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Should neck reinforement run through the body of the instrument? Howabout the truss rod?

PostPosted: Thu Feb 01, 2018 9:03 pm
by Liam McGillivray
I know that typically, neck reinforcement rods and truss rods only run through the neck, but not the body of the instrument. This is roughly the length of the fingerboard. This even includes neck-through guitars (like the one shown below), in which there's one solid piece of wood running the entire length of the strings, yet the reinforcement rods end at the body.
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But is this really the ideal way? I have a feeling that it would be better to have the reinforcement rods running through the entire scale length (from nut to saddle). This would be easy with neck-through designs, but even bolt-on and set-in guitars could have a reinforcement rod running out the neckpiece and through the body. This would give better stability to the shape of the guitar's bend. Being stiffer would give the upper harmonics more sustain (which is good or bad, depending on what sound you want). It might give even more sustain if the reinforcement rods went all the way from the tailpiece to the tuning heads, which resembles the way piano strings are mounted onto a cast iron frame.

As for the adjustable truss rod, I'm less sure. If the truss rod ran the entire scale length (not just under the fingerboard), then would it be better at adjusting the upper frets? When I brought my bass to the shop to have it adjusted, the luthier told me that he couldn't get the upper frets positioned unless I let him hammer them down. I'm not really sure if a truss rod that ran down to the saddle would prevent this. In an ideal guitar, I suppose it should have two adjustable truss rods; one that only runs through the neck and another that runs the entire scale length.


I'm building an instrument for the first time. It resembles a semi-hollowbody bass guitar more than anything. I want to build it with a 36" scale length, long-set neck, and a reinforcement rod that runs the entire scale length, and possibly further. Here's a plan of it:
Image
The issue I'm having is that there aren't many vendors selling 36"+ carbon fibre rods in North America. I might buy a pair of them from Rockwest Composites (which has them in 78" lengths, but they can cut one in half for me), although it seems expensive.

Re: Should neck reinforement run through the body of the instrument? Howabout the truss rod?

PostPosted: Thu Feb 01, 2018 10:07 pm
by Barry Daniels
The carbon can run though the body portion of the neck-through but it is not really needed. But whatever you do, do not run the truss rod through the body. I think that would be a big mistake. The truss rod is used to adjust the neck to the proper relief. Not only do you not need this in the body, but having the truss rod that long would make the adjustment in the neck (where it is needed) somewhat unpredictable.

I buy my carbon reinforcement strips from DragonPlate which sells them in 48" lengths. You can cut them with a hacksaw or a Dremel cut-off wheel.

Re: Should neck reinforement run through the body of the instrument? Howabout the truss rod?

PostPosted: Fri Feb 02, 2018 10:24 am
by Christ Kacoyannakis
The truss rod is going to want to bend somewhere near the middle of its length. If the truss rod ran all the way through the body, you would be fighting the stability of the body (which you don't want to bend) to try to get the neck to bend, and I think you would have difficulty. You want to install the truss rod so that it most easily will move the portion of the neck that needs the relief, which is around the 12th fret.

Re: Should neck reinforement run through the body of the instrument? Howabout the truss rod?

PostPosted: Fri Feb 02, 2018 12:54 pm
by David King
What you also don't want is a weak point in the neck at the body intersection so either have a substantially thicker heel that the CF overlaps into or continue it a bit further into body so that the neck won't get a bend over time where the CF ends.

Re: Should neck reinforement run through the body of the instrument? Howabout the truss rod?

PostPosted: Fri Feb 02, 2018 1:46 pm
by Beate Ritzert
In addition: you can try to entirely avoid an adjustable trussrod if You make the neck sufficiently stiff. Like the body which is stiff simply due to its thickness.

Re: Should neck reinforement run through the body of the instrument? Howabout the truss rod?

PostPosted: Fri Feb 02, 2018 5:02 pm
by Gordon Bellerose
As has already been said, it won't hurt to have the carbon fiber rods run the full length, but do not install the truss rod that way. It is meant to either add or subtract relief in the fret board area.
I am puzzled by your remark about your luthier "hammering the first frets into position".
Can you enlighten me a bit on that?

Re: Should neck reinforement run through the body of the instrument? Howabout the truss rod?

PostPosted: Wed Feb 07, 2018 6:57 pm
by Liam McGillivray
Barry Daniels wrote:I buy my carbon reinforcement strips from DragonPlate which sells them in 48" lengths.

Thank you. I will probably buy them from there now.

Although I appreciate the help from Barry Daniels, I really meant for this discussion to be about the general idea rather than my specific instrument. My instrument will just be a test of the idea. But I meant for the discussion to be about why neck reinforcement doesn't normally run the length of the body.

However, I think it makes sense that fully acoustic instruments don't have a rod going through the whole instrument, as then it would be visible under the soundhole. I suppose it can still be done if that's not such an issue.

Re: Should neck reinforement run through the body of the instrument? Howabout the truss rod?

PostPosted: Wed Feb 07, 2018 7:41 pm
by Barry Daniels
There is no instrument that should have a truss rod running though the body. It is not only not needed, but doing it this way would ruin the functionality of the rod.

Re: Should neck reinforement run through the body of the instrument? Howabout the truss rod?

PostPosted: Mon Feb 12, 2018 10:35 am
by Chris Richards
Running CF rods the entire length of the guitar I think is a good idea BUT it's not something that you can practically do since you have to route out pickup cavities. Rickenbackers used to have a problem in that the front pickup cavity was too close to the fretboard and thus even though they are neck through there's not enough wood left to keep the body/neck angle stable and the necks can hinge up and even with the bridge adjusted all the way down you still end up with a high action... I think in later years they moved the front pickup back to allow more wood around the neck/body junction.

I wouldn't rely on just CF rods and omit a truss rod especially in a bass, I would honestly struggle to fit a traditional truss rod over a bi flex one...Bi flex truss rods are sooo good for minute adjustment and they don't exert stress (crush the wood) on the anchor points since all the compression/tension force is kept within the rod and just the bending force is transferred to the neck over the whole length of the neck.