Removing Cross-Threaded Screws from Hardware?

TeaDaemon asks: "I currently have an expensive (dual CPU) motherboard mounted in a rack case. One of the mounting screws is cross-threaded, preventing me from removing the board. The case is designed to prevent access to the back of the risers, so that's not an option. Does anyone have experience with this sort of problem? Can anyone suggest a reliable way of removing said screw without damaging the board or any of it's components? The screw is next to the PCI slots, and has a couple of capacitors and ICs near by. Any help would be greatly appreciated."

Comments

LH drill bits.

[frankm_slashdot]

use a 2mm or 3mm LH drillbit. drill it out, and when you remove the board, just replace the standoff.

Drill it out

[photon317]

The obvious answer is to drill it out. Since you'll want to be a little careful, you should probably start with an extremely small bit and drill a pinhole into it first, and then work up the bit sizes one by one until the head pretty much falls off the screw. It will destroy both the screw and the mount, but they were crossthreaded anyways.

The obvious issue is of course metal shavings. A small amount of cutting fluid on the bits (or probably any liquid, maybe wd-40) will help to a small degree to keep the shavings from flying around as much (they'll tend to travel up the grooves in the bit instead). More importantly - mask things off. Cut a small 3/4" or so square hole in the center of a large peice of paper. Cover the hole in masking tape. Place the taped hole over the screw, taping the hole down all around it - then cut the circle of tape off the head of the screw where you'll be drilling. You should be able to keep the shavings on the peice of paper instead of on the motherboard shorting out little pins and things.

Re:Drill it out

[PurpleFloyd]

Remember that the belt-drive system of a vaccum cleaner can generate a lot of static electricity. In the wrong circumstances, it can act like a Van De Graff generator. I would suggest using a specialized "computer vaccum" (basically a regular vaccum cleaner with a grounding system somewhere in the hose or motor assembly) or just blowing out the shavings with some canned air (be sure to get in the PCI and RAM slots!

Screw Extractor

[adamy]

The one thing I've seen missing from these posts is the use of a screw extractor. Once you have a small hole drilled into the screw, replace the bit with a screw extractor. This is a wedge shaped bit the that has flanges designed to dig in to the hole as the bit is on reverse. You might have trouble finding one small enough for a motherboard. But it may save the housing , and you will have only lost the screw.

Drill once, then use a screw extractor

[Anonymous Coward]

Once you've drilled the first small hole you can use a small screw extractor (basically a reverse threaded screw) to get it out. The idea is that you screw the extractor into the hole you've drilled in the stuck screw you need to get out, and once it "bites" you should be able to thread it out.

I use them all the time when working on my car. It'll take alot less time and have the added benefit of producing alot less shavings.

Plus it's an excuse to buy more tools! :)

Here is a page that describes the use of a screw extractor if you aren't familiar with them:

http://www.bluepoof.com/motorcycles/howto/screw_ex tractor/

Re:The mechanic's friend

[n9hmg]

Instead of superglue, clean the head... In such circumstances, I just use 70% isopropanol. It's a good solvent for hydrophobic and hydrophilic contaminants, and any leftover dries really clean. Spritz an appropriate-sized philips-head screwdriver head with silicon lubricant. Mix up a little JB-Weld, and work a drop into the head with a toothpick to ensure that it is contacting as much as possible. Set another drop on top of that one and stick your slicked-up screwdriver bit into it - secure with something... I like the little radioshack extra-hands jig thingy. GO AWAY, and leave it alone for a whole day. Then, turn the screwdriver bit. The head WILL turn with it. I can't vouch for the shank. If the shank stays, you'll have to drill it out, or perhaps just do without that mounting point? If you drill it out, be very careful to remove only enough to get a tap in there to clean the threads... you'll probably have to go up one size, as you're unlikely to get it perfectly down the center. Keep a vacuum on the drillpoint to avoid deadly metal slivers.
On larger screws/bolts/studs, I like to get some heavy-walled steel pipe with an I.D. just slightly smaller than the head. Set that on the head, and weld a bead around the inside joint. Take a big old 36-inch Rigid pipe wrench, put a pipe on it if necessary, and move it. I did that once on the upper balljoint on a Dodge dart. It actually took the threads right out of the upper control arm - smooth as if it were machined. Phyrric victory, but I won.

Re:Drill it out (metal shavings)

[littlerubberfeet]

You are doing surgery, approach it as such. Get some thin nylon cloth and use a hole punch or something similar to make a small hole large enough to fit the screw head.

Put the cloth on the motherboard, with the hole centered on the screw. Press it down so that the cloth is below the level of the screw. Drill away, using increasingly larger bits. When removing the cloth, put your finger on the hole. With the other hand, pick up the edges of the cloth, using your finger to seal the hole.

Good Luck