How To Set Up an Acoustic Guitar Neck: The Complete Guide

acoustic guitar | Sandy Music Lab

Whether you are a first-time guitar owner or a seasoned strummer, setting up an acoustic guitar neck can be a daunting challenge, especially when it comes to adjusting the truss rod! So, what needs to be done to set up your guitar neck?

To set up an acoustic guitar neck, first clean and polish the fretboard. Then you will need to check that the neck relief is correct and adjust the truss rod accordingly. You may also need to file or add a shim to the nut or saddle to get the action at a comfortable level for you to play. 

Ok, that sounds pretty scary, right? It really does not need to be. All these steps are straightforward with the right knowledge and tools. In this article, we will be looking at everything you need to do to set up the neck of your acoustic guitar. Let us get started!

Caring for Your Acoustic Guitar Neck Fretboard

This is not so much neck set-up as it is acoustic guitar neck maintenance, but it is a good idea to give the fretboard some care before you start onto the complicated things like truss rod adjustments. With the strings all taken off the guitar, give the fretboard a quick wipe down with a cloth to remove any dirt. If it is a new guitar you are setting up, this might be all you need to do. The fretboards of new guitars have often been recently polished and will not be very dirty. 

If you are making some set-up adjustments on an old guitar, however, you will want to give the fretboard a deep clean. Over time, the dirt and oils on your fingers build up on the fretboard, and this can affect string life! If it is really stuck on, try using a bit of steel wool to remove the grime. Be careful to only move it along the grain of the wood to prevent scratching! 

It is also a good idea to apply specialized fretboard oil like this D’addario Lemon Oil. This will prevent cracking and dryness, as well as helping to stop gunk from building up on the fretboard over time. The fretboard is the interface between your fingers and the neck of the guitar, so it is important to keep it in good condition! While you have the strings off already is a great time to do this since it prevents you from having to take them off specifically for cleaning.

What Is the Action On An Acoustic Guitar? 

Since a lot of the set-up that needs to be done on an acoustic guitar neck relates to the action, it will be helpful to spend some time explaining what it is and how to tell if your guitar’s action is incorrect. In short, the action is simply the distance between the strings and the frets. If that distance is too high, it will be difficult to press down the strings far enough to produce a note, and this will slow down your playing and make it feel less comfortable. 

However, if the action is too low, you will get a lot of ‘fret buzz,’ or you will not be able to play the notes at all. The playing style will affect how high or low you need the action to be. For someone who aggressively strums the strings, a higher action is probably better. That is because aggressive playing causes more vibration of the strings, leading to more fret buzz. Someone who very gently plays will be more comfortable with lower action and will not get fret buzz.

Intonation

Intonation refers to how in tune your guitar is at different points of the neck. If the action is too high, you might find that a note played on one part of a string is out of tune with the same note played on a different part of the neck. In other words, even if you have tuned the open strings to each other perfectly, the guitar might become more and more out of tune as you move further up the neck. 

This is because if the action is too high, there is more distance between the fret and the string at the higher frets. More distance means you can press the string down further, creating extra tension, which can translate to an out of tune note. A small amount of relief is perfect since it means the action will be low at the high frets without causing fret buzz at the lower frets. Getting the right action for comfortable playing without affecting intonation is a delicate dance! 

Checking the Truss Rod Alignment For An Acoustic Guitar

This is perhaps the scariest step involved in setting up a guitar neck since it requires extreme care not to do serious damage to the guitar. Most guitarists recommend going to a professional for truss rod adjustments for this reason, but you can do this at home if you are feeling adventurous and brave. This needs to be done first because later steps will be affected by the truss rod’s tension. 

What Is the Truss Rod? 

A truss rod is a steel rod that runs along the neck of the guitar. When you put strings on a guitar and tune them up, this puts a lot of tension on the neck and tries to force the neck to bend towards the front of the guitar. The truss rod aims to compensate for this tension by pulling the neck in the opposite direction. The truss rod applies tension to the neck to ensure that the tense strings do not cause the neck to bend so much that the guitar is unplayable. 

Does My Guitar Have a Truss Rod?

The only acoustic guitars which are unlikely to have a truss rod are nylon-stringed classical guitars. That is because the nylon creates less tension to compensate for. A steel-stringed acoustic will almost always have an adjustable truss rod. You can check by looking for the adjustment nut. This will either be at the top of the neck at the headstock or the bottom of the neck beside the soundhole. 

Do I Need To Adjust the Truss Rod For An Acoustic Guitar? 

The best way to know if you need to adjust the truss rod is if the action feels really wrong! However, other factors affect the action, so adjusting the truss rod is not the end of the process. It can be tricky to know whether you need to adjust the truss rod and how far to adjust it if you do. Unfortunately, the process for checking how much you need to adjust it can also be quite tricky and complicated. In this section, we will be showing you how to measure this:

Relief and Backbowing

When the neck bends ‘forward’ as a result of the string tension, that is referred to as the ‘relief.’ All guitars should have some relief or else the action will be too low, but the relief will increase over time as the string tension pulls the neck forward. When you tighten the truss rod, you counteract the relief caused by the strings. Tighten it too far, however, and you will end up with a ‘back bow,’ which means the neck is bent too far the other way, resulting in too low action. 

