Adjustable neck design.

[Brian Evans]

So, I am designing my new archtop build. Along with everything else, I want a non-adjustable bridge design. My last guitar has a non-adjustable bridge, but man is it a pain, an adjustment is so not reversible with a set bolt-on neck. So for this build I want an adjustable neck. I've been going through all of the typical adjustable necks and none have grabbed me. So as a machinist I came up with one that I think will work, did some stress calculations (man, I don't remember trigonometry at all) and designed a new heel-less neck joint. Very innovative, totally adjustable, should be totally stable, I am so chuffed. So I keep googling adjustable necks and discover that it was actually invented by National in 1950. Tough, I am using it anyway, and the detail of my installation will be different anyway, but man that is interesting that someone else already did it. http://antebelluminstruments.blogspot.c ... d-top.html

http://antebelluminstruments.blogspot.c ... -neck.html

I thought of it on my own, honest! Mine will use a billet aluminium angle.

Brian

[Peter Wilcox]

So how is the adjustment mechanism attached to the neck? I'm assuming it's an "L" shaped piece of steel, with a thinner, longer leg of the "L" running up the neck under the fret board. On the National it looks like it runs the entire length of the neck, acting as a stiffener or truss rod.

[Brian Evans]

I was going to pocket it about 1/8" into the bottom of the fretboard extension that floats over the top of the body, The joint has to support about 150 lbs of linear pull from string tension and around 6 ft-lbs of rotational force. I was going to use epoxy for the joint, and I have to do some tests to see if it will even work. It's only an idea at this point!

[Beate Ritzert]

I would assume that the steel within the neck might be a T-bar.

[Peter Wilcox]

The joint has to support about 150 lbs of linear pull from string tension and around 6 ft-lbs of rotational force.

And then there are added forces when the guitar falls over.

But seriously, that joint has to be absolutely rigid, with no flexion, or the string tension/pitch will be all over the place while holding and playing the instrument. I don't think that's possible if that joint is the only attachment of the neck to the guitar. But maybe I'm misunderstanding your concept.

[Brian Evans]

My thinking is it has to be as stiff as a wooden neck joint were the forces are reacted over around 2.5" of wood (the 90 degree blend between the neck and the heel). I have to duplicate that with aluminium. My first try yesterday didn't work, the 90 degree joint flexed too much, but the attachment to the neck itself (3" long by 1.25" wide, with just some screws for testing) seemed very stable. So I am adding a gusset today. The gusset should increase the stiffness of the "hinge" by a lot. To increase my knowledge of the stiffness of a typical neck and neck joint I plan to do some deflection testing. I will probably do a fender type neck (telecaster), a gibson solid body type neck (Melody Maker) and a traditional acoustic dovetail neck. The key is how the neck forces are reacted into the body, I think. If that joint is sufficiently strong the neck itself should be the spring, so the deflection test should have the same result with my test neck mounted via my joint, or firmly bolted to my bench. Regardless of how this turns out, I will learn a lot about neck joints, I do believe....

brian