Checking a Top For Bellying or Cupping
Source: Guitar Bridge Plate Repairs
How to Remove a Loose Bridge Plate:
Bridge plates are an extremely important part of the guitar top plate strength and durability. Often as the guitar dries out over time, the bridge plate glue will dry also and begin to separate from the top.
The bridge plate serves the guitar top plate well as it gives a great deal of stability to the most stressed part of the guitar – the top. The strings exert a tremendous prying action on the bridge and that is conveyed to the top and the bridge plate located beneath the bridge. The structural strength of the top is dependent on this structural bond between these 2 pieces of wood to resist this string tension, thereby resisting bowing or bellying of the top.
If you look at the diagram at the beginning of this article you will see the areas that will display a loose bridge plate problem. Be aware that just about every guitar displays a slight amount of bellying and cupping around the bridge area, especially after years of the guitar being strung up. If a guitar does not display “ANY” amount of deformation, then the top is probably built too thick and it could have sounded quite a bit better with a thinner top.
Usually you will not have a problem with the guitar top if the top pulls up about 1/8″ to 3/16″ from the edges. More than this and it is time to start looking for problems inside the guitar.
Tools and Materials:
Stanley 7.5″ Wonder Bar:
Mechanics Inspection Mirror
LED Work Light
Brace Probe:
Inspect The Bridge Plate:
First you should determine if there is indeed a bridge plate problem. You can sure see one from the exterior of the guitar by the classic bellying of the top behind the bridge that is usually accompanied by a cupping of the top in front of the bridge. (be aware that this same condition can be caused by loose or broken structural braces.)
Place an Mechanics Inspection Mirror inside the guitar and with an LED Work Light and the Guitar Brace Probe, try to find loose areas around the bridge plate. If you can extend the probe beneath the bridge plate in any area, you will need to remove it and reset the plate.
Removal of the Bridge Plate:
To remove the bridge plate we need to pry it off with a reworked Stanley 7.5″ Wonder Bar:. The edge of the bar is sharpened at about a 45 degree angle. We want make this much more tapered, say about a 10 to 20 degree angle so we can slip it under the loose bridge place much easier. Secondly, I cut the wonder bar roughly in half so I can easily maneuver it from within the inside of the guitar. Actually I have reworked two of these. One is about 5.5 to 6″ long – this one has the gradual arc. The second one is about 4″ long that has the hook.
I do have one more of these where I heated the hooked end enough to remove the temper and hooked the end completely around itself to form a “U” shape. This one can be maneuvered from the soundhole much better.
Also before you start prying at the loose place you should place a protection piece of wood between the wood top plate and the wonder bar.
Ultimate Guitar Repair Tip: Pay attention to the grain direction for the top. Remember that we had this concern with removal of the bridge as well. The bridge plate space across 2 different top plates and it will be more than likely that you will have to work in 2 different directions to get the bridge plate loose with minimal damage.
Slowly work the pry bar beneath the plate and gently pry upward. Move a bit more and repeat. Now start over and try to shove the pry bar under the plate a bit more. Do this until the plate separates from the top.
Be very careful not to extend the pry bar beneath structural braces.
It’s almost a sure bet that the bridge plate will come out in pieces. Try to keep track of them as we will attempt to make a pattern for a new bridge plate from them.
Final Sanding
Visually check that there are not pieces of the bridge plate left on the top. Try to clean them off with a small flat chisel or a sharpened putty knife if there is.
Finally, sand the bridge plate area with 120 grit sandpaper and work down to 220 grit, until everything is smooth. Make sure you have all traces of glue removed as well.
Tags: fix a bellied guitar top, guitar bridge plate, how to remove a loose bridge plate, replace a bridge plate
