Actually it's pretty useless for modern machine tool teachers as well, round balls are way more perfect and precise with CNC than radius cutters, turning bearings is foolish, just buy the right size. 3mm is a very light cut for a rigid machine with decent tooling, carbide insert holders that fully encapsulate the rear of the insets took over decades ago this is all like 1950s basics. But let's face it he is just making content...
What liquid are you using to harden your tooling. Is it saltwater ??? What grade of tool steel are you using when you make your tooling. You have great videos