bridge pulling away on wavy top. need advice please

[Marley]

I have a top on my acoustic that is somewhat thin and more than somewhat wavy. The wavy top wood has caused the bridge to significantly pull away from the top. While it's still attached, I feel like it could go at any time. I have not tuned this guitar to pitch in sometime for fear it pulling off completely.

It seems like with the wavy top, this bridge could never be glued back to the top in a manner in which it needs to be, meaning full contact between the bottom of the bridge and the top.

What are some other options to consider? I can post pics later tonight. A thought to me, as drastic and ugly as it would be, is to put a screw, or two, through the top of the bridge and underneath put a bar or something that would be parallel to the bridge and put a washer and nut on the screw underneath the top. I would have to imagine this will take care of the bridge not coming off unless the entire top came off, but it would not solve the problem of the bridge being flush and in full contact with the top. Right now, I'd say only 50% of the bridge is contacting the top. It's the 50% that's towards the neck as that's the way the bridge is pulling.

Thanks!

[Fathand]

Nuts and bolts have been used to attach bridges in the past, Gibson has done it. Will it sound as good? Hmmm? Pearl inlay dots to hide the bolts?

If it is a low dollar guitar, I'd go for it.

[Marley]

Thanks for the input! Unfortunately, it is a somewhat higher priced guitar at 3K.

My fear is that short of getting the bridge attached to body in a way that will last, the only other option is a full top replacement, which I don't think I'd do because of the cost. I don't know the cost to do a top job like that, but it seems like it can't come in under 1K and for that, I'd screw the bridge down in 30 min and put my 1 grand into another guitar. My guitar also has an arm bevel so that seems like it can only complicate putting a new top on it and increase the cost.

My other fear if I do nothing is that I'll never play this guitar again. It will sit in the case until I die, and my kids will also do nothing with it because it's unplayable without a bridge. It's a custom-made guitar with my name on it, so selling it on the open market does not seem to be an option either. I'm stuck with it and at this point just want to get it to a playable state and be done with it.

[Mandobart]

A $3k custom guitar that has developed a "wavy top" and the bridge is coming loose? The first thing I recommend is contacting the builder.

[ProfChris]

I'd take it to a luthier. I'd be surprised if it can't be glued on successfully, assuming nothing else is wrong (such as bridge plate failure).

Bolting a solid bar underneath will change the sound and probably lose volume.

Bolts alone concentrate the force in tiny areas, so when the bolts pull through the top they destroy the wood around them. Manufacturers bolts are for ease of construction, its still the glue which holds the bridge in place.

[printer2]

I built a guitar early on that had a thin top and eventually it deformed and the bridge started to peel off (sound familiar?). I added a section of wood to extend the bridge plate a little, glued the bridge back on. Still trucking years after the repair although the sound suffered afterwards, just sounds average now.

[YamaYairi]

The proper way to reglue a loose bridge is as follows:
1. Using heat and gently sliding a thin putty knife under the bridge, remove the bridge.
2. Remove all traces of glue from the bridge and the top, where the bridge was.
3. Tape a piece of 220 grit sandpaper to the top, over the bridge area.
4. Work the bridge back and forth over the sandpaper until the bridge conforms to the shape of the top.
5. Remove the sandpaper and check the fit of the bridge. Repeat step 3 - 5 as necessary until you have an intimate fit between bridge and top.
6. Reglue the bridge and clamp with bridge clamps.
If you do it properly it won't matter if the top is not flat. It is normal for the top to be convex anyway. Bridges usually come off because of glue failure or improper glue application.

[IndianHillMike]

I would also suggest taking it to a luthier for evaluation. Depending on how severe it is, a wavy top might not be an issue if you re-glue the bridge with a vacuum clamp.

[Alan Carruth]

The waviness off the top is nature's way of telling you that the maker made it too thin. You can re-glue the bridge as is but the top will still lack the necessary stiffness. Adding some bracing in the bridge area might do the trick. An alternative would be to figure out some way to lower the string height off the top. The tension on the strings would remain the same, but the torque pulling the bridge up would be reduced, producing less distortion.

Bridge rotation is pretty linear with respect to the string height off the top (technically, the string height above the 'center of moment', but close enough). It's easy enough to measure the bridge rotation under load: I like to use a laser pointer to make a spot on the wall, which gives a nice long lever arm. Gore suggests that, based on his studies, 2 degrees of rotation is about right: more than that suggests that the structure is too flexible, and less that it might be heavier than it needs to be. If the rotation is, say, three degrees, and the strings are 12mm off the top, lowering them to 8mm should reduce the rotation to 2 degrees. That could, of course, call for a neck reset.

[redir]

Pics would help. Also look inside with a mirror and a good light source under string tension and see if any braces around the bridge are loose.

You might be surprised what a good repair tech can do. With heat and steam you can take a top that rotated under string tension and flatten it out again.

If it is indeed due to a top that is too thin then Printers suggestion of a Mario Proulx type reinforcement brace behind the bridge plate might take care of it.

[Marley]

Thank you all! This advice is exactly what I was hoping for. I feel confident that I could do the repairs myself but my time is pretty limited right now. I’m actually going to take it to a luthier today. Curious to see what he says. I’ll report back.
I do have a pic on my phone but it’s not off the top yet a brace I noticed underneath as I was snapping pics. Not sure how much something like this would have to do with it.

Argh. I forgot about the hosting feature of pics on the agf. I don’t have a history option right now to post pics.

[printer2]

Originally Posted by redir

Pics would help. Also look inside with a mirror and a good light source under string tension and see if any braces around the bridge are loose.

You might be surprised what a good repair tech can do. With heat and steam you can take a top that rotated under string tension and flatten it out again.

If it is indeed due to a top that is too thin then Printers suggestion of a Mario Proulx type reinforcement brace behind the bridge plate might take care of it.

Just looked it up, a little different than what I did. It is taller than the bridge plate, I extended the bridge plate about the same as this brace's width but only the height of the plate. In my thoughts on bracing I wondered what would happen if (on other guitars) I put a brace like this one.



http://www.proulxguitars.com/buildup/build6.htm