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Aaagh, screw rusted and head sheered off--help!

Postby Dr Huge Longjohns » Mon Dec 03, 2012 4:06 pm

Taking the bridge plate off one of my Yammy tellies and the screw was so rusted that its head crumbled under the screwdriver. So how do I get the rest of the screw out without making a right mess of the top of the guitar??? ZEN HELP!!!!!
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Re: Aaagh, screw rusted and head sheered off--help!

Postby Hugh Robjohns » Mon Dec 03, 2012 4:10 pm

Depends how much of the screw shaft is left standing proud of the woodwork. You might be able to file flats on opposite sides, then use a molegrip to clamp on and rotate out. or you could use a fine hacksaw to cut a slot in the shaft and use a screwdriver to rotate out. Worse case is you might have to drill it out and replug.

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Re: Aaagh, screw rusted and head sheered off--help!

Postby Frisonic » Mon Dec 03, 2012 4:29 pm

Let's hope one of Hugh's first two suggestions work and once you've got the offending detritus out I recommend you think about treating yourself to one of these!
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Re: Aaagh, screw rusted and head sheered off--help!

Postby Hugh Robjohns » Mon Dec 03, 2012 5:15 pm

If there is little or no shaft above the woodwork, preventing you from filing flats or cutting a slot, then you could use an 'easy out' (miniature) screw extrator tool like these from amazon:

http://www.amazon.co.uk/Laser-3744-Combination-Screw-Extractor/dp/B002TD10P0/ref=pd_sim_sbs_diy_1

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Re: Aaagh, screw rusted and head sheered off--help!

Postby Random Guitarist » Mon Dec 03, 2012 5:41 pm

I wouldn't use mole grips, too much chance of slipping. I don't think a typical bridge scre will have enough meat for an easy out.

Get a piece of tubing with an inside diameter just big enough for the screw. Cut/file some saw tooth type slots in one end. Put the other end in your electric drill and running the drill in reverse gently cut down around the screw with the new tool you have made.

This will drill down around the screw removing the minimum of wood, at some point the scre will bind inside the tubing and inscre out the rest of the way. Then you replug and redrill the hole.

I've used this technique a number of times and it is pretty infallible, the drill speed means you cut through the laquer cleanly and the old screw body acts as a guide for the cutter.

Good luck,

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Re: Aaagh, screw rusted and head sheered off--help!

Postby Random Guitarist » Mon Dec 03, 2012 5:44 pm

Should have said 'metal' tubing, although it is obvious.
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Re: Aaagh, screw rusted and head sheered off--help!

Postby zenguitar » Mon Dec 03, 2012 5:45 pm

What Hugh said, he beat me to it :)

And you are fortunate that the sheared screw is in such an easily hidden location. That more than anything else makes the job a lot easier to take on.

One extra tip that might be worth a try. There is a likelihood that the rust/corrosion has worked its way down the shaft of the screw. That can make it a much tighter fit than it was when it was put in. If there is a little 'head' still protruding you may only get one chance to get a decent grip on it. Consider some fine shavings from a wax candle and put them around the protruding head. Then apply a hot soldering iron, with a fine tip, to the protruding metal of the screw. The heat will make the screw expand a little, which will help it loosen up, and the wax will melt and run down the threads to provide lubrication.

You don't want to make the screw so hot that it burns the wood/finish, just enough heat to make the metal expand a fraction. A similar technique with a soldering iron is used to remove frets too.

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Re: Aaagh, screw rusted and head sheered off--help!

Postby DAGGILARR » Mon Dec 03, 2012 5:53 pm

The best trick I was ever shown about getting old screws out is ALWAYS to tighten them a bit first this way you achieve a bit of movement, risking pressure in the other direction also as screws are tapered this will open up the hole a bit (if it is a wood screw) Not withstanding this when you do get some purchase on this offending stubb the same principle will apply try gentle pressure in the tighten direction first.

A good close up picture would probably help any who may have constructive ideas

Is it steel into wood? or steel into steel machine screw ? The application of a soldering iron onto the stub can cause a useful expansion stretching the hole if its into wood also helping WD40 in if its into steel (though this will in effect lubricate the bit you need to grip as well)

If there is room and you have someone who can help, assuming a grip can be achieved with vice grips wiggle the grips while the other person administers shocks to the shaft ( no carry on jokes here ) a centre punch is good for this.
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Re: Aaagh, screw rusted and head sheered off--help!

Postby Dr Huge Longjohns » Mon Dec 03, 2012 7:09 pm



If there is little or no shaft above the woodwork, preventing you from filing flats or cutting a slot, then you could use an 'easy out' (miniature) screw extrator tool like these from amazon


Sorry should have said, the shaft end is probably 1mm below the surface of the wood.
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Re: Aaagh, screw rusted and head sheered off--help!

Postby Hugh Robjohns » Mon Dec 03, 2012 7:24 pm

Then you either need to use one of these miniature screw extractors, or the core drill technique described previously, and re-plug the hole afterwards.

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Re: Aaagh, screw rusted and head sheered off--help!

Postby Dr Huge Longjohns » Mon Dec 03, 2012 7:27 pm

How do the extractors work, Hugh, they're a new one on me?
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Re: Aaagh, screw rusted and head sheered off--help!

