The truss rod is a component of a
guitar
The guitar is a fretted musical instrument that typically has six strings. It is usually held flat against the player's body and played by strumming or plucking the strings with the dominant hand, while simultaneously pressing selected stri ...
or other stringed instrument that stabilizes the lengthwise forward curvature (also called ''relief'') of the
neck
The neck is the part of the body on many vertebrates that connects the head with the torso. The neck supports the weight of the head and protects the nerves that carry sensory and motor information from the brain down to the rest of the body. In ...
. Usually, it is a
steel
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
bar or rod that runs through the inside of the neck, beneath the fingerboard. Some are non-adjustable, but most modern truss rods have a nut at one or both ends that adjusts its tension. The first truss rod patent was applied for by Thaddeus McHugh, an employee of the
Gibson
Gibson may refer to:
People
* Gibson (surname)
Businesses
* Gibson Brands, Inc., an American manufacturer of guitars, other musical instruments, and audio equipment
* Gibson Technology, and English automotive and motorsport company based
* Gi ...
company in 1921, though the idea of a "truss rod" appears in patents as early as 1908.
Application
A guitar neck made of wood is prone to bending due mainly to atmospheric changes, and the pull created by changing to a different gauge of guitar strings and/or different tuning. Though a similar effect could be achieved with a
roasted maple neck, truss rods are still used for precise adjustments. 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.
Guitar technicians usually adjust a guitar neck to have a slight relief (forward bend) to achieve reasonably low action in high fretboard positions, while letting strings ring clearly in low positions. A lower action in the high fret positions also facilitates more accurate
intonation 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 concert with each other. Too much relief can make a neck feel floppy, slow and lifeless—while too little can make the strings buzz on the frets. Relief is typically measured as the distance between the string and the 7th fret while holding down the first and last fret. The amount of relief many guitar manufacturers prefer for an electric guitar is about .007 inches at the 7th fret.
Truss Rod Adjustment
article on the Guitar Repair Bench Luthier Website
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
The classical guitar (also known as the nylon-string guitar or Spanish guitar) is a member of the guitar family used in classical music and other styles. An acoustic wooden string instrument with strings made of gut or nylon, it is a precursor o ...
, which uses nylon
Nylon is a generic designation for a family of synthetic polymers composed of polyamides ( repeating units linked by amide links).The polyamides may be aliphatic or semi-aromatic.
Nylon is a silk-like thermoplastic, generally made from petro ...
(previously catgut
Catgut (also known as gut) is a type of cord that is prepared from the natural fiber found in the walls of animal Gut (anatomy), intestines. Catgut makers usually use sheep or goat intestines, but occasionally use the intestines of cattle, Domest ...
) strings.
Truss rods also allow builders to make instrument necks from less rigid materials, such as cheaper grades of wood, or man-made composites. Without a truss rod, many of these materials would be unable to properly handle string tension at normal neck dimensions. The neck can also be made thinner, which may improve playability. In fact, the 1923 patent touts the possibility of using cheaper materials as an advantage of the truss rod. Before truss rods, builders had to make the neck out of very rigid woods, and achieved relief by laboriously planing the fingerboard.
The truss rod is not specifically for adjusting intonation or action (height of the strings above the fingerboard) though adjusting it can make an instrument more easily playable.
Construction and action
Truss rods are frequently made out of steel
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
, though graphite
Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on large ...
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) or using different tunings (the lower the pitch of each string, the lower its tension).
Usually, the truss rod of a brand-new instrument is adjusted by the manufacturer before sale. Normally, turning the truss rod's adjustment bolt clockwise tightens it, counteracting the tension of the strings and straightening the neck or creating a backward bow. Turning the bolt counter-clockwise loosens it, allowing string tension to act on the neck and creating a forward bow (higher string action).
Some guitars (notably Rickenbacker
Rickenbacker International Corporation is a string instrument manufacturer based in Santa Ana, California. The company is credited as the first known maker of electric guitars – a steel guitar in 1932 – and today produces a range ...
s) come with dual truss rods that are more stable and not affected by seasonal climate changes. These rods are regarded as being more difficult to adjust.
