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The fingerboard is the surface of the neck where a player’s fingers come into contact with the strings of the instrument.

The player can press down the string at a specific point on the fingerboard to produce a tone or note.

Stringed instruments such as guitars and basses may be fretted or fretless, i.e. they may be with or without frets.

In the Plek software, the fingerboard is often represented as a grey area at the bottom of the screen.

The frets are the jagged “spikes”.

The fretplane is the term used to describe the imaginary line created by joining the tops of the frets.

The orange line represents the actual fretplane.

The degree of curvature of the fretplane is referred to as the fretplane relief.

Similarly, the degree of curvature of the fingerboard is referred to as the fingerboard relief.

Here at Plek, we differentiate between the measured relief of the instrument’s fingerboard and fretplane, and the recommended optimal relief for the instrument’s fingerboard and fretplane.

Recommended optimal relief is based on instrument specifications such as action, string gauge, player attack.

Fingerboard and fretplane relief can be altered by changing the adjustment of the trussrod (if the instrument has one).

The trussrod is the part of the guitar that stabilizes the relief of the neck. Usually it is a steel bar or rod that runs inside the neck, beneath the fingerboard. Some are non-adjustable, but most modern trussrods have a nut at one or both ends that adjust its tension.

A guitar neck made of wood is prone to bending due to mainly 2 factors, atmospheric changes and the pull created by changing to a different gauge of guitar strings. A truss rod keeps the neck straight by countering the pull of the strings and natural tendencies in the wood.

When the truss rod is loosened, the neck bends slightly in response to the tension of the strings. Similarly, when tightened the truss rod straightens the neck by resisting string tension.

Relief achieved through the truss rod combines with the height of the bridge to affect the playability of the instrument. The two should be adjusted in tandem. Too much relief can make a neck feel floppy, slow and lifeless—while too little can make the strings buzz on the frets.

Trussrods are required for instruments with steel (high tension) strings. Without a trussrod, the guitar’s wooden neck would gradually warp (i.e. bend) beyond repair due to applied high tension. Such devices are not normally needed on instruments with lower tension strings, such as the classical guitar, which uses nylon strings.

Radius refers to the curvature of a fret or fingerboard. The fret curve can be imagined as part of a circle, and the radius describes the distance of each part of the fret from an imaginary center.

The larger the radius, the larger the circle, and the flatter the fret surface will be.

In general, the smaller (i.e. more curved) radius is more comfortable for playing  chords (particularly barre chords).

By contrast, a larger, flatter radius is better for low action, single-note playing and bending. A flatter radius has the advantage of making a lower action possible.

This is because when you bend a string on a lower part of the fretboard such as your first or second string, you are bending it towards the middle of the fretboard, which is higher than the edges. If the radius here is too large, the notes will tend to “fret out” – i.e. buzz against the higher parts of the fret, killing sustain.

The best answer to this type of problem lies in the implementation of a so-called compound radius.

On fretted instruments, the fret radius can be corrected, i.e. altered to a different desired  radius. This assumes that enough fret material is available to make the change.

A few fundamental possibilities are illustrated below.

In the first image, the fret radius and the fingerboard are identical. The fret height is consistent across the entire fingerboard

In the second image, the fret has been filed down in the middle in order to give it a greater radius. This means that the fret radius is larger than the board radius.

In the third image, the fret has been filed down at the edges in order to reduce its radius. This means that the fret radius is now smaller than the board radius.

These techniques are frequently applied by experienced luthiers when working on a fingerboard, e.g. as part of a bending dress or to work with a “ski jump” at the body joint.

The Plek machine gives luthiers a high-precision tool for the detailed control of fret heights under each string at every position along the fingerboard, hence making it possible to precisely implement target radius specifications.

See also Compound Radius for further information.

Compound (or conical) radius fretboards are an attempt to get the “best of both worlds” between smaller and larger radii.

The radius of these fretboards changes as you climb the neck, starting out more curved at the nut and gradually getting flatter, with the effect that each fret is a fraction flatter than the one before it. While a normal fixed radius is a segment of a circle or cylinder, a conical radius is actually a segment of a cone.

The idea is that players tend to bend higher up the neck and play chords lower down. The larger radius higher up on the neck lets you get the action down lower and still bend cleanly, while the smaller radius nearer the nut makes chording easier.

Compound radius fret dressing

One way of making smaller radius fingerboards better for bending is to dress the frets from about the 10th or 12th fret with a flatter radius.

This fret dress method makes the fretplane compound without needing to remove the frets, dress the fingerboard and refret again.

This is something that is very easy to implement with the Plek machine. See the Virtual Fret Dress section for more detail.

Fall-off (also known as fall-away) refers to the relief of the fingerboard at the body end of the neck. Typically, this differs from the relief between the nut and the 12th fret.

Here at Plek we have developed a specific unit of measurement to describe fall-off, and normally recommend a fall-off of between 40 and 60.

Plek recommended fall-off typically starts from the 12th fret.

It is however possible to calculate fall-off from any given fret, resulting in what we would call a custom fall-off.

The action is the height of the string above the fingerboard.

As with relief, Plek differentiates between the measured action of the instrument, and the recommended action for the instrument.

The recommended action of the instrument is also based on the assumed attack.

Attack basically means how hard a player hits the strings of the instrument.

The amount of attack has a big influence on the setup of a guitar.

A stronger attack results in greater string movement. This means that strings will need more room to move without hitting the frets, so the action will generally need to be higher.

A softer attack results in less string movement. Strings need less room to move, so the action can generally be lower.

In a factory situation, the real attack of the player is of course unknown, so an average attack is assumed.