One of the most difficult areas to achieve a good finish on a new instrument is around the bridge. Many luthiers mask off the footprint area, but leveling the finish in that area with the tape on it is seldom satisfactory. Some other makers use the traditional toothed scraper to clean the footprint, but it often gouges the wood and leaves a rough gluing surface. Glues like Titebond are not gap filling adhesives and they require a smooth surface for the best bonding. A rough surface on either the bridge bottom or the instrument top weakens the joint. My favorite technique for removing the lacquer under the bridge area is the “hot chisel” method. It works well on all types of lacquer and is worth trying on other types of finishes you may be working with.
This technique requires your total attention. Take the telephone off the hook, turn off the music, and kick your friends out!
The necessary tools are simple. For the chisel I use an extra blade from
a fingerplane. The blade should be sturdy, without much flex. I attach a handle
to this blade by cutting a slit in a ½” dowel, inserting the blade, and
taping it on. It’s not very pretty, but it’s comfortable and effective.
The end of the handle burns up in time anyway. The only other tool needed
is an Exacto knife with a new blade and a propane torch.
To easily locate the bridge position, I drill 1/16” holes
through the saddle slot into the top prior to applying the finish.
Some people use the bridge itself as a guide for cutting through the finish. I have problems with that because the knife blade can easily get caught by the bridge wood and I also have difficulty seeing exactly where the knife tip is in the shadow created by the bridge. Using the bridge and locating pins I make a template out of poster board. After drawing the bridge outline I cut about 1/16” inside that line to create the template, making sure I mark which side of the template is up as the 2 sides of the bridge are never exactly symmetrical. I then place the template on the top and carefully cut around it with the Exacto knife.
The next step is to heat up the tool and go to work. It takes a little practice, but there is lots of area for trials. The tool needs to be quite hot, but not red hot. You can practice in the middle of the footprint, away from the edges. Try pushing the tool as a chisel and then pulling it as a scraper. Only when you have a feel for the tool and how hot it needs to be should you attempt to clean the perimeter of the bridge area. I usually work in the middle area when I have just heated the tool and then move to the edges as the tool cools. If the tip is too hot, you can melt lacquer beyond the area of the edge. It takes me about 10 minutes to clean the whole footprint. I know no other way to do this job as good.
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Once the footprint is clean, you are ready to glue on the bridge. The locating pins make this job easy. Bevel the bottom of your bridge just slightly and it should sit down nicely into the clean footprint area. I use a stiff piece of 80 grit sandpaper to create the bevel as a scraper can sometimes tear the edge or take off too much wood.
