Cool, your build plates came out really nice.
I machined one, and it came out functional, but looks like crap compared to yours because I had a lot of deflection while I was milling and have much less precise angles.
Also, I sandblasted the surface, which I shouldn’t have. A milled finish with a little 300 grit is just about right for printing. Sandblasting generates too rough of a surface that makes it difficult (or impossible) to remove a part without damaging it.