# Instruments and Equipment > Builders and Repair >  carbon fiber instead of truss rod

## papawhisky

I am a player looking at the purchase of a mandolin made with a carbon fiber insert instead of a truss rod.  I'm sure I would wish I could make adjustments to the neck if time were to alter the shape of the neck.  
Is there something about this approach that obviates the need to someday make adjustments?

Thanks!
Papawhisky

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## MikeEdgerton

While you're waiting for an answer take a look through these threads. The applicable topics will be apparent.

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## markishandsome

"Is there something about this approach that obviates the need to someday make adjustments?"

The short answer is yes.  The fiber rod is so stiff the neck should never require adjustment.  Nothing lasts forever of course.  But even a neck with an adjustable truss rod may someday need to be reset or replaned, they don't "adjust" all that far.  It's really a question of what makes you comfortable.  I personally have never felt the need to adjust a truss rod on any instrument I've ever owned, so I wouldn't miss that feature.  YMMV

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## papawhisky

Thanks for the threads.  I actually did a search before I posted but didn't come up with the truss rod vs CF thread.  
Thanks again, I learned what I needed to know.

Papawhisky

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## Stephanie Reiser

_I am almost ready to stain my first CF stiffened mando, and maybe I can give a report in a year or two. I have never had to adjust a trussrod, either. I finished an F-4-type with no trussrod or stiffener at all and the neck is performing nicely. Seems to me that the trench for the TR just weakens the neck, but I am no professional. Most mandos, though, have adjustable TRs. If you are wondering whether or not to order one or buy one with CF for a stiffener, I would not hesitate. I know of at least one full-time professional on this board who uses CF exclusively. In a couple of weeks I will be starting a 12-string guitar with a double CF stiffener laminated neck._

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## Nick Triesch

I have adjusted trussrods in the past on some of the mandolins I have owned.  I was really glad I was able to tweek the neck just a tiny bit to take a little dip out.  Plays like glass.  The thing that sells me on the adjustable truss rod is that most all the great builders out there use this feature.   That just tells me a ton right there.  When I was a pup Martin guitars did not have an adjustable rod.  We all know how hard they were to play.  It was a joke when I was a kid that Martin's played great on the first 5 frets!  Even the salesmen at the top L.A. guitars shops would tell you that!      They all have the adjustable neck now!  Nick

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## Rolfe

There is no comparison between a guitar neck and a mandolin neck.  Out of over 300 mandolins built with a CF bar only three have come back to be releveled and refretted; that's 1%, and it was done at no cost to the owner.  There were far more problems with truss rods in the Unicorn mandolins.  After seeing how well CF worked in the Phoenix mandolins, Rigel adopted them.

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## kestrel

"Seems to me that the trench for the TR just weakens the neck..."

Amen.

Cut away a enough wood from a mandolin size neck, and you're definitely introducing the need for something to take out the bends from the now weakened wood. What's the truss rod going to do for a wind or side bend? A properly sized and installed CF bar will resist stresses in all directions. I can see the desirability of a truss rod in longer necked instruments, but even then, it would seem that CF used used _along with_ the TR would be beneficial in counteracting the other directional forces.

Gene

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## Steevarino

I don't know about that.  If you cut out the trench, and then back-fill it with a steel rod, and maybe a wood filler strip on top of that, I don't think it is weakening the neck.  The weak area, to me, seems that it might be the area you have to clear out around the truss rod neck (on the peghead area) so you can get a wrench around the adjusting nut.

Another issue with this is what the customer thinks.  I get asked quite often if my mandolins have a truss rod in them.  I think that, esp. with such a short neck, one is not really needed.  However, if I were to go "truss-rodless" I feel that it would bring up all kinds of concerns with some potential customers.  Now, there's a poser, eh...?

