The Guitar Neck & Fretboard
On acoustic guitars the neck extends from the headstock to the heel
joint at the top of the guitar body. The neck serves two functions.
Mechanically, it supports the strings, but it also provides support
for the main playing surface - the fretboard.
The neck and fretboard are perhaps the most critical part of the guitar
as far as feel and playability are concerned. Our hands are very sensitive
and to a guitarist, changes in neck dimensions of only a fraction of
a millimetre can make a noticeable difference in the playing feel of
a guitar. This level of accuracy is difficult to achieve and to control,
when working in wood.
The neck - sustain and tone
There are many opinions about how the neck affects the tone of the
guitar. Although the neck is always in contact with one end of the strings,
which are the primary source of the sound of the guitar, it obviously
isn’t directly involved in sound production. Any energy from the
strings that vibrates the neck is really wasted and sustain is lost.
Ideally the neck end of the strings shouldn’t vibrate at all and
the neck shouldn’t adsorb any energy from the strings. In this
case the neck wouldn’t affect or alter the sound of the guitar
in any way and all the energy from the strings would go into driving
the soundboard. Practically this isn’t possible, but a real neck
(including the fretboard and frets) should be as stiff as possible and
have a low internal damping factor. Modern materials such as carbon
fibre, usually used as an insert, make it possible to make very stiff
and strong necks, although currently only custom built and very high
end production guitars feature this construction.
Some makers try to make the neck heavy, even going so far as adding
a metal weight at the headstock and sometimes a counterbalance at the
heel to increase the inertia and lower the resonant frequencies of the
neck. Apparently, weighting the neck can increase volume and improve
the treble response.
Neck woods – mahogany & maple
The wood used for the neck needs to provide good longitudinal strength
and carve easily. The vast majority of acoustic guitar necks are made
from mahogany. However the description ‘mahogany’ is pretty
vague since there are two, completely different, species of wood commonly
called mahogany. Each of these breaks down into numerous sub-species
and to complicate matters even further, other completely unrelated woods
such as, sapele (Entandophragma cylindricum), sipo or utile (Entandrophragma
utile) and launa, are often sold as ‘mahogany’.
Big leafed or American mahogany (Swietenia macrophylla, often called
South American, Brazilian or Peruvian mahogany, also caoba and acajou)
from Central and South America is a true mahogany that is still available
in commercial quantities and this is by far the most common wood used
in acoustic guitar necks. Swietenia mahogani, once logged almost to
extinction, is of the same group and is variously called West Indian
mahogany, Spanish mahogany, or Cuban mahogany.
The second group of wood species referred to as mahogany are members
of the Khaya group and depending on availability, are also used in neck
construction. Since these species grow in Africa they are generally
called African mahogany and include Khaya ivorensis, Khaya anthotheca
and Khaya nyasica.
In general, the mahogany woods are light brown to reddish brown in
colour and are almost always stained, for a darker, richer colour. Mahogany
is lightweight but strong, carves well and has an attractive grain.
However most mahogany is quite open grained, which can cause problems
when trying to achieve a smooth finish and it can tear and split when
cut against the grain.
Hard rock maple, rock maple, hard maple or sugar maple (Acer nigrum)
is an excellent wood for guitar necks. It is most commonly used for
electric guitar necks, although archtop guitars and resonator guitar
necks are almost exclusively made from maple. It is very strong, carves
well and has a tight grain. There are over 120 species of maple which
are often grouped into ‘hard’ and ‘soft’ maple.
Silverleaf maple (Acer saccharum) is one of the ‘soft’ maples,
sometimes also used in guitar construction. Art & Lutherie and Simon
& Patrick, both Canadian companies and part of the Godin group,
use local Canadian silverleaf maple for their necks. Just to make things
really confusing both acer nigrum and acer saccharum are sometimes referred
to as ‘sugar’ maple because the sap of both trees can be
used as maple syrup. Maple is generally heavier than mahogany, which
is probably one reason why mahogany is preferred for acoustic guitar
necks. Many players seem to prefer lightweight instruments and a heavy
neck with a lightweight body may not balance well.
