Got some boards here
and some aluminum
That came from midweststeelsupply.com, which had the lowest prices of any of the US places online or local I investigated… in the case of the 10 by 20 cm panels, literally about a factor of 7 smaller than what couple of other places were charging. (For five pieces. There are only four in the picture for some reason but I did get five. They were all much closer in price for single quantities, but a couple of them didn’t give you any discount for more than one.) Altogether including shipping this cost me about $47. I could only specify to the nearest 1/8" and they quoted tolerances of -0 +1/8". For the 10 cm dimension which is close to 3 15/16" I ordered 3 7/8" figuring I’d rather they were a little narrow than a lot wide. Everything seems to be within about 1/16" of the dimension I ordered, or just slightly over that; I measured one of the small pieces at 99 by 200 mm. I don’t know if the scratching you see is worse than what you should normally expect or not but for now I think I’m okay with the quality here.