Truss rod
Encyclopedia
The truss rod is part of a guitar
or banjo
used to stabilize and adjust the lengthwise forward curvature (also called relief), of the neck
. Usually it is a steel
rod that runs inside the neck and has a bolt that can be used to adjust its tension. The first truss rod patent was applied for by Thaddeus McHugh, an employee of the Gibson
company, in 1921
, although the idea of "truss rod" can be encountered in patents as early as 1908.
When the truss rod is loosened (i.e. moved towards the guitar's body), it allows the neck to bend slightly in response to the tension of the strings. Similarly, when tightened (i.e. moved towards the guitar's headstock
) the truss rod straightens the neck by resisting the tension of the strings.
It is desirable for a guitar neck to have a slight relief in order that reasonably low action is achieved in the high fretboard positions, while at the same time, the strings ring clearly in the low positions. Improved action in the high fret positions also allows for more accurate intonation
, to be achieved with less compensation at the bridge.
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 contributes to a neck that feels stiff and lifeless, while too little feels floppy, slow and imprecise.
Truss rods are required for instruments with steel (high tension) strings. Without a truss rod, 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
(previously catgut
) strings.
Truss rods also allow the instrument neck to be made from less rigid materials, such as cheaper grade of wood, or man-made composites, without which the neck would not be able to properly handle the string tension. The neck can also be made thinner, which can improve playability. In fact, the possibility of selecting cheaper materials is specifically touted in the 1923 patent as an advantage of the truss rod. Prior to the introduction of truss rods, the neck would have been made of a very rigid wood, and relief was achieved by planing the fingerboard: more expensive material, and more demanding construction technique.
, though graphite
and other materials are sometimes used.
The truss rod can be adjusted to compensate for expansion or contraction in the neck wood due to changes in humidity or temperature, or to compensate for changes in the tension of the strings (the thicker the guitar string, the higher its tension when tuned to correct pitch).
Usually, the truss rod of a brand-new instrument is adjusted by the manufacturer before sale. Adjusting the truss rod is not recommended for a novice, as guitar necks can be easily damaged beyond repair in the process. Luthier
s or more experienced players can adjust it when necessary (e.g. if strings of a very different tension are to be used). Turning the truss rod clockwise will tighten it, counteracting the tension of the strings and straightening the neck or creating a backward bow. Turning the truss rod counter-clockwise will loosen it, allowing string tension to act on the neck and creating a forward bow (higher string action).
Some guitars (notably Rickenbacker
s) come with dual truss rods that are more stable and not affected by seasonal climate changes. They are also more difficult to adjust and should be serviced by a professional. Though uncommon there are also left-handed truss rods that need to be rotated in the opposite direction of a normal truss rod.
The truss rod tension is usually controlled using an adjustment bolt (a hex nut or allen key). Depending on the model of guitar, this bolt can be located:
Installing a truss rod in a newly constructed guitar requires woodworking capabilities. Special tools are required including a router with a variety of bits and ability to work with metals. Completed truss rods can be purchased through suppliers or manufactured according to specifications given in literature.
Guitar
The guitar is a plucked string instrument, usually played with fingers or a pick. The guitar consists of a body with a rigid neck to which the strings, generally six in number, are attached. Guitars are traditionally constructed of various woods and strung with animal gut or, more recently, with...
or banjo
Banjo
In the 1830s Sweeney became the first white man to play the banjo on stage. His version of the instrument replaced the gourd with a drum-like sound box and included four full-length strings alongside a short fifth-string. There is no proof, however, that Sweeney invented either innovation. This new...
used to stabilize and adjust the lengthwise forward curvature (also called relief), of the neck
Neck (music)
The neck is the part of certain string instruments that projects from the main body and is the base of the fingerboard, where the fingers are placed to stop the strings at different pitches. Guitars, lutes, the violin family, and the mandolin family are examples of instruments which have necks.The...
. Usually it is a steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
rod that runs inside the neck and has a bolt that can be used to adjust its tension. The first truss rod patent was applied for by Thaddeus McHugh, an employee of the Gibson
Gibson Guitar Corporation
The Gibson Guitar Corporation, formerly of Kalamazoo, Michigan and currently of Nashville, Tennessee, manufactures guitars and other instruments which sell under a variety of brand names...
company, in 1921
, although the idea of "truss rod" can be encountered in patents as early as 1908.
Application
Headstock
Headstock or peghead is a part of guitar or similar stringed instrument. The main function of a headstock is holding the instrument's strings. Strings go from the bridge past the nut and are usually fixed on machine heads on headstock...
) the truss rod straightens the neck by resisting the tension of the strings.
It is desirable for a guitar neck to have a slight relief in order that reasonably low action is achieved in the high fretboard positions, while at the same time, the strings ring clearly in the low positions. Improved action in the high fret positions also allows for more accurate intonation
Intonation (music)
Intonation, in music, is a musician's realization of pitch accuracy, or the pitch accuracy of a musical instrument. Intonation may be flat, sharp, or both, successively or simultaneously.-Interval, melody, and harmony:...
, to be achieved with less compensation at the bridge.
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 contributes to a neck that feels stiff and lifeless, while too little feels floppy, slow and imprecise.
