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FDP Forum / Guitar Mods, Repairs, and Projects / Explain loose truss rod nut

Iwantogo

Rocky Mountains, USA

Playing the west
Apr 8th, 2012 08:01 PM   Edit   Profile   Print Topic   Search Topic

On my Heritage H555, I need to loosen the truss rod to get more neck relief but when I turn the hex nut counter clockwise, the only thing that turns is the hex nut and it just loosens and comes off. I'm not really loosening the truss rod. What is going on? and how do I loosen the truss rod?

Peegoo
Contributing Member
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That chicken

is WRONG, baby.
Apr 8th, 2012 08:34 PM   Edit   Profile   Print Topic   Search Topic

You *are* loosening the rod. The rod remains stationary. It's the nut that turns.

By tightening the nut against the washer, it puts the rod under tension, and that's what counteracts the tendency of the neck to bow under the tension of the strings.



Peegoo
Contributing Member
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That chicken

is WRONG, baby.
Apr 8th, 2012 08:37 PM   Edit   Profile   Print Topic   Search Topic

And, it usually takes a few days for the wood to relax once you loosen a rod. It's always best to move the nut about 1/8 turn and let the guitar sit a day or so and see what that does. All guitar necks react differently to truss rod adjustments--even several guitars of the same model will all be different.

FunkyKikuchiyo
Contributing Member
***

New England

Apr 8th, 2012 09:10 PM   Edit   Profile   Print Topic   Search Topic

If I find some good pictures of how truss rods work I'll post them, but I don't have them handy. They actually are pretty easy to understand, it is just that since they are concealed within the guitar they tend to be a bit of a mystery to most people.

The most basic truss rod just "squeezes" the neck. Imagine squeezing a playing card on the ends, and the center bows up. That is more or less what it is doing, making it bow backwards, and hopefully you can find a happy medium between the bow of the truss rod, the bow from the strings, and not have enough collateral weirdness across the fingerboard to be playable in the end.

Peegoo
Contributing Member
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That chicken

is WRONG, baby.
Apr 8th, 2012 09:33 PM   Edit   Profile   Print Topic   Search Topic

Look here.

The truss rod is not straight inside its channel. It is lower in the center and higher on the ends. This mild U shape is what allows the rod to counteract the tension from the strings, keep the neck straight, and also allow for some adjustability.

If you are into sailing, think of a truss rod as the main mast's side stays on sloop-rigged boat. They add stiffness to the mast by counteracting the mast's tendency to flex under heavy wind loads.

A few cutaway shots.

Peegoo
Contributing Member
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That chicken

is WRONG, baby.
Apr 8th, 2012 09:36 PM   Edit   Profile   Print Topic   Search Topic

Here's a double-acting truss rod. It can add forward *or* back bow, unlike Fender's single rod.

Double-acting

Peegoo
Contributing Member
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That chicken

is WRONG, baby.
Apr 8th, 2012 09:37 PM   Edit   Profile   Print Topic   Search Topic

The "traditional" Martin rod is a steel unit that is not-adjustable. It's glued inside the neck merely to add stiffness to the wood.

Martin steel "rod"

wrnchbndr
Contributing Member
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New Jersey

The otters threw me out
Apr 9th, 2012 08:27 AM   Edit   Profile   Print Topic   Search Topic

More info...
The trussrod (or relief) adjustment can only be measured when the strings are tuned to pitch. The are a few people who stand by the premise that the trussrod should be adjusted with the strings loose but generally most technicians and luthiers adjust the trussrod while the guitar is tuned to pitch as long as this is posible. You can't do this on a Fender with the adjustment at the heel of the neck and old Rickenbackers are an exception where the strings must be lossened first. Your guitar has what is called a traditional one-way adjustable trussrod. Everything that you read about a Gibson trussrod applies to your trussrod.
The concept is very simple. You start out with a neck and fretboard that is totally flat. The tension of the strings pulls the neck in a forward arc and the trussrod pulls it back straight (almost).
The trussrod is normally a steel rod of 3/16" diameter and sits in a fully enclosed slightly curved bed with the middle of the rod closer to the back of the neck than both the anchor point on one end and the adjustment nut at the other. The adjustment nut can be either at the headstock (most, if not all Gibsons) or the heel of the neck (most non Gibson acoustic guitars). Either way, the rod works the same. Two actions happen when the trussod is tightened. Most obvious is that the trussrod counteracts the pull of the strings. A typical set of .010 to .046 strings tuned to pitch has a pulling force of about 116 lbs when static. The major mass of the neck lies between the pull of the strings and the pull of the trussrod and acts as a fulcrum point. The other action that is less apparent is that the trussrod lies in a curved bed and tightening it causes the trussrod to assume a straighter line and reduce it's curvature. The middle of the rod pushes outward while the two ends pull backwards.
Guitar makers intend for an assembled neck and fretted fretboard to be flat when the instrument is unstrung. However wood can be a unpredicatable as it ages, is exposed to the changing seasons, and endurs changes in humidity. In a curved bed, a 3/16" steel rod is more than adequate in strength to deal with counteracting the string the and probably could hold a load of 500 lbs or more. Normally, the wood supporting the two end points will give way before the trussrod breaks but there are exceptions and limits to what the trussrod can do.
The conventional trussrod will address or counteract forward pull of the neck only and it is rare that the forward bend of the neck due to string pull and forward warping of the wood will overpower the abilities of the trussrod as long as the rod is healthy and the nut is lubricated properly. Poorly selected Hard Maple and some of the exotic woods can warp to the point of overwhelming a trussrod but this is rare. Mahogany very rarely creates this problem. What the trussrod cannot deal with is when the neck assumes a backbowed warp that is so great that the strings no longer pull the neck into a forward bow and at this point, the trussrod is useless to do anything at all because it will only increase the backbow. This can cause the neck to be a total write off. I have never seen a Gibson with this condition and I attribute this to proper wood selection by the manufacturer and the ability to predetermine the most beneficial orientation of the lumber before it gets carved into a neck. In twelve years, I've seen about eight Fender guitars out of over a thousand that have a permanent backbow. The number of imported less expensive guitars like this is far greater.
None of this matters at all unless there is insufficient relief when the guitar is tuned to pitch. Optimally, you want the trussrod engaged and performing a counteraction to string tension. As a luthier, I refer to this as the trussrod adjustment window. A guitar in the best of health will have a trussrod adjustment that will both permit adjustment of both too much relief and too little relief. This insures a long lifetime of available adjustment as the instrument ages. Guitars that require extreams of one side or the other are less desireable and should be avoided. But as long as the relief is correct when the instrument is tuned to pitch you can't call it defective or make a warranty claim. Its only that the future health of the guitar is less certain. This is also why many manufacturers now employ a dual adjustable trussrod.
Too much information???

