This is from "Welding tips and tricks" on u tube. Good vid of the tig torch work.
Jody is not a frame builder but obviously an ace welder, he has vids of all types of welding.
You have to smile at his "quality control" at the vids end!
and here is the framebuilder's site that gave him the mitered tubeset:
According to Mike Zanconato of Zanconato Cutom cycles ( thanks for all the help Mike!!) "Compared to 4130, this alloy has about half the carbon and chromium content that 4130 does, but it has about 3 times more manganese and also vanadium added. This allows the wall thickness to be reduced to 0.016" in some cases. "