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I've got an old Sigma 12 string in front of me, the bridge lifted, and has curled quite a bit. Usually on a guitar like this I'd just clean up the bottom of the bridge and refit it to the top of the guitar which usually means removing material from the bottom of the bridge and in the process this deals with the curl. But this bridge is quite thin, and I don't think I'll be able to remove enough material from the bottom to deal with the curl and leave enough material to ensure the bridge is still doing its job. Any suggestions on saving this old bridge, or is it time for a new one?

I suppose it's possible, Conor - but the few times I've tried I wasn't pleased with the result. Sanding to level will work, of course - but as you pointed out, the bridge is already thin. I remember reading about a laminated bridge years ago, but never saw any cross my bench.

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"Act your age, not your shoe size" - Prince

If the curl is not severe I have occasionally had success heating the bridge and clamping it to something very flat for 24hrs. Sometimes this has little effect, however.

For cupped bridges, I have improved the situation by heating and clamping to a heated TJ Thompson belly reducing caul which has the opposite (eg concave) curve.

But on a Sigma a new bridge is the way to go if the customer is open to the extra cost.

Just like with heat pressing necks we can reshape seemingly anything.

Getting it to stay that way is another matter.....

Make a new bridge if you think it's too thin after milling the bottom flat. We don't reinstall bridges flat either we shape the bottom to match the top curve using a single edge razor and/or the end of Dan Earlywine's Dad's belt sander that we have in our shop

Since it's a 12 too even more important for good fitment. Look what happened to the last bridge it came off and shape shifted.

I heat bridges as well to flatten them but let it sit on wet paper towels and allow it to soak in some water first. All of the glue residue (within reason) needs to be scrapped off first, the water needs to soak into the wood a bit. The idea is to generate enough steam to help make the bridge a bit pliable. I use a 3/4" thick block of Aluminum and heat it to no more than 400 degrees. I monitor this with a bi-metallic temp gauge. Dry wood will start charring at that temperature but not when it's been whetted. Clamp the bridge to the heated block quickly as possible, have everything ready in advance. I usually leave it clamped over night but you probably don't have to wait that long, I just want it to be fully cooled off and dry. I have had rather consistently good results doing this.

I’ve went as far (with extremely warped bridges)as boiling the bridge. then when it’s good and hot remove it from the water and clamp it to desired flatness and let it dry. It’s worked every time I’ve had to use that method. I don’t recommend it for the casual repair person.


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OP's doing this for revenue, and he needs to be aware that he can't afford to mess with a warped bridge for an hour with no revenue. That alone turns this job upside down. My opinion: new commercial bridge and out the door. Or the customer pays for time and materials, and that ain't cheap.

Some jobs just don't make economic sense, romance with the instrument notwithstanding. A Yamaha 12-string stands a chance of being better economics than fixing this one.

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Peter Havriluk

There is another option but I've only done this once. Normally I just offer to buy a replacement bridge (cheapest option) or make a new custom bridge (more expensive option). I had one come in with an oddball 12 string bridge that was too thin after flattening it and where no similar shaped replacement was available. I fixed it by laminating another piece of wood to the bottom with carbon fiber cloth in the middle (ala Gore/Gillet). The original bridge had a tight crack along the grain so I fixed that first and the CF cloth was to prevent the bridge from cracking again. It was a bit more expensive than a replacement but cheaper than me making a new custom bridge. I checked with the owner a few years later and it worked just fine.

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Steve Smith
"Music is what feelings sound like"

Conor, if you make a new thicker bridge will the neck angle be OK? I would say that if you plan to reset the neck, make a thicker bridge and set it to that. However it migh not be worth it on an old Sigma 12.

I did end up boiling the bridge and then clamping it flat. Once it was flat it became clear to me that there was such a significant belly to the top of the guitar, which was probably the biggest culprit for the lifting bridge in the first place. Because of the value of the guitar (which was not much in real dollars) I thought I'd try the Thompson Belly reducer set up that stew mac sells. It seemed to work well. I was able to refit the original bridge to the top without losing too much material. I guess time will tell how long that repair lasts, but I kept the guitar going for a while longer anyway.

Done's done. I match-sand the bridge to the soundboard when I'm installing a bridge. Idea is to not force either the bridge or the soundboard into conformance. So far, so good.

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Peter Havriluk

Me too. The logic makes perfect sense.