Postby Folderol » Mon Dec 03, 2012 7:31 pm

Ouch!

What is the size of the screw?

One extremely tedious method I've used with a sunken screw is to drill two very fine holes (about 0.8mm - one of my PCB drills) side-by side in the stub then drill out larger until they join. Lubricate well, and heat treat as suggested above, then ease out with a watchmakers screwdriver.

P.S.
Ideally you don't want the holes to reach the edge of the screw.
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Re: Aaagh, screw rusted and head sheered off--help!

Postby Random Guitarist » Mon Dec 03, 2012 7:37 pm

The conventional screw extractors work by drilling out the centre of the existing screw and then screwing on of the easy outins int the hole left handed. The left handed thread means that as you screw the easy out into the hole it bits into the sides of the hole in the original screw. The harder you turn the more the easy out bites into the screw and the screw undoes.

IN practice the easy outs frequently break if you are even slightly ham fisted, leaving you with a hardened undrillable lump in the middle of your screw. Also you have to drill your centre hole quite accurately for such a tiny screw. I'm not a professional engineer, but I've successfully restored a couple of cars, and I would not use an easy out unless every other possibility had been exhausted.
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Re: Aaagh, screw rusted and head sheered off--help!

Postby Folderol » Mon Dec 03, 2012 7:41 pm

That's my experience too :frown:
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Re: Aaagh, screw rusted and head sheered off--help!

Postby zenguitar » Mon Dec 03, 2012 8:33 pm

Broken inside the wood. Grant's method is the way to go, it'll do the cleanest, most effective, job.

Use one of the other screws that came out without problems to help you pick a suitable piece of metal tubing.

Have fun ;)

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Re: Aaagh, screw rusted and head sheered off--help!

Postby Random Guitarist » Mon Dec 03, 2012 10:43 pm

I'm going to back-track if the screw is slightly below the wood.
Has the screw sheared off flat enought that you might be able to centre punch it? and do you have a pillar drill?

If yes to both then I would try punching and drilling first as you'll have a slightly smaller hole to plug.

If the top of the remaing screw is very ragged or you don't have the drill then I'd stick with a home made centreless drill. The teeth don't have to be super accurate or sharp, they don't even need to be terribly hard, you can use a piece of brass tube.

Last thoughts for coreless drilling on a sunken screw are that I'd use a regular drill bit to carefully start the larger hole as without the screw in the centre of it the core drill can skate around, and start with low speeds.

I hope this is helpful.


Regards,

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Re: Aaagh, screw rusted and head sheered off--help!

Postby Hugh Robjohns » Mon Dec 03, 2012 11:06 pm

Wot ee zed! A hollow core drill is the way to go with this because he screw you're trying to remove is presumably very small. The easy-out tools work by using a counterclockwise threaded screw that bites into a pilot hole you drill first into the broken screw, and as it bites, it unscrews the offending screw. But you nee to be gentle and very accurate otherwise the tool is quite likely to snap or shear itself, making things even worse!

Looks like you're going to ave to drill and replug. Good job it's under the plate ;-)

H
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Re: Aaagh, screw rusted and head sheered off--help!

Postby Jumpeyspyder » Mon Dec 03, 2012 11:31 pm

Hi Huge

Probably not the 'correct' method, but you may be able to leave the broken screw where it is and stick a new bridge on top with a different mounting hole pattern to hide it.

Best of luck
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Re: Aaagh, screw rusted and head sheered off--help!

Postby zenguitar » Tue Dec 04, 2012 12:38 am

And +1 for brass tube. It's nice and soft and will grip the steel screw very well once it starts to 'bite'. Easy to cut the teeth with a triangular file, and widely available in assorted internal diameters from model shops everywhere. And definitely worth plugging the end that you chuck in the drill with a piece of softwood dowel so the chuck can get a good grip.

I think you can sense a broad agreement here Huge ;)

Andy :beamup:
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Re: Aaagh, screw rusted and head sheered off--help!

Postby Dr Huge Longjohns » Tue Dec 04, 2012 10:09 am

Great advice everyone and, as Zen says, if I do totally cock it up at least it's under the bridge plate and there are still four other screws holding it on!
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Re: Aaagh, screw rusted and head sheered off--help!

Postby DAGGILARR » Tue Dec 04, 2012 6:18 pm

It seems you could expend a lot of effort trying to preserve the hole,,, why? once the offending bit of steel is out a hole is an easy thing to fix, an oversize dowel and a carefully matched drill bit, some good glue, jobs-a-goodun; then relocate a pilot hole for the replacement screw.
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Re: Aaagh, screw rusted and head sheered off--help!

Postby Madman_Greg » Wed Dec 05, 2012 12:29 am

The brass tube is its fact a neat trick.

You could try another tack with it

Tube o/d – wider than screw o/d

Tube i/d = smaller than screw diameter

Drill a shallow taper into the tube, maybe 5 mm in depth, you might have to grind a drill to get the right shallow taper profile. Or you could flare it if you have something to do that.

Cut your teeth in the tube

Use the drill in reverse as stated, the friction on the taper on the screw might loosen it
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