Lowering an acoustic guitar’s action may or may not require some work on the guitar’s nut.

• T Slot Nuts Sizes
• Proper Nut Slot Height
• Correct Nut Slot Height Chart
• T Slot Nuts And Bolts
• Correct Nut Slot Height Dimensions
• String Height At Nut

Before starting with adjusting the nut on a guitar it’s important that you are sure that it is necessary. Once you know that this is needed then you are going to need some basic tools and learn some new skills to get the job done (if you are doing it yourself).

This post will first help you decide whether or not your nut needs adjusting and then how to make any necessary adjustments.

How to Tell If the Nut needs Adjusting?

T Slot Nuts Sizes

Of course first of all you need to know that your action needs adjusting full stop. If it does then you need to determine just where it needs adjusting.

Proper Nut Slot Height

The basic idea when slotting your nut is file the slots as low as possible (or to the players personal preference) without going too low and creating any buzz. You also want to consider filing the correct width of each slot, the angle and the spacing between slots. Other factors to consider are the tools at your disposal and the type and material of the nut itself.

The truss rod, the nut slot depths, the bridge saddle radius, the fret tops condition and the playing style all have a role to play in the final string height achievable without fret buzz. Truss rod setting was covered previously, if you need to refer back. String height is adjusted by filing the nut slots until the strings are at the proper height. I check string height by measuring the distance between the top of the first fret and the bottom of the string using a feeler gauge. I shoot for twelve thousandths (0.012) of an inch clearance under the G and D, and ten thousandths (0.010) under the A.

If you aren’t sure whether or not your action needs adjusting or not, check out the article at the link below.

But there are also a couple of simple ways that might give away that the high action is a problem because of the nut.

• By doing the quick ‘preliminary check‘ measurement as per below
• If your guitar is in tune but when you play chords or notes near the nut they sound out of tune (a high action at the nut affects intonation as well as playability)
• If it feels really difficult to play a bar chord in the first fret or first couple of frets

Check the Neck

Once you know that you want your action lowered, then the first step is to make sure that the neck is set properly. You may need to do a truss rod adjustment before anything else to get the neck set right.

This isn’t as daunting as it sounds – but if you don’t set the neck right first and try to do it after adjusting the nut, then things could go bad. So making sure the neck is set right is an important first step. If the neck is right then the next step is to measure the action at the nut end.

Preliminary Check Measuring the action at the Nut End

When you are actually lowering the nut you will want more precise measurements – but if you are still unsure whether or not your nut needs adjusting then you can do this quick preliminary check.

1. Make sure the strings are tuned to pitch
2. Press down on the Low E string between the second and third frets
3. Look very closely (I find closing one eye helps) at the gap between the string and the 1st fret
4. If you are long-sighted you may need reading glasses or the likes to see properly
5. If you are still having trouble identifying the gap try pressing the string down onto the first fret (whilst still pressing on the string between the 2nd and 3rd fret) to get a feel for the gap

When you are looking (or feeling) at the gap, you want to see (or feel) a very slight gap. The string should not be touching the 1st fret – if it is touching then your action is most likely too low. But the gap should be minimal – there should only be a barely discernible gap.

If the gap is large then you probably need to adjust the nut to lower that gap.

If you’re not sure what kind of gap you are looking for check out the post at the link below for a discussion on some standard gaps at both the nut and the saddle end (also check the “take accurate measurements” section below for how to measure the gap more accurately).

If the gaps at the nut end seem fine to you but you still suspect that your guitar’s action needs lowering then you may need to adjust the action at the saddle. Always adjust the action at the nut first though, if it needs it (after making sure the neck is set right of course).

If you do need to lower the action at the nut read on.

Two Methods for Adjusting the Nut

O.k. so you’ve discovered that the nut does need adjusting to fix your action, and you’ve made sure that the neck is where it should be first. Now you need to go about adjusting the nut – you now have a couple of decisions to make. Firstly:

1. Do I pay someone to adjust the nut for me?; or
2. Do I learn how to do it myself

Paying someone to do it will cost more but will be faster and less risky.

