New neck approach - initial results...

[Keith Guitars]

I just finished the prototype of my new neck project.
A quick description:

The maple blank was tapered, and then much of the interior volume was routed out, leaving a semicircular, tapered hollow area.

I shaped a corresponding insert out of quartersawn redwood, which is very stiff for its extreme light weight,
and rings like a bell when tapped, with a very musical resonance. This got epoxied into the hollow area, with a layer of unidirectional carbon graphite in between them.
I used West System epoxy. The carbon was 5 strips of 1"wide unidirectional tape.
A single-acting Fender-style truss rod was routed in on the underside of the redwood insert.

Pics here:
Martin Keith Guitars - What's New

Those pics show the inside of the neck before fingerboard, headpiece "ears" etc. are glued on.
The finished part looks the same as a 'standard' neck, except at the heel where you can see the cross-section.

The body (pics not yet taken) is conventional - African mahogany, maple top, and Duncan SJ5 jazz pickups in wooden covers.

The design goal was to reduce weight while maintaining stiffness, and hopefully include some of the lovely musical character of the redwood in the tone of the finished instrument.

Initial results from this neck are good! Though the finished bass is only moderately lighter than the standard instrument (I kept everything else pretty standard for a better sonic control), the weight distribution of the bass is noticeably better. It hangs nicely and sets on the lap pretty well.

The neck rings clearly when tapped, though at a lower frequency than the solid wood part.
However, the assembled instrument has no obvious dead spots or deficiencies It's bright, but that could also be the brand-new strings. The low end is fast, clear, open-sounding, and strong, and the midrange has a really nice vibrant quality.

Rigidity seems comparable to, or possibly even better than, the 1-piece maple neck.

Considering that I used a softer resin (West w/a room-temperature cure), and that 10-15% of my carbon squeezed out of the joint during layup, I think that's pretty promising.

It means that a better high-temp resin, a little more carbon, and a more controlled layup could get it clearly
stiffer than the solid wood part.

So - worth the effort? Well, probably...I think pushing the core size a bit more, a bit more carbon, lightening the truss rod (Titanium?), and improving the layup procedure should make it better enough than this to warrant the extra work.

As-is, I'm quite pleased with the instrument, and it's definitely a promising direction for further research.

Cheers,
Martin

[Musiclogic]

Interesting concept, saw it in the shop tour. Using a flat roving tape or film laced through the layers of Carbon would have allowed you to keep the layers tight or in place, and would also add to the strengthof that layer. I don't know if I could justify the time to do the neck properly without a CNC, but I think in todays market with all the weight complaints, you have hit on a good selling point if it works out for you. Thanks for sharing.

[Keith Guitars]

Hey Musiclogic,

Actually, I did use tape that was laced together with some glass fibers across the width. Doing this will simple unidirectional "tow" carbon would have been unbearable.

The problem was/is the hydraulic effect of the epoxy squeezing out of the joint. I'm thinking of trying a unidirectional braided cloth for the next one(s) to work around this. A lower viscosity resin will help a lot too.

Surprisingly, the prototype required very little work to make on my pin router. The male and female parts are both pretty simple shapes, made with a matched pair of roundover and ball-end bits. I'd say it took a couple of hours to make the fixtures and generate the initial parts. With refinement and practice, I think it would add maybe an hour to the production time of a neck, which is pretty acceptable if the result is good.

Cheers,
Martin

[Musiclogic]

It's definitely an interesting endeavor, good for you Martin.

[Johnius]

Martin, I don't build basses so maybe these questions are too easy, but if you like the resonance of the redwood so much, why not make the entire neck out of it - why just an insert? Is it too expensive or not strong enough?

[Jason_A]

I think this is a cool idea, and obviously reminds me of Parker. seems to me that it would be worthwhile to consider methods for lightening the body as well. There aren't a lot of lightweight basses, and to have one that doesn't look goofy (i.e. Parker) you'd be filling a niche.

[Keith Guitars]

Originally Posted by Johnius

Martin, I don't build basses so maybe these questions are too easy, but if you like the resonance of the redwood so much, why not make the entire neck out of it - why just an insert? Is it too expensive or not strong enough?

It's a perfectly valid question.

The redwood is a lovely-sounding material, and quite strong for its very low weight.

But, the whole idea of this neck is to remove weight (by decreasing density, i.e. substituting redwood for maple) in the part of the neck that can best afford to lose some absolute strength - which is the middle of the neck itself.

Like an I-beam, a neck is subject to two different forces - compression on the concave face of the bend (i.e. fingerboard surface), and tension on the back.
In between, there is what's called the "neutral bending axis", a line parallel to the faces where there is theoretically neither tension nor compression.

Using the shell of maple, reinforced with the very-high-tensile-strength carbon, puts a small area of great tensile strength right where it counts.
The fingerboard accounts for the compression strength on the front of the neck.
So, inside the neck, on and around the neutral bending axis, the redwood serves to add stability and support to the outer faces, fill up the space, and add some of its own character to how the neck transmits and absorbs vibration.

Jason_A: The Parker influence is pretty obvious and certainly quite clear. I had the good fortune to see how he's building the necks for his new archtop guitars, and this was my first step at adapting the approach to a solidbody bass.

Cheers,
Martin