Guitar maintenance 4: Setting nut action

Once you have set your guitar’s truss rod and set the bridge action, it is time to look at the nut action.

The nut is the “comb-like” part at the top of the neck between the headstock and the first fret, and is usually made from plastic or bone. Basically similar to a fret, it is the starting point for the open strings, but it also sets the string spacing and action at the top of the neck. Nut action is essential to a comfortable play and factory settings can almost always be vastly improved to make a big difference to the feel of a guitar most of the way down the neck. Cutting a nut is a critical adjustment and takes a few tools, so if you are not sure about doing it yourself, take your guitar to a professional.

Tools needed

A set of feeler gauges – these thin metal strips are used for measuring the size of a gap, are inexpensive, and can be found at any auto-supply or hardware store.

Nut files – are specialised tools to easily cut a round-bottomed slot of a precise width. Unfortunately they are expensive and must be bought from specialised luthier supply houses. With care, it is possible to use a small round needle file and a triangular file to cut a nut.

Measuring nut action

First play the guitar to see if the nut needs adjustment. If the nut is too low, the open (unfretted) strings will buzz against the first fret when you play them, but the fretted notes will not. If it is too high, it will be difficult to fret notes at the first position.

There is no universal setting for action, so there are no measurements that suit every guitar and player. Fret heights differ and some players prefer a higher action with a stiffer feel. In these cases it’s better to have the strings higher than the “perfect” low action.

Fret the string at the first fret and slide a feeler gauge between the string and the fingerboard, right in front (body-side) of the fret to measure the gap between the fingerboard and string. If the feeler gauge is loose, try a thicker gauge, or a combination of gauges until a snug fit is found. This will tell you exactly how tall the fret is and will also be the absolute lowest the nut slots can be cut. In practice, we usually set the nut action at least a fraction higher than the fret to avoid any possible problems.

Cutting the nut

If the nut is too high, the grooves must be cut deeper with your files to bring the strings closer to the fingerboard. Detune the first string slightly, so that you can lift the string out of its slot and pull it to one side, away from the slot. Next, place the end of the “fret height” gauge on top of the fingerboard and against the nut.

File the slot at a slight downward angle from the fingerboard towards the headstock until the slot is just above the top of the feeler gauge. The angle makes sure that the string leaves the nut at the front and avoids intonation and string buzz problems.

The width of the slot should be slightly larger than the diameter of the string so that the string should move through it easily without binding. If you need to make a slot slightly wider than the file, rock the file from side to side as you cut to widen it.

Just before the file reaches the feeler gauge, stop, replace the string in the slot and retune. Check that it is not buzzing against the fret. If it’s your first time cutting a nut, it might be a good idea to stop here, as you will already have improved the action greatly and it’s easy to get carried away and cut too far – the difference between buzzing and not is sometimes only one stroke of the file.

Repeat this process for each of the other strings.

Raising the string height at the nut

If you found that the string height at the nut was too low, or you cut the string slots too deep, the string height at the nut can be raised easily by fitting a shim of wood veneer beneath the nut. To do this, remove the nut, cut a shim to the same width and length as the bottom of the nut using a blade, glue the shim to the bottom of the nut and reglue the nut to the neck. Once the nut has been shimmed, the slots can be cut again if needed.