Tilting, lifting and warping bridges - Oct 2006
On a stringed instrument, the bridge supports the strings, determines intonation and, in an acoustic instrument, controls tonal quality by how well it transmits vibration to the ‘sounding board.’ If the bridge has a problem, the instrument has a problem.
Instruments that have floating bridges (violins, violas, celli, basses, banjos & mandolins - some guitars) develop slightly different problems than instruments that have fixed bridges (guitars & bass guitars - some mandolins). Because floating bridges are held in place by the downward pressure of the strings, tuning (tightening and loosening the strings) can tilt the bridge forward or backward. A tilted bridge transfers less vibration, causes incorrect intonation and, left uncorrected, promotes bridge warping.
Until warping occurs, tilting is correctable - as simple as setting the bridge at the angle at which it is supposed to stand. After warping occurs, the bridge must be replaced. This kind of warping is most common in violin family instruments for which a new bridge is quite costly. Mandolins, banjos and guitars with floating bridges can also warp as a result of uncorrected tilting. Mandolin and guitar bridges are also expensive. And, while banjo bridges are not expensive, the money spent on a preventable problem cannot be spent on fresh strings or gas to go to a festival.
Therefore, this issue is important to anyone who has an instrument with a floating bridge. These folks should regularly make sure that their instruments’ bridges have not tilted inappropriately. If you are unsure of the correct placement, ask a qualified repair person to show you. If you know that your bridge is tilted, and have never straightened a bridge, ask a qualified repair person to show you how.
Bridges on banjo-style instruments with flexible heads and mandolin and guitar bridges with adjustment wheels can also warp another way. If the head of a banjo style instrument too loose, the head flexes under the feet of the bridge. Left uncorrected, the bridge will warp downward in the middle. Guitar and mandolin bridges with height adjustment wheels can also warp in the middle, especially if the wheels are screwed far out. If you are not sure how much tension should be in the head of your banjo-style instrument or how your adjustable guitar or mandolin bridge should be set, ask a qualified repair person to show you.
Instruments that have fixed bridges suffer other issues. Because a fixed bridge is glued onto the sounding board and the strings pull upward on it, bridge lifting is the problem for which you should watch - especially if the instrument has had exposure to high temperatures that soften the glue.
When the glue joint begins to fail, a very small gap appears between the bottom, rear edge of the bridge and the sounding board of the instrument. If you catch this problem early, the bridge can be reglued and replacement is not necessary. However, left uncorrected, the gap will grow and the bridge will warp. Once warp occurs, bridge replacement is necessary - a costly repair. To avoid this problem, regularly inspect the rear, bottom edge of the bridge to verify that it’s not lifting. If you find even a tiny gap, seek advise from a qualified repair person.