How to set up a Fretless Guitar
Very few guitar luthiers will know how to set up a fretless guitar correctly. Even professionally supplied instruments can be dramatically improved with just a few simple adjustments. These adjustments are the difference between a great fretless guitar and a guitar that you may find almost unusable.
You will need some simple tools:
A twelve inch (300mm) metal straight edge ruler. (stainless steel is best, a six inch (150mm) is also useful)
A set of feeler gauges, as used by the motor trade.
A set of nut files, these can be expensive, but are well worth the investment.
A Key for adjusting the truss rod.
Additionally you should have a good quality set of strings on the guitar, some cheaper sets are crudely made and may defeat this precise setup.
With glass or metal fingerboards you are usually guaranteed a dead straight neck, and this is essential.
Wood or phenolic necks are usually dependant on the adjustment of the truss rod. With standard neck adjustment there will usually be a little “toe in” that is a slight curve in the neck to prevent buzzing of the strings on the frets. As we don’t have frets, “toe in” is not required. In fact the neck must be dead straight.
Do the following checks with the neck under string tension.
To verify the neck is straight you can first take a sight along it looking from the nut along the neck to the bridge. You should see immediately if the neck is out of true.
At this point you may need to adjust the truss rod to straighten the neck. If you are unfamiliar with this procedure it may be best to get a guitar tech to do the work for you.
To ensure you have the neck perfectly straight, take the metal straight rule and place its edge against the fingerboard starting at the nut. If you hold the guitar neck up to a light source, no light should leak under the fingerboard.
Try this again further down the neck, you will soon determine if it is straight or not. No light will leak out if the neck is true.
In most cases you will be able to get the neck dead straight, by careful adjustment of the truss rod. Don’t go too far as if the neck bends backwards and the straight rule indicates a bevel, the guitar will be unplayable. If you cannot achieve a dead straight neck, the neck itself may have to be planed flat, this is a difficult technical task and should only be done by an expert, or very brave amateur luthier.
The nut itself determines the height of the strings at the start of the fingerboard, and this must be really low, far lower than a normally adjusted guitar.
This critical adjustment will be the difference between a great playing guitar and an average one, it is that important, and this is where the feeler gauges come in handy.
You are aiming to get a distance of 4 thousands of an inch or 0.1 mm string height at the nut. At these tolerances it can be very easy to cut the nut down too far and the string will buzz in an open position. To prevent this while cutting the nut, use the feeler gauge as a limiter on the cutting height of the nut file. Start with a gauge slightly larger than your anticipated height, say 6 thousands of an inch or 0.15 mm. You may have to combine one or more of the feelers to get the right height.
Once you have filed the nut for the first string, check the clearance with the feeler gauges, you may find using the 6 thousand inch (0.15 mm) gauge as a cutting guide will end up as an actual 4 thousands of an inch string height when the string is fitted. Proceed with great care as the last thing you need to happen is be in the position of cutting and fitting a new nut.
At this point it might be worth mentioning that the nut in the pictures has been filed to a very low profile. This modification means notes can be played starting or finishing behind the nut, particularly helpful if you are sliding harmonics.
With the nut being very low profile on this guitar, a string retention bar has been fitted, just to keep everything in its place.
The best bridges for fretless guitar are usually the Fender type where each string’s individual height can be adjusted. If you have a Les Paul type you will have to adjust the optimum position for all strings
At the twelfth position (halfway along the string length) you want to aim for a clearance of about 0.06 inch (1.5 mm) for the 1st string, slightly higher for the 6th string.
This is a trial and error adjustment. Play the string all along the fingerboard, ensure it sounds true at all points. If there is buzzing or there are dead points where the string does not sound, lift the height of the bridge until these disappear. You will soon optimise the position for that particular string set.
The same procedure as on a fretted guitar. Sound the harmonic at the twelfth position on the fingerboard then hold the string with a fingernail at as close to the twelfth position as possible. If the second note is sharp move the bridge piece back, if flat move it towards the nut. Repeat until both sounds are equal in frequency.
Hopefully you have picked up on earlier advice and have four wound strings and two plain top strings. The output of the plain strings will usually be less than the wound strings. Therefore its a good idea to raise the pickup on the treble side, near the 1st and 2nd strings and drop it down on the bass strings. If you have individually adjustable pole pieces, even better. The balance will be personal adjustment, but don’t take the pickup too high so that the top strings are sucked onto the pickup.
To explain: one thing you should look out for is very powerful magnetic pickups, make sure they are not so close to the string as to have a magnetic influence, that is, pulling the string downwards towards the pickup, this will adversely affect very low action set-ups.Fretless Guitar Hardware