Straight from the factory or off the shelf, an instrument rarely has its nut slots cut to ideal depths. Generally they are always cut a little high so that the instrument is buzz free out of the gate. For most people, slightly high nut slots go unnoticed and the tougher feel to the strings near the nut gets taken for granted.
Before proceeding, ensure that your guitar is correctly strung up to pitch using the string gauges you normally use on that instrument and that your neck is reasonably straight with a little relief as per the previous step in this series. Check that your fretwork is not in need of immediate attention. A neck with incorrect relief or one with uneven high/low frets cannot be improved by adjusting the nut and may give false measurements.
Firstly, you need to know what type of nut you have:
The most common nuts found on non-tremolo or non-locking tremolo designs resemble the two above. A simple block of material with evenly-spaced slots. The material varies from plastics/composites, bakelite, bone, graphite and graphite substitutes, ivory, pearl, metals, wood or more exotic materials like carbon fibre or Borosilicate glass. Regardless of the material type, the function is the same. Each string has its own slot filed to the same width. The slot has a slight backward angle so that each string firmly contacts the very front of the slot. The depth of each slot is cut to create a string path over the first frets that is high enough that strings do not buzz over them when open notes are vibrating, but not so high that fretting lower notes becomes more difficult than the rest of the neck.
"Fender type" nuts are installed into a slot milled in the fingerboard itself. "Gibson type" nuts butt up against the very end of the fingerboard, usually with a very small recess to prevent movement.
These two styles are found on acoustics, basses, archtops, violins or in fact virtually any strung instrument vaguely related to a guitar.
The downside to the previous type of nut is friction. In use, strings can bind up in the nut slots when using a tremolo or string bending. This leaves the string out of tune and can cause "pinging" sounds as the string pops out from being bound up. Worse yet, strings slowly grind their way down lower into the nut slots, especially wound strings in softer nut materials. Eventually open strings start buzzing over lower frets.
Guitars with floating/locking tremolo systems such as a Floyd-Rose commonly use a metal locking nut mechanism which clamps strings in place once tuned. Locking nuts usually comprise small metal pad or cam clamps which hold two (sometimes three) strings at at time. The nut slots are precision milled into the body of the nut itself with perfect string witness points and falloff angles at the very front of the bridge itself.
Other Nut Types
Some tremolo systems (eg. a retrofit Kahler) work in conjunction with a standard style of nut, instead locking the strings a short distance beyond the nut. For the most part, these remove the issues of "binding and grinding". The standard nut is adjusted the same as it would be without the additional string locking unit.
Zero frets are a hybrid between a "normal" nut and a fret. An additional fret is placed at the point where the nut would normally be. A guiding nut is placed slightly further back from the zero fret whose sole duty is to manage the string spacing than to set string height. The physical advantage of a zero fret is that they provide the same string height clearances as any other fretted note; automatic ultra-low action with no maintenance! Famous examples of instruments including zero frets are the Höfner "violin" bass and unusually, Brian May's inimitable "Red Special" with it's non-locking floating tremolo system.
Other styles of nut exist also, such as the Fender LSR roller nut, adjustable brass nuts, etc. These require more specific considerations whereas this article is meant to cover the most common examples; an upcoming future update will cover the more exotic styles of nut....
One by one, fret the strings at the third fret or place a capo over all of the strings at this position. Each string should have an extremely small amount of clearance between the bottom of the string and the crown of the first fret. This can be carefully observed through lightly tapping the string at the first fret with a finger and/or measuring using engineer's feeler gauges.
Ideally you should have at least .002"/0,05mm of clearance under the thinnest strings and .005"/0,13mm under the heavier wound strings. Generally speaking, as long as the strings are not contacting the first fret the clearance is fine.
If you do not have feeler gauges on hand, Post-It notes from the small pads (not the big cubes as they're thicker) are approximately .004"/0,1mm to .005"/0,13mm thick. Grab a block of 25/50 Post-Its, measure the thickness of the block with calipers and divide it by the number of sheets.
If this measurement is close or dead on, move on to the next string. You may should jot down the clearances as you move across the fretboard to see the nut slot heights in relation to the fretboard as you progress, especially if you have a locking nut.
Adjusting A Standard Nut
If you have determined that any of the slots in the nut are too low (usually due to wear and age) you may want to consider replacing the nut at this point. There is the option of packing the bottom of the nut slot using a mixture of CA (cyanoacrylate, crazy glue) and baking soda, or a little material sanded from elsewhere on the nut. Backfilling and cutting back nut slots in this manner requires a fair bit of experience and practice; the subject of a whole different tutorial. Nut replacement is generally more reliable, quicker and simpler....they're pretty cheap!
If any of the slots are too high (or you just backfilled one) and excessive distance in the measurement between the bottom of the string and the first fret exists, the nut slot needs to be cut deeper. Special nut slotting files are readily available for this, however they can become expensive as specific file widths are required for each string gauge. Suppliers such as Stewart MacDonald sell nut files with dual cutting gauges, however welding nozzle/tip cleaners suffice for occasional repairs. It is even possible to mount a small piece of an old wound guitar string onto the side of a popsicle stick as a makeshift file of the correct string gauge.
Firstly, remove the string from the nut slot. Usually it can be loosened and temporarily seated in an adjacent nut slot. Using a feeler gauge, find the existing falloff angle towards the headstock in the nut slot. File the slot a little at a time, keeping the file vertical and maintaining the existing falloff angle. Clean the slot from any debris, replace the string and bring it up to tension before repeating the 3rd fret/1st fret clearance test. Repeat the filing process until an adequate clearance is achieved. Replace the string and ensure that open notes ring clearly, otherwise the slot may have an inadequate falloff angle or the string is not seated firmly at the witness point.
Adjusting A Locking Nut
Filing down the metal in the slots of a locking nut is not an option. Instead, height adjustment shims are fitted under the nut itself to alter the height of the entire unit. Nut shims are available in different styles and thicknesses from the bridge/nut manufacturers or luthiery suppliers. Most are available in both full width and half width to allow raising one side of the bridge more than the other. If necessary you can combine several shims to achieve perfect clearance across the fretboard. Sacrificing a couple of feeler gauges is also a swift fix if shims are not easily available!
Step 1: Introduction and headstock area
Step 2: Trussrod and neck bow adjustment
Step 3: Nut height check and adjustment
Step 4: String height and bridge adjustment
Step 5: Adjusting the intonation of a guitar
Step 6: Adjusting pickup height
Solidbody Setup III - Nut height check and adjustment by Brian Calvert is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
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