Fixing a warped guitar top

Issue 303 April 19, 2018

Someone made a really odd attempt at repairing braces inside this Gibson 12-string. That didn't keep the top from twisting into a wave shape. Dan Erlewine shows a simple fix.

Video Transcription

[on-screen text reads: Stewart MacDonald tools + ideas for guitarmaking. Fixing a Warped Guitar Top]

Oddest brace repair Dan's ever seen

Dan Erlewine: Here's a Gibson B25 12-N from 1965, 12 string guitar. Came into the shop with a collapsed top. We've been working on it, and it's better now. It was collapsed towards the sound hole, pulled up at the bridge. That's called the bridge bellies. It pulls up. What happened was whoever tried to fix this cut the X brace out right in here, the main bracing. They sawed it out, and then they put in these braces right through where the X brace was. This is a little box of pieces of cherry, hide glued or epoxied to the back and the top to support it. And it sure didn't work. So we went in there and put some new X braces in here, not the full thing, because you'd have to do some serious top taking off to do that, and this guitar wouldn't be worth that. So we have some partial X braces in there, and we took the pick guard off. That relaxed the top.

A simple solution: The Bridge Doctor

It was splitting here, but there's one more thing that it needs. I'm going to show you with a demo guitar that's cut in half. Here's my demo guitar. It's not a 12 string. It's a six string, but what I'm going to do works for either. I want to keep this top flat after we've done all the work we've done to it, and I'm going to do that with this. It's a device called the Bridge Doctor [on-screen text reads: JLD Bridge Doctor - stewmac.com]. It's not so much a tool, but a permanent installation.

It's really simple. It's a wooden block of poplar with a hole drilled through it, and in that hole is a threaded nylon insert, which accepts this screw. We're going to drill a hole and the screw is going to go right down through the bridge. It's going to screw into that post and suck it up to the bridge blade. That brings the top of the L, that wood, where the most tension on the saddle is. That's going to be tight in there, and then I'm going to go through the sound hole with a wood dowel. You push this against the tail block and make a mark. Then out comes the dowel and in goes the threaded insert. At that point, when you tighten that threaded insert, it's pushing on the dowel, which bears against the tail block, countering the rotation of the bridge. In our case, it's going to be a perfect way to fix the remainder of this collapsed top.

Installing the Bridge Doctor

I think I'm going to need a little light in there to zero in the screw into that post. It's a little tight squeeze. It's a skinny body, very close. The hardest part of this job is getting my hand in there on a body this skinny from top to bottom. Okay. There's the set screw. I'm just going to sort of let it find its way into that nylon thread. Yeah, perfect. It's right online with the strap button hole. I'm going to put a lot of tension on this. I don't want to break it. I'd say now we're done. I've got this little pearl inlay that'll fill right back over it. Now you can't see the Bridge Doctor, but it's in there. Pretty amazing. If you'd ever seen what this looked like when it was at its worst, this is really good, and if it holds there, it's going to be a player.

Dan Erlewine

Guitar Repairman and Builder