A good customer of mine brought in his 1972 Martin D-35 into the shop for me to check out. Upon inspection I quickly noticed that there was a gap behind the bridge.
Sliding a piece of paper under the bridge revealed that it had separated all the way to the bridge pin holes. This bridge happens to be a custom oversized bridge made by a previous luthier. The 70's Martins have a reputation for having the bridge in the wrong location and hence having poor intonation. This custom bridge, along with the saddle extension on the bass string, improves the intonation on both standard and dropped tunings that the customer uses. Unfortunately this bridge may have not been glued down properly or the guitar was in a hot / dry environment and the joint has begun to fail.
Let's pull it off and reglue it.
This guitar has a Fishman Ellipse Blend pickup system which contains both an undersaddle piezo pickup and interior microphone. We need to remove the undersaddle pickup before removing the bridge. I loosened the jack and opened up the housing to gain access to the preamp's circuit board.
See the middle black wire coming up through the board on the bottom of the photo? This is the piezo undersaddle pickup that we need to disconnect. Follow the wire up the board and there are two connections that must be desoldered. The left bare wire is the ground shield and the right side is the hot lead. Make sure you remember which one is which for later.
Here below is an amazing tool for desoldering. It is called a "Soldapullt" and is in essence, a spring loaded vacuum. Say goodbye to your old rolls of copper braid. The copper braid method is very crude in comparison and you always risk burning components trying to get all of the solder to wick up into the braid. With this tool you can apply heat with your soldering iron until the solder melts, then hold the tip of the Soldapullt over the solder and push the trigger. Boom. The solder is sucked up into the tool. Push the ram to eject the solidified solder and it's ready to use again.
So beautiful. You're welcome :)
Ok, now the pickup is removed and I reinstalled the jack so it doesn't flop around inside the guitar. I place the disconnected pickup in my parts box along with the other loose items for this particular guitar. Waverly tuner boxes are excellent for keeping your repairs organized.
Now we are ready to get started on removing the bridge. Most glues used in guitar building are broken down with either moisture or heat, or a combination of both. We're going to keep things dry and just use heat on this bridge. First though, we need to protect the areas of the top that we do not want to heat.
This is just a piece of corrugated cardboard with a cutout for the bridge and covered with aluminum foil. This will reflect the heat and keep the top nice and cool.
The bridge on the other hand, is going to get a sun tan.
This is an infrared lightbulb in a common shop light fixture that you find at the hardware store. This one just so happens to be mounted on an old mic stand with a boom. Whatever stand you use, make sure that it is secure. You do not want anything that is suspended over a customer's instrument to come crashing down.
Another word of caution: never leave any high-heat source like this unattended. Soldering irons, bending irons, propane torches, side bending blankets, infrared light bulbs ... just do not walk away because you are going to get distracted and bad things can happen quickly. This is not a time to multitask.
(stepping down off the soapbox ...)
Ok, after a few minutes of heating I check the bridge with my fingers to see how hot things are getting. You do not want to burn the bridge off. Heat it just enough to soften the glue. When it feels hot to the touch, turn off the light, pull the light away and remove the corrugated_cardboard_covered_with_aluminum_foil thingy.
Now we can test how well the glue was softened by using your pallet knife of choice. Since the bridge was lifting in the back, we have our access point.
This is a gentle process. The more methodically approach prevents a slew of additional repair work for you. If the knife is hard to insert under the bridge, repeat the heating process for a few more minutes. Remember, stay put!
Work the knife from the edges and be careful not to go through to the other side. You want to work from the outside in towards the center. Also be careful of the finish surrounding the bridge. This is a delicate area that is easily damaged by careless knife work.
One more concern is the run out in the top. You need to be conscious if the top has any run out.
"What the hell are you talking about? What is run out?"
Glad you asked.
The simple "tell" that a top has runout is when one half is dark and the other half is light in color. If you flip the guitar around 180 degrees, the light and dark sides switch. The dark side is actually the end grain coming up through the surface of a top that was usually not split in the milling process. Splitting the top blank (or billet) before resawing helps minimize run out because the wood will naturally separate along the grain line. This increases the likelihood of subsequent cuts being parallel to the grain. Larger diameter trees and certain species are less susceptible to run out. Run out in a tree is caused by the tree actually twisting to follow the sun in the sky throughout the seasons. At least that's what I've heard ...
Woah, back to getting this bridge off.
So now that we know what run out is, what do we do about it? We want to work our knife in on the light side of the soundboard. This will minimize our chances of the knife catching this run out and diving down into the top, which is a bad thing. This D-35 top had no signs of run out, so I was free to to go in from any edge.
And here it is. The bridge came off relatively cleanly. Note that you can see that the finish around the bridge was damaged slightly from the previous luthier's bridge removal. Now the bridge is still really hot, so I like to clamp it to something flat, like a piece of aluminum. This allows the bridge to stay flat while it cools and minimizes any further distortion. Usually when you have a bridge that is failing, it can be slightly (or even moderately) distorted because all the string pressure is being held by a reduced portion of the bridge. The bridge can cup upwards slightly. You may have to replace a bridge if it cannot be refit to the top. This one should be ok to refit.
You can see above how much the previous luthier had to move the bridge pin holes by where he / she plugged the original holes with rosewood.
I will let the bridge cool down and then start cleaning off the old glue and refitting it to the top. We want a nice clean, tight fit so the bridge can stay down.
On the side of this guitar just so happens to be Tommy Emmanuel's signature! Pretty cool, just have to make sure I don't get it wet or sweat on it.
I do not repair signatures :)