CF rod reinforcement query

Kalimna

Greetings folks,
For my upcoming uke and bass builds i think I'll use some CF reinforcement in the necks.
However, i'd like some advice regarding cross-section dimensions, please, if anyone has used it.
Cheers,
Adam

WezV

What do you need to know?  I have used quite a bit, solid bars and hollow rods for the most part.

are you adding them for stiffness, stability, or tonal reasons?

Kalimna

Ok, i would be using them in place of truss rods for the ukulele, so primarily stability there. And for the bass (with probably a 30" scale, following advice given in an earlier thread), a combo of stability and stiffness. In neither scenario would the main reason be tonal.

 If it makes any difference the bass will have a rippled maple neck and ebony (boy, this ebony is stunning) on an alder body. Hadnt planned on it, but am quite happy to laminate the neck with purpleheart or simillar. The uke will have necks of ash, afromosia or hornbeam (havent decided yet) onto a hornbeam B&S via a butt joint.

I was planning on using a rectangular cross section rod, but i dont know (despite googling) what dimensions to aim for (depth x width).
Cheers,
Adam

WezV

For a truss rod replacement you want a minimum of 6x8mm solid bar down the middle.  That will be enough on a uke, guitar or bass would need a little more

if you are putting rods either side of a truss rod on the bass I would go with a lower profile.   You don’t need a lot here and it’s possible to make the neck too stiff if also laminated.  Stiff enough that the truss rod doesn’t respond as much as normal 

i tend to use solid bars on modern guitars, and hollow rods when I want to maintain more vintage tones.  The hollow rods don’t add much stiffness, but seem to even out the tension in the neck and keep it predictable.   I am planning to try hollow square bars at some point too

WezV

For a truss rod replacement you want a minimum of 6x8mm solid bar down the middle.  That will be enough on a uke, guitar or bass would need a little more depth

if you are putting rods either side of a truss rod on the bass I would go with a lower profile.   You don’t need a lot here and it’s possible to make the neck too stiff if also laminated.  Stiff enough that the truss rod doesn’t respond as much as normal 

i tend to use solid bars on modern guitars, and hollow rods when I want to maintain more vintage tones.  The hollow rods don’t add much stiffness, but seem to even out the tension in the neck and keep it predictable.   I am planning to try hollow square bars at some point too

Kalimna

Thats great info  thanks WezV. Regarding the ukulele, my previous 2 builds had no neck reinforcement, and seem to be ok. Would the 6x8mm be the minimum you advise? I am just thinking of available space in the neck.
Cheers,
Adam

WezV

No, use don’t need anything really do whatever you add is going to help.  It would be a good choice for a Uke, but not an essential one

  6x8mm is the minimum I would use for a truss rod less guitar neck, assuming it was a short and stiff neck not expecting a lot of tension

layout is important too.  Two bars either side of a truss rod can either be parallel to the truss rod, or parallel to the sides of the neck.  The second option is more difficult, but a bit more stable.  I normally go with the first.  Most importantly, don’t go too close to the edge of the neck as it limits your carve options

if you buy some 6x6mm bars for the bass you could always use two offcuts in the uke neck either side of the centre line, rather than a single central bar.

Kalimna

Cheers for the advice again, giving me a baseline to work from. If i can sort a jig out, rods parallel to the edge seems the way to go.

Ta,
Adam

Sporky

I put some CF square tubes into Sporkbass 1's neck - 6mm square but with a round hole through the middle. It works fine, but I have no real point of comparison.

So probably not a useful answer.

Kalimna

No, thats all good advice. Having 6 home built necks under my belt, and no basses, i am after a starting point. Fine tuning and repeatability of 'tone' can come later I just want them to work.....

Adam

Kalimna

Greetings again folks,
Having taken onboard the above advice, I am struggling to find somewhere that supplies the 6mm sq rod in non-astronomical prices.
Where might I find such CF rods?
Cheers,
Adam

WezV

http://www.easycomposites.co.uk/#!/cured-carbon-fibre-products/carbon-fibre-box-section/carbon-fibre-box-section-6mm-4mm.html

Kalimna

Ahhh. I was looking for *solid* core square cross-section, not box-section. And easycomposites don't do the 6mm solid square...

Many thanks, again, WezV,
Adam

WezV

that's okay, obviously it costs more for solid  it but  its out there - comparable prices to the guitar parts suppliers

https://www.carbonfibreprofiles.com/index.php?main_page=index&cPath=7_155

Sporky

I think that's the stuff I used in SPB1. 

Kalimna

That's about half the price of luthier supply stores that I found via Google. Anyway, a quick trip to the Easycomposite site it is.
I assume there is minimal loss of strength using box vs solid, in the context of a bass neck?
Adam

Sporky

The stiffness of a box section is the stiffness of a solid rod if the same outer dimensions, minus the stiffness of a solid rod of the inner dimensions.

Which makes it hard to answer, because it depends very much on the wall thickness. 

Kalimna

Excuse my continued ignorance, but im assuming that, in the context of the neck, the reduced stiffness is ok?

Sporky

The question is whether it's stiffer than the timber. 

GSPBASSES

I stop using carbon rods many years ago. Quite often I found that they stiffen the neck far too much, where it become almost impossible for the truss rod put in a small amount of relief in the neck. It was far worse using the old-style one-way rods. I find the best way to make sure you have a good neck is to use a multi-laminated neck blank, were all the wood is quartersawn. A lot of the basses I've built in the past were double octave five string 35 inch scale, with all 24 frets more or less outside the body, none of which ever had problems of not being stiff enough. Could not answer the question whether carbon rods change the sound or even affected the sound of the neck. I would not fit carbon rods in a guitar neck that's Gibson or Fender scale. I believe Fender started to use carbon rods in their bass necks . These bit different from the normal shape of carbon rods. They were round but tapered in the centre, this allowed for the neck to have a small amount of relief, not sure if they still do it.

Kalimna

Hmmm, and that rather depends on which timber is being used, doesnt it?
Thing is, i dont have time (3-necked ukulele plus bass guitar for Chrimbo) to get it wrong, so am trying to cover everything before I start.
So. Should I just go with the box section and hope for the best (rippled maple for bass neck and maple or afromosia for uke)?

Cheers,
Adam