I have a question..
How do sleeves with a rod or carbon fibre behave over time?
The stresses exerted on the instrument—if the sleeve remains rigid, aren’t they transferred to the body?
Isn’t there a greater risk of the soundboard bending or becoming deformed?
Does anyone have such an instrument that’s 20 years old and can tell us how it has held up?
Good morning, I’ve considered what you’re saying as a possible cause of the cap or hull cracking, too, but I’ve handled quite a few carbon-fibre instruments, and in fact we have one in the family that’s over 20 years old and doesn’t have the slightest flaw.
As for the carbon-fibre ones, I think the oldest I’ve handled is around 10 years old, and it’s equally flawless.
I’m not an instrument maker, but why do the tensions necessarily have to be transferred, and why does something have to be deformed? I mean, can’t an instrument withstand it? Can’t everything be calculated from the outset?
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What I can understand is that the stresses act between the anchor points of the rod in the karáolo and the dákos. The string tension does not change; it is the same as would exist in any straight neck.
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If an instrument with a wooden truss rod is kept in unsuitable conditions, it will warp—for example, the neck.
If one with a rod/carbon fibre is kept in the same conditions, won’t the body suffer the damage instead?
Will it remain unaffected, then?
It seems very strange to me that it would be like that.
The answer may predate the guitars.
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I don’t know what you mean by “inappropriate conditions”. However, as the temperature changes, because the sleeve either moves backwards or forwards along the rod, you adjust it to bring it into the position you want. I’m no expert, but I don’t think the rod causes resistance in the sleeve; rather, it “guides” it—if that’s the right term—at a specific angle. As for the soundboard, that has nothing to do with the tension created in the neck block. Besides, sinking in soundboards occurs at the bridge, and that has to do with the soundboard, the conditions in which the instrument is kept, the braces, etc.
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Sleeve warping is, of course, quite common. I’m no expert, but I’ve never heard of boat warping. Do the staves warp too?
The question arose from an instrument I picked up a while ago with a reinforced neck.
The maker is irrelevant.
What struck me was that, even though the neck was perfectly straight,
it had a very low bridge. I didn’t measure it, but it was noticeably lower than the usual 11–12 millimetres.
As if the body had actually twisted, or the soundboard had warped,
and, to achieve the correct string height above the fingerboard, someone had tried to compensate by making the bridge much lower. (?)
The neck’s warping may perhaps be related to the fact that we have the fingerboard on top, which is usually made of ebony—a more hygroscopic wood that does not readily release moisture. As a result, it expands and contracts at a different rate from the neck. So I think we have a mechanism that superficially resembles bimetallic strips: when the temperature changes, they expand in different ways and produce deformations which, because the metals are homogeneous, etc., are put to use in various applications such as thermostats and thermometers. Like the ones inside strip thermometers.
Could it be that the stresses—that is, the deformations—in the neck originate from the neck itself, rather than from the instrument as a whole or, for example, from the strings? That is why construction with reinforcing rods, specially cut pieces of wood, care taken to create mutually cancelling stresses, and corresponding alignment of the wood grain directions aims to create a system that will remain balanced under a variety of temperature and humidity conditions.
Have I read all this somewhere in bits and pieces, or am I talking nonsense? Just everyday, obvious stuff, really. Those with greater knowledge, please correct me.
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I think that the neck’s resistance to warping does not (normally) entail the top sinking, because a properly made top needs greater stress to sink than the neck does to warp, which is why warping is far more common than sinking. On a guitar, with a shorter neck, a larger top and different stresses, that may not be the case. Ebony is probably affected by humidity more across its width, which is why I think there is an issue with fret sprout when the frets have not been dressed.
That’s not true. I’ve seen warped tops and backs on instruments without truss rods or carbon fibre. Also, the truss rod isn’t there to correct warping; its function is slightly different. It’s for what they call “relief” on guitars, and for making small adjustments to the neck depending on the humidity and environment you’re in. Sometimes it does help with certain types of warping, if they aren’t too severe. But it depends on how the wood behaves. If it keeps developing a twist, there’s no saving it. You’re simply buying time, hoping the warping doesn’t continue. Many truss rods have been damaged in attempts to straighten a warped neck, rather than merely making small back-and-forth adjustments due to the weather and climate. One thing is different from the other.
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Exactly! I’ve read about them too. I don’t know, though… do all the craftsmen here know these techniques? Do they all use them?
