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Acoustic guitar bridge problem
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=37745		 Page 1 of 1
Author:  Alexander Baev [ Sat Sep 15, 2012 9:26 am ]
Post subject:  Acoustic guitar bridge problem
Hi.
I need advice on solving the following problem. I have a guitar with partly unglued bridge. The problem is that the top is not smooth. It has a cavity from the side of the soundhole and a hump from the other side. Is it possible to level the top? What is the best solution in this case?
http://imageshack.us/photo/my-images/827/p1010137m.jpg/
http://imageshack.us/photo/my-images/820/p1010131m.jpg/
Author:  Daniel Minard [ Sat Sep 15, 2012 11:05 am ]
Post subject:  Re: Acoustic guitar bridge problem
It looks like you have a few challenges to deal with here. First, you will need to remove the shell (or plastic) dots on the bridge. You will probably find screws underneath.
Once the screws have been removed you will need to heat the bridge to soften the glue.
It looks like the top has several open cracks already. It will take care & patience to work the bridge off (with a thin palette knife) without digging large chunks of spruce out of the top.
Once the bridge is off, the loose bits of spruce will need to be glued back down & the area flattened out. Hydrating the top with damp paper towels & clamping the area flat is the next step. This may take several tries over several days, before it stops springing back into its current shape. You will need to make appropriately shaped cauls to do the clamping job.
Then, you will need to flatten the bottom of the old bridge or make a new one.
Once that's all done, it's a fairly simple matter to prep the gluing surfaces & re-glue the bridge.
I would use hide or fish glue.
Author:  Alexander Baev [ Sat Sep 15, 2012 3:21 pm ]
Post subject:  Re: Acoustic guitar bridge problem
Daniel Minard wrote:
It looks like you have a few challenges to deal with here. First, you will need to remove the shell (or plastic) dots on the bridge. You will probably find screws underneath.
Once the screws have been removed you will need to heat the bridge to soften the glue.
It looks like the top has several open cracks already. It will take care & patience to work the bridge off (with a thin palette knife) without digging large chunks of spruce out of the top.
Once the bridge is off, the loose bits of spruce will need to be glued back down & the area flattened out. Hydrating the top with damp paper towels & clamping the area flat is the next step. This may take several tries over several days, before it stops springing back into its current shape. You will need to make appropriately shaped cauls to do the clamping job.
Then, you will need to flatten the bottom of the old bridge or make a new one.
Once that's all done, it's a fairly simple matter to prep the gluing surfaces & re-glue the bridge.
I would use hide or fish glue.

Thanks, Daniel.
Actually the major question was how to flatten the top. I already put off and reglued bridges but on rather flat tops.
Could you please give me more thorough explanation of flattening the top with approximate timing (I mean how long should I apply wet paper and so on). Should I add some braces to the top?
Author:  Josh H [ Sat Sep 15, 2012 3:25 pm ]
Post subject:  Re: Acoustic guitar bridge problem
I've used this with some sucess to flatten tops that have pulled up in the bridge area.

http://www.stewmac.com/shop/Tools/Special_tools_for_Bridges/Thompson_Belly_Reducer.html

Josh
Author:  jackwilliams [ Sat Sep 15, 2012 5:59 pm ]
Post subject:  Re: Acoustic guitar bridge problem
"It has a cavity from the side of the soundhole and a hump from the other side."

just about impossible to correct, short of removing the back, and re-bracing the top...
Author:  dradlin [ Sat Sep 15, 2012 6:05 pm ]
Post subject:  Acoustic guitar bridge problem
This sounds like a place for the JLD Bridge Doctor...
Author:  Mike OMelia [ Sat Sep 15, 2012 9:35 pm ]
Post subject:  Re: Acoustic guitar bridge problem
I think what is missin here is the name and model of the guitar. Second, those pictures are not very good resolution. That is a strange looking bridge. And the top has very wide grain. How old is this guitar? Screws in the bridge is not a good sign. And what are they anchored in? Reach in there and feel around. If this is some kind of vintage guitar of value, then any advice you get here should be based on that.

Mike
Author:  Daniel Minard [ Sat Sep 15, 2012 10:42 pm ]
Post subject:  Re: Acoustic guitar bridge problem
I agree that the dip in front of the bridge is probably not fixable. The hump behind the bridge is a simper matter. Make a caul for the inside that has a slight negative radius so when you dampen & clamp the top, you will be pushing it down in a gentle arc. When it springs back, it might just end up where you want it.
The caul might have to be slotted to miss the internal bracing. A bright light inside the guitar will show you where the braces are located.
Edited later due to dyslexic moment.
Author:  Alexander Baev [ Sun Sep 16, 2012 1:12 am ]
Post subject:  Re: Acoustic guitar bridge problem
Mike O'Melia wrote:
I think what is missin here is the name and model of the guitar. Second, those pictures are not very good resolution. That is a strange looking bridge. And the top has very wide grain. How old is this guitar? Screws in the bridge is not a good sign. And what are they anchored in? Reach in there and feel around. If this is some kind of vintage guitar of value, then any advice you get here should be based on that.

Mike

It is 1987 Bulgarian Kremona so I don’t suppose it’s something of big value. If more pictures are needed just say what point would you like to see.
My plan is the following. Unglue the bridge. Make appropriate caul to curve the top in the direction opposite strings tension. Reglue the bridge. The question is what area should I wet? From the inside or outside? What is the best method of wetting?
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