Fretwork is the most measurable part of guitar building. You can see exactly what you removed, you can measure the result, and the player feels it immediately. It is also the part where shortcuts are most obvious, because a fret job that stops after leveling produces a guitar that buzzes and intonates badly.
There are three operations, in this order: level, crown, polish. Skipping any one of them is not a saving. It is an unfinished job.
Preparation: get the neck straight first
Leveling works by bringing every fret down to a single plane. That plane is defined by the neck, so the neck has to be straight before you start. If the neck is curved when you level, the frets will be level relative to a curve, and the moment you adjust the truss rod the whole job is wrong.
Take the strings off, adjust the truss rod until a notched straightedge shows the fretboard dead flat, and only then pick up the leveling file.
Step 1: Leveling
Mark every crown
Run a marker pen across the top of every fret. The marker shows you exactly which frets you have touched and by how much.
Level with the file flat
Draw the leveling file along the frets in full-length strokes, alternating direction, keeping it flat on the crowns.
Check with a straightedge
Every few strokes, lay a straightedge across three frets at a time and look for light underneath. Stop when they are all touching.
Stop early
Leveling removes metal you cannot put back. Aim for the minimum removal that brings every fret into the same plane.
Every stroke takes the crown down. If you keep going past the point where the frets are level, you will end up with frets too low to crown properly, and the only fix is a refret.
Step 2: Crowning
Leveling flattens the top of every fret. A flat-topped fret has two problems: the string contacts it across a wide area rather than a point, which changes the effective speaking length, and the flat edges catch the string and buzz.
Crowning restores a rounded profile. A crowning file has a concave cutting surface that wraps around the fret, and the aim is a crown that is a smooth dome with a clean contact point in the middle.
- Work along the fret, not across it, so you do not cut a flat into the crown.
- Stop when the marker line at the very top of the crown is gone and the crown is rounded.
- Do not take the crown below about 60 percent of its original height.
- Check every fret with a fret rocker — a three-point gauge that rocks on a high fret.
Step 3: Polishing
A crowned fret still has file scratches, and the strings grind against them every time the guitar is played. Scratched frets wear strings faster, feel rough under a bend, and produce a gritty sound when sliding.
Polishing is progressive: work up through the grits from 400 to 2000, then finish with a metal polish and a buffing wheel or a hand pad. Take the time here — it is the difference between a fret job that feels good and one that feels finished.
Fret ends
The ends of the frets are what the player’s hand touches most. A fret end that is left square catches the hand every time it moves up the neck, and it is the first thing anyone notices about a cheap fret job.
File the ends back at an angle so they follow the fretboard edge, then round them over with a fine file and polish. Run your hand along the edge of the board — you should feel nothing at all.
Put masking tape on the fretboard between the frets before you file. It stops the file scarring the wood, and it takes two minutes instead of a fretboard repair.
Level, crown, polish. Three operations, one order, and no skipping — the fret job is only finished when the strings slide over it silently.
