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In the grand scheme of things for what all goes into the construction of a guitar installing an adjustable truss rod is not really that difficult especially if you are already going to rout a channel for a hardwood insert. It's a bit more work if your access is through the sound hole but even so it's not that difficult. So that's something to consider.

Thanks, Terrance. I've sort of given up on believing the plans from GAL are truly accurate. So, I'm not sure what to do about the doming of the top and back. Also, I spoke to someone who is an expert on Larsons, and he said he's never seen two that were alike.


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The typical placement of a solid rod (just under the fretboard) is at the neutral axis of the neck, which is the least effective location to improve bending stiffness. This means it would need to be a really stiff material to make a substantial difference. If using a hardwood rod, the stiffest placement is at the neck's backside (visible), and preferably wider than 1/4".

Some Ebony is only ~30% stiffer than typical neck woods -- a 1/4 x 3/8 piece of that at the neutral axis would improve bending stiffness a little. Ipe and Cumaru are stiffer, more stable, and readily available. But for long-term creep resistance, I'd suggest aluminum or steel over any hardwood.

Here are Young's Moduli for various materials (*10^6 psi, http://www.wood-database.com/):
Honduran Mahogany: 1.4
Black Cherry: 1.5
Sapele: 1.7
Hard Maple: 1.8
White Oak: 1.8
EI Ebony: 2.0
Gaboon Ebony: 2.5
Jatoba: 2.7
Ipe: 3.2
Cumaru: 3.2
Aluminum: 10
Carbon-fiber epoxy: 5-20
Steel: 29

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David Malicky

Ever tried adjusting neck relief on a guitar without a truss rod?

I would install the truss rod, you can do compression fretting or other techniques to correct neck relief but the rod makes things much easier.

That and some guitars experience neck movement every season, so if you need to do compression fretting and planing to correct the neck every 3 months, nobody is going to want to own those guitars. Note a lot of the older guitars that lacked truss rods have very thick neck, which helps but it's still a pain to adjust its neck relief.

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Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

The downside of no adjustable truss rod is that you could end up with a nice but unplayable guitar.
Go for the Allied double action rod.
String tension will flex the neck a little, if the neck is just the right stiffness string tension will pull in the correct relief. If it's too stiff (as my first 3 were), then there won't be any relief. It's not uncommon to end up with a little backbow without string tension. If the strings don't pull enough, you're out of luck.
There's also the consideration of string gauge. Going from lights to medium (or vice versa) may not be possible without a truss rod, depending on how stiff the neck is.
If you've got the chops to get the neck exactly right, you could use CF bars in the neck to make it stiff enough to resist ANY flex from string tension and plane the relief into the fretboard.

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A man hears what he wants to hear, and disreguards the rest. Paul Simon

As a safety, you could go with a neck that is on the thicker side. Leave it unfinished or just oiled, then after string up, if you needed more relief you could always take a little more meat off.

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Pat

don't leave the neck unfinished or lightly oiled... the neck may warp.

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Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

Unfinished is just temporary. From my experience and observation, it will not warp because of an oil finish.

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Pat

Not generally, but with a shorter scale length, mediums may work better. I was trying to point out potential problems associated with a first time builder and no truss rod. It looks like this guy has the chops to make a really nice guitar first time out, and he's working with BRW. I'm not as sure he can pull off a neck without a truss rod, and I'd hate to see a bad decision at this stage compromise the results.

My idea of the way the truss rod should work is pretty simple, and this only applies to steel strings, nylon is significantly different loading. Think of the neck as a spring, and the truss rod as an adjustable stop. String tension bends the spring until it hits the stop. At this point, the relief is perfect. For this to be a valid analogy, the truss rod has to be stiff enough so that string tension has insignificant effect on flexing the truss rod. I believe this to be valid for double action rods like the StewMac hotrod and the Allied rod, but not necessarily for any single action rod. (Double action rods will flex a little, I think less than 10% of the total can be considered insignificant)

Without a truss rod, there is no stop, so the neck has to carry all the stress and flex exactly the right amount for the relief to be "correct" (different players like different amounts, so correct varies with the player).

I believe it's possible to build a neck stiff enough (using carbon fiber reinforcement) to be unaffected (less than 10% total relief) by string tension, so that the desired relief could be built into the fretboard. I was headed in that direction until I thought , that's way more difficult, and has no real advantage over a double action rod. For nylon strings, it may be a different story, I understand they're sensitive to weight in the neck.
There is some engineering reasoning behind this. With the neck flexing easily til it comes to the truss rod stop, almost all of the stress is being carried by the truss rod which is much more resistant to cold creep, so the neck will not change over time. Of course, with a double action rod, any changes over time can be corrected with the rod, so avoiding changes is not too much of a concern. (If you use a double action rod.)

