Originally Posted by Geof  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. |
Thanks for the confirmation Geof. We learned this after a suggestion and a bunch of trial and error. With the help of masters like yourself, and others in this thread (thanks Bluesman) we hope to correct problems with less trial and error and more advice from experts like yourself.