Nylon-strung guitar necks are sometimes made from Spanish cedar (Cedrela
odorata and Cedrela mexicana) from Central and North America.
The best cut from a log for neck wood is where the growth rings of
the wood lie at right angles to the fretboard. This aligns the natural
structure of the wood so that it is at its stiffest against the pull
of the strings. This is often referred to as 'quarter sawn' whereas
in fact only some of the billets from a quarter sawn log exhibit grain
at a true right angle to the wide face of the billet. Flat sawn logs
are simply sliced into planks along the length of the log, while quarter
sawn logs are first cut into quarters. Planks or billets are then cut
from the alternate flat faces of each quarter, with the quarter rotated
after each cut. Quartering and rotating a log in this way is a more
labour intensive process than simple flat sawing, so quarter sawn timber
is rarer and more expensive. However there will always be some timber
from the flat sawn log that also has the the growth rings at right angles
to its wide face.
Lengthwise laminated necks, made from a number of long strips of different
woods glued together, enjoy a peculiar reputation. They are either found
on low cost guitars, where they make economical use of timber that would
otherwise be too small for a neck, or on very expensive guitars, where
the aim is to produce both a stiff, stable neck and a visually decorative
effect. Martin uses a material with the commercial name of Stratabond,
a form of birch plywood, on their X series necks. Unlike the cross grain
lamination found in standard plywood, in Stratabond the grain of each
2mm veneer, which are often stained in contrasting colours, runs parallel
to the next, but does not line up perfectly, giving a subtle offset
Two views of laminated necks – one on a low cost Epiphone (which
is an excellent guitar with very good stable neck) and the second on
a custom built Olson guitar.
Two close ups of stained Stratabond, a material introduced quite recently
by C.F.Martin on their X series necks.
The truss rod is a metal rod, usually made of steel, inserted into
a channel running along the length of the neck. Its purpose is to counteract
the force of the strings, which tends to bend the neck forwards. Today
there are two different types of threaded adjustable truss rod in common
use, the single action, compression, or ‘vintage’ rod and
the double (double action, double expansion) or bi-flex rod.
The single-action, compression type, rod is usually installed in a ‘concave’
channel cut into the neck. A filler stripe with a complementary curve
is glued in to the channel over the rod. When the rod is tightened it
tries to straighten and pushes up against the filler strip, making the
neck bend backwards. The single rod can only counteract the force of
the strings and straighten or bow the neck backwards. It does have the
advantage that less wood has to be removed from the neck to fit it and
the single rod has lower mass. The bi-flex or double action rods can
bend the neck forwards or backwards, but add more mass and need a bigger
channel carved in the neck. Broken single rods are often difficult to
remove and replace. Double action rods aren’t anchored to the
neck like the singles, so they can be easier to replace.
This cross sectioned neck shows a single action truss rod in situ, with
the pale filler strip glued in above it (pic. by Frank Ford).
The single action rod on
the left is designed to act against the neck itself while the double
rod on the right has one adjustable rod that acts against a second rod
(both marketed by Stewart Macdonald, pictures by Stewart Macdonald)
Early truss rods were simply attempts to stiffen the neck and had no
adjustment. For example many Martin guitars of the period from 1930
to 1960 have necks reinforced with T section solid steel bars. From
the 1960’s up until 1985 Martin used square, box-section steel
tubes, inserted in the neck. Current Martin guitars are fitted with
single action adjustable rods, but the steel rod itself runs through
the centre of an aluminium U channel.
a collection of pictures taken by Frank Ford of the Martin Box and
T rods both in and out of a neck and of the current Martin style
rod in its aluminium U channel.
