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CF rod to be or not to
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Author:  mikemcnerney [ Tue Nov 30, 2021 1:43 pm ]
Post subject:  CF rod to be or not to
What are peoples feelings about using CF rod anymore. I have used it in the past and was going to again, but isit out of fashion now?
Author:  doncaparker [ Tue Nov 30, 2021 2:08 pm ]
Post subject:  Re: CF rod to be or not to
Lord knows I'm no expert, but here is what I think, and it is derivative of things I have read (and agreed with) here on the OLF, particularly from Hesh:

Do you want the neck to be as stiff and unyielding as possible, or do you want the relief to be capable of fine adjustment with the truss rod? Those are different (and somewhat inconsistent) goals. If you want the former, then carbon fiber helps achieve a stiff and unyielding neck. But, of course, the truss rod has to work harder in a neck like that, if you need any relief adjustment. If you want the latter, then leave out the carbon fiber. The presence of the truss rod (if fitted properly) adds enough stiffness to the wood, and its adjustability allows you to dial in the right amount of relief.
Author:  jfmckenna [ Tue Nov 30, 2021 4:39 pm ]
Post subject:  Re: CF rod to be or not to
Once I learned about the engineering principal known as the neutral axis I stopped using them as according to that doctrine it's almost useless. They still might do something if placed off the axis but probably not enough to make it worth it imho of course. And one could argue that they would work against the action of the truss rod.
Author:  meddlingfool [ Tue Nov 30, 2021 5:43 pm ]
Post subject:  Re: CF rod to be or not to
IIRC someone said they only add about 10% stiffness, so not much change either way really.

I use them on one piece necks, but not to add stiffness. I run them out all the way through the face of the neck to stiffen the short grain and prevent headstock breaks...
Author:  Ernie Kleinman [ Tue Nov 30, 2021 5:52 pm ]
Post subject:  Re: CF rod to be or not to
I sometimes use cf squares on soft okoume, sycamore, or cypress uke necks to add stiffness an rigidity . If I was using mahog or walnut . for neck stock . No
Author:  Terence Kennedy [ Tue Nov 30, 2021 7:19 pm ]
Post subject:  Re: CF rod to be or not to
meddlingfool wrote:
IIRC someone said they only add about 10% stiffness, so not much change either way really.

I use them on one piece necks, but not to add stiffness. I run them out all the way through the face of the neck to stiffen the short grain and prevent headstock breaks...


Me too. You can run them out into the fretboard extension on an archtop to strengthen that area also.
Author:  Clay S. [ Wed Dec 01, 2021 8:51 am ]
Post subject:  Re: CF rod to be or not to
Carbon fibre rods might be a good idea for classical guitar necks made from Spanish cedar, where "light and stiff" is desirable.
It could replace the strip of ebony that is sometimes used.
Author:  Alan Carruth [ Wed Dec 01, 2021 3:04 pm ]
Post subject:  Re: CF rod to be or not to
A CF rod located on the neutral axis of the neck (just under the fingerboard surface) is primarily loaded in shear as the neck bends. The CF fiber itself is mostly strong in tension/compression, while shear loads are taken by the epoxy binder. Epoxy's not much better in shear than wood so the rod doesn't add much stiffness. However, once the neck starts to bend the fibers on the top and bottom of the bar can start to take up the load. In theory, at some point when the neck has bent enough, the CF is taking all of the load, and the neck will stop bending. So the rod doesn't add much stiffness, but it does limit the amount the neck will bend in the long term.

An adjustable rod, even the so-called 'Martin' aluminum channel rods, don't add much stiffness either, although they're better than a small CF rod. Tightening the truss rod actually seems to reduce the stiffness of the neck, in an effect akin to tightening a drum head, but in reverse. At least, that's what happened when I measured the effect in a 'free' neck, not bolted into the body and with no strings. There could be secondary effects: for example, if the neck bows up under string load, and you pull it back to straight with the rod, it could end up being stiffer because it's straight.