How to Measure the Relief

Ok, this is a very tricky bit, so we will spend quite a bit of time on this. In order to know whether you need to adjust the truss rod, you will need to know the relief. One clever way to do this is to simultaneously fret the 1st and 14th frets, then measure the distance between the top of the 8th fret and the bottom of the string at the 8th fret. If you have fewer than 3 hands, you can use a capo to fret the string at the 1st fret. 

This is very hard to measure, but for a steel-string acoustic, the distance between the string and fret at the 8th fret with the 1st and 14th pressed down should be between 1/64th of an inch (0.396mm) and 1/32nd of an inch (0.793mm). That is a tiny measurement, and you will need a machinist ruler like this Stainless Steel Machinist Ruler/Rule Scale, which includes 64ths of an inch.

A much easier way, however, than measuring it precisely, is to use a business card. One business card is about 1/64th of an inch thick, and two business cards are about 1/32nd of an inch. In other words, with the 1st and 14th frets pressed down, you should be able to fit between one and two business cards between the top of the fret and the bottom of the string. If you do not have a business card, a credit card is almost exactly twice the thickness of a business card. 

In essence, when you are pressing down the 1st and 14th frets, the string should be very nearly touching the 8th fret, but not quite! If the string is touching the fret, you will need to loosen the truss rod ever so slightly. If the gap between the fret and the string is bigger than 2 business cards (or 1 credit card), then you will need to tighten the truss rod ever so slightly. 

Adjusting the Truss Rod On Your Acoustic Guitar

Now that we know how to tell whether the truss rod needs to be adjusted, it is time to look at how to do it. It is important to say right at the start that when you are adjusting the truss rod, you need to be extremely careful not to turn the nut too far. You should only turn the nut ¼ of a turn at a time! If you tighten it too much, you could end up doing some serious damage to the neck of the guitar. 

The truss rod adjustment nut, called the ‘hex bolt,’ is normally located just inside the soundhole, on the side closer to the head of the guitar. Sometimes, however, it is located on the headstock of the guitar. 

Turning the Hex Bolt

As mentioned above, which way you need to turn the hex bolt will depend on the neck relief, which is measured by fretting the 1st and 14th frets, then measuring the distance between the 8th fret and the string. If the gap is more than the thickness of 2 business cards, you will need to turn the hex bolt clockwise to tighten it. If you are standing at the bottom of the guitar looking towards the head, that means you turn the hex bolt to the right. 

If there is no gap at all between the 8th fret and the string, that means that the neck is back bowed, and you will need to loosen the truss rod. Again, standing at the bottom of the guitar looking towards the neck, you will need to turn the hex bolt ever so slightly to the left (anticlockwise). Keep adjusting until the distance between the 8th fret and the string (with the 1st and 14th frets pressed down) is about the same as the thickness of 1-2 business cards. 

Let It Settle

Some people make a truss rod adjustment, then pick up the guitar a day later only to realize that the relief is wrong again! That is because it takes a day or two for the wood to settle into the new tension. That means you will likely have to make the truss rod adjustment, wait a day or two, then fine-tune the relief again. Do not worry; you can still play the guitar during this time. 

How To Measure the Action On An Acoustic Guitar

In order to measure the action, you will need a ruler that starts the measurements from the very end rather than having a gap between the end of the ruler and the start of the measurement lines. This is so you can press the end of the ruler flush against the neck and take an accurate measurement. Alternatively, you can use a Guitar Ruler String Action Ruler Gauge Tool like this one from Amazon, which will speed up the process. 

To check that the action is correct, one method is to simply hold the guitar in the playing position, then press the end of the ruler against the 12th fret and measure the distance between the fret and the bottom of the string. You should hold it in playing position because the effect of gravity pulling down on the strings will cause the measurements to be ever so slightly off if the guitar is laid down on its back. 

You only need to measure the high and low E strings. There is no need to measure the 4 in between. For a medium action on a steel-string acoustic, the bottom of the low E string should sit about 2.5mm above the top of the 12th fret. The high E should sit a little lower, about 1.8mm above the top of the 12th fret. 

For a low action, which is desirable for gentle playing like jazz solos, the distance between the 12th fret and the low E should be around 2mm, and the distance between the 12th fret and the high E should be 1.5mm. For a high action, which is desirable for aggressive playing like heavy strumming, the low E’s string height at the 12th fret should be around 3.8mm, and the height of the high E at the 12th fret should be around 3.2mm. 

