The local scrap guy told me about another scrap yard on the north end of town. They do not have 8-inch channel, either. The local metal supplier tells me I need to order 25 feet of channel or no channel. So, it is time to figure out how to work with what I have.
The strongest and easiest to weld joints will be with 6000 series aluminum and 4000 series wire. The scrap guy tells me to assume all plate is 5000 series unless it is stamped different and 6000 series plate is very scarce. He showed me some 6000 series bar stock that is wide and flat. He also said the 6000 stuff is marked with alloy designation and temper. Several pieces of 6000 bar were bought for a reasonable price.
My welding settings are for the thickness of the metal and wire as based on the chart on the underside of the welder cover. Evidently there are many different ways to weld the same joint with completely different settings and the guy that put the info on the chart does not know which one I am using. Methods differ as to chamfering, welds on one or both sides, etc. The weld method with the lowest amps and wire feed might be best if heat distortion is a problem. Looking up the joint in a welding book and figuring out exactly what to do is recommended, as per chamfering, wire and gas feed, etc. I was hoping this project would not be intellectual. Maybe not. Some thinking is needed.
The annealing was cleaned off before I welded. The scrap guy said to clean all that off and oxidation too. He said the weld area should be bright and shiny throughout. He welds with MIG and a spool gun like I do. He uses a "stack of dimes" method. I do not know how to do this. Maybe there is something helpful on U-tube. Progress is being made.