Official Luthiers Forum!

Something about the two say they should be mutally exclusive, yet i see some fairly pricey instruments that use both. it dosn't sit well in my brain to add something that resists bending and then throw something in there that tries to bend it.

So the question is:
CF inserts in the neck by itself...
Truss rod only...
or both?

I think i like the idea of a truss rod. New england humidity changes so much that it may make sense... or am i better served by CF???

If it makes any difference, the neck may well be a traditional neck and not a bolt-on... (which is still a debate in my heart)

Thnx!
Rob

Go for the truss rod, CF is optional.
My opinion is that CF is overkill for an acoustic guitar neck, the neck wood and truss rod are more than adequate. Now for a long scale 5 string bass, CF in addition to the truss rod would be a good idea.

As for the mutually exclusive, think of it this way. The strings apply a load that causes the neck to bend. Some of that load is carried by the neck wood (and CF), the rest is carried by the truss rod. The truss rod is working with the neck wood and CF against the string load, unless the neck is so stiff that it doesn't bend enough for adequate relief. Then you have to adjust the rod for correct relief, and the rod is working with the strings and against the neck wood and CF. That's why CF is overkill for acoustic necks.

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

Need the truss rod. I put CF in also just on account of because.

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Joe Beaver
Maker of Sawdust

Use a truss rod. Setting things up without a rod has it's own built in problems that make it much easer to use a rod. I have used CF inserts with the standard 2 way over and under truss rods. I now use a Stew-Mac aluminum channel Martin style rod and epoxy it in place. They are one way and you have to allow for that but they do make a stiff neck.
Tom

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

I put adjustable truss rods in both SS and classical guitars, as a growing number of makers are doing. They both have exactly the same issues, so why wouldn't you use a truss rod in classicals, too? Make them adjustable at the sound hole end and nobody knows they're there (until they need to use it).

To get a decent improvement in stiffness by using CF, you have to build it in a long way off the neutral axis. Where the CF is usually placed, just under the fretboard, it makes less than 10% difference in stiffness (and it's not adjustable).

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

One reason to do it is to have a more consistent neck stiffness. Tightening the rod can make the neck stiffer, which can change the sound of the guitar. Adding CF reduces the amount of truss rod adjustments that are necessary.

Weight.

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John

Not that one again!

Mass of one of my folded steel truss rods =96grm
Mass of 2* CF rods 5mm * 13mm =101grm
(5mm * 13 mm is about the minimum size to make a useful contribution to stiffness).

There's nothing in it. If you use a simple tension rod (old Gibbo style), you can drop the steel truss rod number by ~40%

Lets look a little further:

Mass of a typical ebony fretboard = 195 grm
Mass of typical rosewood fretboard = 135 grm
(6.5mm board, 62mm average width, measured density data)

Mass of a set of roller bearing Sloane tuners 185 grm
Mass of a set of standard Schallers 140 grm
Mass of a set of Gotoh Stealths (if you want really light) 72 grm
(data from Stewmac and LMII)

So, the "high quality" classical with ebony board and Sloanes will weigh in over 100 grm heavier than a good guitar with a rosewood board and Schallers. One could easily conclude that mass in the neck is good!

A typical Smallman style classical will weigh in at ~3.0 - 3.2 kg
A typical traditional rosewood guitar will weigh in at ~1.6 - 1.8 kg

Funny how taste takes precedence over mass, every time.

Tells you how considerations of mass really stack up in the scheme of things.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Thinking about carving my neck out of soapstone now...

One interesting point here is the way Collings uses steel bars in their steel string necks. I'm sure this adds a little stability, but I have also suspected that their intent is to limit the vibration of the neck so that most of the energy is dissipated in the body.

Trevor (not Gore)

(c:

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http://www.PeakeGuitars.com

When I said 'weight' I am referring to balance. Classical guitars are usually played on the lap, and a neck-heavy guitar is a turn-off for most players. You can go the Smallman route, where weight is added to the tailblock, but then you have a 4+ pound classical guitar.

Classical guitars only have about 60% of the string tension of steel strings, and the shorter, wider neck means that they can function for a long time with no added reinforcement.
The same is not true with a steel string.

Even if I use the lightest of rosewood density figures (~50 lbs/cu ft), and the heaviest ebony (~70), I still don't get that much difference in the weight. Besides, the classical customers I deal with would not even consider a rosewood fingerboard.

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John

I wish I could explain why, but from my experience on banjos mostly, using CF in the neck with or without a truss rod makes a big difference in consistency of tone up and down the fingerboard. CF seems to help eliminate weird dead or weak spots on a neck. Probably due to the tension issues John mentioned earlier. Or maybe just adding a homogenous but still resonant material to a non-homogenous piece of wood. Whatever. I don't hear the same consistency using metal rods alone.

On banjos, I usually use CF only with no truss rod, but banjo necks don't have anywhere near the same level of tension on them that guitar necks do.

Dave

I've not seen a Smallman with weight added to the tail block. The mass is in the 3/4" ply used for the "tonewell" (aka "toilet seat") and the thick laminated back and sides.
An adjustable truss rod is about relief control, not (specifically) for compensating for cold creep or static deflections. Ebony moves more than most woods longitudinally with humidity variation, which jacks the relief about substantially. An adjustable truss rod means the playability can be controlled much more efficiently.

So, clearly, mass is not very important.

All Kenny Hill's Master series guitars have adjustable truss rods, BTW, so I'm far from a lone voice on this subject. Maybe just a loud one.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Trevor, your comments echo the results I saw when I was with PRS (they looked at using CF instead of truss rods on their steel strings). How many guitars have been built that did not require some adjustment of the truss rod upon stringing them up? I'm guessing not many...!


Trevor (not Gore)

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http://www.PeakeGuitars.com

Internet forums are the natural home for loud voices! For better or worse, and sometimes both.

It is next to impossible to argue that truss rods aren't helpful. And yet I still try hard to not use them.
I also agree that the rectangular CF bars most use don't do too much besides add weight (and maybe kill dead spots-). Doesn't mean it can't be used effectively though.

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

they ARE helpful- but you need to excavate a whole lot of wood in order to have one. then you have a skinny metal rod in a largely vacuous cavity, maybe packed with foam or epoxy to keep it from rattling around....and by the fact that you removed a bunch of wood, well, now you NEED to have a truss rod or else.....i just don't like the concept. with maple necks it is counterproductive i think; with mahogany, likely a good compromise- but a truss rod will always be a compromise no matter what material it is polluting

One is not exclusive of the other. In other words, it is certainly possible to build a lightweight guitar with an ebony fingerboard.

I suppose the ones I am remembering are from the 1980's. That is when I was building and playing classical guitars.

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John