Drilling a bolt out is very easy once you've cut/ ground it off as short as possible as long as 1: you use high-speed- steel drill bits and some type of oil to spray on the drill as it works in order to aid the metal cutting and cooling 2: Use a pointed punch to establish a small divet/crater in the center of the bolt to be drilled. This because the hole needs to be centered in the bolt. 3: Use a center-drill to start the hole. A small drill (1/16") bit can be used instead but center drills are cheap 4:Use multiple drill bit sizes for holes over .25". In this case I'd use 1/8, 1/4, 3/8 and final size. It may sound like a lot but once the first hole is drilled each subsequent pass is easier. This stepped approach spreads the workload out and allows the bits to work most efficiently. 5: Apply 'persuasive force' to the drill. Too much produces more heat. Let the bit work. A little smoke is OK, a lot means slow the drill speed and/ or less pressure. Blue chips mean you're toasting (annealed/ softened) your drill bit because it's too hot. 6: The largest drill size should be the 'tap drill' size. Smaller is better because too big means you're removing the threads in the hole. A couple of sizes smaller than tap-drill size (1/32") will leave enough of the bolt to crush and twist out in one piece.
