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Hi Folks

What size rods are people using in a steelstring as neck reinforcement?

I heard 1/4" x 0.200" is about right?

Thanks.

G.

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www.leddingtonguitars.com

IMO, that's too small to bother. Try 1/8" wide, and 3/8" or 1/2" tall. And glue them in with epoxy. This stuff is good and cheap if you don't use epoxy very often: https://hobbyking.com/en_us/ev830-20g-30-min-cure-clear-epoxy-glue.html

FWIW there seems to have been a spate of threads recently were the utility of CF rods have been questioned. Convincingly enough that I doubt I'll use them again. I don't know if you saw them, but if not you may want to do a search.


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I am sure to be in the minority, but I like smaller carbon rods. I use two rods that are .092" wide and 1/4" tall. If you go much bigger you will be placing stress against any adjustment of the truss rod. These smaller rods still add noticeable stiffness and stability to the neck.

ive only used it once and it was 1/4" tall.

i have a question for you. i´ve only added a CF rod once, long time ago. meanwhile that batch of epoxy has expired. would z-poxy finishing resin hold the CF rod in place or should i just order some new epoxy?

thanks!

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member of the guild of professional dilettantes

The epoxy may still be useable even after the date. I often use 2 to 3 year old glue even when the hardener has started to darken and thicken. Mix up a small test batch and see if it cures normally.

I missed that one. Anyone have a link? It sounds interesting.

Sorry to be a pain but i did a search and notthing specific came up? Do you remember the post(s)??

Thanks.

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www.leddingtonguitars.com

Gary here's one thread where someone.... introduces the idea that CF improperly applied can be a problem.

http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=47762&hilit=CF+rods

Now to be clear there will be stakeholders who won't like the idea of someone dissing routing additional slots, spending hard earned money on CF rods, and introducing highly dampening.... ep*xy to an instrument where we are supposed to be encouraging vibration. It's likely not what they want to hear.

But said with the BEST of Holiday Spirit from me, they can kiss my hairy butt..... BTW I'm joking about the kissing part so lighten up....

We've seen self inflicted issues by small builders attempting to add stiffness to a neck but instead making the truss rod work so very hard that it either breaks... or loses it's anchor. I'll add that a perfectly straight neck is not desirable and that's why skilled freternarians.... learn how to shape the fret plane at will.

Again as the contrarian here who only has repaired thousands and thousands of guitars that were not built well.... just exactly what problem are people trying to solve with CF rod augmentation in the neck? Only about 50,000,000 successful guitars have been built without CF rods and we're not exactly seeing the usual suspects and industry leaders embracing CF augmented necks either now are we?

OTOH do what ever you like I'll just make more money when your truss rods fail and someone brings it to me to adulterate anyway I wish..... BTW you should hear what owners say about builders when they have to pay us......

Please everyone this is a well intended, good natured post including the part about my hairy butt.....

Happy Holidays, Merry Christmas

Cool... thank you for the time spent replying... i shall endeavour to investigate further....

G.

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www.leddingtonguitars.com

Hesh, I’ll see your hairy butt and raise you...actually, nevermind

But I have heard of builders using epoxy to attach fretboards, on the theory that you don’t want to introduce a water based glue into that joint.

Are you suggesting that any anomalies introduced by water can be managed in the fretboard truing/fretting process?

Enquiringly minds need to know. About the fretboard. Not the butt

Thanks

Steve

Finishing resin is just that --- used for finishing, not building. Seeing as the person who asked about it is considering using it to hold in a neck reinforcement, my suggestion is to go get some West Systems epoxy and hardener and practice with it till comfortable with mixing and applying the stuff. Masking tape is your friend. We use West Systems stuff in aircraft fabrication; I trust its inherent quality.

A comment on parts fit, as applies to carbon fiber, don't install it with an idea that it can be trimmed down to size. Major effort required for that, better that the c/f fits completely inside of wherever it's going.

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Peter Havriluk

That's the spirit Steve! Good thing my camera is not charged up....

I used Titebond for my fret boards until I read about using a quality ep*xy such as West (a proud Michigan company...) and then I used West. Then my friend Link made a very good argument that ep*xy was pretty dampening and he didn't like it's use on fret boards. Link won the debate and I went back to Titebond.

I have to say that I never noticed a difference using either glue for fret boards.

Remember too as you know very well Steve we shape our fret boards on the neck and with the neck on the guitar before fretting. Any minor issues are milled out before fretting.

