How Can I Repair A Lifting Acoustic Bridge?

[Stew]

Well someone gave this to me to experiment with repairs. He found this in a rummage sale, sitting in it's case in direct sunlight for hours. He opened the case and found the wooden bridge mount coming unglued and starting to lift off the soundboard by the string tension.

The bridge has individual flat head screws to mount (not glued) and I found underneath the pearloid inlay, is two hidden phillips head screws. But the screws are larger in diameter than the inlays. I thought maybe the inlays were to cover up the screws. The screws don't seem to have any connection with the bridge at all. The screws are flush under the raising bridge. Here are some pics to better describe what's going on.

The glue has hardened. So what can I do to remove the bridge and reglue? Of course I will remove the strings and pins first.

[tirapop]

Have you checked out the bridge repair tutorials at frets.com?

[Mattia]

Go look at FRETS.com, register at MIMF.com and read through the library, using the catalog to find the appropriate repair disccusions.

Mostly: get the strings off of there, a little heat and a spatula, maybe some humidity (touch of water) will let you get the bridge all the way off (watch for electronics! Take those out first if possible), then it's down to cleaning off all the old glue on both surfaces, getting a good match, and gluing the bridge back down. If that dopey saddle adjustment nonsense isn't crucial for the pickup system, I'd also replace it with a proper, non-adjustable bone saddle for tone.

[sdantonio]

Well someone gave this to me to experiment with repairs. He found this in a rummage sale, sitting in it's case in direct sunlight for hours. He opened the case and found the wooden bridge mount coming unglued and starting to lift off the soundboard by the string tension.

The bridge has individual flat head screws to mount (not glued) and I found underneath the pearloid inlay, is two hidden phillips head screws. But the screws are larger in diameter than the inlays. I thought maybe the inlays were to cover up the screws. The screws don't seem to have any connection with the bridge at all. The screws are flush under the raising bridge. Here are some pics to better describe what's going on.

The glue has hardened. So what can I do to remove the bridge and reglue? Of course I will remove the strings and pins first.

Typically these things are held on with yellow glue, something like tightbond. Most guitar makers don't use the good stuff.

Tight bond can be disolved in acetic acid, either warm white vinigar (pop some in the microwave for 30 sec) or 30% of the pure stuff (at room temp) if you have access to a chemistry lab. Brush it on liberally and let it set. I have never had it hurt the finish. It takes about 30 to 60 min to work. It will only discolor the wood if your wood contains large amounts of iron (oak sometimes has this problem). Using a heating blanket is another way to melt the glue, but this will sometimes delaminate the finish if you have nitrocellulous over a shellac ground coat (typical for a guitar finish).

Pry it off gently with a wide flat knife trying not to take off to much wood. A butter knife works well here, or a narrow putty knife.

Now LET EVERYTHING DRY COMPLETELY BEFORE GOING ON

use a cabinet scraper to remove any glue from the underside of the bridge.

use a very sharp chisel to remove the glue from the area on the soundboard where the bridge sits. Check to see if you have taken off the finish everywhere the bridge sits. Often in mass produced instruments the top is masked off where the bridge goes and then finished. Afterwards the bridge is glued on. If any finish has worked it was under the masking tape the the bridge wont stick well. This is likely to be the cause of your problem to begin with.

Replace and wood lost in the process with scraps of spruce glued in place and releveled with the chisel.

reglue the bridge, use a good glue, preferable hide glue (the crystal... DO NOT USE the liquid hide glue crap), but if you cleaned the area well then tightond will work this time.

the bridge may me sitting a little lower doe to loss of wood, so you may have to raise the saddle or make a new one.

Steven