"Have you had anyone build this from machined aluminum other than wood? Obviously wood is the most economical solution for the average home builder but I have access to a machine shop ..."
Thanks for your interest.
The plans just became available two days ago so I don't think anyone has built anything yet except for me.
People have asked about aluminum and molded plastic ribs.
With metal ribs, I would be concerned about altering the balance, making the reflectors heavier on the bottom than with the wood. Because the reflectors are more or less balanced, they are easy to rotate and the force required to move them is very small. Aluminum is heavier than wood. I'd imagine that with the greater strength of aluminum, you could trim away most of the material where the big holes are and still have the strength while keeping the center of mass at the collector? I'd keep the 1/2" or so thickness since that spreads the contact area where the rib touches the reflector sheet and gives strength where the bolts attach. You could thread holes in the aluminum or plastic and do away with the cross dowels. What about galvanic corrosion between aluminum ribs and the copper collectors?
I'd love to have a source that I could send people to for the ribs. There is no doubt that these are the most time consuming part of the project. The rest is relatively straightforward.
For those of us without a machine shop, wood is the most economical material and with a bit of time on a band saw and a router, you can make quite serviceable ribs. Using MDO (weather sealed sign material) all but eliminates the finishing step for wood. Perhaps you could make one prototype reflector this way first to study the way it's put together and how it behaves and then work on improvements before you make the whole array?