Carbon fibre rods and truss rod adjustability

[Mark Day]

Hey everybody, long time, no post.
I'm building three Les Paul style guitars and I'm working on the necks now. I bought the StewMac double action truss rod and carbon fibre reinforcement rods. The CF rods are 5x6mm rectangle and 455mm long. My plan was to put one on each side of the truss rod about 10mm or so to either side of the truss rod. Necks are Sapele laminated to achieve vertical grain. Two of the necks are two-piece lams and the third is three-piece Sapele with Black Walnut sandwiched between.
I'm wondering about how this will affect future adjustability? I've looked around a bit on the interwebs but I trust the advice here the most.

[Marshall Dixon]

... My plan was to put one on each side of the truss rod about 10mm or so to either side of the truss rod. Necks are Sapele laminated to achieve vertical grain. Two of the necks are two-piece lams and the third is three-piece Sapele with Black Walnut sandwiched between.
I'm wondering about how this will affect future adjustability?

I put a dual action truss rod between the fibre beams on the steel string guitars I make. The bottom of the Stew-Mac truss rod is round so I use a round bottom router bit purchased for the task. I also put them in about 1/8" deeper and compress the rod with a filet of wood glued on top to compress the rod and take up any slack. I had one develop a sympathetic rattle that wouldn't go away with tightening the rod. It wasn't a Stew-Mac product though, and the latest I got from them are near totally wrapped in a plastic sheath of some kind. But I'm still going to do it with the filet on top. Fixing that was a one of those tasks best forgotten.

I put the graphite bars closer to the center and cut their channels about 1/8" from the rod. So you end up with all the hardware in the centermost portion of the neck. What can happen if the bars are farther off center is that they can show through when shaping the back of the neck if the neck profile is too thin. I learned that one the hard way too, even putting them close to center.

As far as future adjustability goes; I don't think you have anything to worry about there. The graphite gives superior stability and adjustments are going to be fairly small. Even with maple necks I can put in more than enough relief.

[Mark Day]

Thanks Marshall. My 10mm estimation was a bit exaggerated! I modeled it up in Fusion 360 and spaced the channels for the CF rods 6mm from the center TR channel, which is about 1/4". I see what you mean about spacing them too far apart and running into them when carving the neck. That would suck. Good call on the round bottom slot for the TR. I'll use a ball-end mill.
My truss rod measures 11.5mm deep so I modeled a 14mm depth and was also planning to cap it with wood. I don't know if 2.5mm will be thick enough but I was afraid to cut the channel too deep.

[Marshall Dixon]

My truss rod measures 11.5mm deep so I modeled a 14mm depth and was also planning to cap it with wood. I don't know if 2.5mm will be thick enough but I was afraid to cut the channel too deep.

Capping the truss rod channel like that is how I was taught to do it. When I was building my 8th or so I thought to follow the suggestion that came with the truss rod and eliminate that extra step, and have the flat bearing surface of the rod up against the fretboard. There was considerable play in the middle of the rod in the neutral position and the offending note that caused the buzz was g, on 6th or 3rd strings. I did squirt some caulking in the channel as suggested and even tried removing the 5th fret and injecting more through a hole drilled in the fret slot.

The caution with the graphite bar is to set it in a hair too deep so you don't have to level it! There is some talk about setting it in as deep as possible for added strength, but don't feel that adds much and after my experience with it showing through (although it was minor) don't want to take that chance. I ground a chisel tip on an old file that I use on graphite to spare my chisels.

I don't have any hardware running through the nut/fretboard juncture, but with a Les Paul the tradition is having the adjustment nut in the peghead. Personally, I'd break with that tradition and put it on the body end.

[Mark Day]

I was still planning on having the adjustment at the headstock end but I am using the TR with the small Allen key nut so it requires a smaller cavity than the Gibson style adjuster nuts. I'm hoping between constructing the neck with a scarf joint and that smaller TR excavation at the headstock my LP's won't be as susceptible to the Gibson headstock breaks.