Truss rods are required for instruments with steel (high tension) strings. Without a truss rod, 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
Classical guitar
The classical guitar is a 6-stringed plucked string instrument from the family of instruments called chordophones...
which uses nylon
Nylon
Nylon is a generic designation for a family of synthetic polymers known generically as polyamides, first produced on February 28, 1935, by Wallace Carothers at DuPont's research facility at the DuPont Experimental Station...
(previously catgut
Catgut
Catgut is a type of cord that is prepared from the natural fibre found in the walls of animal intestines. Usually sheep or goat intestines are used, but it is occasionally made from the intestines of cattle, hogs, horses, mules, or donkeys.-Etymology:...
) strings.
Truss rods also allow the instrument neck to be made from less rigid materials, such as cheaper grade of wood, or man-made composites, without which the neck would not be able to properly handle the string tension. The neck can also be made thinner, which can improve playability. In fact, the possibility of selecting cheaper materials is specifically touted in the 1923 patent as an advantage of the truss rod. Prior to the introduction of truss rods, the neck would have been made of a very rigid wood, and relief was achieved by planing the fingerboard: more expensive material, and more demanding construction technique.
Construction and action
Truss rods are frequently made out of steelSteel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
, though graphite
Graphite
The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...
and other materials are sometimes used.
The truss rod can be adjusted to compensate for expansion or contraction in the neck wood due to changes in humidity or temperature, or to compensate for changes in the tension of the strings (the thicker the guitar string, the higher its tension when tuned to correct pitch).
Usually, the truss rod of a brand-new instrument is adjusted by the manufacturer before sale. Adjusting the truss rod is not recommended for a novice, as guitar necks can be easily damaged beyond repair in the process. Luthier
Luthier
A luthier is someone who makes or repairs lutes and other string instruments. In the United States, the term is used interchangeably with a term for the specialty of each maker, such as violinmaker, guitar maker, lute maker, etc...
s or more experienced players can adjust it when necessary (e.g. if strings of a very different tension are to be used). Turning the truss rod clockwise will tighten it, counteracting the tension of the strings and straightening the neck or creating a backward bow. Turning the truss rod counter-clockwise will loosen it, allowing string tension to act on the neck and creating a forward bow (higher string action).
Some guitars (notably Rickenbacker
Rickenbacker
Rickenbacker International Corporation, also known as Rickenbacker, is an electric and bass guitar manufacturer based in Santa Ana, California...
s) come with dual truss rods that are more stable and not affected by seasonal climate changes. They are also more difficult to adjust and should be serviced by a professional. Though uncommon there are also left-handed truss rods that need to be rotated in the opposite direction of a normal truss rod.
Location and adjustment
- On older Fender-style electric guitars with bolt-on neckBolt-on neckBolt-on neck is a method of guitar construction that involves joining a guitar neck and body using screws as opposed to glue as with set-in neck joints. The term is a misnomer, introduced mostly by Fender whose guitars traditionally had "bolt-on necks". Real bolted joints are uncommon in guitar...
s (and vintage re-issues) — on the heel of the neck. Adjustment of such truss rods can be done by a Phillips screwdriver and requires prior removal of the guitar's pickguardPickguardA pickguard is a piece of plastic or other laminated material that is placed under the strings on the body of a guitar, mandolin or similar plucked string instrument...
or neck.
- On newer Fender-style electric guitars — behind the nut, uncovered and can usually be adjusted by a 1/8" (3 mm) Allen wrench.
- On set-neckSet-in neckSet-in neck is a method of guitar construction that involves joining guitar neck and body with a tightly fitted mortise-and-tenon or dovetail joint, secured using some sort of adhesive...
electrics — under a cover-plate behind the nut. GibsonGibson Guitar CorporationThe Gibson Guitar Corporation, formerly of Kalamazoo, Michigan and currently of Nashville, Tennessee, manufactures guitars and other instruments which sell under a variety of brand names...
& Epiphone guitars have their truss rod bolt covered with a signature bell-shaped plate. Most Gibson electrics have a 5/16” (8 mm) or a 1/4" (6 mm) hex adjustable truss rod nut that can be adjusted with a hex box spanner wrenchWrenchA wrench or spanner is a tool used to provide grip and mechanical advantage in applying torque to turn objects—usually rotary fasteners, such as nuts and bolts—or keep them from turning....
.
- On acoustic guitars — inside the guitar body, accessible through the sound holeSound holeA sound hole is an opening in the upper sound board of a stringed musical instrument.The sound holes can have different shapes: round in flat-top guitars, F-holes in instruments from the violin or viol families and in arched-top guitars, rosettes in lutes. Bowed Lyras have D-holes and Mandolins may...
, or on the headstock. Martins use a 3/16" (5 mm) Allen wrench and Gibson uses the same as for the Gibson electrics above.
- Counterclockwise adjustment will decrease the truss rod tension (correct an underbow) and clockwise adjustment will increase the truss rod tension (correct an overbow).
Installing a truss rod in a newly constructed guitar requires woodworking capabilities. Special tools are required including a router with a variety of bits and ability to work with metals. Completed truss rods can be purchased through suppliers or manufactured according to specifications given in literature.