The Day I Overtightened a Collet and Cracked a Shank
I had been running gun drills for about three years when I thought I had the tool holding figured out. Tighten the collet until it feels solid, then give it another quarter turn for good measure. That was my system. It had worked fine on every machine I had run, so I did not question it. Then we got a new job running 8mm gun drills in 4340 steel, about 500mm deep. The first few holes went fine. Good chips, consistent surface finish, everything looked normal. Around the fifteenth hole, I heard a noise I had not heard before. It was not the usual cutting sound. It was a sharp crack, like a twig snapping, followed by the spindle stopping hard on a torque alarm. ...