Carbon fiber option

[Rôckhewer]

Hi folks.
So I haven't yet bothered with reinforcement strips on my 5 string necks, because I usually do a 9pc. wenge, bubinga & maple ...and don't try to make them insanely thin.
Have had no problems.

But my current 5 string build is for a client with small hands, & he's requested a very thin neck...
And instead of bubinga.... this neck includes mahogany along with wenge & maple.

So,...gonna use some carbon fiber strips.
BUT, The size that Stewmac sells, for instance seems seems a bit much to me.
I honestly feel I dont need 2 strips at 1/8" x 3/8"

I found some on ebay that are 6mm x 1mm (roughly 1/4" x a heavy 32nd ")
I could route these in nice & tight using my dremel router base, & have very minimal wood displaced.

My Question would be.... has anyone used strips this small and do they provide any significant support at all??
Or would I be better off going with the big ol' nasty thick ones ?
Looking for more direct experience based info, rather than opinion.
Sometimes we can be a bit paranoid to the point of overkill....
Thanks a bunch!

 

[Gilmourisgod]

Rock
I used two 1/8" x 1/4" x 22" CF rods, I was actually worried they would make the neck TOO stiff, but that doesnt seem to be the case so far. I was able to adjust the trussrod pretty easily to cancel tiny backbow, we'll see what happens under string tension. The accepted minimum wood thickness under the trussrod and CF rods of 1/8"-3/16" then sets your minimum neck thickness. Like everything on TB, opinions vary on the usefulness of cf rods. I did it because I have a Warmouth neck with rods, and its really stable. Curious to hear what the pro builders say about this.

 

[Bruce Johnson]

If you want to stiffen the neck, what matters is the depth (the vertical height) of the carbon fiber strip. The width means very little to the stiffness. Extra width just means adding more plastic to the neck.

The ideal ultimate carbon fiber stiffener bar/plate would be 1/16" wide x 5/8" deep at the heel, tapering to 3/8" deep at the 1st fret. Saw them out of some 1/16" carbon fiber laminate sheet or strip stock. That will make a super stiff neck. One of those on either side of the truss rod, and you'll barely be able to move the neck with the truss rod. You install these stiffening plates by routing a slot, say, 1/4" wide, and then putting in the plate with a 3/16" thick slice of maple beside it to fill the gap. Or, you can put a single slot down the center which holds the truss rod with a plate on either side, and a maple filler strip under the truss rod.

Also, you don't have to use carbon fiber for these stiffening plates. Aluminum works just as well. Standard 6061 aluminum plate, 0.063" thick, is easy to cut and work with. And it's actually lighter than the comparable carbon fiber bar. And less expensive

I make a special version of my truss rods that is a wedge-shaped cartridge, made for simple installation by my clients. Last year, I made a couple of prototypes of this cartridge truss rod, with a pair of these aluminum stiffener plates built in, on either side of the rod. They were like I've described above, 1/16" wide x 5/8" at the heel, tapering to 3/8" at the 1st. My client (another pro Luthier) installed one in a sample guitar neck to test. The neck was so stiff that the truss rod could barely move it 1/16". Too stiff, actually. On the production units, I'm now cutting additional slots in the outboard ends of the stiffener plates, to allow the outboard end of the neck to flex a bit more.

Using this design of stiffening plates, either carbon fiber or aluminum, you can make the neck as stiff as you want.

Remember, stiffness and stability are two different things. A stiff neck can still be unstable if it isn't built correctly. You still need to dry the wood, select for grain/ring orientation, eliminate pre-stresses, seal it up, etc. All the usual good technique.

 

[Rôckhewer]

Thanks for your input Bruce.
The laminations used in my necks are precut, slightly larger than they will be when used & have been acclimating in my shop for months. Prior to glue up, any subsequent warpage is jointed out, then they are planed to final dimension.
Apposing pieces of the same species have been typically cut from the same board which have been selected for straight grain, and similar uniformity of growth ring at each end. When I assemble, I not only appose the grain of the same species on either side of center, but I also appose the grain of the dissimilar back and forth as they fall in order...and the center beam is as flatsawn as I can find...something like this: 《\/\||/\/》
This particular client wants a very thin neck.
But...he also wants lights in the fingerboard.
That means I cannot make the fingerboard as thin as I would like to help reduce overall thickness. So all the reduction has to come from the neck beam itself. To a point....I'm not going to make it so thin to the point of failure. But it is currently thinner than I like when just using one single dual action truss rod.

 

[Bruce Johnson]

Lights in the fingerboard.....Ugh. To me, that's the point where a fine musical instrument becomes a stage prop toy. But, that's just my opinion, and I know that some customers want them.

Anyway, yes, the neck you are describing could use some reinforcements. I'd use a single truss rod in the middle and two aluminum stiffening plates. Make the plates as deep as you can get away with, for the thickness you have to work with.

If you haven't glued up the laminations yet, another option is to rout shallow 1/16" deep recesses into the sides of two of the strips. Glue the stiffener plates in at same time as you are gluing up the laminations. Then rout your slot for the truss rod.