I gave in to temptation once and used a curly walnut neck on a 12-string. The B&S wood was also curly walnut, and it looked cool. The curl figure reduced the stiffness of the neck, and I had to remove the neck and fingerboard and put in some CF, as far below the neutral axis as I could, to stiffen it up. Not fun, but it worked.
Author:  Jim Watts [ Thu Dec 02, 2021 11:37 am ]
Post subject:  Re: CF rod to be or not to
I did an FEA analysis of a neck with carbon fiber in it as people typically install it several years ago and a 10% increase in stiffness seams about right if I recall.
Also just to note: carbon fiber is really on strong in tension, not compression.
Author:  Fred Tellier [ Thu Dec 02, 2021 12:28 pm ]
Post subject:  Re: CF rod to be or not to
I find carbon useful on necks for players who use alternate tunings as it reduces the twisting caused by changing string tension. The worst case scenario is drop D that reduces tension on the bass side and most of the strings are affected and need to be touched up. With carbon this is reduced and most players do not notice tuning changes on the other strings. I find the force to turn the truss rod is increased a bit but not enough to worry about.

Fred
Author:  ballbanjos [ Thu Dec 02, 2021 2:47 pm ]
Post subject:  Re: CF rod to be or not to
I used CF without a truss rod in most of my banjo necks, but the tension on a banjo neck is considerably less than on a guitar's. I ran the CF rod through the peghead for a little extra strength there too. I built a lot of banjos this way, and never had a problem. As an added bonus, it seems like the CF in the neck made the notes more consistent in tone and volume going up and down the neck without any dead spots like I've occasionally found with banjo necks with no CF. I'm not sure why this happens though.

Dave
Author:  Hesh [ Fri Dec 03, 2021 4:29 am ]
Post subject:  Re: CF rod to be or not to
It's not necessary only about 1,765,932,982,821 guitars have been built and been successful instruments without CF reinforcement. :)

It also depends on the implementation. We had one builder's nightmare product in our shop that the neck could not accommodate basic, seasonal adjustments with the truss rod. The truss rod could not over power the CF.... and that made the instrument impossible to set-up well without expensive and creative fret work. I'll add that a big box store person.... who attempted to adjust the truss rod before we got it stripped out the rod he/she had to tighten the wrench so much.

So I ask the question what problem is it that you are trying to solve? From simple string gauge changes to seasonal RH swings we need to be able to adjust our levels of relief.

If I was to employ CF in my builds (and I did too) it would not be in the neck and I would instead invest in the highest quality, double action rod that I could find and that passed my clamp-the-sucker-in-a-vice-and-wrench-on-the-adjuster-trying-to-make-it-fail tests.

By the way this is the season of thousands of guitars being brought into professional Luthiers because they got dry from heating systems turning on. One of the most common characteristics of a dry guitar is fret sprout, the ends get sharp protruding and the neck goes into back bow, the dome reduces and the strings come down onto the frets. Double action rod and zip, zam someone is on their way with a well playing guitar in 30 seconds. No double action rod........ sol time.
Author:  jfmckenna [ Fri Dec 03, 2021 8:32 am ]
Post subject:  Re: CF rod to be or not to
Big plus one on the double action rods. I used to 'build in' to the neck a double action using a single action rod by tweaking a back bow into the neck and leveling it. But with the double action rods it's all there.
Author:  mikemcnerney [ Fri Dec 03, 2021 9:19 pm ]
Post subject:  Re: CF rod to be or not to
I'm not that experienced and it just sounded good but Y'all have changed my mind. I guess I'll just make a kite out of my CF stock. thanks
Author:  Toonces [ Fri Dec 03, 2021 11:11 pm ]
Post subject:  Re: CF rod to be or not to
As mentioned, it doesn't strengthen the neck that much -- but I think that is a good thing as Hesh pointed out, you WANT the neck to be weak enough that a truss-rod can exert control. I use CF in my necks mostly for the headstock and also because the necks are just a bit stronger. In short, I feel like CF is worth the added cost/effort and because I use single piece necks. Structurally, I think laminate necks make the most sense but I don't like how they look.
Author:  Hesh [ Sat Dec 04, 2021 4:01 am ]
Post subject:  Re: CF rod to be or not to
Toonces wrote:
As mentioned, it doesn't strengthen the neck that much -- but I think that is a good thing as Hesh pointed out, you WANT the neck to be weak enough that a truss-rod can exert control. I use CF in my necks mostly for the headstock and also because the necks are just a bit stronger. In short, I feel like CF is worth the added cost/effort and because I use single piece necks. Structurally, I think laminate necks make the most sense but I don't like how they look.