There’s more risk involved doing it yourself, it will take a bit of time to learn the first time around (but you’ll get faster if you need to do it for more than 1 guitar) but it will be cheaper.

Secondly, if you decide you need to do it yourself then you need to choose the method you want to use. If you decide to pay someone to do it you need to find someone who can do it (it’s usually not that expensive).

There are two methods for lowering the action at the nut.

Method 1: Filing the nut slots

Method 2: Sanding the base of the nut (much the same as lowering the action at the saddle)

In theory perhaps method 1 is the best way to do this – but in practice this is a much more complicated process with much more room for error.

Method 2 is easier for amateurs to do and should do the job fine. However, you still need to take a lot of care and if you aren’t confident doing this yourself then take your guitar to a professional to have it done.

This post will be only looking at method 2. Method 1 really requires that you have tuition and is something that I can’t say I’ve ever done before or would ever try myself without hands on training. If you would prefer to have method 1 done then my advice is that you take your guitar to a professional.

But for the sake of completeness I will briefly cover what’s required for method 1.

Method 1:

Method 1 requires that you purchase 3 very specific guitar files. Each file is a different size on each side so that there are 6 different sized files – one for each string slot.

You will also need feeler gauges but you will want to get these for either method (but they are pretty cheap – only a few dollars).

You then need to file each nut slot individually enough so that the strings sit at the height you need them. These need to be filed at a particular angle.

In order to maintain proper string resonance it’s not a good idea to lower the slots too much which would submerge the strings too far into the nut and effect the sound and resonance of the instrument. If you went too far then you would need to file off some material from the top of the nut – which is a delicate process I imagine.

The plus side of this method is that you don’t need to remove the nut from the guitar but otherwise this is much more complicated and something I would personally get a professional to do.

I’ve never had it done so I don’t how much they would charge but I can’t imagine it would take very long for a pro who has all the proper tools and expertise.

By the time you take off the cost of buying the files and tools then I don’t imagine getting it done professionally would cost too much more than doing it yourself. And then you don’t have the stress, the high chance of getting it wrong – and the extra cost again if you had to get a new nut because of critical errors.

Method 2:

If you don’t want to pay a pro to do it, then method 2 will be easier.

The trickiest part of method 2 is removing and replacing the nut – but hopefully it will come off easily. Usually this is the case.

Assuming your slots are seated correctly (which should usually be the case) the easiest way to change the height of the nut is by taking material off of the base of the nut.

What Tools You Will Need

Correct Nut Slot Height Chart

• Feeler Gauges
• Craft knife or scalpel
• Block of wood
• Hammer
• Sand Paper

Take Accurate measurements

Some people do this by feel but I like to be more accurate. So I measure the action before and after making any adjustments.

To measure the action at the nut you are dealing with a very small gap so it’s important that you get this accurate. Whilst you may get away with a ruler when measuring the action at the other end of the guitar, a ruler just isn’t going to cut it at the nut.

So you will need feeler gauges. Feeler gauges are sets of thin metal blades with different thicknesses (which are written on each blade).

Basically you just:

• Place one of the blades on the top of the 1st fret and if it moves the strings up then you need to choose a thinner blade.
• If there is still a gap between the blade and the string then you should choose a thicker blade.
• Keep trying different blades until you find the one that fits in by just touching the string but doesn’t move the string up.
• Write down the number on that blade.
• This is the measurement of the action at the nut

NB: You are not pressing on any strings when you do this as you did in the preliminary check above.

Now let’s say for example that your measurement is .040 inches on the low E string and you want your nut down to .030 inches.

T Slot Nuts And Bolts

Removing the nut from the Guitar

Do this carefully!

Even if you are replacing the nut that is currently on the guitar you still need to do this carefully because you don’t want to chip the wood around the nut. And if you are using the existing nut it’s important that you don’t damage it.

