Hi,

I must turn bar stock .250" steel 4140 down to .156". I was using Sandvik 55deg turn insert, grade PF4015, machine - swiss. For some reason surface finish looks bad, very bad. I was playing with speed from 4500RPM to 3000RPM at feedrate .001ipr and nothing. Maybe some smart head will put some light on me how to machine that material, I'm looking for feed, speed or maybe I have to buy different insert.
Thank You for any answer Guys