Are carbon fiber bars/rods worth it?

Discussion in 'Luthier's Corner' started by Low8, Apr 23, 2019.

  1. Low8

    Low8 Supporting Member

    Mar 30, 2014
    Several years after they've been in use, what is the general opinion of carbon fiber/graphite stabilizer bars when used in maple necks? I'm sure they help in the stabilizing process... but do we think they're really worth the expense?

    When most carbon fiber I've been around is thin and narrow in shape, it flexes fairly easily in human hands. I'm wondering if the constant movement of a maple neck in temperature and humidity changes wouldn't simply move these bars with ease... and thus, rendering the bars ineffective.

    Does anyone have any information or examples on the bulk/strength of the carbon fiber weave used in stabilizer bars? I'm sure it's beefier than some types of weave.

    I recognize I'm walking on a well-trodden path... but is there a better mousetrap to achieve the intended result of stabilizing a Fender-style neck?

    Thoughts? Opinions? Thanks!
  2. T_Bone_TL


    Jan 10, 2013
    SW VT
    Some collected background reading. Pay attention particularly to Bruce Johnson's posts. He's not much of a fan of the rods, as you'll find out. But, in essence, you are comparing how an isolated strip of material behaves and (mis-)applying that to how it behaves as part of a system. The way that carbon fiber helps necks (when properly applied) is by being very strong in tension (which it's extremely good at) near the backside of the neck beam (which it's only a small part of.) Large portions of the "usual bars" are doing bleep-all as typically applied, but if a small part of them is near where the carbon is useful, they work anyway. A small amount of carbon, embedded in epoxy, at the right location, works just as well, per lots of years of Bruce's experience which he's been kind enough to share.

    Reasonably Priced Source for Carbon Fiber Rods?

    Less expensive carbon fiber reinforcement

    My Les Paul Bass Build - I need a Gibby too...

    Winter build off 2019 – Two Birds of Different Feathers


    I don't know that any of the typical reinforcements use weave - the cross-ways stuff would be wasted. Some folks have mentioned using tubes, which may be spriral-wound or diamond-weave patterns. "The Church o' Bruce" uses TOW, which is entirely unidirectional, and the 24K TOW I have a big roll of rather tediously calculated out to being something like 836 lbs of loading for a single ribbon. Given that even my upright is only putting 250-300lbs on the string side, plenty (IIRC Bruce mostly uses 12K which is likely about half that (slight variance for different particular products) but still far more than any set of electric strings I can think of having looked at the tensions for put on the front-side of the neck.
    Last edited: Apr 23, 2019
  3. Beej


    Feb 10, 2007
    Vancouver Island
    I've used carbon fiber spars quite a few times. The ones I used were really stiff, and would hardly deflect at all under my attempts to bend them. I cant see how humidity changes would overcome the ones I've used. Most of my necks nowadays are multilaminate plus have reinforcements so mine are probably overkill anyway. :D

    I've used narrow aluminum spars in a few necks now too, and those seem equally stable, and way cheaper. :)
    MattZilla likes this.
  4. HaMMerHeD


    May 20, 2005
    Last edited: Apr 24, 2019
    Dadagoboi likes this.
  5. What I don't like about most carbon rods is you have a butt joint at the end of the channel somewhere around the nut. While the rods adds strength to the neck along the length of the rod it creates a weak spot at the end where it often has epoxy filling the gap between carbon and wood. Ultimately I'd like the rod to extend into the headstock or be part of a lamination though that opens up issues with shaping and finishing if any of it is exposed.

    I think it might be more practical to run it in the underside of the fingerboard than in the neck wood.
  6. Gilmourisgod


    Jun 23, 2014
    Cape Cod MA
    I have only anecdotal experience on two basses, one a two piece maple laminate, the other a 5 piece walnut/maple assembly. Both have two 1/8" x 3 /8" pultruded rods set either side of a DA trussrod. The two piece has been done for over a year, so its been through the full range of seasonal changes. So far the neck seems very stable, i havent had to adjust it once since initial setup. I’ll admit I Drank the Coolaid on CF rods, and so far it seems to have worked, or at least done no harm! Bruce has made an exhaustive study on the subject, so I’ll defer to his expertise, but as an "insurance policy" of sorts, they seem to have worked for me.
    Last edited: Apr 24, 2019
    Huw Phillips likes this.
  7. Huw Phillips

    Huw Phillips Life is like TV if the channel sucks change it Supporting Member

    Jan 4, 2019
    I put a strip in below my truss rod and it seems to have worked out, it was very little effort and expense, I went the Bruce route, I routed a channel painted epoxy placed the carbon fiber and flooded the channel with epoxy, leveled it with the router and placed the truss rod then the fretboard, some folks put a strip of wood on top of the carbon I saw no need.
    A very kind TBer let me have a 6 ft piece of TOW enough for 2 necks thanks if your reading this
    Gilmourisgod likes this.
  8. In rod we trust!

