Enthusiasm for getting a bolt tight enough and an unforgiving environment conspire to cause bolts to break off at the most inopportune times. If you are lucky enough to have some of the bolt above the surface, vise grips will often solve the problem. If it breaks flush, it is time to break out the power tools.
Use the center punch and hammer to make an impression as close to the center of the bolt as possible. This will allow your drill to bite without wandering.
Chuck the drill into the drill motor and carefully center the tip of the bit in the impression left by the center punch. Drill slowly, keeping the drill parallel to the shaft of the bolt. You do not want to wander and damage the surrounding threads. Drill at least 2/3 of the length of the bolt.
Insert the screw extractor in the hole you have just drilled. Some types require that you tap them with a hammer. Using a wrench, turn the extractor counterclockwise to remove the bolt.
