Originally Posted by STS_John  We have had problems with carbide drills chipping in mill applications (drills under 1/4 diameter). We tried pecking cycles dry (no coolant) and pecking cycles with flood coolant (pecking with coolant). We got our best results cutting dry with no peck. We would appreciate hearing any better ways. |
I think you have found the better way. The chipping you encountered with coolant was almost certainly due to thermal shock. The best result obtained by not pecking is probably because 4340 can work harden; when you peck everytime the drill re-enters the cut it has to break through the work hardened surface from the previous peck. Driving full depth in one pass means the drill never encounters a work hardened surface.