What Causes the Action To Change On An Acoustic Guitar

There are a few different reasons the action might change on your acoustic guitar. The bridge and neck of a guitar consist of a complex set of moving parts that can drift out of position over time. Even if you never play the guitar, the action will eventually change so much that the guitar will be unplayable. Fortunately, there are things you can do to slow down this process significantly. Here are a couple of the main reasons why the action might change:

Temperature/Humidity

This is the most common cause of action changing. Really, it is the humidity that does most of the work, but I have included temperature since the two are highly related. As the temperature goes up in the summer months, the air can hold more moisture content. This moisture is absorbed into the wood of the guitar, causing it to expand. High temperature also causes some expansion and low temperatures can cause the wood to contract slightly. 

When it is hot, the action is likely to rise slightly because there will be more moisture in the air. If it is too dry, the wood will lose some of its moisture content, causing it to contract. This means that the action will generally be lower in winter. The ideal humidity level for an acoustic guitar is between around 40% and 60%. One good way to reduce big humidity swings is to always make sure your guitar is stored in its case!

String Tension

As we have discussed already, the strings on an acoustic guitar hold quite a lot of tension, so much so that the truss rod is required to counteract the pull. Over time, this tension can cause the saddle and nut indents to deepen, lowering the action. The string tension is also what causes the neck relief to increase, so it is the reason you will need to occasionally adjust the truss rod to keep the action at a comfortable level. 

Other Ways to Adjust the Action On An Acoustic Guitar

Adjusting the truss rod is by no means the only way to adjust the action on your guitar. You might well find that once you have finished with the truss rod and allowed it to settle, that the action is still not how you want it. That does not mean that you need to adjust the truss rod again! Here are a couple more ways to adjust the action on your acoustic guitar:

Adjusting the Saddle To Lower the Action

The saddle is the small white strip made of plastic or bone which sits on the bridge of the guitar. Since the strings sit on top of the saddle, reducing the saddle’s height means you are also reducing the action. To do this, you will have to file down the bottom of the saddle. You have to be really careful about this! Because you have to remove the saddle in order to file it down, you cannot see what the filing is doing to the action until you have replaced the saddle. 

Once you have measured the action and you know how much you want to lower the action, you will need to relieve all the string tension before you can slide the saddle out from the bridge. If you know exactly how much you want to file off, mark the saddle using a ruler and a marker before you start. This will help you see how much you need to file off and ensure you file in a straight line, which in turn ensures that the saddle will fit back into the bridge. 

Always file less than you need to, then wind the strings back up to proper tension and check the action. You can always file off more, but you cannot stick the dust back on once it has been filed. If you file off too much, you will need to purchase a new saddle! File the saddle in very small increments to ensure you go far enough without going too far. Eventually, you will have the action you have been looking for. 

Adjusting the Saddle To Raise the Action

If you are experiencing a lot of fret buzz when you play, or some of the notes are not playing at all, then you likely need to raise the action. You can not do this by simply loosening the truss rod to allow more neck relief since this will damage the neck over time. If the neck relief is correct, the right way to raise the action is to install a shim under the saddle. A shim is a piece of wood or bone that extends the saddle’s height without losing tone.

First, you will need to either buy or make a shim. I would recommend buying a Bob Colosi Saddle Shim Kit. These kits are made from ebony, meaning you can install them without risking any tonal loss. It really is as simple as removing the saddle, then gluing the shim to the bottom. Bob Colosi’s kits come with various sizes of ebony strips, as well as super glue to attach them to the saddle. Simply add the strips one at a time until the action is high enough for your liking. 

Adjusting the Nut To Lower the Action

This is a very similar process to adjusting the saddle, but there are a few things that are worth mentioning when it comes to the nut in particular. If the nut is too high, for example, you will have trouble with the action of the lower frets as well as the higher. Some people do not think to adjust the nut as well as the bridge since they test the action only at the 12th fret. It is worth having a look at the action on the lower frets to see if you need to lower the nut.

Lowering the action at the nut works in the same way as doing it at the bridge. Simply slacken the strings until you can remove the nut from the headstock, and then carefully file it down until the action is low enough. Remember to only do a tiny amount at a time, then tighten the strings back up and test the action again. Once you have filed too much, you will have to buy a whole new nut and start the process again. 

Adjusting the Nut To Raise the Action

Again, this is very similar to the process which happens at the other end of the neck. For the simplest solution, buy a Bob Colosi Nut Shim Kit and follow the instructions. You will just have to slacken the strings, remove the nut, glue the shim to the bottom of the nut, replace the nut, then tighten the strings back up. These kits come with several thin strips, so you can experiment with the action by trying out different configurations. 

Summary

Understanding action and the reasons it changes over time can go a long way towards helping you to be able to set up the neck of an acoustic guitar correctly. Perhaps the trickiest and most dangerous step is adjusting the truss rod. 

Once you understand how to adjust the truss rod and know how and when to file the saddle and nut or add a shim, you will be able to set up an acoustic guitar neck so that it is comfortable to play and has the correct intonation. 

Good luck setting up your guitar neck!

David Sandy

Hey there! My name is David Sandy and I'm the founder of Sandy Music Lab. I've been playing guitar for several years now and created this site to be able to share and explore music with others. Check out my recommended guitar gear!

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