How to File Down a Guitar Bridge

High action makes guitars uncomfortable to play, and the additional bending of the string when fretting a note can mean you’re constantly off-pitch when playing. File down the bottom of the bridge (or saddle, specifically) of an acoustic guitar to correct your action, which is the distance between the strings and the fretboard. If your action is high, notes can be hard to fret, and when you do manage to play a note, it will often be slightly sharp. Conversely, low action can cause fret buzzing, meaning that care must be taken when sanding down an acoustic guitar bridge to adjust action.

Measure the action on your acoustic guitar. Do this by measuring the distance from the top of the 12th fret marker to the bottom of both the low and high E strings. Find the 12th fret marker by looking for the vertical strip of metal between the 12th and 13th frets. The distance from the top of the fret marker to the bottom of the low (thicker) E string should be 3/32 of an inch, and the distance to the bottom of the high E string should be 2/32 of an inch. The low E string can be as high as 7/64 of an inch and the high E string can be up to 5/64 of an inch and still be in normal range. Note the distance by which your strings are too high, if they are.

Remove the saddle from your guitar. Most acoustic guitar saddles will be drop-in saddles, which can be removed by pulling them up firmly with your hand or a pair of pliers. Take out your guitar’s saddle in this way. If you can’t do it, you may have a glued-in saddle, which must be heated prior to removal to loosen the glue. Your guitar’s lacquer (coating) is particularly susceptible to heat, so get a heat shield and cut a saddle-sized hole in it. Heat the saddle with a hair dryer prior to removing.

Mark a line on the bottom of your saddle according to the measurements you took of your action. If you need your strings to be 1/32 of an inch lower at both ends, draw a straight line 1/32 of an inch up from the bottom of the saddle. If the two sides require slightly different adjustments, plot both onto the relevant sides of the saddle and draw a straight line connecting them.

Lay some sandpaper down on a flat surface. Hold it in place and sand the bottom of the saddle down on it. Sand it up to your pencil line for an accurate adjustment. You can use a file to remove the excess saddle if you wish, but sandpaper is easier for most people. Move the bottom of the saddle back and forth across the sandpaper.

Drop the saddle back into its slot, restring the guitar (or at least the two E strings) and check the action again. Make further adjustments if required.