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Adjustments are what setups are all about, and the first adjustment to make is the truss rod. Almost all electric guitars have adjustable truss rods, and few setups would be complete without tweaking the truss rod.
Occasionally a guitar neck is perfect as is, and doesn't require adjustment. If you have one of those, don't mess with a good thing. This chapter will show you how to recognize a neck that's perfect, and how to adjust a neck that's up-bowed or back-bowed. Our goal is a state of controlled straightness, with a very slight curvature called "relief."
Up-bow refers to a fretboard that curves in the direction of the string pull, creating a valley under the strings. This makes for high, stiff action.
Back-bow refers to a fretboard with a hump in the center, occurring when a truss rod is so tight that it bows the neck away from the string pull. Back-bow makes a guitar completely unplayable because the strings buzz against the humped frets.
Relief is a controlled up-bow, deliberately adjusted into a straight neck to create string-to-fret clearance that allows for the strings to vibrate without buzzing. Not every guitar benefits from relief, and not everyone likes it. The choice between relief or a straight neck is up to the player. But such a great majority of setups require relief that you can consider it a standard.
Truss rod control of the fretboard's straightness goes hand in hand with setting the string height at the bridge and the nut. These adjustments together produce the playing action, so a professional will simultaneously adjust a truss rod while raising or lowering the bridge and measuring string height at the nut. This process involves watching, measuring, and adjusting the neck, then measuring, watching and adjusting some more. It's a dance involving all of this at once, so you'll need to refer to the nut and bridge chapters as you work with the truss rod information presented here.
Truss rod adjustment tools
Truss rod types and how they work
There are other designs, such as a U-shaped metal channel instead of a round rod, but they're performing the same function. These typical designs are one-way, or single action, truss rods. They apply tension in one direction only.
Some truss rods are two-way designs. When tightened, they exert pressure against the strings like a one-way rod, but if turned the other direction, they will push the neck forward rather than relying solely on string tension.
Some necks are not adjustable at all, with a truss rod that is simply a stiffener embedded in the neck (rare these days). And some older inexpensive guitars such as Kays, Harmonys, and early imports have adjustable rods that work so poorly they may as well be considered non-adjustable. These are rare too, and it's a pretty safe bet that your guitar's truss rod will do the job.
Some adjusting nuts screw onto the threaded end of the truss rod (vintage Gibson, Guild, Gretsch, and Fender models), and these can be removed for cleaning and lubrication. On other designs, such as PRS guitars, the adjusting nut is welded to the rod and can't be removed.
Use a backlight to read the neck
Mark the adjusting nut before turning it
Adjusting standard one-way truss rods
Tighten: To tighten the truss rod, turn the adjusting tool clockwise. This straightens an up-bowed neck, pulling the peghead away from the tension of the strings. This reduces relief, lowering the string action (height of the strings over the frets).
Loosen: To loosen the truss rod, turn counterclockwise. This adds relief to the fretboard by letting the string tension pull the peghead forward. The result is higher string action.
Loosening a truss rod nut can't harm anything, but over-tightening can. Loosening the truss rod adjusting nut simply allows the neck to relax and be pulled by the strings. No problem. If you over-tighten the nut, however, you can cause damage. If the nut has been tightened to the end of the threads on the truss rod, then continuing to crank it can strip the threads out of the nut or off the rod. In worst-case scenarios, I've seen the threaded end of the rod completely break off in this situation. This renders the truss rod useless, but I've repaired dozens of these with the "Truss Rod Rescue Tool" from Stewart-MacDonald.
Always loosen the adjusting nut first By loosening the nut before tightening, you know that you're starting at the beginning of the nut's travel. If it's a removable nut, this is also a good time to take it off to clean and lubricate the threads inside the nut and on the exposed truss rod. Vaseline applied with a Q-tip is a good lubricant.
Do not start turning the nut as if you were tightening a bolt. Starting from the snug zero point, the adjusting nut will do its work immediately, and an ideal neck adjusts perfectly with a mere quarter or half turn. In extreme situations a nut may require one full turn, but be careful—this isn't like winding a clock!
