I was a machinist at a CAT dealer for my last 15 years of working. They NEVER had us work on removing a broken bolt until they broke a drill bit, easy out or a tap in the hole! A carbide burr bit is the best way to remove these with out enlarging the hole any more the needed. It has to come out to repair the hole with a heilcoil or thread sleeve if the hole gets to large. Jerry's right, keep the welder away from it!
