i am just starting out on making a 3 stringed cbg... well i am starting to think about it rather than starting to make it i have no concerns about the body or electronics only about the neck 

 

my plan at this point is to have a string ( low E i imagine) running down a groove on the back of the neck

1 end anchored to the base of the neck ( near the body ) and the other end connected to a normal machine head ( inverted ) pointing the wrong way. as it tightens the theory is the rear string under tention

will pull back any curving of the neck created by the 3 'front' strings 

has anybody tried this idea ...and does anybody think it will work 

 

carl

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Assuming you use a relatively strong neck, you won't need any kind of truss device. Three strings don't put enough tension on the neck to warrant using a truss.

 

IMHO

Unlike 6 string or bass guitars 3 stringers don't need any kind of truss rod, a good length of "2x1" American Oak will not bend, even with 4 strings...!  (-:

 

...imho

LIke the others are saying, I don't think you need it, but in general, I think the design would not be strong enough to do what you want it to do. Maybe a stronger cable could work if you wanted to go that route. 

I have only seen adjustable truss rods, non adjustable rods, carbon fiber rods, and in antique Gibsons, wood laminations, or just using a very thick neck.

I am sceptical. It's a nice idea, but there are problems. Let's assume for a minute that it is needed (unless you are using very flexible or thin piece of wood it most likely isn't). The playing strings are on one side of the neck exerting normal tension. Imagine a line running down the centre of the neck. This line is a bit like a series of pivot points. To exert a balancing force the cable has to be the same distance from that line as the strings, but on the opposing side. It would also need to be pulling the same tension as the combination of the three strings. With a guitar string you are unlikely to be able to equal the tension of another three before it snaps. Also, your string will be nearer that line, which gives it a mechanical disadvantage, meaning you need much more tension (greater likelihood of it snapping.

It really is a very interesting idea, but I think you may be trying to solve a problem that doesn't exist. Out of interest, what wood do you plan to use?

My feeling is that if you need it (because you plan to make the neck out of balsa) then you need a better solution. On the other hand, if you are using a more suitable wood there is no point.

Now on the other hand, if you were to make a hollow neck with room for an extra string or strings to vibrate you could have a sympathetic string arrangement, something like a Hardanger fiddle. Sorry. I'm getting carried away, but if that interests you I am fairly sure that Henry Lowman has done something similar. If it doesn't, I apologise for sidetracking.

IMHO, you'll end up with the tension of 4 strings. Then when you try to offset the forward bow, that much more tension will be need on the back string .... equaling much more tension. That , IMHO will cause more bow.

While the theory seems sound, it will not be putting the same stress on the neck a rod will.

The rod will contact and put resistance the entire length of the rod. All the string idea will do is anchor the ends of the neck.

 

 

Matt

 



Roadkill a.k.a. John Maw said:

I am sceptical. It's a nice idea, but there are problems. Let's assume for a minute that it is needed (unless you are using very flexible or thin piece of wood it most likely isn't). The playing strings are on one side of the neck exerting normal tension. Imagine a line running down the centre of the neck. This line is a bit like a series of pivot points. To exert a balancing force the cable has to be the same distance from that line as the strings, but on the opposing side. It would also need to be pulling the same tension as the combination of the three strings. With a guitar string you are unlikely to be able to equal the tension of another three before it snaps. Also, your string will be nearer that line, which gives it a mechanical disadvantage, meaning you need much more tension (greater likelihood of it snapping.

It really is a very interesting idea, but I think you may be trying to solve a problem that doesn't exist. Out of interest, what wood do you plan to use?

My feeling is that if you need it (because you plan to make the neck out of balsa) then you need a better solution. On the other hand, if you are using a more suitable wood there is no point.

Now on the other hand, if you were to make a hollow neck with room for an extra string or strings to vibrate you could have a sympathetic string arrangement, something like a Hardanger fiddle. Sorry. I'm getting carried away, but if that interests you I am fairly sure that Henry Lowman has done something similar. If it doesn't, I apologise for sidetracking.

may be its to simplstic but the way i see it is if u have a tent with 3 guy ropes on 1 end and 1 guy rope on the other ( even if the ropes were at diff angles say 30 degrees and 60 degrees the single guy rope would still produce an effective counter acting force even if it were not perfect it will still b better to have that single guy than not to have it ..... but i value your constructive view on this matter thank u .... regards 

sure the  tension in total will be greater but the stress would now b more equal not all on 1 side .... ok i am not sure but thanks for your views in any event ....regards 
Artist Formerly Known as Matt said:

IMHO, you'll end up with the tension of 4 strings. Then when you try to offset the forward bow, that much more tension will be need on the back string .... equaling much more tension. That , IMHO will cause more bow.

While the theory seems sound, it will not be putting the same stress on the neck a rod will.

The rod will contact and put resistance the entire length of the rod. All the string idea will do is anchor the ends of the neck.

 

 

Matt

 

Guys,

For some engineering proof that this concept is neither needed nor workable for the application desired, check out this neat little widget:

http://www.mcdonaldstrings.com/stringxxiii.html

I plugged in Keni Lee Burgess' 3-string tuning A-D-F#, assuming a 24.5" scale length, and wound strings from a set of Mediums. Here's what you get:

A = 0.044 gauge = 29.44 ft-lbs
D = 0.032 gauge = 27.72 ft-lbs
G tuned down to F# = 0.022 gauge = 26.2 ft-lbs

Total string tension: 83.32 ft lbs

E = 0.056 gauge = 27.37 ft lbs

A low E simply won't get the job done.

If you look at the way a Gibson style truss rod works, you will realise it has nothing to do with directly counter-acting the tension of the strings with an equal and opposite tension. The trussrod is curved, it mechanically levers the neck straight against the pull of the strings..if I hadn't had so  much to drink I right now could probably draw a vector diagram of the forces involved.  To figure this sort of thing out you need to have a really sound practical working knowledge of this sort of stuff or a good grasp of the physics of compression, tension in materials and the calculation of vectors. If you've got a good handle on both practical and theoretical aspects, you quickly realise that no amount of imagining people pulling on tent ropes will build you a guitar neck that wont bend.

 

A substantial 3 string hardwood neck won't bend significantly...stop thinking about it and start making it...and start playing some guitar...

it may well be that its not needed i am not sure....... but all that proves is the low e string at the 'correct tuning' ( happy to give it a few more turns) is not producing enough tension..... but even using your calucations the neck tension goes from 83 down to 56 ... that must be good rather than bad ???

Chickenbone John is correct. My previous post before the string tension calculator one above, got zorched somehow; in it, I mentioned that the strings in tension cause the wood cells of the neck nearest the fretboard to be in compression, while those on the thumb or palm side of the neck are in relative (ex)tension. The truss rod levers the neck straight relative to the strings, relieving these compressive and extensional forces. Also, take a look at a truss rod, it is much thicker than the total diameters of all the strings on a standard 6- string.

Get yourself some decent neck wood! As an aside, I use two pieces of 5-ply plywood laminated together for my necks, because good hardwood (or even softwood) is outrageously expensive where I live. I used plywood necks on my first two 3-string builds, using A-D-F# and G-D-G tunings, respectively, from sets of Medium Phophor-bronze wound acoustic guitar strings. Neither of them has suffered any neck bowing over the last few months, in highly variable heat and humidity conditions. Believe me, I check this routinely for my commercially produced guitars, as well, because I have to be my own guitar tech here in the Middle East.

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