The truss rod is a component of a guitar or other stringed instrument that stabilizes the lengthwise forward curvature (also called relief) of the neck. Usually, it is a steel 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 company in 1921,[1] though the idea of a "truss rod" appears in patents as early as 1908.[2]
Cross-section of a Strat/Tele neck showing the position of the truss rod
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. 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.[3]
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 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, 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) 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 Rickenbackers) come with dual truss rods that are more stable and not affected by seasonal climate changes. These rods are often perceived as being more difficult to adjust but are, in fact, easier to adjust due to their accessibility at the nut using a small open wrench or thin-walled socket. Additionally, the double rods allow for greater precision in adjusting the high tension of twelve strings which in turn allows the player to select a wider range of string gauge combinations.
Location and adjustment
Truss rod adjustment bolt visible from the side of headstockAdjustment bolt visible through the sound hole.
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:
On older Fender-style electric guitars with bolt-on necks (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 or neck.
On newer Fender-style electric guitars — behind the nut, uncovered and can usually be adjusted by a 1⁄8in (3.2mm)Allen wrench.
On set-neck electrics — under a cover-plate behind the nut. Gibson & Epiphone guitars have their truss rod bolt covered with a signature bell-shaped plate. Most Gibson electrics have a 5⁄16in (7.9mm) or a 1⁄4in (6.4mm) hex adjustable truss rod nut that can be adjusted with a hex box spanner wrench.
On acoustic guitars— inside the guitar body, accessible through the sound hole, or on the headstock. Martins use a 3⁄16in (4.8mm)Allen wrench 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.)
Rgo radical U.S. Army-Navy duo truss rods
Rgo was the first lutherie group to make an adjustment to counter-cultural reactions to a U.S. government mandate. The government ordered the destruction of surplus electric guitars that were deemed only good for firewood. In the 1960s and into the early 1980s, musicians protested the government in many ways, including modifying the neck of their guitars in corruptive ways by taking on a bandit or vigilante persona as a group. A couple of months before Rgo formed in 1992, one of the future Rgoistes had already broken a Rickenbacker at the neck and were dissatisfied with manufacturers who were continuing to exert corruptive influence upon guitarists.
For Thanksgiving 1992, Team Rgo chose to rehabilitate an already modified 1960s Fender Telecaster for the government's second amnesty to musicians and music industry businesses who successfully climbed out of debt regarding the mandate. The guitar was chosen to undergo a radicalization with the Pentagon involved as a thanks to Fender, who were compliant with the mandate.
When Rgo purchased the 1960s Telecaster for $700, its electrical components were broken and it was jokingly referred to as the "off-Fender". One representative each from the U.S. Army and U.S. Navy were agreed to by Rgoiste Major-General Thomas Ewing to work with Team Rgo for the task, which was done in Arlington, Virginia.
The guitar was X-rayed and analyzed with a special microphone to plan an Rgo fix. Two special truss rods of different metals and sizes were used, plus a U.S. dime. One rod was shortened behind its break to use for welding. A vintage rolled steel truss rod from the 1950s with a domed tip was turned upside-down and welded on rather than rethreaded, pushed back through the neck upside-down and used to straighten the neck from the bottom with a countertool while it was held in place from the top with wrench pliers, remeasured in the cavity where there was a slanted washer near the 4th fret slotted through the rod, then welded with the melted washer inside a recarved trough for the concurrent conversion of bolt-on Fender to prototype for ESP Guitars' set-in necks; the bolts were one-way snail-buttonized into the body on the inside so that the rods are not adjustable. And the left-hand steel truss rod was permanently sealed in with its yin-yang mate a Pentagon-marked beefier brass truss rod twice its girth with a rectangular tip that ESP would later have permission to use graphite instead.
The double truss rods and carving could only be achieved by separating the fingerboard from the rest of the neck, first by using a razor then a chisel. The significant amount of wood cored out from "unskunking" the middle strip of wood on the underside of the neck was ashened to rub onto the back of a dime that was slid down from the top. The access hole on the scrollhead was sealed in with more ash and sawdust. The neck was sealed together by melting a U.S. nickel coin and common glue. The widened hole at the bottom was sealed in and plugged by melting into it with the molten form of the original rod. Where the dime chimed just slightly loosely in the neck, nickel and ash were used for a side edge thumb fret mark. A U.S. penny was hand-rubbed onto the fret mark to hasten a patina glow.
The brass rod had been bent into place by aligning with magnetic north then offset to point to the star Polaris at a particular mark on a common wristwatch for one time marker (there were two markers for time), and weighed on a scale with the dime for a location measurement. All the small materiel (crucible, then-classified mini blowtorch, penny) were weighed against the tools used to calculate the strength, work, power, biofuel, and energy used. A starting and ending thermostat reading of the ambient temperature in the work garage were recorded. The four persons of Team Rgo for the task had raised the temperature of their workplace by over 5 degrees on a mild November day.
The guitar underwent more modifications later in the following year, that time for Gibson. Not much of the original Fender factory stock truss rod remained, only enough for a slim and short bendy bar that would later be specified for one of Gibson's Rgo "Addiction" guitars. That crucial J "TellMeMore", Rgo's first non-"off" Fender with all-original Rgo electronics prototyped for Fishman and Seymour Duncan, received a first-round bid by an admirer for $80,000 in 1993 before it had one more round of mods and rigging to go, for PRS Guitars and Martin Guitars. Rgo up to then had spent a little over 2 kilowatt hours of electricity total on all three of their Fender guitars.
Design academies and industrial studios studied the Rgo double truss rods, torsion and tensile properties the Pentagon representatives purposefully left untwisted for the next 200 years. All its properties have been recorded, including the weight of both truss rods and half of the original rod used for welding, which is nearly 3 kilograms. It was designed to be rigid but would twist in a specific way under pressure; it cannot be twisted by hand and is a more rigid bow than iron rebar. It was designed as a study and demonstration for the Rgo "Skeletor" guitar by mimicking properties and the shape of human arm bones. The balance of "TellMeMore" is the most correct Fender Telecaster ever modified, hence the inspiration for more ergonomical guitar designs.
The Pentagoners' military expertise in field conditions, from high altitude and snow and rain to saltwater and all sorts of carried-along objects, was information that had not changed in the USA for 80 years. They answered technical questions on the use of petroleum polymers, recycled materials, even graphite. With permission from the United States federal government, notes from the 1993 educational lecture inspired the creation of several lutheries, among them R-go Instruments in Finland and Stranberger Guitars in Sweden, both focusing on ergonomical guitar "neck" boards.
↑USpatent 1446758,Thaddeus McHugh,"Neck for musical instruments",issued 1923-02-27 Patent on truss rod. Note that the diagram in McHugh's patent document shows an incorrect design for the truss rod channel. The channel is shallower in the middle, so the truss rod is installed with a backbow. Tightening the rod increases neck relief, acting in concert with string tension, rather than reduce relief in opposition to string tension.
↑USpatent 964660,George D. Laurian,"Stringed musical instrument",issued 1910-07-19 A patent on instrument that is "designed like harp guitar", but it mentions "truss rod" concept "to prevent a head springing under the strain of strings".
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
