Acoustic Guitar Repair: Glues for bracing?

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ottokbre
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Acoustic Guitar Repair: Glues for bracing?

Post by ottokbre » Fri Feb 11, 2005 2:53 pm

I have to repair a Martin OOO-x1 that I need to repair the back on. Someone tossed it and chipped the lower inside bout, and it disconnected itself. The lack of torsional rigidity is making the guitar torque just enough to hold a tune, but it has also raised the action.

I am going to have to clamp this thing into two axis, which should be easy enough with Jorgenson Bar Clamps, but two questions;

What kind of clamps can I use on the inside?
What is the best glue to use? Titebond Woodglue?

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Re: Acoustic Guitar Repair: Glues for bracing?

Post by kingquasar » Fri Feb 11, 2005 3:30 pm

Tite bond is fine. "A Bond Stronger than Wood". I've used it on all the guitars I've built. Just make sure that you clean the two surfaces that you are gluing VERY well and you let it dry (clamped) for at least a day.

For Clamps, go here.

-kQ

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Re: Acoustic Guitar Repair: Glues for bracing?

Post by puls » Fri Feb 11, 2005 4:55 pm

Actually, I believe it's called titebond II, is what the guy from Stewart-McDonald uses a lot. Traditionally horse hide glue was used, & many luthiers still used it becuase it is completely reversable w/ heat & water - if you screw up or the repair comes undone in 8 years or so, you can remove the old repair & do it over. However, it's a hassle to use - comes in flakes & you mix it in different amounts w/ hot water according to have well it has to flow for the repair. For interior 'clamps', many luthiers make thier own fron old oversized hypodermics (or similar cylindrical items) & springs, so that the hypo's telescope over each other. Are you planning on using any cleats? If the crack stays closed on its own you probably won't need them (be sure the glue gets worked into the crack surfaces & not just on the top), but if it tends to open up, you'll probably need some cleats on the inside of the box to hold the edges together. It's hard to say without actually seeing the instrument. I didn't really understand from your explaination where the crack is - on the side or back or front? If it's a nice instrument and/or a spendy one, it would probably be well worth your trouble & exspense to take it to a professional luthier to see it's done right. Remember, a well made & maintained acoustic guitar will outlive you (I've got a couple of medium grade guitars - not top of the line - older than my parents, & I'm no youngster).

JWP
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puls
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Re: Acoustic Guitar Repair: Glues for bracing?

Post by puls » Fri Feb 11, 2005 5:08 pm

After re-reading your post & checking out the link I need to correct myself. If you're just regluing the brace & it's way down in the corner, the bridge clamps may not be long enough. Go w/ the telescoping cylinders & spring if thats the case. You don't want to use an excessive amount of clamping pressure so that you deform the instrument, because it will then be glued in that shape. The idea is that everything fits together well on its own & the glue just holds everything in place. If the glue sets in a way that it holds the guitar body in a deformed shape, it will set up internal stresses in the wood & inhibit the free vibration of the top. Or that's how my luthier explained it to me. Forget about the cleat thing, those are for surface cracks in the top/back/side, not bracing.

good luck

JWP
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Re: Acoustic Guitar Repair: Glues for bracing?

Post by ottokbre » Fri Feb 11, 2005 5:14 pm

awsome advice, thanks!

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Re: Acoustic Guitar Repair: Glues for bracing?

Post by rolandk » Fri Feb 11, 2005 6:26 pm

Totally up to you of course, but a nice guitar like that I'd take to a pro. I've messed up 2 guitars trying to work on myself and save the $50.00 a shop charges (and I'm pretty handy with tools). One was installing a pickup in my '78 Martin D18 and the other was installing an LSR roller nut on my Strat.
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Re: Acoustic Guitar Repair: Glues for bracing?

Post by ottokbre » Wed Feb 16, 2005 10:35 am

thanks for all the comment. i did this slowly to let all the glue bond well, but here is what went down. it isnt perfect, but it brought the action back to where it belonged, and it sounds great. you can kinda see how i got the shape re-aligned in the first pic;a strap around the body with a clamp putting force into the waist to bring the lower bout to the right curve. glue the perfs and clamp down.

I did the first major point (this photo)
Image

that really brought the guitar back. then i did a second point on the waist curve, which tucked everything back in.

I was lucky enough to have the chipped wood-lam from the larger hole, so i just did my best to glue that back on;
Image

it's not perfect, but playable and i can chalk the imperfection up to "charecter" :wink:

Image

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