DO NOT TOUCH the nut slots…ever!

I am outside the country for a little break, but while here, an interested reader raised a query which has resulted in this blog post. His question was which tool I used to lower the string slots of a nut.

I told him I used nothing, because I never lower the slots!

As eyebrow-raising as you might find it, I don’t like to touch nut slots. If I have to lower the first fret action, I take measurements of how much lower I want the strings, loosen them, knock the nut out, and sand its bottom as much as I wish to lower the strings, just like I would work on a saddle.

Let me explain this a little more clearly. When reducing the action on an acoustic guitar, changes have to be made at three places:

  1. The truss rod (for dialing in the exact amount of relief required),
  2. The saddle (shaving it to bring down the action to the required height at the 12th fret), and lastly
  3. The saddle slots (to get the required action at the 1st fret)

While the first two procedures are relatively straightforward, the third one is seriously tricky. Ideally, you want the strings to sit just half their diameter in their respective slots.

So, if you bring down the action by lowering the nut slots, what happens to the half-and-half rule?

Yes, I know that the world over, action at the 1st fret is brought down by filing down the nut slots. But is there any harm in taking a different route from the known and recognised wisdom which may yield better results?

Of course, taking the first route, you loosen a single string, work on its slot, put the string back and tune up. In the second case, you loosen all strings, take the nut out and sand its bottom.

But it is quite possible that you may have to take off a little more from either the bass or the treble side than the other one. All that one needs to do is measure properly, mark accurately and sand slowly…you overshoot the lines and you are looking at making a new nut! 

But what is the problem in filing the nut slots, you may ask? The problem lies in the angles that you create with whichever tool you use to file down the slots. Instead of the slots being just lowered, your tool may deepen the slot at one side more than the other. It may even alter the points of contact of the string in the nut, affecting intonation.

Badly cut nut slots may also pinch strings in them, which is a major cause of tuning issues, string breakage. How often have you heard a string go ‘pinnnnggggggggg’ while you’re tuning it up? That sound is the effect of a string caught in nut slot and finally releasing. You may also recall the nightmare you experienced tuning that particular string.

The (bone) nuts I use, are cut through a CNC, and have near perfect string slots. The only alteration I need to make to them is to dial in the exact height they need to stand to, to give the perfect 1st fret action.

The only time that I work on the string slots, is if I have to lower between .004″ and .002″! Then, I just use old strings as saws! It takes a lot of attention and lots of elbow grease but the job gets done.

Amit Newton

An experienced guitar tech with over 10 years of experience working on acoustic Gibsons and Martins in the Gulf region. There is nothing that cannot be repaired; the only consideration is the price at which it comes. And yet, if there is sentiment attached, no price is too high! WhatsApp/Call me: 7080475556 email me:

5 thoughts to “DO NOT TOUCH the nut slots…ever!”

  1. Though we may never need this kind of job to be done, such nuanced explanations give us a better understanding of the instrument we play. Such insights are invaluable for all those who strum a guitar. Thanks for continuing to enlighten us ❤️

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