Hello. I am trying to bore a 1.8 in dia x 5.25 inches deep in a CNC lathe. The starting hole size is 1.75. The material is 3.5 inch round 4142. I am holding on to .55 inches of the part in jaws. I am using a 1.25 " shank Kennametal bore bar which is the biggest shank my machine can hold. I am using a triangular Kennametal insert with 321 corner. I have the bar extending 5.35 inches. What speeds and feeds would you fellow CNC'ers recommend? How deep of a cut per pass would be recommended? I have tried different speeds, feeds and depths but still get ugly chatter. Please help. I am very frustrated.