Adjusting two-way truss rods
Fender supplies a 1/8" long-reach Allen wrench to adjust its Bi-Flex truss rod, which is accessible through a hole in the peghead near the string nut. Paul Reed Smith guitars use a truss rod nut that resembles Gibson's traditional acorn nut. The PRS nut, however, is welded to the rod and, like the Bi-Flex, is not removable. It adjusts with a 5/16" socket driver that drops into the truss rod cavity to do its work. Also pictured is my long-handled version of a Gibson truss rod wrench, which gives easy access while keeping the turning action well away from the peghead.
To pull the neck against the string tension, lowering the strings and reducing relief, turn the adjusting tool clockwise just as with one-way rods.
Loosen the rod and give relief to the fretboard (letting it go with the pull of the strings) by turning the tool counterclockwise.
Many imported guitars have adjustable truss rods that adjust at the peghead and with an Allen wrench. Sometimes a standard Allen wrench isn't really long enough for the job. In this case, I recommend buying a long-shaft, T-handle Allen wrench. I heated and bent mine into an L-shape that keeps my hand clear of these Fender tuners. You might want to do the same with the help of a metalworking shop.
Help for difficult truss rods
A truss rod is a pretty slender length of steel, and we ask it to do quite a job. Not only does it maintain neck position by countering the force of the strings, we expect it yank the neck and strings into new alignments, too. That's too much to ask. It causes unnecessary strain on the truss rod.
I like to help the neck by bending it to a new position externally, so the truss rod only has to hold it in position. It amounts to "pre-adjusting" the rod beforehand. Here's how I do this.
I loosen the strings and place a small block of soft pine over the frets at each end of the fretboard. If I want to leave the strings on, I use blocks that are notched to fit over the strings. I lay a metal bar (my carpenter's level) across these two blocks. With a rubber-padded protective block against the back of the neck, I use a small bar clamp to apply gentle pressure to the neck and the metal bar. This curves the neck into a slight back-bow. With this back-bow established, I tighten the adjusting nut. Now the neck has a back-bow without the truss rod having to work to get it there; it just has to hold the position. From here on, I just loosen the truss rod to let the neck pull itself into the straightness or relief I want for this setup.
Here's a tougher case: The truss rod nut being marked on page 48 is on an old Les Paul. It was as tight as it could go, yet there was still too much relief in the neck (a whopping .027" at the 9th fret). There was also a lot of truss rod thread coming out of the adjusting nut, which isn't normal. This nut was over-tightened by someone who didn't realize the nut was maxed out. They didn't stop when the nut didn't want to turn any more. They pressed on to the point that the nut compressed the wood of the neck itself. There's a metal washer in front of the adjusting nut, and it was crunched deeply into the wood. With a little more of that, I suspect the threaded portion of this truss rod would have snapped right off!
The metal washer in front of this adjusting nut is there to spread the nut's pressure evenly against the wood, and provide a low-friction surface for the nut to turn against. It's a half-moon shape, with a flat side facing the truss rod cover. I removed the nut to clean and lubricate it, leaving the washer where it was. Before the nut went back on, I added a second half-moon washer. That doubled the metal's thickness, lessening the amount of protruding thread and giving the adjusting nut a fresh start.
Adjusting at the body end of the neck, Fender style
The first way is the easiest (and therefore the most common) method, although it's not the one I prefer. I think it's a little risky, since the neck is never completely removed from the body. If you're not extremely careful, you're likely to scratch the body or a pickup with your adjusting screwdriver. Still, it's the most common method, so here goes:
Now that the neck's free from the body, it's easy to adjust using the methods described above (lubricate the nut, help the neck by clamping, etc.).
If the nut has been over-tightened to the point of crushed wood (like the Les Paul example), this is the time to add a metal spacer. It's a pretty small hole compared to the Gibson, however; I have sometimes made brass spacers on a small lathe in my shop for this purpose. At other times I've used small flat washers from the hardware store, ground or filed down so they'll fit in the hole. If you stop by a local machine shop and show them the problem, they can make you a spacer easily.
When there's no hurry, I leave the neck strung overnight to settle in before making a judgment. The truss rod will continue to exert pressure (or give way to string pressure), and the neck may look different the next day. Patience is a virtue.
Now that the truss rod has the neck in the shape we want, let's move on to the ends of the neck. We'll start at the nut.
Need to know more? Pick up a copy of Dan Erlewine's book, How To Make Your Electric Guitar Play Great!
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