Part of Lesson Plan: **Broken Bolt Extraction Methods Part 1 (updated) by Robert Thayer
Activity Overview / Details
Using a video camera projecting the image on a screen behind me (or simply demonstrating without a video image), I begin removing the broken bolt using a typical series of steps.
At this time, put on your safety glasses. Have any students in the front row/s put on safety glasses. If the drill is loud, have students put on ear protection. Point out the importance of having long hair tied back, and of securing or removing loose clothing or jewelry.
Method A: Vise Grips and Penetrating Oil
Explain that, if a piece of the bolt is sticking up above the surface, you can try to grab it with some vise grips, and twist it out that way. Try soaking it with some penetrating oil first.
Demonstrate using this method. Explain how to adjust vise grips properly, and how to orient the jaws in the right direction to increase mechanical advantage, but don't remove the bolt with this method. Save that for the "easy out" method.
(Note: I usually don't demonstrate the next two methods because many students in a real world setting will not have access to a torch or a welder to perform these techniques, and because the easy out mentioned in this lesson will usually work just as well.)
Method B: Vise Grips and Heat
Explain that by using a propane or acetylene torch to heat the bolt, then letting it cool, and then striking it with a hammer, it can sometimes make the "vise-grip" method work better.
Method C: Creating a New Head
Explain that you can weld an appropriate size washer on the broken piece, then weld an appropriate size nut onto the washer. After that, you can sometimes twist the bolt out with a wrench or socket.
Method D: Left Hand Drill Bits
If vise grips don't work, cut or grind off the piece that's sticking up (make it as flat as possible), or if it originally broke flush or below the surface, take out an appropriate size punch and ball peen hammer.
Demonstrate how to properly make a punch mark in the center of the bolt. Emphasize the importance of getting it as close as possible to the center. Tell them they can us a centering block, if possible.
Tighten a small (1/8th inch) diameter left hand drill bit into a (preferably) low speed, high torque drill. Demonstrate how to drill a pilot hole in the bolt. Emphasize the importance of putting the drill in reverse mode, and of going in straight. Use a centering block, if possible.
Explain that by using the next larger bit size, it will hopefully jam in the hole and twist the piece out, because the bits are left hand style.
Don't remove the bolt with this method. Save that for the easy out method.
Method E: Right Hand Drill Bits and Easy Outs
Using the hole that you made with the left hand bit, pick an appropriate size easy out, place it in a T-handle holder, tap the easy out with the hammer, and begin pushing and rotating counterclockwise to remove the broken piece. Explain that easy outs can be used with right hand drill bits, which are more common.
You may remove the piece at this stage, if possible.
Pass the piece around the classroom or the shop, so students can see the finished product.
Method F: Drilling Out the Piece Completely
I usually don't demonstrate this method, but it's a good time to mimic the actions of using incrementally larger bits to drill all the way through the broken piece until all that remains is the threads, at which time students can use a pick or a die to remove the threads and the remaining pieces. Emphasize the importance of not drilling into sensitive areas below the bolt, as well as the importance of drilling straight and through the center.
Also, point out the importance of not breaking off a drill bit or easy out in a bolt, because these objects are made of hardened steel and are very difficult to drill through. At that point, only a machine shop will have the special equipment necessary to remove the broken bit or easy out.
Take appropriate questions throughout the demonstration. Ask for questions at the conclusion of the demonstration.