I deal with a lot of bellied guitar tops in my shop. Many acoustic guitars develop a bulge at the bridge, where the string tension has pulled the top up and caused the action to be excessively high. This is extremely common and usually isn’t something worth worrying about too much – it’s usually a fairly simple, inexpensive repair. Occasionally though, I get a guitar that just doesn’t want to cooperate, as was the case this week when I fixed up a Gibson J-45 Banner Reissue. It had a severely bellied top, and the bridge was warping and pulling off. This is a pretty expensive guitar, and was only a few years old – I was immediately suspicious. I usually see bellied tops on guitars that are decades old, not on something this new. As I got into the repair on this guitar, my suspicions were revealed to be well founded
Before beginning the repair, I thoroughly inspected the guitar inside and out. I determined that there weren’t any loose braces, so there wasn’t anything broken as such to cause such a severe belly. But the bridge plate on this guitar was pretty small, and there wasn’t much bracing around the bridge to keep the string tension in check. The bridge plate itself was warped along with the top and the bridge, so it clearly wasn’t helping much.
My thought was that even if I debellied this top, it wouldn’t stay flat for long, since the area around the bridge seemed pretty weak. I consulted with the guitars’s owner, and offered a couple of suggestions: either remove the bridge plate and make a larger plate, or overlay the original bridge plate with more wood to increase it’s stiffness. Since he was concerned about keeping the guitar as original as possible, we opted to go for a bridge plate overlay, which could always be removed later if necessary.
I began by removing the bridge, which was already starting to lift off the top. I used a heat lamp to very carefully heat the bridge, softening the glue underneath, and gently sliding a palette knife between the bridge and the top. This is a delicate operation: the bridge has to get hot enough to melt the glue, but not so hot that the guitar catches fire! As always, I took my time, and it came off without a hitch:
Next I debellied the top using my Thompson belly reducer cauls, which I’ve covered in detail in a previous blog here: http://www.strangeguitarworks.com/acoustic-guitar-debelly/
After a series of heat presses on the top, it flattened out nicely. Now the trick was to make sure it stayed that way, so I painstakingly made a bridge plate overlay out of 2mm thick section of rosewood. This was tedious work: there was no way to measure the bridge plate while it was still attached to the inside of the guitar, so I eyeballed it – check the shape of the bridge plate with a mirror, shave off a bit of wood, check again, shave off a bit more wood, check again, shave off more wood… repeat, repeat, repeat. A daunting task, but I think it came out ok:
Now that the top was flat and strengthened with the bridge plate overlay, all I had to do was reshaped the bridge to fit the top and glue it back down. Typically, this is simple enough, but with this guitar ain’t nothing easy. I first cleaned up the top with a small chisel and a razor blade, then taped some 80 grit sandpaper over the bridge area, and carefully sanded the bottom of the bridge to match the shape of the top:
Here’s where I ran into trouble. The top had been so warped (and the bridge along with it), that when I finally got the bridge to match the now flat top, it’s foot print had shrunk and now wouldn’t cover the exposed spruce top! I’ve never run into this issue before, as most bridges have squared off edges (as opposed to this bridge, which curved down to the bottom), and subsequently don’t shrink in size when sanded; and most guitars have some finish overlap under the bridge’s footprint. Now I had about .25mm exposed on each side of the bridge. No good.
Now, I had a few options here: make a new bridge from scratch, attempt a finish fill (which would present an impossible color match), or lay down some paper thin rosewood under the bridge. The owner had been concerned about keeping the guitar original as possible, and he didn’t want a new bridge made, so I decided to lay down some rosewood to camouflage the exposed spruce. This would be easily removable, and could always be covered up by a larger bridge at a later date.
I cut some small pieces of rosewood I had in the shop, trying to match grain and color as best possible with the bridge. There was no way this was going to be invisible, but hopefully it wouldn’t be obvious. I sanded them down as thin as possible off the guitar, then glued them down, and then very slowly and carefully sanded them so thin that they were flush with the finish on the top. Yet again, I was faced with some painstaking, delicate work – one stray move and I’d scratch the finish. Fortunately I didn’t have any problems, and it came out pretty well, methinks.
I determined the the bridge still matched the top, and glued and clamped it down. My camouflaging job wasn’t too bad:
Now that the guitar was all together, I let it sit for a few days to make sure that it was going to stay flat. It now appears that everything is staying put, so I’ll chalk this bridge plate overlay as a success. The guitar is now much more playable, the tone hasn’t been affected negatively, and the whole thing is completely reversible. Huzzah!