Truss Rods may be installed,
either with the adjustment nut or socket at the heel end of the neck,
accessed via the guitar soundhole, or with the adjustment at the headstock
end of the neck, accessed through a hole or channel that is covered
with a small plate. Although truss rods with the adjustment at the headstock
are easier to get at, it is felt that this method of mounting the rod
can weaken the junction between the headstock and the neck.
Nylon strung guitars aren’t usually fitted with truss rods because
the tension of the strings is lower than on a steel strung and doesn’t
bend the neck as much.
Truss rod adjustment
Wooden guitar necks may bend significantly forwards or backwards due
to changes in temperature or humidity, requiring a small adjustment
of the tension in the truss rod. A change of string gauge, or use of
an altered tuning, may also require a truss rod adjustment. Normally
only a quarter turn at most is needed, and although there is usually
some resistance, the adjustment nut or screw should turn relatively
easily. If a neck does not respond immediately it can be encouraged
by bracing it across the knees and pushing firmly with a hand in the
middle of the neck. Even with this encouragement most necks take time
to settle after an adjustment. Exactly the right spanner or hex key
should be used to make the adjustment so that controlled amounts of
force can be applied without damaging the truss rod nut or socket. It’s
important to know the type of truss rod and the required turning direction
for the desired effect.
If a neck doesn’t respond and the adjustment won’t seem
to turn without excessive force the rod may not be working properly.
Removing the strings and slackening the rod until it is loose and then
re-tensioning may help. Double action rods should have an obvious slack
point between bending the neck forwards and backwards. With single action
rods the adjustment nut can be removed and its threads lubricated with
a small amount of Vaseline or paraffin wax (candle wax).
The heel joint
The ‘heel’ refers to the curved block of wood that is usually
found on an acoustic guitar at the point where the neck joins the body.
Traditional Spanish gut or nylon strung guitars don’t separate
the neck and neck block at this point, the end of the neck is either
carved in one piece or built up into a block that passes right inside
the body and the sides are simply joined to this block. This approach
can be used because high actions were and are regarded as quite acceptable
on gut or nylon strung guitar, so fine control over the neck angle isn’t
Prior to around 1929 the necks of steel strung guitars joined the body
at the twelfth fret. Today the vast majority of guitars join, neck-to-body,
at the fourteenth fret, providing a significant increase in the accessible
note range of the guitar. Twelve-fret-to-the-body designs do offer an
advantage, or at least a difference in tone, because the bridge is sited
closer to the centre of the vibrating portion of the guitars top. This
is also true of the 'classical' nylon strung guitar.
Steel strung guitars with a ‘traditional’ neck joint have
a wood block inside the guitar and the neck is joined to this block
with a dovetail joint. The dovetail is carved onto the inside face of
the heel and secured to a matching cavity in the body block with glue,
usually a hide glue is used. The end of the fretboard that extends over
the body is also glued to the guitars top.
This method of joining the neck to the body is often referred to as
a ‘set’ neck and although the neck angle can be controlled
by trimming the dovetail, setting the initial neck angle is critical
to playability and tone and requires great skill. Advocates of this
method say that it provides the closest possible bond between the neck
and the body and so produces the best tone and sustain. Unfortunately,
over time, all acoustic guitars tend to hinge about the neck to body
join and to suffer from a rising soundboard. Under the continual strain
from the string tension, the action height gradually increases and the
guitar becomes less and less playable. With a traditional set neck,
correcting this problem, by re-setting the neck, is a highly skilled
and expensive business.
In recent years manufacturers have started bolting necks onto the body.
