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I've recently glued the bridge back onto a Yamaha 12 string acoustic, using Titebond. I left it a good few days before re-stringing, but as soon as the strings were up to tension, off came the bridge. Any suggestions? I'm assuming Titebond is ok for gluing bridges. The top is actually slightly bellied which kind of gives the strings a head start (because the bridge is already at a slight angle) but I don't think that's the issue. What am I doing wrong?

I'll let others provide you with a walk through on this topic, as I've never done it. However, I think you should reconsider your name, especially since you just have one post. Which Titebond did you use?

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David Morris

Titebond Extend. Don't understand what you mean about my name.....

ThanksTodd. I only just re-strung the guitar an hour ago so I haven't removed the bridge fully to inspect. I've released the tension and walked away........ I'll have a closer look tomorrow.

It's considered a racial slur in some parts of the world.

Check this out (Warning! Offensive content.):
http://www.urbandictionary.com/define.p ... e%20monkey

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David Morris

Jeepers!! Point taken. I use that id on all my online accounts and nobody ever mentioned it before. For the record, there is absolutely no racist intent. When my son was about three he had a sweater with a picture of a monkey driving a train and the slogan underneath read "Jungle Monkey drives the train", so I thought it would be a good user id. It isn't really known in the UK as a racist slur so it never crossed my mind.

Yeah, yeah. When I first saw it, it caught me off guard, but I realized it doesn't mean the same thing the the UK it does in Texas. Go figure.

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David Morris

How did you go about the repair?

I always recondition the bottom of the bridge before I replace it, assuming it isn't too warped. After I try to clean the top surface as best as I can, I've found over the years the top doesn't have to be pristine, but as flat as it can be to accept the new or repaired bridge. After that I use a violin knife to cut crossways into the top (lightly) and the bridge (a little deeper than the top cross). This gives the glue somewhere to seep in and hold (i use tightbond 99% of the time). After, I use 4 cam clamps and a good bridge plate caul and clam as much pressure evenly on top of the bridge as I can. It's crucial to get a good press for the glue to set and bond properly. Too little and the glue is just brittle and will pop loose under tension. I've tried the stew mac bridge clamping caul, but it was a pointless waste of money... It flexed under the tension it needed to properly squeeze the pieces together. Let it all sit for 24 hours for the glue to really take hold before removing the clamps. Then I usually let it set and without strings for another 24 hours just to make sure that the glue sets and all excess moisture is out of the top before I restring.

I do this repair about once a week, the only time I've had it fail (after learning the technique I use today), is if the bridge was planed down too thin to correct warp-age or a former bad repair. When in doubt, just make a new bridge. OH! Also make sure you let the guitar sit for a day or so after removing the bridge if you've steamed it off... don't want to introduce any extra moisture into that glue joint. Sometimes after steaming I'll take the chance to clamp a caul across the top and back to flatten out slight bellies. Also gives you a flatter surface to glue the bridge back down to, assuming the belly isn't there by design that is!

Note: (clamping overkill! But better safe then sorry!)

I didn't score the underside of the bridge. Don't know why because I scored the top........ Also, I didn't accurately check the profile of the bridge to check that it matched the top. I used the StewMac horseshoe clamps, but I felt you just couldn't get enough pressure using the little knurled thumbwheels. I used heat, not steam so that shouldn't be an issue, and as for the bellying, I'm not sure it's supposed to be there. There are no loose braces, but the bridge plate feels a little concave. Interestingly, the edge of the bridge plate stops almost in line with the bridge pin holes, which would effectively create a weak area behind the bridge, whereas on my Martin, it extends a good 1/2 to 3/4 inch beyond. I suspected all along that this may have been the main contributing factor as to why the bridge came off in the first place. (Aside from the fact Yamaha appeared to be economising on glue at the time.) By the way, don't apologise for the clamping overkill, mine looked like the Forth railway bridge in Scotland. (Google it, you'll see what I mean.) Thanks for the tips.

Joe, have you got something between the bridge plate and the guitar back so that you can clamp like that on the bridge wings?

Even though I haven/t reglued a 12 string bridge, I have the same setup ,stu-mac+ cauls and 1 ibex alum clamp and 1 chinese ibex knockoff. Thanks for the photo todd

fwiw, I've had the bridge reglued on my old D12-28 by Bryan Kimsey - I assume that he used Titebond but it could have been hide. No problems after 6 or so years. That guitar had a pretty bad belly, I tried a JLD bridge doc (which didn't work) - when the neck was reset and bridge reglued the belly partially went away.

I have also used Titebond on the two 12 strings (and everything else) that I have built - again, no problems.

I'm kind of curious what kind of glue you think was used before and how you got it apart. Old Yamies were supposed to have very hard neck joints to separate - the story is that they used some sort of epoxy and they are very difficult to reset. I have one that needs a reset, I'm just trying to get as much info as possible.

