Repairing Minor Cracks in Bridges
Source: Guitar Bridge Repairs
Repairing Minor Bridge Cracks:
Just about every Acoustic Guitar will suffer a cracked bridge at some point in it’s life. The reason for this is the relentless amount of tension pulling on the bridge from the strings, coupled with weak areas that exist between all of the bridge pins of the belly bridge or prism bridge.
What can make this even more pronounced, is the manner in which the bridge pin holes are placed and how much flex there is in the top plate of the guitar.
Arched Bridge Pin Layout:
There is something good to be said about the arched pattern of bridge pins, that you see on certain guitars. Note that on Ultimate Guitar Building Plans we usually give you an option for an arched bridge pin layout as well as the standard, straight-pin layout.
My feeling is that the arched layout will give you a more crack resistant design. The reason this is because the grain of the bridge wood typically is very straight and travels the along length of the bridge. Where does wood usually crack? Yes, you guessed it, right along the grain. With an arched pin layout, the pins do not follow the grain pattern nearly as closely.
Another factor in the arched pin layout is the distance between the pins is slightly more. Now we are not talking a lot of distance here, but even a fraction of a mm can make a difference.
Repairing The Minor Cracks:
This repair technique if for minor, cracks, such as hairline cracks or a crack that is open no more that say the thickness of a calling card, not a crack that is big enough to throw your hat through!
If the crack is larger than this or if it shows signs of displacement, for instance, the back half, behind the crack is slightly higher than the portion in front of the crack, you definitely have to remove the bridge and repair it or make a new bridge.
Prepare The Guitar:
Remove the strings, bridge pins and protect the top with a top template. Place a strip of masking tape inside the guitar beneath the bridge pins to keep glue from dripping into inside of the guitar. Don’t worry about the pin holes. If you get some glue in them you are going to drill them out afterwards anyway.
Since a crack usually an indicator of a structural defect in the bridge, or a weakness in the wood, you need to use the strongest glue possible for the repair. That glue would be the slow set 2-part Epoxy Glue.
Make sure the glue is fresh and you mix exactly a 50/50 mixture and you mix it very very thoroughly.
Next take a artists spatula and smear it over the crack quite thickly. If the crack is slightly open try to work it down in the crack as much as you can.
Now take your finger and rub it across the crack, working the glue in the full depth of the crack. Keeping doing this until no more glue goes in the crack.
Now make sure the glue is slightly proud of the crack to take care of any glue shrinkage. Let the bridge dry overnight.
Bridge Clean-Up:
Take some 180 grit sandpaper on a sanding stick and sand down the glue to the bridge surface until all traces of the glue is gone. Finish up with 220 and then 400 wet/dry sand paper.
Next you can chuck up a drill in a portable drill and drill out the bridge pin holes after removing the tape under the bridge.
Inspect The Bridge:
Next make sure that the bridge has adequate string ramps so string life is maximized and also make sure that the pin holes are slightly countersunk to create a nice aesthetic appearance.
String up the guitar and you have a bridge that will last a long time.
Tags: bridge crack repair, bridge repair, guitar repair, how to repair a cracked bridge, repairing minor bridge cracks
