If they were able to do it in ww2 then you can do it too. Multiply your diameter by .003 or .03% and get rid of chatter by slowing down your rpms and you can go 4x the diameter through steel using hss or carbide. Chip loads will make you faster not rpms. I have proof .03% work great when I cut through a 303 stainless bar .750 deep in one shot with a carbide 2 flute. Just remember the constant of .02% of you diameter for hard to cut conditions and 1% for very easy to cut conditions use this for any size tool and keep it under the recomendé sfm or lowere if it chatters. Get rid of chatter even if you have to spin that spindle by hand.