Use a Screw Extractor
Did your bolt or screw break off when you tried to remove it? When a bolt or screw breaks off below the surface of the material it is threaded into, you can use a screw extractor to extract the remaining portion. A screw extractor is similar to a screw, but with a tapered, reversed thread. Once you know how to use an extractor properly, removing those broken screws will be a breeze. All you need are a few simple tool and you'll have the screw out in no time!
Steps
- Assemble your tools:
- 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.
- 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.
- A sharp, pointed centre punch made for punching into metal.
- A hammer.
- A T-shaped tap handle from a tap and die set.
- A padded work glove (optional).
- Cutting oil (optional).
- Locking (preferably) or slip joint pliers (optional).
- Centre punch the screw before drilling, to avoid having the bit wander.
- 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 center line 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.
- Insert the extractor: Put the tip of the extractor into 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.
- 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
- A penetrating oil may be effective in loosening corroded bolts. Alternatively, try acetone. It has been shown to be just as effective as penetrating oils.
- Use cutting oil on your drill bit. It will greatly increase the life of the bit, while speeding the drilling process 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 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.
- There are two more effective methods than using a screw extractor. 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 friction and it mustn't cool down.
- In some circumstances you may find you must drill the bolt out completely. In the event the bolt is attaching a component to a large enough item, you may be able to re-thread the resulting hole with a slightly larger bolt. However, this will not work on balanced components like engine flywheels.
- 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.
- Instead of using a screw extractor, use a sharp center punch near the perimeter of the broken part. Hold the center punch at a 45° angle and drive the broken part in a counterclockwise direction. Do at several spots on the bolt. If the broken part doesn't start to move fairly quickly then stop and use another method (above), Be careful that you do not splay the metal into the threads of the receiving hole, otherwise you risk making it more difficult to drill out.
- Grind a properly sized Allen key into a shallow taper, keeping the edges of the hexagon as sharp as possible. Drive this into the hole you drilled in the steps above and you may be lucky....or not.
Warnings
- 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.
- 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!
- 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.
- 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.
- 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).
Things You'll Need
- the drill motor
- suitable twist drills (bits)
- the extractors
- a centre punch
- a hammer (preferably made from softer brass)
- a tool for turning the bit
Related Articles
Sources and Citations
- OzDiyHandyman.com.au - How to Remove a Screw with a Broken or Stripped Head - Original source of content and images, shared with permission.
