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Fret Repair
Fret repair is a common job performed by luthiers and  guitar technicians, though it is often necessary for all fretted instruments. There are many factors that can contribute to fret damage including regular wear, mishandling of the instrument, and humidity.



Fret Leveling
Regular fret wear causes a flat spot on the previously round top of the fret. This can result in buzzing, poor intonation, and difficult playing. Unless the damage is severe or the fret has become too short, the issue can often be resolved without replacing the frets. Generally, frets shorter than .030 inches do not have enough material remaining and are often replaced instead of repaired.

Fret leveling is a process that sets all frets to a uniform height, which ensures minimal fret buzz even at low action. Before leveling can occur, the neck of the instrument is checked for straightness by placing a straightedge along the neck. Leveling frets while the neck is curved results in uneven frets once the neck is corrected. On modern guitars and  electric basses, necks are straightened by adjusting the truss rod. Loosening the truss rod corrects a neck with backbow, while tightening will correct a neck with upbow.

Before performing any fret work, the fingerboard and body of the instrument are covered with low tack tape to prevent any damage from files and other tools. Leveling is achieved by running a leveling file or leveling bar lengthwise up and down the neck. This process takes .002 to .005 inches of material off the frets, bringing them to a uniform height while creating flat tops on the frets.



Fret Crowning
The flat tops on the frets that result from the leveling process are removed to achieve good intonation and comfortable playing. A crowning file is used to remove material from the sides of the fret, creating a round shape to reduce the area of contact between the strings and the fret. The most common types of crowning files are triangular or concave. The very top of the fret is left untouched leaving a small flat strip along the fret. This creates the ideal fret shape, while leaving the top of the fret intact and keeping all of the frets at the same height.

Fret Dressing
Leveling and crowning leaves the frets marred and rough. Sandpaper is used to remove the marks and smooth the frets. Different grades of sandpaper are used for the smoothing process, starting with low grade sandpaper between 220 and 400 grit, moving up sequentially to higher grade sandpaper between 600 and 1000 grit. Once the frets are smooth, they are polished with an abrasive pad. Grade 0000 steel wool is also commonly used for polishing but leaves tiny metal fibers that are magnetically attracted to guitar pickups.

Exposed Frets Ends
Dry weather and low humidity causes the wood in many instrument necks to shrink and contract. Because the metal frets in the instrument do not shrink, the ends of these frets will protrude on each side of the neck. To avoid uncomfortable playing these ends are filed flush to the neck. The file is tilted between 20 and 40 degrees to match the bevel of the frets. Filing is stopped just before contacting the wood or finish of the instrument. Once the frets are flush with the neck and beveled they are smoothed and dressed to avoid any sharp edges. To prevent exposed fret ends and other common issues, the ideal humidity for most instruments is between 40% and 50% humidity.