Neck-through Emulation

[Runewalker]

I have always wanted to do a neck-through project. I like how the mfg or luthier is able to smoothly conture the neck-body transition, and generally prefer the solidness of set-neck style construction. And while neck throughs are not set-necks they act the same way in terms of neck to body coupling strength.

Over the years I have been struck how Jackson, Ibanez, et al build their angled headstock bolt on necks with a scarf joint. Obviously that is to save the waste from carving the angled headstock/neck from one piece of wood. But that scarf joint is intriging.

I have seen a lot of Gibbies with broken headstocks at the angle transition. This makes sense because the angle is conducted over an end grain transition, which is a weak point, especially with the string tension. Scarf joints eliminate that weakness since the transition is directional grain not end grain carving.

But it is counter-intuitive that an end-grain to end-grain glue joint, that does not even have finger joints or other milling to strengthen it, would take the string tensions. But they do, times hundreds of thousands.

So that got me to thinking: I am thinking of glueing up an extension slab to a bolt-on, emulating a neck through. Then carve the transition and put on body wings.

If the end-grain to end-grain joint is strong enough for scarf joints, the flat to flat should be stronger, assuming all finish is thoroughly stripped and the glued stock pieces are clamped. I could even mill a key to strenthen it.

Anyone aware of similar experiments?

I am a little concerned about neck angle issues on this idea though, and of course the glued up extension would be unadjustable.

[flateric]

An interesting post.
What would concern me is the leverage. Handling the guitar and string tension at the mid point would make a joint at the transition from neck to body prone to more stresses than the joint at the angle of a headstock. I would think you must introduce a better reinforced rigidity in the joint so the integrity of the construction is not compromised.

[pollyshero]

SCARF JOINT is what you'd want for this project - not a butt joint. It's a far superior joint in overall strength - it will help spread the tension load and last much longer (read: "forever").

I'm not a physicist so I can't explain it scientifically... I do know that a scarf joint actually increases the gluing surface area - more glue = stronger joint(?). Aside from that, just look at my crappy drawing & visualize the effect of "folding" each joint. The butt joint will fail much sooner than the scarf joint.


If I had to guess why you don't often see the scarf joint used to join two pieces along the same plane, I'd say it's because they're a pain in the a$$ - the cuts must be precise to keep them square to the plank. Once sawn, the cut ends must (well.. should be) be planed (best) or sanded (effective but not recommended) smooth to create the optimal gluing surface.

I'm not endorsing the brand of adhesive at this link - but I liked the little article.

www.glen-l.com/supplies/pxman-apscarf.html

Now here's the rub... You'd have to cut a perfectly sound bolt-on neck latitudinally(sic?) and then cut your through body piece at the same angle & then match them up. Difficult, but not impossible. Should be child's play for a true Texan...

If you decide to take this on & you want actual hands-on help, PM me & I'll pack up the saws & head up.

PH

[newey]

RW-

I'm with flateric on the physics of this thing. His "big lever vs. little lever" analogy came immediately to my mind as well. Something about Archimedes (I think!) claiming that, with a big enough lever . . .

Anyway, you want to smoothly contour the neck/body transition as the goal of this exercise (without having to actually carve out a neck at one end of a wider wood blank, as would be done in a real neck-through.)

In making a neck-through from a piece of wood, one essentially carves away every bit of wood that is "not neck". You're starting with a neck that's already made and attaching a piece of wood, and then you're going to remove wood from one or the other side of the very joint that's in question, further compromising its potential strength.

This is not to discourage you from trying this, but unless you can really achieve that smooth transition I'm not understanding the usefulness of doing this.

If you do build this, consider wearing safety glasses the first time you string it up. It might fail in a fairly spectacular manner.

[sumgai]

Rune,

I asked you to stick around, and possibly start a controvery or two......... Oh boy, do you ever take me literally! ;D

While a scarf joint is a mechanically superior joint, I don't think you've expressed the whole enchilada, nor has anyone else picked up on it.

In point of fact, if you're going to modify a bolt-on neck, then the first thing you need to consider is "what's on the underside of that piece of wood, where it used to mount (with screws) to the body?" Your extension will need to cover this area too, or your body will be mighty thin overall, if'n you don't intend to add some beef in some other way. Seems to me the added beef should start right here, at the heel of the neck.

So, what you're really contemplating is replacing the neck-to-body screws with a solid joint, right? Then why not fashion your extension such that it encompasses the two planes of the neck's heel, the underside (where the screws mount) and that surface perpendicular to the fingerboard (where you sometimes encounter a tension-adjusting nut). This means that your extension, when viewed side-on, will look like a rabbet has been cut into the end, to accept the neck as if it were a tenon.

Not obviously to most GuitarNutz, but very much so to old wood butchers like you and me, one would benefit if one could do a biscuit joint. This keeps the two workpieces in perfect alignment during the glue-up, and has the advantage of not being visible, yet delivering some much-needed additional strength. As an alternative, you could simply dowel the joint after the glue-up, and either use nice wood for the dowels (interesting end-grain), or plug the holes over the recessed dowels with a body-familiar wood. Your choice, of course.

