As someone who worked in valve manufacturing, this guy is finishing the seat of a gate valve, the seat is a v shaped wedge that gets jammed into the body of the valve to seal. While it looks absolutely shit what he is doing, I suspect they have made many parts this way. OSHA has made CNC milling just about the only reasonable way to machine these seats, and milling these faces is still much nicer that whatever the ---- surface finishes a giant counterweight like this gets on a shit old lathe.