Yup, so true; when i am in the middle of making the flash hole, sometime i can feel the drill vibrate in the cut. Before i get to this place, the drill has been cutting smmooothly, but then i feel a vibration. At that point, i have either continued with the hole, or quit, and blow out the chips. I believe the reason it chatters is because there is no lube left, deeper into the hole. So stopping the process, blowing out the chips, and lubricating the hole, and starting anew, seems to be the best way to proceed, however i have experienced drill breaks at this restart. Other times, i stubbornly continue with the hole even though i feel the chatter; sometimes the drill punches through; other times it breaks.

Is there a technique to get lube into the hole without stopping, and removing the drill? I don't think there is, so i stop the cut, and remove the drill, clean out the chips, and relube. I try to do this before the work hardens, but i sure do break a lot of cobalt drills @ $3 each.

It is hard for me to know when to hesitate or proceed. Either way i break drills. Some drills are better than others, but i forget where i got the better ones so far. I just received new drills today, and tried one out. It cut the stainless like hot butter for about 1/8", but then started to chatter. I believe the steel hardened, and dulled the drill. I think i should have quit drilling sooner. It took 3 tries to finish the hole, which it did, but i am concerned, it won't be able to finish another. I have another drill that has made about 10 stainless ventliners, but i can't remember where i got it. Gee, i wish i had more like it.