Anyway didn't mean to highjack or turn this into a glue thread. Just wanted to suggest that not everyone sees CF rods in the neck as actually providing any value at all and instead possible problems if we get it wrong. That's all I wanted to suggest.

I have used two 1/8” X 3/8” bars on almost all my guitars after taking the Fox course. Epoxy for fixation. I run them across the headstock joint for a little insurance there.

I usually level with some tension on the rod just to be sure I can get some relief. It seems like mainly the 12 fret necks are the ones that may wind up a little stiff if you don’t do that.

They sure don’t hurt the tone as far as I can tell and I can’t see them impeding any future repair issues.
I plan to continue to use them. I know some testing has been posted here that they do not actually stiffen a neck that much if at all but my experience suggests they do and I think that’s a good thing.

I epoxied a few fretboards after Rick Turner was pushing it here a number of years ago. I don’t think it had any discernible effect on tone but I had to remove one once for a failed weld on a brand new truss rod and it was a sticky mess. I quit doing it after that. Went back to Tightbond Extend and leaving it clamped up 48 hrs.

I think like so many other areas in lutherie lots of stuff works, and you pick your poison.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Well said, Hesh. It was just this thinking that led me to stop using CF rods in the neck. That said...

Did you notice those kids on your lawn? Somebody's got to do something about that!!! Right?!!!

Those rotten kids.....

I moved about a year ago into a condo as I transition to dotard status so no lawn anymore. But at my last house my neighbors called me (affectionately..) the lawn nazi..... I had the best yard and grass in the sub and I even striped it with my Gravely zero turn and on occasion during election season wrote obscene messages for the flights on final to Detoilet Metropolitan Airport.

One neighbor and dear friend would pick a dandelion from his yard and call me and send his boy over to stick it in the middle of my front yard. I had no weeds, not a one.... He would bet his wife money and other neighbors too on how long before I looked out the window and ran out and picked it up....

Yep I take hypertension medication.....

Most of the discussion in relation to cf rods/bars in necks seems to concentrate on neck stiffness but there could be other things going on. This is the last of Mike Doolin's articles on intonation (well woth checking them out here http://www.doolinguitars.com/intonation/intonation1.html):

"My Weirdest Intonation Horror Story

I have a client whose ears are a phenomenon of nature. She can hear intonation discrepancies that I have to strain to discern. This remarkable ability is both a blessing and a curse: she sings absolutely perfectly in tune, and tunes her guitars perfectly by ear, but little intonation discrepancies in her guitars drive her nuts! Having her as a client has motivated much of my investigations into guitar intonation. I'm happy to say that she's more satisfied with the intonation of her Doolin Guitar than any other she owns, and believe me, I had to work pretty hard to achieve that distinction.

She brought me a very nice Martin "M" model which she had played for years. She had taken it to a good repairman who had trued the fretboard, refretted the neck, and compensated the saddle, but it still sounded wrong to her so she brought it to me to see if I could do any better. I agreed that it wasn't playing in tune, so I did a detailed intonation study of every fret on every string.

What I found surprised me so much that I borrowed another Martin (a dreadnought) and did the same intonation study, with the same results:

All the strings were in tune at the 12th fret, and reasonably close at every other fret, except
at the 2nd, 3rd and 4th frets, the low E was quite sharp and
at the very same frets, the A was quite flat!

This completely blew my mind. I checked the fret placement, and it matched my precision fretting template perfectly. There was no excessive fret wear or neck warpage since the guitar was newly refretted. I tried several brand-new sets of strings and got the same results, from both guitars. How could different strings be out of tune in opposite directions at the same few frets, when they were both in tune above and below those frets? I would have thought that the fret would have to be slanted or staggered to accomplish that.

I did the same detailed intonation study of one of my guitars, and every fret played in tune, no exceptions. I'm not saying this to prove that I make a better guitar than Martin, I only mean to say that something I was doing saved my guitar from this anomaly that was common to both of the Martins I studied. So what was I doing different?

