I have a 2.175" bore to make 6" deep in 4130 hardened to 22 rockwell. I am using a kennametal 1" diameter boring bar that is 12" OAL and I have around 8" hanging out of my tool turret. I have tried between 300-675 sfm at .01-.015"ipr. but I keep getting a diamond pattern rough chatter. can anyone offer any input? thanks