Jeff: Sure do, I have a felt covered back plate clamping caul I use that evens out the pressure on the back (and doesn't leave a mark). On this particular bridge shape (I believe it was a Tacoma) i just needed a little more pressure on the edges.

Todd: Been scoring for so long it's just became second nature. Though, when I started scoring the bridges I also changed a few other techniques I was using to prevent the bridge from coming loose again. I just never took the time to figure out which change I made had the greatest effect! It's been working so I haven't had to fix it

Jungle: yeah the holes being that close sounds scary indeed. You may try dowel plugging the holes to give you a bit stronger of a bond, then just re drilling them clean after it's set? What do you all think? Also, googled the railway

Also a lot of imports i've come across have been doing that with the bridge plate, not as extreme but I've noticed when installing a few K&K pickups that the plate isn't extending much farther than the saddle slot itself... Which is really disheartening...

I think what Jeff means is do you have a support inside the guitar so that you will get even clamping pressure and you won't crack the top or a brace with those outside clamps?

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Ken Franklin
clumsy yet persistent
https://www.kenfranklinukulele.com

Exactly

Titebond Extend is perfect for bridges, and has superior heat and creep resistance in comparison with Titebond Original (although either one will work.) Most of the bases have been covered already in this thread, but I feel like throwing in some extra depth for anyone who's curious.

Scoring or otherwise roughing up a bonding surface is unnecessary and if anything detrimental to bond strength, when water based wood glues are to be used. PVA based adhesives such as Titebond Original/Extend/II/III, etc. rely on proximity between bonding surfaces to achieve maximum strength. While scoring will increase the effective surface area, it also increases the average glueline thickness... and that leads to all kinds of other problems. The description of a glueline exceeding 0.005" as being too thick makes me smile, and it is entirely accurate. I wish I had exact figures on strength loss as a function of thickness, but that study is considered academic since we know that thinner lines are stronger.

There's your answer. No one knows better than Hugh Evans.

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David Morris

Hugh! Thank ya for the insight, I'll be bringing this up when I start an discussion with my boss (the master Luthier I apprenticed under) Always makes for good times when we can BS back in forth on the subject of repairs and such.

Jeff/Ken: Oh yeah, I made a few clamping cauls out of thick aluminum for that purpose. All the force from the clamps are being used to push the plate/top/bridge together no stress on braces and such.

The Clanps you have on the bridge wings seem to clamp from bridge to back of Guitar. Do you have anything inside to stop the top and back being forced together?

Thank you Hugh, for commenting. Academic is okay. If you stumble across the stats for glue line thickness v.s. tensile strength, we'd welcome it--one more thing to argue and obsess about. I stopped scoring glue lines a long time ago. No failures yet. For those of you in N. California, UCB has a wonderful library of wood science. It's open to the public. That's where I learned to glue smooth, planed surfaces. To get to the library you have to pass hall after hall of large wood specimens. I found this a gauntlet I could endure--Redwood 10'x30', Persimmon 1.5'x5'...Sometimes I didn't make it to the library.

For Epoxy, most of the information is in the engineering library. Epoxy glue joints don't behave like other glue joints. The surface prep required for gluing aluminum airplane assemblies makes wood gluing seem like kindergarten.(The engineering library is also open to the public.)

I'm wandering a bit, but UCB also has a complete collection of Carleen Hutchins' Cat Gut Journal. That's curated by the Music dept. You'll have to go out to a warehouse in Richmond. If you're not sure what you want, they don't have it. If you're confident, they'll call the fork lift, and move things around, and then..."bingo": Hutchins, Benade, Rodgers, Carruth....

Thanks for posting this Hugh. It's great to get this directly from the source.

I do wonder though, what is the tradeoff with repairability? If a bridge glued with Titebond Extend ever has to be removed, what are we looking at here? Blow Torch, Chisels and a Sledge Hammer? Is it realistic to be able to 'unglue' the Extend product without destroying the guitar?

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Jim Hansen

Extend will steam apart almost exactly like Original. If only heat is being employed to release the bond, it could take a little more effort... But as you get the glueline past 200°F, strength drops off rapidly. Blowtorches, chisels, and other implements of destruction could also suffice. However, hot spatulas and steam may prevent the cure from being worse than the disease.

Freeman:- I don't know what glue was used but it came apart relatively easily, using heat (I made a heating iron like the one StewMac sell) and a thin artist's palette knife. Having said that, there didn't appear to be an awful lot of glue holding it on anyway. I think a combination of this and the inadequate bridge plate (see earlier comments) contributed to the original failure.

Anybody:- As for the glueline, is it not the case that even if you ladled the glue on, once clamping pressure was applied the glue would just squeeze out anyway leaving only the necessary amount of glue? Or is it best to start off with only a thin glueline?

Thanks for all the comments so far, it's an education.

Thin gluelines are the result of
-parts which fit together perfectly
-adequate clamping pressure

Thanks Jeff. So obvious when you see it spelt out........