All I can do is speculate, but I believe that the problem was resonances in the necks of those two Martins. I inlay two strips of graphite in my necks, one on either side of the truss rod. Graphite is about 15 times stiffer than wood for the same amount of material, and stiffer means higher frequency. I speculate that the Martin necks had resonances close to the notes that were playing out of tune, and that those resonances were pulling those notes sharp or flat. I knew that graphite would make my necks more resistant to warpage, and had noticed that it prevented "dead spots" as well - every note on my guitars has about the same tone color and sustain. I think that the graphite also raises the resonant frequencies of my necks above the fundamental frequencies of the notes on the neck. Since the neck doesn't sympathetically resonate with any note more than any other, it doesn't sap away any energy, and it doesn't drag the pitch of any note away from where it should be.

At least, that's my theory. The use of graphite as neck reinforcement has become pretty commonplace, and I was happy with the results even before this weird intonation experience. Now I'm even more sold on it. "

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Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

Tunings can move quite a lot, up to 30 cents on responsive guitars IME, when two resonators (e.g. string and box) over-couple. This is one of the challenges when making responsive guitars: how to get them both responsive and to play accurately in tune all over the fretboard, and is one of the reasons modal tuning is important (and why "good" responsive guitars are quite rare). Coupled resonances tend to "repel" each other in frequency, so a string trying to vibrate at, say 98 Hz (low G on a guitar) coupling with a main air resonance at 97Hz will tend to push the string frequency higher and the body frequency lower. All the maths and physics supporting that are in the book (or Fletcher and Rossing or any other decent text on the theory of vibrations). This manifests itself exactly as Dave has quoted Mike Doolin, and in the example above, notes closely above G would tend to play sharp and those below G would tend to play flat, depending on the degree of over-coupling. But rather than being an issue with a neck resonance, it is much more likely to be an issue with a body resonance, seeing as the main air resonance on most guitars sits somewhere between 90Hz and 100Hz and is very active. Neck resonances are typically in a different frequency range and tend to be much less active, so aren't normally a problem.

Regarding CF rod sizes, some time ago I did an analysis on the extra stiffness imparted by using two CF bars (3/8" deep by 1/8" wide iirc) fitted just below the fretboard and it increased the neck stiffness by ~9%. It's easy to find a 9% stiffness variation in the Young's modulus of wood, or by slightly varying the fretboard thickness. That's not to say do or don't use CF in a neck, but think hard about what outcome you're trying to achieve. In most cases an adjustable truss rod works just fine and is all you need. However, if you use an unusually small transition radius between the neck shaft and the heel, you might need something to support that...

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Did you run the bars across the headstock joint into the peghead Trevor? When I started doing that I noticed a definite increase in stiffness manifest in more difficulty getting relief at initial string up. Most notably on 12 fret necks. leveling the fretboard with some tension on the truss rod helped with that.

The theory taught to me which may be deemed simplistic by a real physicist was that a stiffer neck absorbed less energy from the vibration of the top and had a positive effect on sustain and tone. I know the late Bill Collings put steel bars on either side of the truss rod citing that reason.

For whatever reason the way my guitars sound has been a very good selling point. It's probably a million little things combined but rightly or wrongly I plan to stick with the bars and not rock the boat plus I've got a few to use up!

If I was using the old Martin/Gotoh box channel rod epoxied into the neck I probably wouldn't use bars. It does not seem that the Blanchard rod I am using now imparts that much inherent stiffness outside of the adjustability.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

What I did was an analysis of the flexural rigidity (Young's modulus of the combined materials x second moment of area of the combined materials) at a section through the neck.



What seems to matter is that you want the wave in the string to be reflected (rather than transmitted) at the neck end, so more energy is available to produce sound at the body end. The larger the mechanical impedance mismatch between string and neck, the greater the amount of string energy reflected. Impedance is proportional to SQRT(mass x stiffness) so either (or both) of increasing mass and stiffness will get to a greater impedance mismatch. However, given the general nature of guitars, it tends to be the increase in mass that does the heavy lifting (if you'll pardon the pun) with regard to increasing the impedance. In the Bill Collings case you quote, the increase in mass due to the steel bars will be having more effect than the (marginal) increase in stiffness he obtained from adding the steel, likely quite close to the neutral axis where it will have little effect on stiffness. But the mass is always there.



The adjustable truss rod typically supplies mass and adjustability. It's a device to induce deflection (one way or the other) rather than stiffness. In its neutral position, it supplies only mass, because it carries no load.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

I stopped using CF bars in the entire length of the neck. I do still use them to renforce the peg head to neck shaft transition area. I've had a couple necks break in transit at the nut but since I've used CF in that area, no neck breakage due to the shipping gorillas

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tim...
http://www.mcknightguitars.com