I finally cracked the chatter on my boring bar after 3 weeks, and it was one dumb mistake on my part
Spent 3 weeks chasing chatter on a 4140 shaft at the shop in Wichita, tried every speed and feed combo, swapped inserts twice, then found out my tool holder was sticking out 4 inches too far from the turret, pulled it back and the chatter vanished on the first pass, has anyone else ever been that far down the wrong rabbit hole on a setup?