You have a ready source of material right there in Seattle and they will cut it to size. Check out On-Line Metals. The transceiver project has a 4 x 8 inch base plate I bought from them and the front and back are pieces of single sided copper PC Board. The support material is 1/2 inch aluminum angle stock (Home Depot). Interesting use of round aluminum pillars. The front and back are stabilized using 1/4 inch threaded aluminum spacers that were fitted inside of small diameter hollow aluminum tube I bought in a hobby shop. A dab of Gorilla Glue holds the spacers inside the tubing and it forms a rigid support structure.
The subject of mechanical construction is a good one and perhaps Bill would like to cover that in a future podcast. That said I do have a bench top 3 axis manual milling machine and a 3 axis CNC milling machine (that one cost me about $250K). The cost was not in the machine but the cost of sending my youngest son to WSU where he got an ME degree. He designed and built the machine for me.
Boeing Surplus (now gone) in Kent used to sell aluminum plate by the pound and a lot of my stock (now all gone) came from there. As a retired Boeing employee I used to get a discount.
And here is a slide show illustrating Pete's technique:
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