This is what I mean and thanks for this Simon, it depends on the implementation and this is a good implementation. There is also added value here, how Simon rolls out CF of strengthening the headstock and they do break so this is good.

All I ask as a repair guy is that the truss rod is still 1) present...... 2) double action, 3) quality and 4) work. It's not for me either it's so your clients and mine get real value from those of us who call ourselves Luthiers. That's what really matter to me at the end of the day.
Author:  rlrhett [ Sat Dec 04, 2021 1:12 pm ]
Post subject:  Re: CF rod to be or not to
I’ve given up on selling my guitars, but I still have some friends giving it a go. They put them in.

CF reinforcements are like bound headstocks, “roasted” maple necks, and solid black fretboards. They add nothing to the guitar, but the customer demands them.


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Author:  Stuart Gort [ Tue Dec 07, 2021 10:22 am ]
Post subject:  Re: CF rod to be or not to
Attachment:
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If you have engineering experience using the stuff it becomes a LOT more clear when and when not to use it. Some of the comments in this thread are are grossly misleading about what carbon does. What kind of a statement is "it doesn't strengthen the neck that much" and "they add nothing" when there are infinite variables that decide that?

C'mon....I can design a neck with carbon that will break your kneecap before it bends one iota. I can also design a neck using carbon that will easily bend, balanced somewhat against the truss rod load. .

Carbon fiber in your neck alters tone. In a GOOD way...provided the piece was molded properly and resin to fiber ratio was CONTROLLED when making the stick. The volume of fiber and more importantly, the PLACEMENT of the fiber determines its bending strength. This neck is rigid like rock yet barely weighs anything. No truss rod here. Not that much carbon here. The carbon is being used quite efficiently here...and still there's room for improvement.

The point is that carbon fiber sticks are your limited way of using carbon fiber as a reinforcement or the main loadbearing material. If you could mold carbon you'd have an infinite world of potential iterations. If you can't mold it you have to rely on other people that mold it into sticks for you....not much control since you don't know how well it was processed. Sticks of carbon are of no use to me since I can KNOW what I have my hands is a more efficient use of the material. I control CF when I use it. I control everything about how it was processed. I control its density, strength, durability, ALL its mechanical properties when I process it.

When you buy sticks if carbon...you know relatively little about any of this. My advice to people enamored with carbon fiber is....learn more before you decide it's what you want forever in that neck.
Author:  Stuart Gort [ Tue Dec 07, 2021 10:55 am ]
Post subject:  Re: CF rod to be or not to
Once having mastered the basics of my methods...I won't use anything BUT carbon fiber in my electric necks. No adjustable rods from here on out.
Author:  Toonces [ Tue Dec 07, 2021 2:33 pm ]
Post subject:  Re: CF rod to be or not to
Hi Stuart,
Burton Legyt is doing something similar to you (not quite as advanced) with his necks and the idea appeals to me. I've also wondered what it might do to the tone - maybe good, bad, or indifferent and I simply wouldn't know until I tried it out on my guitars. My one concern tho' is over adjustability and it seems a truss-rods ability to dial in an "aspect of neck action" is a benefit to players. If someone wants to use light gauge strings or medium gauge strings -- well, the truss-rod will allow them to get a similar neck relief and it doesn't seem like your style of neck reinforcement would let that happen.