    aproud1 and MYLOWFREQ like this.
  9. T_Bone_TL


    Jan 10, 2013
    SW VT
    From a structural engineering standpoint (which, in its small way, is what we are doing here) that's just about useless. Why? it's on the compression side of the neutral axis (do an image search, I'm not going to draw it) of the neck beam. Carbon fiber is nothing special in compression - most of the compressive strength in use is that of the epoxy it's bedded in. Of itself, you might as well be pushing on a rope. Carbon fiber excels in tensile strength, which is why locating it near the back of the neck beam, where the tension is, is so effective.
  10. MPU


    Sep 21, 2004
    Valkeala Finland
    In Bruce I trust!
    I’ve made three necks with Bruce’s truss rod design and they are so far the best sounding and behaving necks I’ve made. Carbon tow under the truss rod really works and works better than bars under the fretboard.
  11. Carbon fiber is not added for its tensile strength unless you play gigs at a zoo and gorillas try to pull headstocks off. Modulus of elasticity is what you should look into. That's what Modulus named their company after.
  12. 5tring


    Sep 16, 2018
    Can’t resist an engineering conversation!

    It is true that the fretboard side of the neck is in compression, but a carbon/epoxy composite rod under the fretboard will still act to resist the deflection due to bending more than the equivalent piece of wood you have removed in order to fit it (as long as it is bonded in properly) You cannot decouple stress/strain from bending deflection. Overall you will have increased the modulus of your neck by fitting a carbon rod in this way. Even if you centred it on the neutral axis it would still have some effect due to its own thickness, although that would be a daft place to put it.

    What Bruce does is definitely more elegant (in the engineering sense of the word) because it puts the carbon material in the position where you get the most ‘bang for your buck’ in terms of ‘increase in stiffness per expensive strand of carbon’, but routing a channel either side of the truss rod and gluing in some carbon rods is such a simple exercise I would say it is a good compromise.
  13. Kubicki Fan

    Kubicki Fan Supporting Member

    Oct 3, 2014
    CFs are no guarantee against dead-spots.
    Spirit of Ox likes this.
  14. Spirit of Ox

    Spirit of Ox Supporting Member

    Feb 2, 2012
    Chelsea Mass
    The Warmoth necks use steel but have an option for graphite. I had a used one once but it didn't fit the body quite right so I sold it. Killer sound and stability but it definitely added weight and I'm sure it did something extra to the tone.
  15. Spirit of Ox

    Spirit of Ox Supporting Member

    Feb 2, 2012
    Chelsea Mass
    I always hear MIA Fenders have dead spots and they are using graphite reinforcement. Warmoth states that graphite won't eliminate dead spots but the steel reinforcement will.
  16. 5tring


    Sep 16, 2018
    This ‘dead spot’ thing is a bit of a mystery to me never having experienced it, but I guess it’s a resonance thing. In which case adding stiffeners will change the stiffness and the mass, both of which affect resonant frequency. I suspect it’s quite hard to design.
  17. Tim Skaggs

    Tim Skaggs

    Sep 28, 2002
    Consider yourself lucky not to have dead spot experience. It's not something you want to become proficient at recognizing or you will notice it much more.

    It is definitely a resonant frequency thing where a note is at or near the resonant frequency (or harmonic of Fr) of the neck / body unit. Playing that note puts the neck / body in sympathetic vibration that kinda soaks up the energy of the vibrating string. Use of stiffening material in the neck is one of the methods to attempt to reduce the vibration, which I'm sure helps in most circumstances, but is not a 100% solution.
    Kubicki Fan likes this.
  18. GMC


    Jan 1, 2006
    Wiltshire, UK
    I think it really depends on what material you are making your bass neck from and how wide / how many strings it's going to hold. I personally think that maple is a really bendy wood material. So yes it REALLY benefits from an old style aluminium U channel truss rod or a pair of carbon graphite rods. If you are making it out of pure wenge...less so. Purple heart...even less so. Wenge and Purple heart are some of the most rigid and unflexing wood materials I've used, it's astonishing how little they move under string tension compared to maple.
    I built a 34" scale 6 string bolt on with a single truss rod (shocker) and no carbon rods (more of a shocker) and it's very stable. The neck was a 5 piece laminate with a wide Purple heart center laminate, wenge laminates either side and then the far edges made from maple. The fingerboard was a thick slab of wenge. It looks great and is really stable. I think it might have been a little more stable if I'd used a pair of carbon rods but it's pretty stable and barely moves tuning from week to week. In this image, you can see the rod installed with the maple fillet.
    Kubicki Fan, BritFunk, 5tring and 3 others like this.
  19. Kubicki Fan

    Kubicki Fan Supporting Member

    Oct 3, 2014
    I think my Warmoth neck probably didn't benefit from having CF in it. It's an upcharge that has dubious value. I'd rather have a quarter sawn & laminated neck than one with CF in it. The only deadspots I ever encountered are in my Warmoth neck (half sawn roasted maple with CF reinforcement). I must say for Warmoth though, everythig fits with microscopic precision and aside for the "deadspot" on the 9th fret on the G string every note sustains like crazy. So, I won't throw the baby out with the bathwater.
  20. Kubicki Fan

    Kubicki Fan Supporting Member

    Oct 3, 2014
    It is a crap-shoot, nature of the beast. QC can catch it in a fully assembled bass but when buying parts basses it is a possibility. G&L has never let me down and even the cheap SX jazz and Chienese Squier don't have deadspots either.
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