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HOW-TO: Extract Stuck Screws
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HOW-TO: Extract Stuck Screws - March 1, 2006, 09:43 AM

Good article!


By Eric Murray, ericm@motorcycle.com
Imagine this: You're doing the first tune-up on your newly acquired bike. To get the oil filter cover off you need to remove three cross-head screws. You apply your trusty $1.89 K-Mart screwdriver to the first screw, and turn. The screwdriver slips out, so you try again, pushing harder. It slips out again, rounding the screw head a little. But you've got your trusty Vice-Grips in the tool box, so you clamp them onto the screwdriver's shank and really bear down on the screwdriver... this time stripping the head completely. Arrrgh! If you've worked on bikes at all you're probably nodding your head right about now, saying "yeah, I did something like that." Bikes today have higher-quality fasteners than they did 10 or 20 years ago, but still the various forces of entropy conspire to stick fasteners together a little stronger than they're designed for. Here's a guide to un-sticking stuck fasteners.

Impact Driver

The best remedy for a stuck screw, or one whose head has been stripped, is the impact screwdriver. An impact screwdriver is essentially two weights held apart by a spring. The bottom one holds screwdriver bits. You smack the top one with a hammer. In between them is a spring and a circular ramp. The ramp makes the bottom weight with the bit in it turn. So when you hit the top weight, giving it momentum, it compresses the spring and hits the ramp which turns the screwdriver-bit-holding bottom weight. The beauty of the design is that the force you impart to the impact wrench by hitting it with the hammer is forced into the screw, helping the screwdriver bit bite into the screw head (or what's left of it). Most impact drivers will let you set them for left and right turning, to loosen or tighten screws.

The high-quality, hardened screwdriver bits that come with impact drivers usually fit the screw heads much better than even the best screwdrivers, which helps all by itself. So at the first sign of a recalcitrant Phillips head screw, reach for the impact driver! Impact drivers are commonly available and cost about 15 (American) dollars - check your local auto supply store.

Some cheap impact drivers have (relatively) stiff springs which require a heavy hammer to compress and get the ramps to turn the bit. Be warned that the force needed may be damaging to the assembly in which the screw is stuck, or may be difficult to counteract on an awkward piece. These impact drivers can benefit from being disassembled and having the springs shortened slightly (no more than 25 percent) to reduce the spring preload. After this modification the driver will not require as much force but may not work quite as well on really badly buggered screws.

Screw Extractor

When an impact driver can't remove a screw, or there's not enough of the screw protruding to grip, the next step is to drill off the screw's head and then use a screw extractor.

A screw extractor is a very hard reverse-thread bit. You drill a hole into the screw, then carefully tap the proper extractor (which has a smaller initial diameter than the hole, and quickly flares out) into the hole, and use it to twist out what is left of the screw. The reverse flutes on the extractor cause it to bite harder into the metal of the screw as you put more force on it. Screw extractor bits are made of very hard metal, so they are very brittle. It is very easy to break one off inside the screw. When that happens you are screwed (sorry for the pun)- the extractor metal is harder than any drill bit, so you can't drill it out. The only recourse will be EDM (see below). To turn the extractor you should use a tap handle
commonly used to turn threading taps. The screw extractor has a square end to fit into the tap handle. Using a regular wrench to turn the extractor is almost guaranteed to break it.

You should be very careful when drilling the hole in the screw. Obviously you don't want to drill into the material surrounding the screw, so be careful to line up the drill in the center of the screw. Use a drill press if you have one and the part is small enough that you can set it up solidly in the press. Drill slowly and stop often to check your progress. Drill a small pilot-hole first, using a punch to mark the spot before you start drilling.
Many times, drilling the hole in the screw will be enough to loosen it as the pressure is released, and you will be able to ease it out with little force on the extractor.

Drilling out screws

If that doesn't work, the next option, depending on the design of the cover that the screw holds down, is to drill out the screw head completely. Often times, removing the head of the screw releases the pressure of holding two parts together, and again will come out easily, unless of course it is rusted or frozen. In this case, if there is enough of the screw-shank sticking out after the cover's removed to let you file flats on it, use locking pliers to turn it.

Use a drill bit that is just large enough to take out the screw's head; it should be slightly larger than the shank of the screw so that when you drill through the head and get to the shank the head will come completely off. Obviously you need to have the hole exactly centered to do this without touching the surrounding material. If the buggered screw head is irregular this is difficult to do with a hand-held drill, as the drill will catch on the protruding bits and go off-center. You may be able to even out the screw head with a small file or a pointed grinding-stone in a dremel-tool (small high-speed hand-held grinder) then center-punch and drill.
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