hi , you just it to shave of steel.. it works like a plane..
there use to be machines made called metal planers or planer mills... i think in the 1700s they were invented in france or england..
in medival europe there was hand opperated ones used to shape sword blades later they go quite complicated,,, water powered and later steam..
its a hard sharp steel blade that scrapes away the soft unhardened steel..
now metal planes are no longer made but they are still in use, mills and surface grinders took their spot in industry..
many of the old metal planes in america and europe were sent to china and india in the 70s and 80s in china they are still a regular machine to see.
they are still in use but i dont know if there is any major producers of them still making an effort to premote newer updated machines of this type there is still makers but mostly for specialized tasks,, these use to be what rotary mills are today
with the hand plane after rough filing or grinding to make the surface smooth and ready for abrasive finishing and to remove hollow spots a metal plane is used. this is they way they got sword blades so smooth as grinding alone gives hollows
so basically its cutting away the steel. other types are used to cut the grooves in the blades ect.