RE: Small, broken drills in aluminum...
Patrick, how thick is the aluminum? The bit is most likely not retrievable if buried in thick aluminum. I have tried heating the aluminum to expand it, then pick at the broken bit to work it loose. In the end the only way to salvage the project is to drive out the bit with a punch and re-think your attachment choices. I never try to cut virgin 2-56 threads in anything thick. I think #4 is as low as I'll go, even #6 can be dicey. Only the best cutting tools will do with this tiny hardware.