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  #1  
Old 06-21-2022, 07:09 AM
skouri1 skouri1 is offline
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Default Dry Fit on Bridge Reglue

Hello All,
Posted in general discussion and was advised to come here.

I bought an Alvarez Mf60om that needed a little love. Came with some bridge lift, so I investigated the reglue procedure and decided to take it on myself. (famous last words).

I work a lot on bicycles and have done some furniture repair etc, so I am mechanically minded and thought I would go slowly.

I have seen some disastrous stuff on YouTube (people prying up super hard on bridge and taking tons of wood with them) as well as cold removals (which scare me but actually worked ok it seems for them).

1. So far, I created a heat shield and carefully removed the Alvarez bridge with a spatula and iron. Bridge came off cleanly.

2. I sanded off the glue from the bridge and scraped the top. (oddly, there was some sort of remnants of very thin fabric, felt like material at the interface.)

3. I traced the outline of the bridge with a razor and carefully removed the excess thick lacquer that created a "shelf" and probably inhibited the good glue bond to begin with.

4. I did a few dry fits with a bridge caul (see here )

5. Because of the Bi-Level design, the wing nuts got the bridge tight on the lower bout but not on the part facing the sound hole.

6. So, I bought a deep reach C clamp and fitted it on the bridge plate and the top of the metal caul.

Now the problem, this clamp evened out the pressure and generally appears to have a good fit all around. No visible gaps and finger nail cannot get under at all. Spatula will also not enter, of course.

However, a piece of paper can get under the bridge during the dry fit at various points.

Now, I am afraid to tighten the clamp more. The wings are tightened and the wing nuts in the metal caul are also tightened to where I feel comfortable. I did not make a caul for the bridge plate.

In your opinion, will the titebond original simply take up the small, paper thin space as long as I apply liberally and wipe away squeeze out?

Or do you recommend I continue to sand or make a bridge plate caul and crank down the clamps further?

Or should I use small shims under the clamp /caul to try to distribute pressure more evenly.


I would have tried sanding the bridge to the top, however, there are two pegs that align it, so that's a no go.

Thanks in advance for your comments/advice !
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Old 06-21-2022, 08:12 AM
BradHall BradHall is offline
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You can still sand the radius for the bottom of the bridge by placing sandpaper below the obstructing pegs a few inches and slowly, carefully, rubbing the bridge front to back. There won’t be much, if any, change in the top radius in that small distance. As you have surmised, a gap big enough for a piece of paper to slide in is too big. IMO of course.
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Old 06-21-2022, 09:42 AM
skouri1 skouri1 is offline
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Thanks. It may also just be a question of clamping evenly. The bi-level Alvarez bridge complicates this a bit. I thought the caul + the clamp would be enough, however maybe I need 2 more clamps unfortunately...
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Old 06-21-2022, 10:13 AM
Carey Carey is offline
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Keep in mind that the bridge will tend to swell on its glued side when you apply the water-based Titebond: what is normally concave (assuming a slightly domed top) will become temporarily convex. Dry runs and tests are a good idea, to see these effects and make appropriate adjustments. You'll get a feel for it.

