Introduction
The geometry of a classical guitar is essential to its tone, playability, and long-term stability. Two stages are critical: leveling the fingerboard and installing the frets.
For a guitar to play correctly, string height, neck angle, fingerboard profile and fret levelness must all work together. Small deviations accumulate — and each one has consequences that are felt by the player on every note.
Action at 12th fret
3 mm first string
4 mm sixth string
(string underside to fret top)
String height at bridge
10 mm first string
11 mm sixth string
(a high saddle compresses the soundboard)
Fingerboard thickness
5 – 7 mm
depending on neck angle method and wood species
I
Fingerboard leveling
Two construction methods
Neck aligned with the soundboard plane — fingerboard leveled afterward to achieve neck angle and control string height above the top. Used in most 19th- and early 20th-century guitars.
Neck angled upward during assembly — set one or two degrees above the soundboard plane, resulting in a fingerboard of uniform thickness. An adjustment is required after the 12th fret to accommodate the angle. The more modern method.
Template & jointer plane
Calculating fret spacing by hand leads to inaccuracies — most luthiers use templates supplied by specialized manufacturers. The fingerboard is then flattened using a jointer plane, a long-soled hand plane. The blades must be perfectly sharpened.
Setting the neck angle
To set the neck angle without installing strings, a straightedge is placed on the fingerboard and the gap at the future bridge position is measured. This gap directly determines the final string height above the soundboard.
Bass slope & fall-away
A slight slope on the bass side lowers the future saddle height, producing a 1 mm difference between the first and sixth strings (rather than 2 mm on a completely flat fingerboard). After the 12th fret, a slight fall-away is created across the width of the fingerboard to prevent string buzzing. Since string tension pulls the neck forward, the amount of fall-away depends on the flexibility of the wood — minimal for ebony, more pronounced for rosewood or softer woods.
II
Fret slots
Deepening & chamfering
The fret slots are deepened using a special saw with adjustable cutting depth. A small chamfer is then filed into the edges of each slot with a triangular file — this prevents tear-out during any future refretting work.
III
Installing the frets
Hammer, hide glue & fret rocker
Frets are installed using a plastic-faced hammer, with hot hide glue to secure the wire. Once three frets are installed, their level is checked with a fret rocker. If the tool rocks back and forth, the middle fret is too high and needs another light tap. This process is repeated for every fret. The last fret is inserted from the side using the hammer.
IV
Trimming & beveling
Ends, bevel & softening
The fret ends are trimmed flush with a file — with the soundboard carefully protected, the file runs along a metal guide. A bevel is then created along the fret ends, generally between 30 and 35 degrees. Sharp edges are softened with sandpaper.
V
Leveling & finishing
Diamond leveling stone
After carefully protecting the fingerboard and soundboard, a diamond leveling stone is used to bring all frets to the same height. Material is removed gradually along the entire length until every fret is perfectly level.
A flat fret shifts the contact point toward the bridge — the note plays sharp.
Crowning, rounding & polishing
The crown of each fret is recreated using a fret-crowning file. This step is crucial: a flat fret shifts the contact point toward the bridge, causing the note to play sharp. A small specialized file is then used to round the fret ends, and each fret is polished with very fine steel wool.
A small amount of drying oil is applied to nourish and protect the fingerboard — and the job is complete.