I'm curious about your thoughts on what I've said above. Regardless, I think your design and implementation work here is rather brilliant and creative !!!

Lastly, the comment I made about CF "not strengthening a neck too much" is a qualitative one - to answer your question. I'm assuming the traditional use of CF reinforcement alongside the truss-rod. IME and in that context, CF does add some strength but not so much that it seems significantly different. If an engineer asked the OP's question, obviously my answer wouldn't be appropriate but I think it is certainly useful in the context of this particular thread. You have a background and skill set that many of us don't have and experience with CF that seems quite innovative in terms of what it could do for luthiers. As such, I'm always quite interested to hear what you have to say in your posts. But remember - put out good vibes and you'll usually get positivity returned in some way.
Author:  Stuart Gort [ Thu Dec 09, 2021 9:38 am ]
Post subject:  Re: CF rod to be or not to
Toonces wrote:
Hi Stuart,
Burton Legyt is doing something similar to you (not quite as advanced) with his necks and the idea appeals to me. I've also wondered what it might do to the tone - maybe good, bad, or indifferent and I simply wouldn't know until I tried it out on my guitars. My one concern tho' is over adjustability and it seems a truss-rods ability to dial in an "aspect of neck action" is a benefit to players. If someone wants to use light gauge strings or medium gauge strings -- well, the truss-rod will allow them to get a similar neck relief and it doesn't seem like your style of neck reinforcement would let that happen.

I'm curious about your thoughts on what I've said above. Regardless, I think your design and implementation work here is rather brilliant and creative !!!

Lastly, the comment I made about CF "not strengthening a neck too much" is a qualitative one - to answer your question. I'm assuming the traditional use of CF reinforcement alongside the truss-rod. IME and in that context, CF does add some strength but not so much that it seems significantly different. If an engineer asked the OP's question, obviously my answer wouldn't be appropriate but I think it is certainly useful in the context of this particular thread. You have a background and skill set that many of us don't have and experience with CF that seems quite innovative in terms of what it could do for luthiers. As such, I'm always quite interested to hear what you have to say in your posts. But remember - put out good vibes and you'll usually get positivity returned in some way.


I'm not sure what vibe you mean. It isn't useful at all to describe "carbon fiber" without understanding it. With carbon fiber sticks that you buy....you didn't process it. It's black and it's shaped like a stick....and that's ALL you know unless you process it yourself and KNOW the fiber to resin ratio was controlled. There's crap to 100% efficiency based on PROCESSING alone.

If there IS control during the processing then you'll have something worthy of discussion.

Then, if you can't control the geometry of shape of the carbon reinforcement you are limiting what carbon will accomplish...in a major way. It's the POSITION of the carbon relative to any tension load that produces bending strength. Half of the carbon placed correctly (and molded properly) would accomplish more. You aren't using carbon fiber correctly if you take sticks someone ELSE molded and put them in your neck. You are putting something in there that you can't KNOW.

You aren't really using carbon fiber correctly if changing strings one gauge makes a noticeable difference in your playing action. I regularly switch. Of course, I raise the bridge if I need to. I never need to. The electrics are rock rigid but an acoustic may change a tiny bit...maybe. It depends on HOW you use the carbon near the neck block. What would be the shame of carrying an extra bridge if you needed to? I don't know too many players that switch string gauges often. Do you? I know a lot of players that like precisely what they like and never change.

Now, as far as two way truss rods go...fine...use them...but also...know the way that rod is going to bend YOUR neck. The adjustable rods you buy impart load unevenly...if one were able to measure it. Do you know precisely WHERE your neck is going to bend with any particular truss rod load? So that's a variable that must be understood even before a conventional rod does you much good. Do you build necks knowing precisely how a particular two way rod is going to bend it?

