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Tech Notes: Truss Road Adjustment


By Larry Darnell

Why Bother With a Truss Rod

Having a truss rod is pretty much like having a car jack. You may never use it, but it's sure helpful if you need to change a tire. You may never need to use the truss rod, but if you're reading this, perhaps you are thinking about it.

The point of having a truss rod is to easily adjust the string height to your preferred playing comfort. It's no fun to have buzzing strings too low or difficulty pressing strings when they are too high.

Depending on where you are, the annual changes in temperature and humidity can affect your guitar's neck so it moves: raising or lowering the strings. A truss rod adjustment can change this for you.

While it may seem like a murky process, we're going to simplify it so you can do it yourself. Conceptually, the mechanical process is about as simple to understand as using a tuning machine to tighten and loosen a string. You can skip to the TAKE OUT YOUR WRENCH section to get right into it.

A Little History

Since 2000 all Hill Guitars have had an adjustable double-acting truss rod adjustment in the neck. Prior to that, many guitars made in the Mexico shop had truss rods. The truss rod's placement in the Master Series guitars was challenging to access since it was buried in the second brace above the sound hole. Directions and rationale for this appears farther down this page in the original 'how to' truss rod adjustment article.

While the truss rods have been the same design from the beginning, the new ones are easily accessible at the end of the fingerboard in all Hill and New World guitars. Most New World Guitars come with an Allen wrench to adjust the truss rod. Hill Guitars do not. The Allen wrench size for Hill guitars is 9/64" which is accessible at most any hardware store. We will send you one if you wish.

Let's Do it - Take Out Your Wrench

Put the guitar on a flat surface like a table with the neck to your left. You can leave the strings on and tuned so you can check the string height by playing the guitar as you adjust the truss rod.

Insert the Allen wrench into the nut and turn [pull or push] it in the direction you wish. If you want to lower the strings, push the wrench away from you [clockwise], this is also called reducing relief to the neck. If you want to raise the strings and get rid of a buzz, pull the wrench toward you [counter clockwise], this is also called adding relief to the neck.

A 1/4 of a turn could be all it takes. Take out the wrench and play the guitar. How does it feel? Continue to repeat this process until the string height feels right.

You should not have to push or pull very hard, but there will be some resistance. It may make a creaky noise, don't worry about that. If you find pushing or pulling to be difficult, do not force it or torque it very hard.

There is nothing more satisfying than having your guitar optimized for your own preference. You will be happy how much better it makes you play.

LD - June 2019

PS. Some people still worry the truss rod adds weight and creates a bad sounding guitar. There is one case where they are correct, although they don't know it. Since the truss rod can move the neck in 2 directions, there is a place in its movement when it can be precisely in the middle of its run such that it is under no tension at all. In this case, it is possible the truss rod can vibrate in sympathy with the instrument causing a buzz. A simple turn to get the truss rod under a little tension will make that buzz go away.



By Kenny Hill

I put a truss rod in all of my Masters series guitars. Although this is not traditional in classical guitars, I find it a most useful remedy when a guitar neck changes due to climate changes or age. I like for a guitar to play very well, and even subtle adjustments in the neck can make a big difference in how easily a guitar plays.

This truss rod works both forward and backward, which means it can adjust for both a back bow or a forward bow. It is accessed through the sound hole.

Here's how to do it:

It's easiest to do with the strings loosened, although I personally do it with the strings up to pitch so I can look at the neck under tension. If you do it up to pitch, just lift up the 2nd and 3rd string at the nut and move them over to the 1st string nut slot. Do the same thing with the 4th and 5th string, moving them into the 6th string nut slot. Then you can reach into the sound hole between the 3rd and 4th strings. The strings hurt the forearm a bit, but it's manageable.

Set the guitar on a workbench with the neck pointing to the left, tilt the body toward you so the sound hole is facing your belly. Then reach in with the 9/64 inch Allen wrench and put it into the Allen nut, which appears through the very upper cross brace of the soundboard, right by the end of the neck. Although it will offer a certain resistance to turning, it doesn't take much movement to cause a change.

Turn counter clockwise (imagine looking at the Allen nut) to add relief or correct a back bow. Turn clockwise to reduce the relief or correct too much forward bow.

It's easiest to remove the wrench by lifting the guitar up on it's bottom end and just let the wrench drop into your hand.

Sounds easy, huh? It usually works very well. The hardest part is getting the wrench into the allen nut, since you can't see it. But with a little practice it's easy.

Finding the Allen nut is a little challenging the first time because the cross brace just above the sound hole is in the way; you have to maneuver around it to get to the Allen nut.

Don't forget that a neck is not supposed to be straight - it's supposed to have a little forward bend, called relief. I measure it with a straight edge and a feeler gauge at the 6th or 7th fret, or I just sight down the edge if the finger board. I like between .003' and .008" relief on the bass side, and a bit less on the treble side. I don't consider it a repair problem until the forward bow gets above .011". If a neck is perfectly straight I'll usually not worry about it, but any back bow at all makes it impossible to get a low action without buzzing. Just leaving the guitar strung to pitch will often pull a back bow out, but if not, something needs to be done. (And that's another story.)

Yes, the Palo Escrito has a two way acting truss rod. Until recently it has been 5/32" size allen wrench, and in the last two months has changed to conform to our Master series wrench, which is 9/64". These are both standard allen sizes.

There is no tradition for using truss rods in classicals, but the usefulness is th same as in any other type of guitar. It not only helps to correct real problems that can develop from changes in climate, age, etc, but it helps to set up a brand new instrument into perfect playing condition with the neck relief exactly right. Installing truss rods was one of the best decisions I've ever made.

© Kenny Hill, Felton, CA

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