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Hello chaps. I have just "finished" guitar no. 5, which is for a friend. I am still learning a lot, and have a lot more to go...

Anyway, I got a bit overexcited and adjusted the trussrod in such a way that it has caused almost parallel cracks on the underside of the neck, under the first fret, where the neck blends into the headstock, and the thickness of wood between the bottom of the trussrod slot and the back of the neck is a matter of several millimetres.

I have attached a couple of photos. The trussrod is now in the correct position, giving me the required relief, and is no longer bearing on the affected area in the same way. But I wonder how best to repair this? Would it be possible to try and slightly open up the cracks and work in some CA glue, or does this really require a major operation (i.e. a new neck)? I very much hope it is the former or something similar, but am (sort of) prepared for the worst.

Expert advice very much appreciated.

Thanks,

Rob

You might be able to open the crack by misadjusting the rod again, work some LMI or titebond glue into the crack, release the tension on the rod, and clamp the crack if necessary. The neck would be as strong as it was before, but it is up to you to decide if it is strong enough. CA might also work but you will have to work quickly.

I would use a small amount of slight watered down title one. I'd be worried about wicking in too much ca and binding the rod itself.

So as suggested, gently reproduce the problem to open the cracks, rub some glue in, release tension, wipe off the glue, and let sit overnight...

My opinion about cracks is the fact that you can repair the visible part but it is the sections of it that you can't see that can be a problem later on. The situation is made worse because it is the major stress point caused by the truss rod.

The ideal repair would be to remove the fretboard and truss rod and find out exactly the extent of the crack. You can do that by applying naphtha on the outside and see where it seeps through you will then be able to repair the complete crack. But that does require a lot more work than just gluing it and hope you got it all.

You will have to make your own judgment on the proper fix but just keep in mind that that part of the neck will always be under stress. Not only just from the truss rod but also from humidity issues. Chances are the crack is much longer than what you are actually seeing and probably goes right into the truss rod channel.

I have fixed similar type cracks and usually use the thin CA glue because it will penetrate all along the crack and even in the parts of the crack you can't visibly see. The issue about CA getting into the truss rod is something to be concerned about so you will have to weigh your options. And since you have the guitar in hand you are a better judge than any of us looking at a picture so it really comes down to your judgment.

I would use the naphtha trick and see you can tell how big the crack really is. It will evaporate out and won't stain the wood so it is a good safe way to find a crack.

Sucks when things like this happen but it can be a great learning opportunity as well.

Good luck and I am sure you will figure out the best way to repair it.

Bob

Rob:
No worthwhile suggestions for repair but a suggestion for better prevention. I use the Martin copy one way rods with aluminum channel. See the Stew-Mac site. These are epoxied into place, thus spreading the load over the length of the groove rather then just three points like the regular rods. They also help to stiffen the neck in the process. Maybe fruit for thought for future guitars.
Tom

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I had the same problem on #1 with a StewMac hotrod. My problem was that there was not enough wood at that point to handle the stress. I removed the fret board, added some wood to the bottom of the slot, and put in a new, shallower, truss rod (Allied). I also moved the end point of the rod closer to the nut so there was more wood under the bearing point. I put in a new fret board and the guitar has been great ever since. These days I have gone to the Martin two-way rods.

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Steve Smith
"Music is what feelings sound like"

I'd like to know which rod you used, please?

Thanks

Thanks all for the advice - I have decided to try the naptha trick to find out the true extent of the crack, then go from there. I will have a think about truss rods in future guitars as it does seem to be a handicap to have the force of the rod bearing on only a few points, one of which is particularly thin and weak, under the first fret.

Cheers, Rob

I'm assuming you used something like the StewMac Hot-rod - I've seen this exact crack many times before. Working from this assumption (still not sure which rod you used), before looking at solutions let's clarify the underlying causes and problems.

Conventional single compression rods do not have this issue, as they only apply longitudinal force along the back half of the neck. Self contained rods like dual-rod double action or the old Martin single action supports work entirely different, in that they only apply force perpendicular to the neck rather than along it's length.

If the system spreads this load across a suitable area (both in width and more continuous contact along it's length), then there is typically not enough stress on any given point to worry about rupturing the wood. In a dual rod system with blocks at the end however, there are many things working against you. First is that with typical assembly methods, you are placing the bulk of the force against a very, very small surface area under the end block. Second is that with the height of these rods, the slot has to be so deep that there is just not much wood to support the force against it. This setup in my opinion, is a recipe for disaster.

On to solutions. First, you're faced with the fact that regardless of how you approach gluing the crack up, it will be just as likely to break again in the future as it did this time. If this guitar is going to be around for decades, then at some point someone will adjust the rod a bit too far and it will break again, no question. So you should take this in to consideration in problem solving.

Now if this were a paying client the answer would be simple - make a new neck (with a different truss rod). Since it sounds like a project for a friend with strings attached (i.e., it's a learning project with some flaws to be accepted), then there are other options.

How you glue it up I would say is not that important. You could use white glue, super glue, hide glue, epoxy - if you can pry the joint open by tightening the rod you shouldn't have problems getting suitable penetration to the joint. I would be inclined to use a regular PVA wood glue or hide glue, as CA or epoxy would run greater risk of binding to and seizing up the free rod if you're using a double rod system, though if done carefully these glues still could work.

The more important part is what to do after it's glued to prevent it from happening again, and my solution would be this - compression fret the hell out of it. Refret it with an oversized or heavily crimped tang, glue the frets in with the neck pressed in backbow, and you should be able to set it in to enough backbow that the rod should never have to leave reverse engagement, and will only ever put pressure upward toward the board and never against the back of the neck. You'll have to evaluate how much movement it's capable of delivering in up bow to gauge how far to push it, but I would aim so that in the end the neck were still in back bow and never beyond straight when the rod is loose.

Not a perfect solution, but probably the best odds of giving the guitar a fair shot at a long life short of replacing the neck entirely.

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Good write up David.

Excellent answer Dave, many thanks. You are correct that I used a dual rod system, and in thinking about this problem and reading through responses here I don't think I'll be using it again. You're also correct that it's a learning project for a friend and he will (have to) accept some imperfections! I like your compression fretting idea, I hadn't thought of that at all. I would quite like to avoid taking the fingerboard off and pulling out the truss rod to glue the crack, so I think I'll do as you suggest, carefully working in some CA glue by gently opening the crack again, then doing your re-fret and see how we go.

This forum is great!