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severe wood tear out from bridge removal
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=28936		 Page 1 of 1
Author:  usAcoustic [ Mon Sep 06, 2010 1:04 pm ]
Post subject:  severe wood tear out from bridge removal
Hello, new guy here.

A little background about me: I started doing set ups and some "limited" repairs on acoustic guitars a couple years ago. Along the way I've repaired several broken necks, partial fret work, and even sectioned in a new piece of spruce on a top that had a hole punched in it.

I've invested in the correct tools for each job that came along, and have a line of sight on some classes given by recognized luthiers. Until then, I'm doing random repair jobs, learning more, and adding to my skill sets.

A friend of a friend recently brought me a guitar for repair that has me sitting here just staring at it. Hoping someone with more experience might chime in.

This guitar has had the bridge removed. I don't know whether they used a machete or prybar (or combination of both), to get it off. It is a mess. I think someone put steel strings on it, and it lifted, and then someone finished the job...so to speak. I don't know what they were thinking... :?

Personally, I think it's a candidate for the toothpick pile. But, apparently it belongs to a kid, and the family can't afford to replace it. So, here we are.

It is a nylon string guitar, with laminate top. The area under the bridge is no longer uniform, with some areas torn out, gouged out, deeper than others.

Couple questions:

How much of a gap can glue effectively bridge? I'm estimating that about 40% of the area between soundboard and bridge will have good, solid contact area, with the rest kinda iffy. gaah

Can anyone comment on polyurethane glue? I'm thinking about using that because, as I understand it, it has less shrinkage than wood glue, and might be more effective at filling the random voids between bridge and soundboard.

Thanks.
Author:  Kent Chasson [ Mon Sep 06, 2010 1:23 pm ]
Post subject:  Re: severe wood tear out from bridge removal
On a cheap laminate guitar, I'd use a good epoxy. It should bridge the gaps just fine and hold plenty well for nylon strings.

The problem is cleaning squeeze-out. I would carefully wax the top around the bridge and the sides of the bridge and peel off the squeeze-out when it's hard but not completely cured.
Author:  usAcoustic [ Mon Sep 06, 2010 2:20 pm ]
Post subject:  Re: severe wood tear out from bridge removal
Thanks for the tip about the wax...hadn't thought about that. [:Y:]
Author:  Darrel Friesen [ Mon Sep 06, 2010 3:26 pm ]
Post subject:  Re: severe wood tear out from bridge removal
Definitely not polyurethane. Any gap at all means foam with next to no strength.
Author:  chinito [ Mon Sep 06, 2010 3:39 pm ]
Post subject:  Re: severe wood tear out from bridge removal
You can also use plain old white vinegar to clean epoxy squeeze before its hardens.
Author:  bluescreek [ Mon Sep 06, 2010 3:51 pm ]
Post subject:  Re: severe wood tear out from bridge removal
Why not inlay a piece us spruce under the bridge , make the repair easier and in the long run much longer lasting. You can rout out the area fast and inlay a new chunk and sand flat and you will be good to go. Just my 2 cents
Author:  Daniel Minard [ Mon Sep 06, 2010 11:54 pm ]
Post subject:  Re: severe wood tear out from bridge removal
On a "good guitar" I would agree wholeheartedly with John, but on a cheap laminate top I'd use a good quality epoxy. Sanding a spruce insert repair flush, without damaging the surrounding finish will be very difficult. Finish repairs are fraught with complications & can take more time than the instrument is worth.
Just one more opinion...
Author:  John A [ Tue Sep 07, 2010 7:26 am ]
Post subject:  Re: severe wood tear out from bridge removal
If steel strings were on there - the top may also be permanently deformed - so after you fix the bridge - the action may be discouraging for a child. I would go with the $25 plan and pick up a new one - and a new classical better than the one you have, will run about $50.00 - you can set that up and make a child happy. Although the kid probably really wants an electric.
Author:  usAcoustic [ Sun Sep 12, 2010 2:04 pm ]
Post subject:  Re: severe wood tear out from bridge removal
bluescreek wrote:
Why not inlay a piece us spruce under the bridge , make the repair easier and in the long run much longer lasting. You can rout out the area fast and inlay a new chunk and sand flat and you will be good to go. Just my 2 cents


Yeah, you were right, it was quick to rout it out. That was the first thought that came to my head, but I thought it would take longer, and was looking for quick solution.

I applied light tack masking tape to protect the finish, took some measurements and clamped some guides in place to stop the router from overrun, I was actually quite surprised at how little time the job actually took. A few seconds of chisel work in each corner...done.

I routed out the area down to the deepest point of damage, and also to the shape of the new bridge. I ended up with a slightly recessed area to drop the bridge into. And, I didn't have to worry about "creep" while it was clamped up for gluing.

So, now, I had the clean, but raw routed edge adjacent to the bridge. Maybe a couple thousands gap. I took a toothpick, dipped it into polyurethane, and came up with a tiny drop on the tip. I touched the tip to the gap, and as I pulled the toothpick along, the poly "flowed" right behind it. A few drops later, it's looking good.

I don't know how orthodox it is, but the end result is pretty nice.

Next step, string it up and check the action...I don't foresee any issues, the top looks ok. Plus, I think by dropping the height of the bridge (relative to the top), that will be advantageous to fine tuning the action.

Thanks for the ideas/feedback, everyone.
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