interest in the assembly and has been diagramming our progress. It should be noted that assembling this structure absolutely requires more than one person, since someone has to help hold and brace the pieces while they are being put in place.
I'm constructing small pieces of the dome a few struts at a time on the ground and then lifting them into place to limit the amount of work that needs to be done in the air. The outside of all of the straps is attached before the pieces go up so that they only need to be screwed from the inside.
This open hexagon is where the door will be eventually.
From the other side of the dome you can see the 2x4s that we used to prop up the pieces as we connected them in. At this point none of these are technically required anymore, since the dome can hold itself up, but we left them in place for greater stability (especially if we encounter very much wind) until we can finish the other side.
We had sustained winds to 40mph and gusts to 55mph the next day. The structure didn't move at all. Although I have faith in the strength of the final structure I was worried when I woke up this morning. Nice to see that even a portion like this is strong.
It's time to lift the other patch of the top of the dome up and fasten it in place.
First I added all of the struts to support the piece and everything on the sides which didn't directly connect to it. At this point the constructed portion was basically symetrical, except for the door and one dangling strut above it.
Two of us lifted the double hexagon into place on ladders while two others braced it with long 2x4s in the hubs. We then fastened the bottom ends as we were able to line them up. Finally, we added two struts at the top of the dome to connect it to the other side. At this point the only things left to add were the connecting struts on either side of the piece we had just added and the 5 central struts of the pentagon on top.
We had to push and pull the parts of the structure to make each connection line up properly. Sometimes this required bracing various points with 2x4s and sometimes it simply meant that someone heaved on it while it was fastened. Gravity made some of the portions sag, while the difficulty of maintaining perfect positioning of the base was responsible for other misalignments. We managed to get everything into place though, and each section we added gave further rigidity to the structure.
It got dark while we were putting these in place, and started to sprinkle a little bit.
We next went back and added the rest of the side struts, leaving only the open pentagon on top.
Here's a closeup of one of the hub connections, showing how everything is attached. The first screw is attached closer to the hub, at an angle. I actually insert the screw at a steep angle and then pry it back to tension the strap a bit. When the screw goes all the way in, it tensions the strap even more, taking all of the slack out of it and pulling the joint tightly together. The second screw is then placed further out to provide greater strength. This being cedar, the wood is quite soft, so two connections is a must. Also the second screw prevents the connection from rotating, adding more stability. As I mentioned above, these are 22 gauge straps, so they're a bit stiff to work with, but strong. My DW actually climbed up onto the first tier at one point when we were pushing the connections into place, and I can attest that the joints are better able to support weight than the struts themselves.
She's the one that said that I should include this closeup photo, but she didn't know that I was going to mention her climbing up on the structure.
Here's a picture of the first screw being put in. Note that the strap itself is bent out from the wood, so that the point of entry of the screw into the wood is farther away from the center than the hole in the strap itself. This is what pulls the strap tighter when the screw goes in.
We assembled the five spokes of the pentagon on the ground and then I carried it up the ladder and poked it through the hole to rest a bit off center on top. It took a bit of work to get all of the spokes butting up against all of the right hubs, but once they were in place everything fit perfectly and I was able to screw them all in without pushing or pulling on anything. This was a good thing because by this time the rain was picking up and bringing a bit of wind along with it.
We were all so wet and tired by the time we were done that we took everything inside and turned out the lights without even getting a picture of the finished dome. Here I am putting in the last screws.
Paul I am wanting to build a geodesic dome from wood and l am wondering about your hub connection.It appears that the straps were run through the PVC pipe and screwed to the 2x4 on each side. What inch of pipe did you use? Did you have any special angles on the 2x4's for the connection? What size is your dome? Do you have lenghts that you cut each piece?
We built a geodesic dome from polystyrene 30 yrs ago to live in and now I want a greenhouse. Thanks for any information that you can provide. Debbie
I'm seeing your post very late, as I don't visit here very often, but most of your questions are answered in Part 1, linked at the top. 3" pipe, varying angles and lengths per strut as listed in Part 1.