DIY Guitar Set-up: Part2

Set string height by adjusting the bridge and checking the nut.


Stephen Barker

2021-05-23 7 min read

DIY Guitar Set-up: Part2
String height

Adjust the Bridge

The easiest way to lower your string action is to lower the height of the bridge saddles. This is perhaps the simplest way to improve the playability of your guitar. This is because many electrical guitars have a simple way to adjust the string height at the bridge. These fall into two main types: Those like a Les Paul which have a fixed saddle heights, and an overall bridge height, and the Strat or Tele type which have individually adjustable saddles. There is also the Floyd Rose type which has overall bridge height adjustment and stepped saddles, but shims are frequently used to customise the saddle heights.

Assuming you're happy with the neck relief (Part 1), you should now measure the string height of the first and sixth at the 12th fret with a string action ruler. Make a note of the heights. Now you can start to set the string heights to the optimal action for you playing style. An easy way to do this is lower the saddles until the strings are touching the frets. Lift the saddles until each note plays cleanly without 'fretting out' (playing a semi-tone sharp) or buzzing excessively*.

Once you are happy the guitar is not fretting out, try some string bends. Can you bend the strings to the extent you need to? If you cannot, the strings need to be higher. There is a direct relationship between the radius of the fingerboard of your guitar, the action and how far you can bend the strings. There may be a formula for this? I don't know, but put simply, the smaller the radius, the steeper the arc, the higher the strings need to be to bend the strings. Old Fenders have a tight radius sometimes 7.5” (higher action, harder to make bends), Gibsons tend to be quite a bit flatter (lower action, easier bends) and 'shredders' have a flat fingerboard (super low action, easy bends).

The action of an acoustic guitar should not be as low as an electric guitar. The string height allows you to get volume from your playing. The majority of acoustic guitars do not have adjustable saddles. Acoustic guitars tend to have a strip of bone or plastic. The only way to reduce the action is to remove material from the saddle. Some people cut grooves into the saddle from the top – similar to a nut, but you need to get your string spacing bang-on. I don't favour this method as I think it looks untidy.

A much tidier way is to pop the saddle out and file material off the bottom. You need to make some estimates before doing this. If you want to remove 1mm from the action at the 12th fret, you would need to remove roughly double that amount at the saddle. Finding the right spot however, takes some trial and error. I usually leave the strings attached at the tuner end, and pop them in and out of the bridge until I am happy with it.

If the action is too high for your playing style and some frets are still fretting out or buzzing, you may need to perform a full or partial fret level.

Check the Nut Height
You will need some fine tools and accurate measuring devices to perform this aspect of the set-up, or a lot of trial and error. Typical tools for this job: craft knife, fine nut slotting files, protective metal bars, feeler gauges, hammer. Materials: veneer or fine sheet metal for shims, super thin superglue, bone dust or bicarbonate of soda.

Strings too low – If this is the case you might be lucky because you may not need the expensive fine nut fines. To check, play each string open and listen for any buzzing sound. If the strings buzz when played open, then the strings are sitting too low at the nut. There are two ways to resolve this without changing the nut. Firstly if the problem is across the nut, then you can shim the nut. To do this you will need to remove the nut and insert some material under it before re-fitting.

To shim a nut you need to remove it first. Slacken or the strings enough so they can be out of the way. I slacken them enough to be able hold them back with a pencil, 3 each side of the neck. A locking nut will be screwed into the top of the neck. To remove it unscrew the locks to reveal the fixing screws. Simply unscrew and shim with enough material to allow the strings to clear the first fret. For a glued in nut you should check to see if any paint or lacquer conceals where it joins the fingerboard, neck and head. If it does you will need to score lines to avoid chipping. Next you should warm the nut with a hair drier to soften any glue that holds the nut in place. Once I've done this I tap it gently with a small hammer towards the head. Once the nut is out, clean any glue from the nut and fingerboard/neck. Next you place carefully sized slithers of veneer onto the wood. Don't glue anything in yet. Pop the nut in, slide the pencil out, pop the 1st and 6th string back on, bring those up to pitch and see how the string height is. Once you're happy with the height, you can glue the shims and nut in place. It is recommended to use animal hide glue as this can be heated for safe replacement in the future. In reality a lot of the time two tiny drops of superglue will suffice. You only need to hold it in place, the strings will hold a tight fitting nut in place well enough.

Strings too high - If the string height is high at the nut, open chords will feel spongy and you may also find the notes are out around the 1st and 2nd frets – this is especially common with the G and B strings. Intonation is always approximate on a standard guitar, but careful re-cutting the nut can improve the intonation at the nut end.

Re-slotting a nut is a precision job and if you are going to attempt it yourself, you will need to invest in the right tools. You will need fine luthier nut files. The cheap ones found on internet market places really are not up to the job. I would stay away from these completely. The proper ones are expensive, but they do the job. Handy, but not essential are the metal bars of varying thickness that stop you cutting too deep.

Assuming your nut slots are spaced correctly all you have to worry about is the depth. It's generally accepted that the closer the strings are to the first fret without buzzing, the better. You should be looking at for like 0.5mm at the 1st string and 0.75mm at the 6th. Use feeler gauges to check this.

Before you start, slacken the strings and hold them out of the way as above. Protect any area you might accidentally scratch with the file with masking tape. Once you have done this if you are using a stop bar, rest that on the fingerboard and hold it against the nut.

To make the actual cuts match the file to the string. Professional luthier files have the corresponding string gauge marked on them. Gently push the file through the slot towards the head. I aim for where I intend my string to finish winding on the tuner peg. This allows for the maximum contact with the bottom of the slot. Rocking the file will give a slight bevel which will give a gradual curve allowing for trouble free tuning.

Once I've drawn the file through the slot a few times I pop the string back in, bring it to pitch and check it. I repeat this process with each string until I've reached the desired action for each string at the 1st fret.

If you cut too low, all is not lost, you can do the backing soda and superglue trick.

The baking soda and superglue trick involves packing the low slot with baking soda (or bone dust) and dropping a drop of super thin superglue onto it before re-cutting the slot to the desired height.

*Fret buzz, unlike fretting-out, is a relative thing. Metal strings vibrating against metal frets will inevitably buzz to some degree. What's acceptable to you is all part of the compromises you need make in your search for guitar perfection.

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