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'68 Martin D-18, install adjustable truss rod or not? Opinions..?

Hi!
I have just restored a '68 D-18. The guitar was "upgraded" a long time ago; scalloped braces, enlarged soundhole, replacement ebony fingerboard. When strung up with medium strings, the neck has a pretty severe upbow. I did a refret with wide-tang fretwire, which did not help. There is not enough fingerboard left to do any tapering of the thickness. The fingerboard is glued with white glue. I think the thin fingerboard compensates well for the chunky neck, so I would like to keep it if possible. I am thinking that I have two options; either reinforcing the square tube truss rod with carbon fiber and epoxy, or installing an adjustable truss rod. What would you have done? Obvously, the carbon fiber soulution is the easiest, but will it provide sufficient stiffness to straighten the neck? Can I install a Martin style adj rod without having to remove the neck? The neck angle is pretty good as it is, and I suspect the dovetail joint might have been epoxied at some point... If I go for the adj rod, will it affect the value of the instrument? Thanks for your time!

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click on Franks little guy at the right of the screen ask Frank but I would do the truss rod what value is a guitar that dose not play
I've tried the the graphite reinforcement in the square tube, and it helped a lot. The D-28 I installed it in had .022" relief, and .007" relief after installation.
I would rather do that than install an adjustable truss rod. You will have to remove the neck from the body.

Jim
Peter,

I have performed this operation several times. It can be done without removing the neck, but you must be adept with chisel and scraper. Bear in mind that once you extract the square tube, you only need to enlarge ( by scraping mostly) the channel by a 1/16", so in a way this is a lot friendlier than implanting a carbon rod which may or may not work. (don't know, haven't tried it).

Be aware of the fact that some of these replacement rods are not made with the same quality aluminum. You will want to choose a reliable source.

You will also need to reinforce the upper transverse brace in the area of the "notch". You must guard against the possibility of this brace sinking, because even a slight change in its position will affect the "set" of the neck. I've used carbon fiber for this epoxied on the backside of the brace where it is less noticeable.


There are a lot of collectors out there who will immediately identify the lack of originality in this repair, but it seems that there are other mods done that have already affected the value, and as Paul has pointed out, what is the value of a guitar to a player if it does not play properly.

By the way, two of my customers have remarked that there was an improvement in the sound of the instrument after this repair was performed. I have no way of verifying this, but if you do this operation (or anyone else out there) , please let me know if you get similar feedback.
First -any thought of modification reducing the value of the guitar should be abandoned. That already happened with the other mods. That said, I can't stress enough how significant the glue joint can be in some cases. When I've simply removed and reglued a fingerboard with hide glue, the difference in stiffness was immediately noticeable. And, there's no reason not to fill the square tube with carbon fiber and epoxy to help keep the neck solid.
Frank-

Was this w/o any flattening of the FB & neckshaft?
Thanks for your advice, folks! I really appreciate your help! I believe I will try filling the square tube with carbon fiber and epoxy and gluing the fingerboard with hide glue. If that doesn't work, I will go for the adjustable rod. I will let you know when it's done! Thanks again!
Are you wedded to the medium strings? This seems the first, easiest, and least intrusive manner of correcting some of the neck bow. And FYI medium strings sound too "dark" on the bass strings and limit overtone production if you use any sort of "slap" type or percussive technique (which I really like). And you can always break up a set with lighter bass and heavier treble strings. Also I believe the "silk and steel" type strings are still available - haven't used them in decades - which were made to allow a steel string type sound from a nylon string guitar. They have much metal string sound with low tension.

To repeat - especially for a mahogany or koa body - light gauge strings really seem to open up the tonal signature but YMMV.

Rob
It took some time before I got to this guitar, but now it's done and I figured I'd let you guys know how it went:

When I removed the fretboard, I discovered that the steel reinforcement was not seated properly. I removed it with heat, bent it a little and epoxied it back into the slot, which gave the neck a slight backbow. Then I spackled the surface with z-poxy and finally glued the fretboard with hide glue. The neck feels MUCH stiffer now than it did before, even though I did not add any carbon fiber. Now it has zero relief (dead straight) with medium strings, and it plays great. I'm a happy man! Next time I'll go a little easier on back-bending the steel tube so that I will end up with a tiny bit of forward relief instead of nothing. Thanks for your guidance! Take care

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