That's some of what I do when I'm not making knives... that's a 15mm thick steel plate with a 12mm (almost half inch) deep trench milled in it and some counter sunk holes and other goodies. I don't know exactly what it's for myself! I just made it according to the drawing. Always some serious pucker factor watching a 12mm carbide endmill from Ingersoll fly through the steel like it was butter. Noisy though. With my "little" Haas mill I cannot come close to reaching the speed these cutter are capable of ... still, I ain't complaining!