(This message was last edited by wrnchbndr at 08:31 AM, Apr 9th, 2012)

amphead4

Cincinnati, USA

Apr 9th, 2012 08:41 AM   Edit   Profile   Print Topic   Search Topic

wrnchbndr, very good! All I can add is some guitars have straight truss rod channels and put the neck into compression. This resists the relief caused by string tension because the neck material yields to the compression force more than the fingerboard material. I'm thinking specifically of a Martin with an ebony fingerboard with a straight truss rod channel under the fingerboard.

Iwantogo

Rocky Mountains, USA

Playing the west
Apr 9th, 2012 08:58 AM   Edit   Profile   Print Topic   Search Topic

So by turning the nut conter clockwise till it is so loose that it comes off means that I have relaxed the truss rod all the way and I shouldf have a significant ammount of releif, correct?

I would think that I would be getting a lot of relief from a set of 11-50 strings on a ES335 style guitar. I hit notes on the 9th fret and am getting conciderable buzz from the 10th fret. It only happens on the 5th and 6th strings but it's not very playable that way. And it just seem to happen over the winter. Anyway, I wanted to get a little more relief to get rid of the fret buzz at that area but it seems I cannot loosen the nut or truss anymore if all I do is inscrew the nut off the treads of the ttruss rod.

amphead4

Cincinnati, USA

Apr 9th, 2012 10:22 AM   Edit   Profile   Print Topic   Search Topic

Has it been refretted?

FunkyKikuchiyo
Contributing Member
***

New England

Apr 9th, 2012 10:28 AM   Edit   Profile   Print Topic   Search Topic

Wow, some great info here! Thanks for finding those pictures, Peegoo. I'll add a few more things:

"So by turning the nut conter clockwise till it is so loose that it comes off means that I have relaxed the truss rod all the way and I shouldf have a significant ammount of releif, correct?"

Correct. Righty-tighty, lefty-loosey. Tightening engages the rod and works against string tension. The exception to this is bi-flex rods. The most common one on the market is the one used in American strats & teles. The giveaway is the large walnut plug and the 1/8" wrench. Bi-flex only works so well and I'm not a huge fan, but it does work in small amounts.

If you're getting buzz when playing at the 9th fret, I don't think the problem is the neck being too straight. The truss rod isn't a be-all-end-all solution for buzzing. Once you get the neck to its optimal place, the solutions lie elsewhere. Also, buzzing that far up could mean too much forward bow in the neck. It is a common mistake to have a bit too much relief and then drop the bridge down. If you find yourself fretting out easily past the 14-15th frets, that is another give-away.

To elaborate on a couple points wrnch made: Manufacturers will often make necks with a forward bow as insurance that the back bow won't happen. Different climates can change the relief, and this gives them enough tolerance that they'll have fewer rejects for being backbowed too far to set up properly. They make instruments and then have to ship them out promising that they'll work in all sorts of different climates, so they like lots of wiggle room. I think most manufacturers overshoot that mark personally, but that's just me. Fretting when the tangs are bigger than the slots can also cause a back bow.

Necks with separate fingerboards also can have issues of extreme bow (forward or backward) as the glue joint "creeps". Letting the instrument sit with too much bow either way for a long time can cause this, and it often happens when they're left in hot vehicles. This can be corrected fairly easily. It involves clamping the neck into place, heating it, and allowing it to cool gradually. On a one piece neck you have fewer options.

I'd also defend the idea of adjusting the truss rod without string tension for certain applications. If you have a lot of travel to do, the nut turns more easily without string tension and you're less likely to do damage stripping something out if it needs a lot of cranking. The neck has a chance to settle in to a straighter position if you don't have the strings cranking on it. Fine adjustments are obviously a lot easier to do with string tension when possible/practical.

FDP Forum / Guitar Mods, Repairs, and Projects / Explain loose truss rod nut




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