Initial setting and even precisely re-setting a bolt-on neck, using
thin shims, is far easier than adjusting a glued, dovetail-jointed,
neck. The use of this method has been pioneered and developed by Taylor
Guitars. Although they had used a simpler, butt-joint, bolt-on system
on their earlier production, in January 1999 Taylor introduced their
NT or new technology neck joint. Taylor use state-of-the-art CNC (computer
numerical control) cutting machines to cut precise mortises into the
end of the body and into the top. Thin graduated wood shims can be laid
into these mortises for precise adjustment of the neck angle. The neck
heel and the fingerboard, supported by a solid extension of the neck,
then fit very accurately into these mortises. Two bolts, one above the
other, pass through two holes in the neck block on the body and screw
into a threaded aluminium block set in to the heel on the neck. A third
bolt passes through the top and holds the fingerboard neck extension
firmly in place.
While the Taylor NT neck joint and other bolted neck joints, look from
the outside, identical to a traditional neck joint, complete with the
bulky external carved heel, there is another form of ‘bolt-on’
neck (usually the ‘bolts’ are long screws) that closely
resembles the neck joint found on many electric guitars. In this joint
the neck block inside the guitar is quite large and extends almost to
the soundhole. A rectangular neck pocket is machined into the top of
the guitar and the neck, which is square ended and extends the entire
length of the fingerboard, drops into the pocket and is held in place
by four long screws that pass through holes drilled in the back of the
guitar. This joint, although not exactly elegant, has the advantage
of simplicity and has no heel at all. It was originally used by Fender
on their Kingman guitars and is currently used on some of the Tacoma
range of instruments (ironically, Tacoma is now part of the Fender Musical
Instrument Company group).
One solution to the neck set/reset problem is an adjustable neck. This
idea first appeared in the 1800’s on the guitars of Johan Stauffer
with a ‘hinged’ neck, adjusted by turning a square clock-key-style
screw through a hole in the heel. This idea has recently been resurrected
by Greg Smallman because he wanted to avoid his customers making action
adjustments by filling down or replacing the saddle. Saddle and bridge
height can have quite an effect on volume and tone, particularly on
hand-tuned concert instruments.
Jeff Babicz has recently designed a range of guitars with a true ‘up-and-down’
neck adjustment that can be adjusted very easily, with no change in
tuning, by turning a hex key inserted into a socket in the back of the
Guitars moulded out of plastics and composite materials can do away
with the heel joint altogether because the neck, back and sides can
be moulded in one piece. For example CA Guitars X Standard not only
does away with the heel joint, but extends its sweeping cut-away behind
the neck for unparalled access to the upper frets.
This series of pictures taken by Frank Ford show the routing, adjustment
shims and bolts in the Taylor NT neck joint.
The Babicz adjustable neck
shown here with the hex wrench in place, allows smooth and continuous
adjustment of the neck relative to the strings, with almost no effect
Moulded in one piece, into a sweeping cut-away, the carbon fibre construction
of CA Guitars X Standard completely eliminates the neck joint.
Neck profile, width and thickness
Guitarists at any level of ability will find a guitar with an accurate
neck and a good setup easier to play. It also helps if the neck dimensions
suite their hands. In an ideal world guitar neck dimensions should be
tailored to the individual player’s hand. It’s not uncommon
for famous players to have their favourite neck duplicated on a signature
model, or for players to ask for necks based on their favourite features
from several guitars, when commissioning custom built instruments. Perhaps
in the future the leading guitar companies may be able to offer an off-the-peg
neck fitting service to their general customers, based on hand measurements.
Older or vintage reissue instruments often feature a neck with a pronounced
V profile. This neck shape provides a little extra strength and thickness
down the centre spine, but compensates for that with shallow curved
sides, so it isn’t too much of a handful. However this shape doesn’t
appeal to everyone, so the vast majority of guitars made today settle
for a generic semicircular profile.
All of the larger steel-strung acoustic guitar manufacturers today
seem to be trying to please the habitual electric guitar player. So
most acoustic necks are made with a fairly narrow nut width of around
43 to 44mm. These narrow necks require a very good setup and light gauge
strings to play well. This is perhaps unfortunate since on an acoustic
a wider neck is arguably better suited to fingerstyle playing and medium
gauge strings provide better tone and dynamics.