Last edited by Carey; 06-21-2022 at 10:19 AM.
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Old 06-21-2022, 11:05 AM
BradHall BradHall is offline
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Carey, are you saying a rosewood or ebony bridge will swell from the water content in the glue? I would think it’s more likely the spruce top would absorb the water. Always looking to learn something.
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Old 06-21-2022, 11:34 AM
Carey Carey is offline
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Quote:
Originally Posted by BradHall View Post
Carey, are you saying a rosewood or ebony bridge will swell from the water content in the glue? I would think it’s more likely the spruce top would absorb the water. Always looking to learn something.
Yes, definitely. It really helps to do the tests.. wetting one side of a piece of ebony or rosewood with a bit of glue, or a touch of water, and get a feel for it.
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Old 06-21-2022, 11:41 AM
skouri1 skouri1 is offline
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Thank you for the idea. I did not think about a "wet" dry run
It seems to me that you can't have it smashed up to tight or you will squeeze out all glue. Having said that, you do want solid wood on wood contact...
Interestingly enough, when I'm watching the videos of repairs most people seem to do a visual inspection of the dry run.
It makes sense to me that the glue/ swelling of the "wet bridge" will take up the last bit of paper thin space.
I am still going to do more investigation though and I will try to heed all advice before proceeding with the wet run. With Titebond, worst case I end up repeating process and or giving up and heading to luthier.
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Old 06-21-2022, 12:15 PM
Carey Carey is offline
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If you use an animal-protein glue like hide or fish, you can do a "sized" joint, which lessens the issues I mentioned. That's not possible (in my experience) with a glue like Titebond or other PVA, though. I use Norland fish glue quite a bit, because I'm not super-good with hide glue and its short open time and other stuff.
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Old 06-21-2022, 12:16 PM
Howard Klepper Howard Klepper is offline
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Mechanical clamping is always about making a sandwich. Each place you apply pressure on the top should have the same pressure from a caul inside. The clamps on the wings usually need cauls that are fitted around the braces (I have no idea how Alvarez bracing goes). So making a caul for the bridge plate is a no-brainer, as well as making sure the wing cauls are fitted to not crush any bracing.

Forget about the idea that you will squeeze all the glue out. The "starved joint" from overclamping is a myth. What can sometimes happen is that if insufficient glue is applied to a very porous surface (like end grain) it will get sucked up into the wood and leave the joint too dry. But that is not about too much clamp pressure. It is actually very hard to generate as much pressure with the kind of clkamps we use as the glue manufacturers recommend. A thinner glue line makes a stronger joint than a thick glue line.
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Last edited by Howard Klepper; 06-21-2022 at 12:22 PM.
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Old 06-21-2022, 12:34 PM
Carey Carey is offline
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It's real good to see Howard Klepper here, and you should listen to him.
I hope he starts making guitars again.
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Old 06-21-2022, 12:46 PM
skouri1 skouri1 is offline
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Thanks again for your insight, Howard. A privilege to have real luthier chime in.

I will have to get the mirror out and look at the bridge plate on the Alvarez. I was honestly worried about glueing in the caul, but I doubt that could happen easily given the glue is between bridge and top (and a minimal amount would make it through string holes after clean up if at all. )

I will still try slightly wetting bridge to see what clearances look like then.
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Old 06-21-2022, 01:19 PM
BradHall BradHall is offline
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I cover the surface of my bridge plate caul with clear packaging tape. Nothing I have found sticks to it. I use a 3/4” thick caul to make sure the clamps clear all braces. You can also try putting a very bright light source inside the guitar in a dark room. The braces will often “telegraph “ through the top plate and you can trace them onto a thin piece of paper. This will give you a true shape for your caul.
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Old 06-21-2022, 08:56 PM
Carey Carey is offline
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Howard K, your PM inbox appears to be full. No rush at all, but I'd like to send you a message when the stars align.
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Old 06-28-2022, 05:56 PM
skouri1 skouri1 is offline
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followed howards advice.
sanded down the interface a bit more and after putting a caul on my clamp to go over the bridge plate, i got way better results. it took a while for me to work around the bi-level bridge plate, but the caul was critical in getting rid of the gap i previously had.
after successful dry fit, added some titebond original, clamped, wiped squeeze out) which reassuringly came from the wings even. and now we wait. and wait and wait.
i have heard its important to double manufacturer's recommendation. For titebond that should be 24 * 2 = 48 hours. I will probably give it another day or so as I am drying not to make a mistake with the finish line in sight.
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Old 06-28-2022, 06:42 PM
Carey Carey is offline
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Sounds good! Giving the joint plenty of drying time is a smart call, too. Thin and well-formed glue line = strong joint.
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