Carbon rods

They add stiffness - but more importantly, they add stability (stiffness over time).

You still need a truss rod if you want to dial in the best action all over the neck.

 

How about trying it without the CF?
A truss rod is a wonderful adjustable tool, like it's supposed to be.
Your other alternative would be using stiffer neck woods.
Sorry to stir the pot, but this one always grinds my gears.
Dirk

 

Hey John,
Even on my sixes I've never had a problem with 1 rod only, no CF. But my current formula is Wenge, Purpleheart and Hard but figured maple. Never had a single issue over several years with that combo. I can't even remember the last time I had to even adjust a truss rod in any of them.
You might check on the moisture content of your woods, I've only seen things move when they weren't dried completely.
Dirk

 

CF inserts resist the pressure of the strings to bow the neck. CF inserts also resist the action of the truss rod to remove the bow.

 

CF has a higher stiffness/volume ratio than any wood - so one thing CF helps you do is to make a thinner neck that would have the same stiffness as a thicker one made of all wood.

 

The Bass I made back in March used 2 CF rods...and I've moved from England to Colorado, so I had that change in environment in mind while I was designing it. I must say that the rods have made the neck rock solid, but like Dirk says, the stiffness they add also reduces the amount the neck can be adjusted. Then again, there's no bow in the neck, so I don't have anything to adjust.

On Barnaclebeau's project, the CF rods are put into the neck horizontally, (e.g. _ ) so that there is a slight addition of stiffness, but the flexibility of adjusting the neck via the truss rod still remains.

I set the rods vertically (e.g. | ) into my Bass, hence the greater stiffness, but reduced adjustment capability, so I'd say it's down to personal taste...but so far, I'm glad I did it

 

Were the wenge, purpleheart and hard maple quartersawn or flatsawn?

 

I'm absolutely a quartersawn fanatic. Especially with the neck woods I like, that's the only way that works for me so far. I haven't made that many, but the one characteristic they all hold is very solid strong necks. By the way I have tried them in many different sizes and orders and they all seem to be very consistent.
Strong, dense woods like to stay straight.
Dirk

 

I was thinking about using a straight piece of aluminum as the center of the neck and then having the fret/finger board fastened to it with the ideal (for me) neck shape built into it. Another piece of wood for the back of the neck and headstock would be added and, for all practical purposes, I would have what looks like an all wood neck that was as stiff as if it contained perfectly rigid carbon rods.

 

Why? Aluminum has ~1/3 the stiffness of steel (which Warmoth uses) and you can't adjust it. Martin used to build their acoustic guitars like this until just after WWII - but for the most part they were gut string and not steel string, which has way more tension.

Why the aversion to a truss rod? They've been used since Leo Fender's day (more than 50 years) and they are proven - why try to reinvent the wheel? If you're going to install any kind of reinforcement, it is just as easy to install a truss rod as it is an aluminum bar.

 

I personally prefer 1/4" round tube CF. 2 of those and a TR. Adds a little stiffness and shifts the resonant freq of the neck away from bass freqs=no dead spots.

 

this theme is fun to watch. majority would never go without a truss rod, pointing out it's stabilising and adjusting functions. we can say it's a conservative approach but logically correct and well tested over the years. from time to time here comes a rebel with wish of avoiding a truss rod. ones are unexperienced and want to simplify the building process, others want to escape from the rules in the name of unharmed vibration transfers and new designs and believe they can make neck of great stability so it can preserve the fine-tuned action setting. and yes there are $7-10k artworks like that. i personally think truss rod is not 100% neccessary but its not easy and safe way. fragile variables besides those mentioned earlier are also neck length/width ratio and finish. seems to me it's more suitable for new designs like neck through singlecuts etc. and i'd try it only with very old wood that won't betray me.