Repair And Restoration
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Gibson J-29 bridge lifted
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Gibson J-29 bridge lifted
This is a local musician’s main acoustic. It’s a 2014 Gibson J-29. As you can see the bridge was lifted when I got it, and the top has been pulled up into a bulge. The bridge came off pretty clean, but I noticed how the spruce broke behind the pins. I didn’t score this side of the bridge, but it looks like it must have been scored for the wood to break that cleanly. Could this have come from the factory like that?
I don’t know why Gibson would use such a narrow bridge on a steel string, it really reduces the glued area.
Is the best thing to do here to try and just glue the spruce back down and hope for the best? I also need to try and flatten the top. The bridge is perfectly flat on the bottom.
I’m curious as to why there is about a 1/4″ plugged hole near the middle of the bridge.
The guy says he’s owned this about 8 years and doesn’t know of any work done on it before.
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4 Replies
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It could have been done at the factory. It’s a really subtle thing to do, cutting around the footprint of the bridge and taking the lacquer off. Even just a slight cut into the spruce creates custom runout and a point of failure for bridge adhesion. It’s one of the reasons a lot of factories have moved to the rabbited bridge, although that is another can of worms for the next guy as well.
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I completely agree with Ian, this probably happened at the factory when they scored the lacquer around the bridge placement. They finish the top without the bridge on it, then score around the bridge to scrape the lacquer off. Just a bit too much pressure and they cut into the wood.
The top has a slight dome to it whhen built, so realistically the bottom of the bridge should have a slight concave shape to it. It it’s truly flat, there’s a good chance that’s what caused it to come loose (along with the cut fibers of the spruce top). Some areas of the glue are shiny, which means they were not actually in contact with the top when the glue dried, like a small void between.
For checking the top flatness, have you looked inside to see what kind of shape the bridge pad is in? Or checked to see if any of the braces are loose? Again though, there is supposed to be a bit of a dome, even brand new. Any idea how far the middle protrudes above the sides?
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I did inspect inside and everything seems sound. The bridge plate looks to be in good shape.
I didn’t measure the as-received dome height to the outside edges, and I can’t do it now because I’ve already started to flatten the area. I stand corrected on the fact the bridge does have a little concavity which would match the expected dome radius. I also thought that the shinier areas under the wings indicated a poor glue joint.
The main problem, beside bridge lifting, was the bulge under the bridge extending across the width of the pins. You can see this in the attached photo.
This morning, after removing the clamps and cauls, the top has a pretty low dome profile across the bridge area from side to side, and the bridge matches it pretty well. I’ll sand it to make sure it’s contacting the whole surface. There is still a little belly when checking longitudinally; a slight swell below the bridge area with a dip towards the sounds hole, but I think it’s not excessive. I think the most important thing now is to get a sound glue joint, as the owner was happy with the way it played before the bridge lifted.
Looking more closely it does seem like the factory scoring along the bottom edge of the bridge is pretty deep. I would think by now they would have better quality control over this.
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Well at least the underside of the bridge was cut to match the dome. Their quality control has been really spotty for years, I think they are finally cracking down on it. Sounds like you are on track here, once you make sure the surfaces mate, a good glue and clanp job should do the trick.
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