Profanity is often the first impulse after breaking a bolt. I completely understand. After that, try these ideas.
- If it’s not a situation that requires immediate repairs, soak the area for 24 hours with Kroil, PB Blaster or any good penetrating oil formulated to “bust rust.” Bolts that resist initial attempts to remove are often magically easier to remove when allowed to soak overnight.
- Left-handed drill bits are always a good first approach to remove broken bolts. They simultaneously drill a hole, create heat and apply reverse torque to the broken bolt. In many cases left-handed drill bits spin out broken bolts less than 1/2" in diameter.
- If the left-handed drill bit drills through the bolt without spinning it out, use a bolt extractor in the hole drilled by the left-handed drill bit. Bolt extractors are tapered, high-carbon steel bits with aggressive left-handed threads on their exterior surface. Screw them counterclockwise into the hole in the broken bolt and apply torque once they lock up in the hole. Firmly tap the butt of the extractor with a hammer while twisting it with a wrench to help jar things loose.
Remember to be gentle. Breaking a hardened-steel extractor inside a bolt justifies an even higher level of profanity than the “snap” of the original bolt breaking. Options include a hammer and small sharp punch to shatter the brittle extractor, or a dental bit in a Dremel tool to drill out the extractor. - If your first attempts fail, add heat from an oxy/acetylene torch. Carefully heat the area around the broken bolt. With a little bit of luck the surrounding metal will expand at a different rate than the broken bolt.
Reapply penetrating oil to cool and lubricate the threads after heating. Try again to remove the bolt with a left-handed drill bit or bolt extractor. - Broken bolts larger than 5/8" in diameter can sometimes be coerced from their casting with a very sharp cold chisel or centerpunch, if they are broken close enough to the surrounding surface.
Position the tip of the chisel or punch on the outside edge of the broken surface and carefully tap counter-clockwise. The repeated impacts of tapping can be surprisingly effective in rotating bolts out of their holes. - Another option for large bolts broken flush with the surface is to weld a nut onto them. It’s a challenge, but carefully weld through the center of the nut to the top of the broken bolt.
Reapply penetrating oil to cool the heated metal and relubricate the threads. Then you can use a wrench to turn out the bolt.