Location and adjustment
The truss rod tension is usually controlled using an adjustment bolt (a hex nut
A nut is a type of fastener with a screw thread, threaded hole. Nuts are almost always used in conjunction with a mating bolt (fastener), bolt to fasten multiple parts together. The two partners are kept together by a combination of their threads ...
or allen key
Hex keys of various sizes
Socket head screws of various sizes
A hex key (also, hex wrench, Allen key and Allen wrench) is a simple driver for bolts or screws that have heads with ''internal'' hexagonal recesses (sockets).
Hex keys are form ...
). Depending on the model of guitar, this bolt can be located:
* On older Fender-style electric guitars with bolt-on neck
Bolt-on neck is a method of guitar (or similar stringed instrument) construction that involves joining a guitar neck and body using screws or bolts, as opposed to glue and joinery as with set-in neck joints.
Methods
The "bolt-on" method i ...
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 pickguard
A pickguard (also known more correctly as scratchplate) is a piece of plastic or other (often laminated) material that is placed on the body of a guitar, mandolin or similar plucked string instrument. The main purpose of the pickguard is to pro ...
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 Allen, Allen's or Allens may refer to:
Buildings
* Allen Arena, an indoor arena at Lipscomb University in Nashville, Tennessee
* Allen Center, a skyscraper complex in downtown Houston, Texas
* Allen Fieldhouse, an indoor sports arena on the Unive ...
.
* On Fender American Elite Series — an adjustment wheel at the base of the neck on the top of the instrument.
* On set-neck electrics — under a cover-plate behind the nut. Gibson
Gibson may refer to:
People
* Gibson (surname)
Businesses
* Gibson Brands, Inc., an American manufacturer of guitars, other musical instruments, and audio equipment
* Gibson Technology, and English automotive and motorsport company based
* Gi ...
& Epiphone
Epiphone is an American musical instrument brand that traces its roots to a musical instrument manufacturing business founded in 1873 by Anastasios Stathopoulos in Smyrna, Ottoman Empire, and moved to New York City in 1908. After taking over his f ...
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 wrench
A 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.
In the UK, Ireland, Australia, and New Zealan ...
.
* On acoustic guitar
An acoustic guitar is a musical instrument in the string family. When a string is plucked its vibration is transmitted from the bridge, resonating throughout the top of the guitar. It is also transmitted to the side and back of the instrument, ...
s — inside the guitar body, accessible through the sound hole
A sound hole is an opening in the body of a stringed musical instrument, usually the upper sound board.
Sound holes have different shapes:
* round in flat-top guitars and traditional bowl-back mandolins;
* F-holes in instruments from the vio ...
, or on the headstock. Martins use a 3/16" (5 mm) Allen wrench Allen, Allen's or Allens may refer to:
Buildings
* Allen Arena, an indoor arena at Lipscomb University in Nashville, Tennessee
* Allen Center, a skyscraper complex in downtown Houston, Texas
* Allen Fieldhouse, an indoor sports arena on the Unive ...
and Gibson uses the same as for the Gibson electrics above.
Modern designs also include adjustment from the side of the heel of a bolt-on neck. When looking from the body of the guitar to the head, counterclockwise adjustment decreases the truss rod tension (correct an underbow) and clockwise adjustment increases 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.
Dual action truss rod
A dual action (also known as ''two way'' or ''double expanding'') truss rod is a more modern design and it is currently being used by some luthiers in lieu of the vintage single truss rod. The dual action rod is installed in a straight channel in the wood as opposed to the curved channel used by vintage rods. The two-way rod can warp the neck in either direction, either creating more relief or less.
A neck with a two way rod installed is often more stable and less influenced by climate changes, as well as being able to restraighten twisted necks, which can be a hefty repair for other guitars. However, some players believe the dual action truss system has an adverse effect on the tone of the instrument, due to the weight of the second rod and the additional wood removal required for installation (although not all two-way systems use a second rod.)
See also
*List of guitar-related topics
The following outline is provided as an overview of and topical guide to guitars:
A 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 si ...
References
Simple guide on how and why to adjust the truss rod
created by Guitarbitz Guitar Shop
Guitar parts and accessories