How To Use a Screw Extractor

When a bolt or screw breaks off below the surface of the material it is threaded into, there is no way to grab it with skip joint or locking pliers to remove the remaining portion of the screw or bolt. There is, however, quite a simple and very affordable solution. Buy a screw extractor, which is similar to a screw, but with a tapered, reversed thread. Here's how to use one.

Step 1  

Assemble your tools:  

1. A screw extractor about 2/3 the diameter of the screw you are extracting. You can buy screw extractors individually at a hardware store as needed, or you can buy a set of screw extractors at a hardware store or home improvement centre.
2. Drill bits suitable for drilling into hard metal (e.g., high speed steel, titanium coated, or tungsten carbide), to drill into the embedded screw. You will need a 1/8" bit to drill a pilot hole, and additional bits in 1/16" or 1/8" increments up to the size hole recommended in the instructions that come with the screw extractor—typically 1/8" smaller than the screw you are extracting.
3. A sharp, pointed centre punch made for punching into metal.
4. A hammer.
5. A T-shaped tap handle from a tap and die set.
6. A padded work glove (optional).
7. Cutting oil (optional).
8. Locking (preferably) or slip joint pliers (optional).

Step 2  

Centre punch the screw before drilling, to avoid having the bit wander.

Step 3  

Drill a 1/8" pilot hole in the centre of the broken screw. Using larger drill bits, in 1/16" or 1/8" increments, enlarge the hole until you reach the diameter recommended to accommodate the extractor. Be careful to keep your drill centred in the screw, drilling straight down the centreline toward the screw's point (see Warnings below). Drill to the depth recommended in the screw extractor's instructions, typically about 3 times the diameter of the largest bit used to make the finished hole. When using the extractor, you do not want the extractor's point to bottom out before the lands (threads) engage the sides of the hole securely.

Step 4  

Insert the extractor: Put the tip of the extractor ito the hole you drilled and tap it in with a hammer. Then, using a tap handle (the T-shaped handle that comes with a tap and die set), twist the extractor counter-clockwise into the pilot hole. As the screw extractor tightens itself into the broken screw, the screw will slowly start to turn. Using a padded work glove will enable you to get a firmer grip on the tap handle. If you use a tool to turn the extractor, take care to turn the extractor exactly around its axis; avoid any lateral pressure on the tool, as this may unseat the extractor.

Step 5  

Continue turning the screw extractor counter-clockwise until the broken screw is free. Or, once enough of screw emerges from the surface, you may switch to locking (preferably) or slip joint pliers to continue turning the screw to complete the removal; the pliers may give you more leverage.

Tips

• Using cutting oil will greatly increase the life of the drill, while speeding its cuts considerably.
• Using a reverse twist drill may free the broken bolt without the need for an extractor. The metal will heat up as you drill, and the force of the drill turning into the metal in can sometimes bind with enough force to break the offending bolt loose and turn it. On the other hand, if this does not work, you may be worse off than when you started.
• Using a penetrating oil like Liquid Wrench or PB Blaster may be effective in loosening corroded bolts.
• Sometimes using an acetylene torch to heat the bolt before using the extractor is effective. Make sure the material you are heating can withstand the temperatures without damage before trying this.
• In some circumstances you may find you must drill the bolt out completely. In the event the bolt is attaching a drillable component to a large enough item, you may be able to rethread the resulting hole with a slightly larger bolt. This will not work on balanced components like engine flywheels, however.
• Having had an extractor set for 40 years and NEVER extracted a bolt with it there are two more effective methods. Always apply penetrating oil and leave overnight. Heat if possible (a large soldering iron can apply spot heat).Strike the end of the bolt with a hammer to break corrosion.If any of the bolt shank is available grip it with good quality vice grips set as tight as possible. They will usually squash a flat on the bolt and give a good grip. Try turning both ways with a rapid back + forth movement increasing the amount turned as the bolt loosens. Once it is moving DON'T STOP - you have heated it with the friction and it mustn't cool down.
• If that fails drill as above and grind a suitable sized Allen key into a shallow taper, keeping the edges of the hexagon as sharp as posssible. Drive this into the hole and you may be lucky....or not.
• Instead of using a screw extractor, using a sharp centre punch at the circumference of the broken part in a counter clockwise direction and at a 45 degree angle will sometimes quite easily remove the broken part. Do at several spots on the bolt. This is more likely to work when you've broken the bolt whilst tightening it. If the broken part doesn't start to move fairly quickly then stop and use other methods above otherwise you risk peening the bolt into the thread or making it more difficult to drill out.

Warnings

• Always wear safety glasses when drilling, especially when drilling into metal. The screw extractor could shatter, the drill bit could break off, or the broken screw could fly out as you drill into it. Safety glasses could save you from losing an eye!
• Make sure the end of the bolt does not have a diagonal break, since this will make center-boring impossible without a drill press or guide assembly. IF the bolt is broken diagonally, you may be able to chip it flat with a center punch or roll pin punch, assuming it is not a grade 8 or higher alloy.
• Using an extractor or bit that is too large will damage the internal threads of the hole you are extracting the bolt from, making it unusable.
• Screw extractor bits are very hard, and very brittle, so it's possible that it could break off within the screw. Since the bit itself is hard, you won't be able to drill into it. You'll either have to forget about the screw, or look into electrical-discharge machining (which is expensive).
• Do not use pliers or a wrench to turn a small-diameter screw extractor; that can exert undesirable lateral forces. A tap handle is the correct tool, because it equally distributes the force.

Things You'll Need

• the drill motor
• suitable twist drills (bits)
• the extractors
• a centre punch
• a hammer
• a tool for turning the bit