Acoustic Guitar Bridge Plate Repair

Bridge Plate- The bridge plate is a thin veneer (usually around .100+/- thick) of maple, rosewood or other material that is glued to the top directly beneath the bridge, inside of the guitar. It offers the top strength and stability and is vital to the tops integrity. A cracked or warped bridge plate can cause structural problems which may result in excessive bulging of the top (bellying), cracking and loose bridges. Problems with bridge plates should not be ignored.
In most cases bridge plates are removed using special chisels and spatulas while working with your arm stuck in soundhole. Not a job for the faint of heart. As you can imagine, you are performing much of the removal by feel and not by sight.

A 1940 D-18 that I have just removed the bridge plate from.
Around this period of time it is not uncommon to find the plate itself "tucked" beneath the tops X-brace on Martin guitars. In order to remove the plate it has been cut right at the edge of the brace, leaving the ends to fill the notches cut in the X-brace for it's installation.

There are and have been a few different bridge plate designs over the years. As seen in the photo above, some bridge plates are tucked beneath the tops X-brace, locking them under the braces and making removal far more difficult. On others you may find large or overly thick plates made of laminate material which deaden the sound.
The size of the bridge plate undoubtedly plays a role in the voice of the instrument and should be considered when replacing it.

Repairing Worn / Oversized Holes in The Bridge Plate

The ball ends of guitar strings can do damage to the bridge plate over time. The cleaner the original hole was drilled thru the plate at the factory the longer they tend to hold up. One thing many people notice is that the winding at the end of the string which twists around the ball end is now far more visible and nearing the saddle.  This is happening because the ball end of the string is not locking against the bridge plate (as seen below) but is actually coming up into the enlarged hole. The further the ball end pushes into the bridge plate the closer the strings end winding comes to the saddle. If enough of this winding is protruding, it can hit the saddle and cause other problems (tuning, intonation).

Another common symptom is flying bridge pins. Because the strings ball end has chewed away a portion of the bridge plate it is now able to begin working it's way back up the bridge pin hole. When that happens the bridge pin actual holds the string in place by jamming the ball end in the hole with the pin instead of the ball end bending nicely around the corner of the bridge plate.

Take a peek at my pathetic drawing and simple explanation.

Repairing worn holes can be done by drilling those holes larger, plugging them with wood and re-drilling them to the appropriate size. You may also opt to install a thin small plate (metal or wood) over the bridge plate holes which has normal sized holes drilled thru it. These plates are small and thin, they are not permanent and my personal opinion from my own personal experience is that they do not hurt the sound.