It’s worth making sure that neck width allows enough room for
clean fingering by comparing guitars with clearly different neck widths
when shopping for a new acoustic. Larger makers, such as Martin and
Taylor, offer a range of neck widths and shapes. Martin currently use
four neck profiles – low oval, modified low oval, low profile
and modified V and four neck widths at the nut 1 11/16 (42.86mm), 1
¾ (44.45mm) 1 7/8 and 1 13/16ths (46.03mm). Taylor offer three
neck widths - 1 11/16 (42.86mm), 1 ¾ (44.45mm) and 1 7/8 (47.62mm).
In Taylor’s case their bolt-on NT neck makes it possible to change
necks for a different width. National Reso-Phonic single cone resonator
guitars have a neck width of 46.35mm at the nut.
Compared to the steel strung, nylon strung guitar neck widths are commonly
close to 50mm (2 inches). Although this for guitars with a flat fretboard
and is making allowance for the thicker nylon treble strings it also
indicates that complex and precise fingerings really need a wider ‘board.
Cross sections of the four neck profiles used by C.F. Martin.
The fingerboard or fretboard, a relatively thin slab of wood (usually
no more than 6mm at its thickest) glued onto the front of the neck,
is the main playing surface on the guitar. Metal frets, mounted in slots
cut across the width of the ‘board, allow the guitarist to select
the pitch of notes by pressing the string down behind a fret. Classical
and flamenco, nylon strung guitars, always have a wide, flat, fretboard.
Steel strung guitars often compensate for the extra force required to
finger the strings by having a narrower neck with a cambered or radiused
fretboard. The camber effectively bends a wider playing surface to fit
a narrower neck, so reducing the strain on the player’s left hand.
Camber radius on acoustic steel-strung guitars is typically between
12 to 16 inches, in general, the wider the neck, the flatter the radius.
Most guitar necks get wider towards the body, providing more finger
area on the fetboard as the frets get closer together (the exceptions
are the classical and the flamenco guitar with their very wide fretboards
and some jazz archtops with narrow but almost constant width necks).
When the fretboard is cambered on a tapered neck the camber should follow
the contours of a cone rather than a cylinder. Although it’s easier
to shape the fretboard into a cylindrical radius and cambered fretboards
have often been shaped that way, in recent years the conical camber,
known as a ‘compound radius’ has become popular. Although
this is of more importance on electric guitars, where extreme string
bending is often used, a compound radius on a tapered neck does provide
a very comfortable playing feel.
Fretboards are traditionally made from some of the scarcer hardwoods,
so guitar makers are starting to use synthetic materials, such as micarta
or phenolic resin, even on guitars of otherwise very conservative design.
Micarta is a trade name for composites made from layers of linen or
paper bonded together by phenolic resin. Interestingly, Lignin is the
natural phenolic polymer that gives wood its hardness and strength,
so in effect, Micarta, made from natural plant fibre and phenolic resin,
is a synthetic wood.
Indian rosewood also known as East Indian rosewood or Bombay rosewood
(Dalbergia latifolia) is the most frequently used wood for fretboards
because it has low internal damping (it is very resonant) its grain
can look very attractive, it is hardwearing and, due to its natural
oils, can be polished without an additional finish. It’s the dark
heartwood that is used, the sapwood is a pale yellow-cream in colour.
Unfortunately the quality of available rosewood is now so poor that
new fretboards often look very dry and unappealing.
The other favourite fretboard wood is the dark heartwood from ebony
trees. The sapwood is light grey and is known as white ebony. Various
species of ebony grow in central Africa (Diospyrus crassiflora and Diospryus
piscatoria) in Sri Lanka and India (Diospyrus ebenum, Diospyrus melanoxylon,
Diospyrus tomentosa etc.). Like rosewood, ebony is also very hard wearing
and has a low damping factor. Some players prefer ebony because its
grain is much finer than that of rosewood. In its natural state even
the heartwood ebony is not jet black and often exhibits grey and white
streaks, so it is almost always stained to achieve a uniform deep black
appearance, providing a nice contrast to inlays and fret markers.
