Today we’ll talk about the best way to adjust the truss rod on an acoustic guitar – a very delicate task that should be done carefully and gracefully. One wrong move and you’ll end up messing up your musical instrument – and who would ever want that?
That’s why I’ll do my best teaching you here how to adjust the truss rod today – yes, I know – boring! But bear with me – it’s for your own good.
Guitar necks that are purely made out of wood will tend to bend as the strings are tuned up. This is because the string tension puts a considerable force onto the neck, which causes it to bend so that the fretboard appears to have a concave curve along its length.
This curve can pull the strings away from the fretboard giving poor playing performance and intonation problems. This is not a problem with guitars that have gut or nylon strings.
One way around this problem would be to make the neck a lot thicker, but this isn’t what guitarists want for easier and better playing.
In order to deal with this problem, a rod is put in the back of the neck to apply an opposing force which will help to straighten the neck out.
This is called the truss rod.
The top end of the truss rod emerges at the headstock end and will either be in a shallow cavity or in the form of a bullet shape projecting out of the headstock.
Both types of truss rod are adjusted by the use of a hex spanner which is inserted into the end of the rod.
Guitar necks don’t want to be absolutely straight because the strings need some clearance over the frets lower down the fretboard when different notes are played.
The ideal shape is to have a very slight concave shape to the neck profile. In this way, the clearance for the frets at the bottom of the fretboard is achieved.
As stated before if the bow in the neck is too concave, then you will be having high action problems.
In general, most necks are set up correctly, and you might not need to adjust the truss rod ever.
Times where adjustment of the truss rod may give an improvement in the playability of a guitar include:
- when you change the gauge of the strings drastically for example between .008 sets and .010 sets and the other way round;
- putting a new neck on a guitar;
- if the frets are very worn and you can’t afford to have somebody stone down the frets.
The easiest way to do this is to sight down the neck along the side edge of the fretboard to see what sort of bend is actually in it.
When doing this, you need to make sure that you sight along the tops of the frets.
If you look along the binding below the frets, you will get the wrong idea because these often vary in how they are fitted along the length of the neck.
It is the frets and surface of the fretboard that we are interested in:
- If you see a slight concave bend in the fretboard as you sight down the neck, your guitar is probably set up correctly.
- If the neck has no curve in it or is bent the other way giving a convex profile, then you will need to adjust the truss rod.
- If the profile is very curved in a concave way then once again there will be some adjustment needed to the truss rod.
Another way of checking on the curve in the neck is to use a long steel rule:
Place the edge of the rule along the length of the fretboard and then look at the rule sideways on.
- If there is no gap under the rule in the centre or it wobbles up and down as you are trying to place it along the length, then the neck is either too flat or convex in shape.
- If there is a small gap towards the centre of the rule, then the setting is probably right.
- If there is a large gap under the centre of the rule, then the neck is probably too concave.
There will, of course, be other indications that the neck is not set right.
These could be such things as the inability to set a low action for the guitar without lots of buzzing or the inability to set the action because it is always too high.
You can next check to see if the settings match those laid down by Fender:
- With the guitar tuned to concert pitch, put a capo on the first fret.
- Next, fret the 6th string at the fret where the neck joins the body.
- Take some feeler gauges and check the gap between the string and the surface of the 8th fret. The recommended size for this gap is about 0.10 inches.
Once you have decided that the truss rod needs adjusting, then the first thing to do is to decide who is going to do it.
A lot of people get scared about adjusting truss rods because there are many tales of people over tightening them and breaking the rod inside the neck.
This, then, would be very costly to repair.
If you are confident about what you are doing, then you shouldn’t have any problem.
The best thing to do first is to practice on a guitar that is relatively inexpensive before you tackle that vintage Fender Stratocaster.
This is what I did. Once I had set up a few cheaper guitars and then sorted out a few of my friend’s guitars, I was happy to have a look at my 70s Stratocaster!
The procedure for adjusting the truss rod of a guitar is pretty much the same for all guitars:
- Insert the correct size hex spanner into the truss rod adjuster in the headstock of the guitar.
- Turn it a little until it fits into the hex socket of the truss rod. You need to decide which way you need to turn the spanner to get the correct adjustment.
- If the neck had a concave curve in it, you need to tighten the truss rod so that it gives a force against the tension in the strings.
- This will then reduce the concave bow and give a flatter neck profile.
- In order to tighten the truss rod, you need to turn the spanner in a clockwise motion in the same way as you tighten a nut on a bolt.
- Make only small adjustments at a time no more than half a turn.
- Once you have made this adjustment you need to check the gap at the 8th fret once again with the feeler gauges.
- Each time you do this, make sure that the guitar is still tuned to concert pitch. If the adjustment isn’t enough, then you need to go through the procedure again until you get the effect that you want.
- Be careful when tightening the truss rod because over tightening it can break the rod.
If you find that turning the adjuster is having the opposite effect on the curvature of the neck, then you are probably turning it the wrong way, and as a result, you should turn it the other way.
If your neck is too flat or has a convex bow, then the truss rod is applying too much force to the neck.
This can happen if you go from very thick gauges of strings to very thin gauges. In this case, you need to slacken off the truss rod. Turn the adjuster in an anti-clockwise way as if you were undoing a nut from a bolt.
Once again, it is crucial to make small adjustments of no more than half a turn and to check the results before adjusting the rod anymore.
Once you have finished your adjustments, make sure that the guitar is at concert pitch and remove the hex spanner from the truss rod adjuster.
You should have at least a quarter of a turn on it.
If you find that there is a huge amount of resistance when turning the adjuster in either direction or that there is still a convex bow in the neck even when the truss rod adjuster is completely loose, you should seek advice from a professional luthier.
The first time is the hardest – after that, you’ll end up doing everything on the go without thinking about it twice!
Here is a great visual guide for you!
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