When I design a neck with carbon...the reason IS to get rid of metal in the neck. Properly processed carbon fiber WILL add a higher sheen to the tone. Highs will carry a bit further and will be brighter. This only when the fiber to resin ratio is tightly controlled. Ultimately....tone can be controlled to a great degree by processing carbon into its particularly efficient shape for THAT application.

Off the cuff I can think of about 10 cross sectional shapes I'd like to try just to compare the TONAL differences of carbon placement. I know already that a variant of the "T" shape offers the easiest to mold, and probably also has the best capacity to transfer tone directly from the fretboard to the carbon. Making the carbon sing....that's the next step in using carbon in guitars.....make it be TONAL. The material...processed correctly is QUITE ABLE to be a musical medium. Maybe better than wood in many respects. Not without control of the molding process though.

That means controlling the molding process AND controlling the SHAPE. No control otherwise. I'm sticking to the "grossly misleading" comment. You asked what I thought. That's what I thought. I've studied CF. I've studied it for almost three decades. I've been making custom cnc molds for nearly 25 years.

Carbon sticks don't make it with me. :) They used to add this TINY strip carbon down the middle of surfboards in Huntington Beach.....Jacks. In hindsight...carbon did nothing for the board but the use of the term "carbon fiber" CERTAINLY DID. I also managed one of my competitors in the field of propellers. That guy also used a tiny strip of carbon in his propellers...which didn't add a dang thing to strengthen it....but it DID sell them better. I grew up around people that didn't know anything about the stuff. I learned the stuff and it took a while. Once I learned 1/4th of what I know about carbon fiber I knew I needed the cnc/cad/cam ability to make custom molds. I'm saying you can't ever use it correctly without the ability to know the resin ratio of the finished part....that YOU shaped because you understood the the geometry of the part is at least half its strength.

You asked. If you don't like a "vibe" say what specifically you mean...because I don't know what you mean. I try to be clear when I write. The vibe you don't like may be..."learn why you do stuff before you do it" ...but I live by that (ex-flight instructor here - early death attends pilots that do NOT learn why they do things) and I find it generally works for everyone....in every endeavor.

Emmerson said, true genius is when what is true for you in your own heart is true for all men. Well...to that I say...people that use carbon fiber should understand it first.
Author:  Stuart Gort [ Thu Dec 09, 2021 11:25 am ]
Post subject:  Re: CF rod to be or not to
Ultimately, a "T" shape. The fretboard (using a cnc produced caul) glues directly to the top of the "T" prior to that assembly gluing into the receiving neck. This produces uncanny stiffness and DIRECT contact of the fretboard to the carbon.

My mind wonders about this tone. I already know how stiff and straight it will be. Max.
Author:  mikemcnerney [ Thu Dec 09, 2021 12:51 pm ]
Post subject:  Re: CF rod to be or not to
when I asked what I thought was a simple question I had no idea...Well I'm not going to use the CF "STICKS". It would be interesting to hear what Ken Parker would add.
thanks all for the input
Author:  Barry Daniels [ Thu Dec 09, 2021 2:54 pm ]
Post subject:  Re: CF rod to be or not to
Well, I am going to keep using carbon fiber bars. They work fine for me. I use two .092 by .220 bars from Dragon Plate. These are small enough to not be too stiff for the truss rod to function. Yet they add some stiffness and stability to the neck and seem to make it more resonant. One could cast doubt on their effectiveness since it is subtle, but they certainly do no harm.
Author:  rlrhett [ Thu Dec 09, 2021 3:04 pm ]
Post subject:  Re: CF rod to be or not to
Ken Parker apparently bladder molds carbon fiber into a hollow neck. Similar to what I assume Stuart is doing. I am anticipating his neck videos, but have so far been sitting through bowl gouge videos instead. :-(

I don’t think bladder molding carbon fiber into hollow necks is something many of us will try. Getting back to the ubiquitous little rods, I defer to Hesh who has serviced hundreds of guitars and generally is not a fan. That said, if I was selling a high end guitar I don’t think I could get away with not putting them in. I am pretty sure the people buying them could claim to smell the difference.


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