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A man hears what he wants to hear, and disreguards the rest. Paul Simon

You guys sure are smart! Thanks for engaging this topic. BTW... what is "cold creep?"

Basically materials deforming under constant stress, without the application of heat.

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Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

"Cold creep" is the plastic deformation over time of a material under stress (or force/area). The deformation is roughly proportional to the stress, and frequently the deformation reduces the stress that is causing the plastic deformation. All materials cold creep, wood much more quickly than say, aluminum. It's usually a concern when materials are highly stressed, like guitars and aircraft.

There's two types of deformation, elastic and plastic. Elastic deformation will return to it's original position when the stress is removed, plastic deformation does not. They can both exist at the same time, like when you loosen the strings on an old guitar, some of the belly behind the bridge goes away(elastic deformation), but some of it stays(plastic deformation).

Materials have an elastic limit, which is the maximum deformation a material can withstand and still return to its original position. When stressed beyond this elastic limit, the material either fails or deforms plasticly. Cold creep happens below this elastic limit, but takes some period of time. The closer to the elastic limit, the quicker the cold creep will happen.

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A man hears what he wants to hear, and disreguards the rest. Paul Simon

But the point is, wood tends to cold creep unless you are building with massive necks. Steel strings exert over 100lbs of force on the guitar so it's reasonable that the wood tends to creep a bit. It is also why neck resets are necessary on all steel stringed guitars eventually (if you made the soundboard so thick that it doesn't need neck resets ever, it will sound about as good as an unplugged solid body electric guitar).

Just because you use a truss rod doesn't make you an inferior builder. I have seen a hand made classical guitar that has a truss rod in it. The maker felt it was necessary to include a truss rod even though it wasn't a steel string, and I've seen other factory made nylon string guitars that has a truss rod as well. It certainly makes setup 100 times easier for sure... I really hated telling a customer that there isn't much I could do for his guitar because his non-truss rod guitar had string buzz due to insufficient neck relief... I just told him give it some time and the string will pull things into the sweet spot...

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Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

I think this is good advice!

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Burton
http://www.legeytinstruments.com
Brookline, MA.

I'm not usually qualified to disagree with Mr. LeGeyt, but he's been building too long to remember!
That's good advice for a second or third guitar, but the first one needs to be easier than that.

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A man hears what he wants to hear, and disreguards the rest. Paul Simon

Everyone is qualified to disagree with me!

It's not necessarily simple either way, and most first guitars certainly require some fret leveling, adjustable rod or not.
Your point is well taken and I am sure Steven is weighing them all himself.

As someone who is very interested in non-adjustable necks, I would say that it is never too soon to jump right in.
With the caveat that you will get a ton of (understandable) grief, especially from repairmen.

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Burton
http://www.legeytinstruments.com
Brookline, MA.

Burton, what you're doing is a good illustration of what I was talking about. It takes good engineering and execution to make something that ends up with the correct relief and stays that way. Every step counts.

Steven, if you end up going the non truss rod route, check out what Burton is doing. http://www.acousticguitarforum.com/foru ... ton&page=3

Now that we've covered cold creep, one more thing to consider is humidity. I used to believe that humidity related differential longitudinal dimension changes (that's a mouthful) between the fretboard and neck were not significant enough to bow the neck very much. Then I got a call from a client in the Northeast after a cold front came in. If your guitar will see relatively large humidity swings, that's another good reason to have a truss rod.

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http://www.chassonguitars.com

Vigier does not use trussrods. http://www.vigierguitars.com/html/Descr ... ck_us.html

That black carbon fiber down the center might be called a truss rod.................................?????
Tom

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A person who has never made a mistake has never made anything!!!

Do a bolt-on neck and NO truss rod make sense?

Dude, you gotts to be kidding me...nothing on this planet makes sense...even Oblio and Arrow know that...or was that the Pointless forest? No matter, same difference. Or as Terence McKenna pointed out..."nobody knows Jack $hit" about nuthin...so may me most humbly suggest you build the sucker however you want and then live with it...don't like it ...build another one.
Of course you can always buy one on ebay, for $199, in any size or colour you want...with truss rod and case.... and, and, and yes free shipping. Oh my!


blessings
?adma

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Audiences and dispensations on Thursdays ~ by appointment only.


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