Here's a cocktail-napkin sketch of what I mean:



After that, you could shape the new joint to emulate a "relieved" corner that further enhances the hand's grip while playing on the higher frets. I'm sure you can find examples of what I mean, or you can concoct your own flavor of that enhancement, right?

HTH


sumgai

[ChrisK]

I'd just use a Carvin neck thru neck blank and add the body wings of my choice.

[newey]

Sumgai's suggestion certainly makes for a stronger joint, by adding the heel back in, then inviting you to sculpt it!

If you're going to do that, you might consider a test mule first- find some old basket case guitar with a bolt-on neck, remove the neck, discard the plate and screws, and dowel-and-glue the joint as Sumgai suggests. Then sculpt it down to your liking at the transition. String it up and see what ya got. That way, you don't stand to ruin a good neck and a quality piece of wood on your first attempt.

To really test it as close to what your final goal is, you could bandsaw off the old ratty body down to the width of a neck-through blank, leaving you with a sort-of half-a***d Steinberger.

[Runewalker]

I was not too clear in the description. Underdog, yes a joint like you drew would be be 'on-drugs' (pun intended). I meant a multiple surface joint like Sumgai drew. I should have included a visual but was in a hurry.

The modern glues are amazing and I am confident as long as the milling was careful, and the glue up was clamped, the joint would be strong. And yes biscuits or dowels, or even hidden dowels would be an enhancement. The dowels would add some significant strength.

The argument that the stresses at the body to neck joint are greater is interesting. Adrien Balew used to get vibrato by leveraging the headstock and holding the body to loosen the strings. I had to wonder about how that bolt up joint held up over time. I don't use that technique or Jimi's smash it on the stage approach, so I don't know that the kind of stress that normal playing induces is likely to separate a well glued body-to neck joint, but it is something to consider, since the string tension essentially forms a bow.

Yes of course CK, I could just buy one from Carvin, but that would cut into my ruining another week-end with the frequently labor intensive folly of this hobby. As long as you place no value on your time, effort, tools, neighbor's acceptance and your sanity, it's free right? But we gave up the sanity part long ago, or we woulda just bought a harem of PRS-s.

RW

[ChrisK]

Adrien Balew used to get vibrato by leveraging the headstock and holding the body to loosen the strings.

I have an Ibanez GhostRider 540 with the same built-in vibrato.

It has a mahogany set neck (for now), but is still effective.

[JohnH]

For structural wood members, glue lamination is often used to get a larger section with better more consistent properties than can be found in individual pieces, using a sandwich of many thinner sections. Where one lamination is jointed end to end along the length of the member, the splice is usually a finger joint, with a glued surface over a very shallow zig-zag with many fingers, giving a massive glue surface and a smooth transition. These joints can develop the full material strength.

Cutting a zig-zag to create several fingers, into a neck, and matching it to an extension piece may challenge the backyard wood machinist. However if it was possible, I reckon it would be the best.

It would be better if the finger board could be added later, over the top of the joint, and a similar thickness of body material under the joint, so that these upper and lower layers bridge across the transition, reinforcing it and concealing it.

That I think, would be a rock solid joint and Pete Townsend would not have been able to break the guitar there before it broke somewhere else.

John

[sumgai]

John,

Rune did say in his first post that he could mill in a key, if such were recommended. What you've proposed is nothing less than a box-joint, with appropriate spacing, which amounts to the same thing. I'm not in favor of such, unless a dove-tail bit were used to mill the keyway(s). But that's a fair chunk of wood to remove from the neck's heel, and I'm not comfortable with that much wood going away.

I still think it'd be better to simply lash the pieces together, and dowel the results. I'd use 3 each ¾" dowls, measured to go through the extention and into the neck itself no less than ½ of the way through. Doing a quick stress analysis on that, I see that the joint could handle, with simple Elmer's Carpenter's Wood Glue, at least 850 lbs. of force at a 3% angle (on a 25½" scale). This is far more than necessary for playing, and staying in tune (given Chris's proclivity to "make vibrato wherever one can"!), although I have to say, in a collision of the Pete Townsend sort, all bets are off!


Rune,

Persuant to the above, I like the idea of cutting a junker body, and getting some measurements. This should save having to make any radical adjustments after the glue-up job. However, you could make adjustments afterwards...... if the bridge is too high, "merely" plane down the top surface (re-saw it, the wings aren't on it yet, it'll fit through bandsaw), or if the action is too low, skin the top to the appropriate height.

In fact, after assembling and adjusting as above, I'd skin the back, just to hide the dowels. Unless you're were intending to show off different woods banded together in a pleasing pattern, then the skin(s) would be attractive, and hide a lot of sins! ;D

HTH



sumgai