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Let me clarify again that I’m not an instrument maker. However, it is common knowledge that the warping in an instrument’s neck, which is very slender in relation to its overall mass, is caused by twisting brought about by the disruption of stresses when weather conditions change. Two approaches have been developed to avoid these twists as far as possible: first, avoiding a single piece of wood for the neck (before the fingerboard is glued on), initially using three pieces instead of one, and later five, which are glued together in such a way that the stresses between them cancel each other out; and second, reinforcing the neck by embedding a metal rod of a suitable cross-section, bent appropriately to prevent the neck from twisting. These methods have been well known and generally used over the past few decades, depending, of course, on each maker’s knowledge and experience. Beyond that, anyone interested will look for the right craftsman, who knows and applies these techniques better than others.
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Because of the tension of the strings, combined with the system’s low mechanical strength, the soundboards sink. This is why there is also a discussion that, in the instruments from the “golden” era of the bouzouki, the soundboards sank in all, or almost all, of them because they were thin (a factor reducing the system’s mechanical strength) in order to have a powerful voice, since these two quantities appear to be approximately inversely proportional.
(I’m obviously not an instrument maker either 
)
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Good evening, Americans have been putting a rod in their instruments since 1942… And they behave well…
The atmospheric humidity in America is nothing compared with our climate. We don’t need the rod if the craftsman is good.
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Well, this is “something”… Yes, humidity really has nothing to do with it, but neither does anything else relating to the climate (the Atlantic and Pacific are major “players”, and this year we also have “the little one” (El Niño). Besides, where exactly in America? A friend in Denver, in the desert, has a humidifier (rather than a dehumidifier) to keep the humidity at a minimum of 50–55% — and quite rightly so: dryness can destroy an instrument, whereas humidity usually merely throws it out of adjustment.
There are many, far too many, factors involved in deciding whether or not to use a truss rod.
Do you want one made from wood (properly dried? Here today, it is difficult to find a fingerboard; a friend mentioned it above as well. After a year, the frets push out and cut because the fingerboard is continually losing moisture and shrinking — evidence that you bought it “wet”, despite all the promises about the drying kiln and so on.)
Do you want one as a matter of principle? Many people consider a truss rod and other reinforcements to be evidence of a lack of craftsmanship (in my opinion, that is absolutely not the case).
Do you want a “traditional” approach? There is a firmly established view that “such innovations are inappropriate for traditional instruments”, ignoring not only what Adonis says above about truss rods in guitars, but also solutions involving large nails and coach screws in 15th- and 16th-century lutes.
Not to mention that — especially with three-course bouzoukis — the drive towards ever thinner necks has changed their geometry and strength.
I am saying (writing) all this not as an advocate of truss rods — quite the contrary — but one cannot look around without realising that truss rods, screws, carbon fibre and anything else are simply “means” or “tools”, like pencils or knives. It is their use that makes the difference — if anything does.
The juiciest point, however, was made by Tasos Theodorakis. I like it very much and repeat it often: “The instrument maker is like a cook with his recipes: if you don’t like one person’s moussaka but do like another person’s, well, choose the one (you like).”
I don’t think the cook or the moussaka is to blame. Some people add cinnamon and I can’t eat a single bite — so I ask, or I don’t order the moussaka.
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I think the original character of the thread, with the question that was asked, concerns bouzoukis and how the truss rod or carbon affects the soundboard and the body, rather than the overall debate of truss rod versus no truss rod.
But since the discussion is heading there… None of the Greek and Armenian acoustic-guitar makers used truss rods. Their instruments remain in use after many years. Perhaps they do not offer the same ease of adjustment by the player as instruments with truss rods, but I think they are nevertheless quite respectable instruments.
Of course, it all comes down to personal taste—pumpkin pie, moussaka and everything else!
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True, but it has already been answered—to some extent, at any rate.
So I agree that there is no direct connection between any reinforcement of the neck and possible warping of the soundboard. Obviously, it may happen, but in my opinion the relationship is not one-to-one. Anything else could be responsible, e.g. insufficient internal reinforcement around the rim, an insufficiently rigid soundboard, etc., etc.
Then, as @gibson355 says quite rightly:
we’re talking about tenths or fractions of a degree. If the neck warps and the soundboard sinks at the same time—as far as the bouzoukis I’ve seen are concerned—the soundboard’s deformation is considerably greater (the neck has warped and playing would be uncomfortable, but the soundboard has sunk and the instrument is completely unplayable). My view is that such damage (sinking) would most probably occur independently of the damage to the neck.
As worded, I understand this as a general claim about “remaining in use”—I assume it logically also means “without problems”. I don’t have the repair experience of Theodorakis or Fronimopoulos, for example (or Adonis, mentioned above), but I find it difficult to endorse that claim. “Many of their instruments”, or even “most of them”, sounds more accurate to me.
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