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Most stringed instruments with fretted necks utilize a truss rod to help protect the neck from warping and bending. Truss rods are an important component in these instruments in order to maintain the instrument’s integrity. But with such a short, substantial neck, does a mandolin even need a truss rod?
Most quality mandolins have a truss rod to strengthen the neck and protect it from bending under the pressure of string tension. Some cheaper mandolins do not have truss rods and thus have no reinforcement to keep the neck straight and aligned. Without a truss rod, even the short neck of a mandolin could warp over time.
There are some pretty straight-forward physics at play here that can help explain why some mandolins have truss rods while others do not that can help you decide if you want this in your mandolin.
A truss rod is a part added to the neck of stringed instruments used to strengthen and stabilize the neck. They create resistance against the pull of the strings that are created when tuning and playing the instrument. Without them, the tension from the strings pulls the neck upwards and eventually into a bowed, arc-like shape. A bowed neck will then cause issues in tuning and intonation. While a small amount of bowing is fine, too much bowing can make an instrument difficult to play. When effective, a truss rod will hold a neck straight and allow the bowing to remain at a minimum.
When building an instrument, often manufactures use a steel rod or thin bar inside the neck for the truss rod. These modern truss rods may or may not be adjustable depending on what was used or how the instrument was built, but most are adjustable, made with a nut on one or both ends that adjust tension when turned. These adjustments help to correct any warping that has occurred.
Why Truss Rods Work
When a force is applied to the neck of an instrument, no matter the material, there are actually two different things happening to it. The side that is becoming the inside part of the bend is going through compression, while the opposite side–the outside part of the bend–will be subjected to tension. But at some point in between exists a place where neither compression nor tension takes place. This is considered a neutral axis…and so enters the truss rod.
Placing a truss rod in the neck will help keep the opposing compression and tension forces in balance. In theory, it should keep the neck from bending at all, though in reality that is not always practical. But truss rods are designed so you can adjust them back into a more stable and supportive position when mal-alignment occurs.
Truss Rods for Mandolins
While some mandolins have truss rods, others do not, and the need for truss rods in mandolins is a fairly polarized debate among musicians. Some people swear by them, while others have determined them to be unnecessary. Ultimately, it all comes down to two main points: neck size and overall integrity of the instrument.
The thing about mandolins is that they have 8 steel strings and these strings subject the instrument to quite a bit of tension. There is a lot of pressure being put on the neck of a mandolin and a truss rod can help the neck from becoming misaligned over time.
Some vintage mandolins you may find today were probably built by a master craftsman with practical knowledge about the mechanics of this (perhaps only this) instrument. Additionally, the quality of wood used to make these older mandolins and other instruments was far superior to woods available and used today. So it is possible to find a mandolin that not only doesn’t have a truss rod but doesn’t need one, either.
These days you can find many people who build mandolins and other stringed instruments as a hobby. (Perhaps you are one of them and you are reading this to determine if you need to bother with a truss rod or not.) Chat boards online are filled with opinions on the necessity for these in mandolins, and as it were, some feel they are necessary, while others will argue against them.
Here’s a video made by a hobby builder that provides an argument for truss rods and shows how you would place a truss rod in a mandolin you build yourself.
Indeed, some arguments are very logical and appear to be proven true, such as the argument that a short neck shouldn’t require a truss rod, or that the quality of wood used will affect the necessity for a truss rod or other reinforcement because sturdy, strong woods won’t be as easily coerced out of shape (recall the vintage example). Additionally, reverse grain-matching is a practical technique that appears to naturally work to keep a neck straight and well-aligned.
But these arguments are most valid in mandolins and other stringed instruments of shorter neck lengths. This, once again, has to do with the physics of bending (compression and tension), which tells us that the amount of pressure and force needed to bend a short mandolin neck is far beyond the ability of the strings, so warping shouldn’t even occur. But as the instrument’s necks get longer through the string family, the need for a truss rod is increased.
There are also other factors at play that can cause neck bowing such as humidity and temperature.
Do I Need a Truss Rod in My Mandolin?
As a general rule, a mandolin will play properly when a neck is flat and level, so it is to your benefit to keep your mandolin neck aligned. And while the mandolin does have a shorter neck that protects it from extreme bending, things like temperature and humidity or even your playing technique can also affect your instrument and cause warping and bending. For these reasons, you may want to consider purchasing a mandolin that has a truss rod. If you are building a mandolin, consider having a truss rod set in it.
You can find mandolins either with or without a truss rod from big-name manufacturers, and most all will be adjustable rods. If a truss rod is not used, then the neck will be reinforced with something, commonly a carbon fiber strip, or perhaps multiple pieces of laminated wood pressed together. Typically you can tell if a mandolin has a truss rod from looking at it, as the nut (which is turned to make adjustments) may be visible.
You can see from the picture below that the truss rod adjustment on my Ibanez mandolin is accessible from the headstock. This is the most common place to find the truss rod adjustment and only requires the turn of a wrench to make adjustments.
How to Adjust a Bent-Neck Using a Truss Rod
Misusing or mal-adjusting a truss rod can cause even further bending in an instrument’s neck (probably not a mandolin’s because of its size) or it can cause the truss rod to break.
And a broken truss rod, quite frankly, is a nightmare of an experience for instrument and musician alike.
So how do you straighten a bent neck and adjust a truss rod? Start by removing or slackening the strings. If the nut is not readily accessible, you may need to locate it under a small cover on the headstock.
Once you’ve done that, and the neck is set straight, tighten the nut (which tightens the truss rod). Any adjustments made should be small, as a mere ⅛ or ¼ turn can be very effective. Check the alignment after every small turn to avoid an over-correction. When the nut is tight, retighten and tune the strings.
Mandolins may have truss rods though they are not always necessary. The short size of the mandolin’s neck is stable without the need for reinforcement. Some mandolins will use a different reinforcement to keep the neck stiff such as a carbon-fiber insert. When using a truss rod, you must be sure to adjust it correctly to avoid damaging your instrument.