Two Laminated Neck

[Jorge Fernandez]

Hi all,

Two questions:

I'm planning a neck-tru guitar but with the wood sizes I have, I've to build a

two mahogany strips. I was wondering if that is a good idea because the

truss rod channel will go over the glue joint.

The neck has to be thin too, is there any experience on routing some portion

of truss rod channel in the fingerboard to avoid routing so deep on the neck

wood ? I've seen the topic

http://projectguitar.ibforums.com/index.php?showtopic=31108

where thegarehanman talks about it but no more info is added.

Thanks!

[Mickguard]

Well, since no one else has answered this, here's my experience.

I've just finished a neck like that--it was my first attempt at building a neck so I didn't want to waste my single-piece blank while I was learning (I ended up finishing that neck first though).

This one was built more or less as you describe it, it's made of two pieces of wood (they're from the same plank, with the grain reversed). The wood was dry, and I'd glued up the blank a good year before I finally built the neck. The glue-up went really well--you really had to look hard to see that there are two pieces of wood there, so the profile is still beefy enough. Since the fingerboard is fairly thin, I didn't carve away a lot of the neck wood. The neck is also reinforced with carbon fiber rods. It's finished with nitro, and it cured for more than two months before polishing it.

Well. The neck has been under string tension for about a week now. And guess what I discovered today?

There's a tiny ridge developing along the glue line. It extends from about the end of the first fret into the fourth fret. It's a very slight ridge--with a magnifying glass I can see that the finish has cracked/chipped ever so slightly--enough so that I can feel it with the back of my hand. And I know it wasn't there a couple of days ago.

So that's my experience with this kind of neck. I think next time I'll use at least three pieces, if I try a laminated neck. But if I were you, I'd just buy a real neck blank, they're not that expensive.

On the other hand, I have another guitar with a two-piece mahogany neck, and it shows no signs of this problem. But that one was factory built, or at least built by someone with a lot more experience at this that I have!

As for this neck....it's still playable, but who knows for how long? I've decided to use it to practice leveling and recrowning the frets, since I've never done that before.

[Mattia]

I laminate 2-piece necks, frequently. The latest one I did (nice and easy to compare to a 1-piece, similar dimensions, same species of mahogany) taps and rings out just as well as the 1-piece. I also prefer to glue up the blanks and let them rest for weeks to months before working them, as glue takes a while to even out. Never had raised ridges, though, and I'll continue to make most - if not quite all - of my necks from 2 pieces of flatsawn mahogany, cherry or walnut. The ridge is likely merely an expression of wood that wasn't quite dry/stable enough when carved (I also like to pre-carve necks a little, and let them sit around before final carving), and/or decided to move a little, and the situation wouldn't be any different with a 3-piece neck (although....3-piece with contrasting wood can look very, very nice). I very much doubt it'll 'slip' so far as to make the whole neck unplayable or anything.

And sometimes, it's just plain old bad luck. Wood will be wood and all that.

[j. pierce]

Mick - what was the glue/finish combo on that neck?

You've described something that sounds like structural damage/fatigue, but I have had in my experience, some water-based finishes having the glue lines telegraph through the finish at a later date.

The case I'm thinking of in particular was a KTM-9 over Titebond - It was a similar situation, with wood that had been glued for quite some time, and didn't show until a while after the fact. And it pretty much looked/felt like what you described at first until it became apparent what it was upon closer inspection, and the fact that this was a top rather than a neck, so there shouldn't have been too much stress on it, unlike your case where string tension and a truss rod could have made things worse. (The whole thing arose from when I tried doing an inlaid top under a solid finish as practice since I was adding a cap to a rebuild of an older project that I was going to thin out and chamber to lose weight on)

Not saying this is what you have, but it did make me think of this. I have had similar issues with other waterbased finishes and some glues on my furniture builds, but I can't remember exactly what the combination was in those cases.

-josh

[Mickguard]

Mick - what was the glue/finish combo on that neck?

It's nitro, the glue is just standard wood glue. I'm not so sure it's structural though, I've looking at it again, and it could be that the nitro has shrunk some more, and more on one of the laminates than the other--that might account for the ridge. Or maybe it's possible that the glue joint became contaminated somehow at that point on the neck, which is causing a reaction with the finish? And maybe it's the weak spot on the finish that's affected by the tension from the strings and truss rod.

[GuitarGoat]

Yea I used Nitro and regular wood glue too, and I can now see most of the glue lines! I don't think its too big of a deal though... I hope not.

[Mickguard]

Well things appear to have stabilized, the little ridge I felt hasn't gotten worse. I polished the area again and now it's no long detectable. We'll see what happens down the road.

[doug]

Sometimes this can happen with too much glue in the point, then not enough pressure during clamping. We're splitting hairs here though... The glue line should be non-existent for the most part, though there may be some slight visibility of the glue. Basically, if the glue is visible then you may very well end up with the ridge you describe.

The wood itself will shrink and expand with humidity/temp changes of course. The glue, on the other hand, changes differently. The glue, the finish, and humidity/temp are all related. Later, we sometimes get a surprise like you did.

Over the years I've figured out that a glue line is less visible if the two adjoining surfaces are not too smooth. You could rough the surfaces with 100 grit prior to gluing to "fluff" it up. Surface prep is huge.

-Doug