The frame was built in two parts. Essentially it is part TIG welded aluminum tubing and part sand cast aluminum. My reasons for doing it this way was to have the strength, serviceability and appearance that I was going for while at the same time keeping overall cost down. That said, the result was fairly heavy thanks to the sand-cast portion. The production version will probably be some combination of stamped and stock aluminum parts TIG welded together in a jig.
The sand casting was actually two halves that were welded together. Not a single piece as shown here.
Because I am a horrible TIG welder, I enlisted the help of my friend Brian at Alloy Weld Works in the Inland Empire. When taking on these big, multi-component projects. I definitely recommend building a strong network of people willing to help. I for one wouldn't have finished the project in the required time without the help of some good friends. For more information on building your network check out the book: Tribes by Seth Godin.