1. Remove the strings – see this post for restringing a guitar to see how to remove the strings if you’re not sure
2. If your acoustic has a truss rod cover on the headstock this will most likely need to be unscrewed as it is likely to be in the way of the nut
3. Score around the edge of the nut anywhere it’s attached to the guitar with your craft knife/scalpel.
4. Take your block of wood and lie it down on the fretboard so that the flat piece of the wood is pressed up against the nut
5. Very lightly tap the other end of the wood with your hammer. This is a very light tap. Tap it a couple of times.
6. If it does not come off with a couple of taps and the nut just bends back then move your block of wood to the other side of the nut and repeat the process knocking back the other way
7. Repeat the process as many times as you need to until the nut comes off. Don’t hit harder to remove it or you are likely to damage the nut or the wood around the nut. Keep making light taps from both directions of the nut until it comes loose.

Mark the Nut

Now take a pencil and mark the nut roughly where you want to sand it down to. You should always do this so that you take off less than you need to begin with – we will be fine tuning later on. But it helps to have a target so that you don’t go too far and also don’t do too little.

The key here is to be patient. This is a multiple step process and won’t be perfect first time.

Sanding the Bottom of the Nut

The grit of sandpaper you use will depend on how much material you need to remove from the nut. Generally speaking anything from 150 – 250 grit is a safe bet and should remove the material fast enough but not too fast.

I wouldn’t go any coarser than 120 (the lower the number the coarser the sandpaper) and I wouldn’t go any finer than 600 as it will take forever to take anything off (and I would only use anything above 250 for very very minor adjustments).

Now it’s very important that you sand so that you sand evenly across the bottom of the nut so that you retain a completely flat surface.

• To achieve this I like to use a block of wood or a thick ruler to press against as I sand so that there is no subtle rocking going on (you should make sure that anything you use is completely square of course!).
• And also make sure that your sandpaper is on a completely flat surface.
• Then I take the nut and hold each end between my thumb and middle finger and press on the middle of the nut with my index finger so that it is pressing the nut both down into the sandpaper and into the square block of wood (see images below).

Correct Nut Slot Height Dimensions

Replace the nut

Now put the nut back in place (don’t glue it on yet though!).

1. Place your new strings on the guitar and tune to pitch.
2. Re-measure your action height at the first fret following the directions above
3. Measure both the Low E and High E sides with your feeler gauges
4. Re-measure using the preliminary method described earlier in this article (always pays to do two types of measurements)
5. Play the guitar and see how it feels

If it’s how you want it, congratulations!

If it needs more lowering – which is often the case – then loosen off the strings.

You don’t need to remove them completely this time but make sure they are really loose so that you can easily lift them out of the nut slots without damaging the nut slots, and push them to the side of the neck so that you can get the nut back out.

Repeat

Repeat the sanding process, again making sure that you are sanding completely flat. Only do a very small amount this time.

Repeat the whole “replace the nut” process again as above.

Repeat until you have your nut at the desired height.

Remember that it’s much easier to remove more material than to add material to your nut – so do this in small steps until you are happy with it.

Re-glue the nut

Once you are happy with your nut height you should re-glue the nut in position.

To do this, use wood glue. Just a small amount is needed. Make sure it is evenly spread across the base of the nut. Some people even water down wood glue so that it’s easier to remove the nut if you ever need to again.

String Height At Nut

Some people use superglue but I wouldn’t use this. It could make it very difficult to remove again if you ever want to make more adjustments or if you decide to replace your nut with a new one. I imagine removing a super-glued nut is far more likely to cause damage to the wood around the nut or to the nut itself.

Thanks for Reading

I hope this post has taught you how to successfully and safely lower the action on your acoustic guitar at the nut end.

To see the full process of adjusting your action including truss rod adjustments and saddle adjustments check out the link below.

Again, if you are at all unsure then get a professional to do it. They know what they’re doing and can do things like this pretty quickly so I can’t imagine it would cost too much.

If you have any comments or questions, or if you do have a way of doing it that’s different to the methods above, please feel free to leave your thoughts in the comments section below.