20' Geodesic Dome Greenhouse

Step 4: Make the struts

First, we took the boards and ripped them to be 3/4" x 3/4" x 4'.  This took several hours with two of us, but we also did twice as much as was necessary.  Stick with 25 boards.

Next we'll need to determine strut length.  We'll work with 4' boards and you can adjust if your doing a different size dome.  Add the length of hose in the middle of the vertices, the part that doesn't have any wood in it.  If you are doing a 6" hose, and have a 2" hole bit, each end of the strut is in 2", and that leaves you with 2 inches to add to your strut length.

So our 4" strut will actually be 4' 2" with the extra empty hose.

Go to the reverse dome calculator and enter 4.166 (4' 2") and choose strut C (the longest one.)  It will give you the length of all the 3 different strut lengths, and how many of each are necessary.  Now subtract those 2" of hose to arrive at your strut lengths.

A  3.521 = 3' 6 1/4"   - 2" = 3' 4 1/4"
B 4.067 = 4' 13/16"  - 2" = 3 10 13/16"
C 4.166 = 4' 2"           -2" = 4"

As the chart says, you need 30 of A, 40 of B, and 50 of C.

The number of struts will always be the same for a 3v 3/8 dome, the only difference is length.  So if you make a smaller dome, you'll use the same number of struts, they will all just be shorter.

I chose for longest one to be 4' because that was the length of the boards I bought.  As you can see, only strut length A had very much waste, and I was able to make some of those out of boards that had ends break off while ripping them.

Make sure to clearly mark the different lengths, this will save you later!

The following could be eliminated by using home fabricated vertices that can take square struts.

Next we have to dowel off the ends of all the struts.

First use the drill press to round the ends of the struts.  Be careful, the stick will be wobbly, and the drill bit will hurt if you get yourself!

After that you have to trim of the corners that are still on the struts.  We used the chop saw in a way that is probably not recommended by the manufacturer.  If you're doing this, be careful!
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KEUrban2 years ago
Pretty scary rounding the ends of the struts... Have you ever seen rotary tenon cutters like this?

http://www.rockler.com/product.cfm?page=11459&rrt=1