Hard maple has on occasion been used for fretboards, most notably on
the fretboards of resonator instruments made by the National company
where it was always dyed black to resemble ebony.
Despite being only around 5mm thick the fretboard would help to stiffen
the neck if it weren’t for the saw slots that hold the frets.
Proper fret installation is critical to maintaining neck stiffness.
Over the years a number of different methods of fitting frets have
evolved. Early instruments had tied-on frets made of gut. Today, metal
frets are normally fitted to a fretboard by hammering, or pressing,
the frets into the slots in the ‘board. Sometimes the frets are
glued in to slots that are intentionally made for a slightly looser
fit and sometimes a combination of force fit and glue is used. It’s
very common to repair frets that are lifting at the ends with a drop
of superglue and a clamp.
Most frets today are ‘T’ shaped with a rounded playing
surface, or crown, on the top of the ‘T’. It’s the
vertical leg of the ‘T’, called the fret tang, that is hammered
in to the sawn slots and this has small teeth, or barbs, along its sides
to help it hold in to the slot. Pre 1934, old Martin frets, known as
bar frets, had no tang and were made from flat strip or bar fretwire.
Tang width and saw slot need to be correctly matched. As each fret is
installed it tends to force the sides of the fret slot apart. The net
result of installing all the frets is an overall back bow to the fretboard
and neck. If the fret tang size and fret slots are correctly matched
the pull from the strings will be enough to counteract this back bow
and even pull the neck into a slight forward bow. This type of fret
installation is known as compression fretting because first the frets
tend to force the fret slots open, then the string pressure forces the
sides of the fret slots closed, helping to hold the frets in place.
With this method, if the saw slots are too wide the frets may be loose
and neck stiffness can be affected.
With the glued method of fret installation the fret slots are almost
a loose fit for the fret and it’s the glue, usually a hard epoxy
glue, that is relied on to fill all the gaps around the fret and assure
a stiff neck.
New frets are cut longer than needed and then trimmed and bevelled
once they have been hammered, or pressed, into the fret slots. This
often leaves an open end to the slot under each end of the fret. On
un-bound necks these small gaps are filled before the neck finish is
applied. Alternatively, neck binding is a more expensive method of concealing
the slots. On a bound neck the edge of the ‘board is routed and
the binding, of plastic, wood or bone, is glued on and trimmed after
the fret slots have been cut. Each fret must then have the tang ground,
or cut away, from each end, before it’s fitted, so that the remaining
tang fits between the bindings. The ends of the fret crown then overlap
the binding on either side.
Fretwire, which is available in a range of crown sizes, is almost always
made of ‘German silver’ or ‘Nickel silver’ although
stainless steel is also sometimes used. German/Nickel silver has nothing
to do with silver, but is an alloy of nickel, copper and zinc. The usual
alloy mix for fretwire is 18% nickel, 65% copper and 17% zinc.
This close-up of a section of un-dyed ebony fretboard shows several
empty slots and one fitted fret.
In the next article in this series …..
In my next article we’ll take a look at fret spacing, tuning,
temperament and scale-length.
-----> Link to Scale length, fret positioning,
tuning and intonation
By Terry Relph-Knight
My thanks for their help in writing this article to – Taylor
Guitars, to C.F. Martin & Co., to Stewart-MacDonald and once again
to Frank Ford of Gryphon String Instruments.
Taylor guitars company website
www.martinguitar.com – C.F. Martin guitars company website
www.stewmac.com – Stewart MacDonald - guitar parts supplier
www.frets.com – Frank Ford’s guitar information website
www.gryphonstrings.com – Gryphon Stringed Instruments –
US guitar retailer