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## amowry

So far my experience has been the same as Rolfe's-- With the 30 or so mandos I've built with CF, the necks have been consistently better than my previous ones with trussrods. By "better" I mean that the relief is always where I want it, the necks are noticably stiffer, and they've shown no signs of changing over time.

I still offer trussrods at no extra cost, but no one has taken me up on it yet.

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## Nick Triesch

I think that if folks put out thousands for a cool mandolin that they want the ability to adjust the neck just in case it gets a little out of wack.  My Weber Fern is 5 years old and a few years ago it seemed a bit hard to play.  I took it to our local high end shop and the repairman said it just needed a little adjustment on the truss rod.  So I went home and took out my handy wrench and it's been perfect ever since.  I think it is a great invention.  My 1923 Gibson neck is still straight as an arrow!!! Just got a comment on that the other day at Old Time Music in San Diego.  My point is.....it has worked for 86 years.       Nick

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## markishandsome

I wonder: if CF had been discovered before the adjustable truss rod was invented, would we be having this conversation?

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## amowry

I'm certainly not saying that I think there's anything wrong with trussrods, and I agree that there's something to be said for tradition. Different builders also have different results with the same materials and techniques. I'm just saying that for me cf has yielded better results, and there's something to be said by the fact that more builders (and some of the best, not that I put myself in that category) are switching to it. It also corresponds better to my overall approach to building instruments that are stiff yet lightweight.

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Karl Hoyt

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## kestrel

Hlo Steve. How goes it?

If you cut out the trench, and then back-fill it with a steel rod, and maybe a wood filler strip on top of that, I don't think it is weakening the neck. The weak area, to me, seems that it might be the area you have to clear out around the truss rod neck (on the peghead area) so you can get a wrench around the adjusting nut.

Im assuming that by backfill it with a steel rod, youre referring to a truss rod. Ive never used a truss rod, and I havent built all that many instruments, so Im certainly not saying that Im an expert. But, the reason I dont use truss rods, is that I cant make myself believe that by taking a quarter of the wood out of a piece thats only 1-1/16 to 1-1/8 wide, and between ¾ and 7/8 high/thick (including fretboard thickness) at the nut, and not much greater than that halfway down the neck isnt weakening the neck. I cant see that a free-floating rod in the channel, even with a filler strip on top, will do anything but little to re-strengthen that narrow piece of wood. And, I certainly agree that hogging out the quantity of wood needed to give access to the adjusting nut in the already weakened bend, weakens it even more. Im sure that this horse has been kicked well beyond recognition, and I dont mean to belabor the issue, but the natural internal stresses in a piece of wood, unless reinforced by something capable of resisting those stresses, will move in the direction it wants to move. Removing a significant portion of that wood, and the stresses has even less to keep them from moving. Just watch a piece of wood close tightly behind the blade as you rip it on the table saw. IMO, a small steel rod, floating in open space, is not going to have much effect on those forces. A solid steel bar (or, as I prefer, carbon fiber), filling that slot, and glued tightly at all points will. No movement  no need for a mechanism to counteract movement. 

As far as being concerned about what clients want, I guess Im lucky in that respect. Being retired, and having done the Yassuh boss thing for fifty-years, I build my instruments purely and simply because I love to. I build an instrument. If someone wants to buy it, Ill sell it to him or her. If someone wants me to build them an instrument, and asks, Do you use a truss rod? I attempt to educate them into my way of reasoning. If I can do that, I build them an instrument. If I cant, I tell them about all of yall. Retirement and an independent attitude is a wonderful thing, but I can certainly understand where yall are coming from.

Truss rods? Carbon fiber? Steel bar? I suppose good and bad can be said in all directions. For myself, The Model T was a wonderful thing for its time. A Lear Jet will get you from New York to LA much faster, and far more comfortably. Ill stick with CF, unless somebody can convince me otherwise.

Gene

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## Craig Norconk

Carbon fiber so easy to install .20 in wide CF bar is the same width as a Circular saw blade, cut the trench, little routing with a 1/8 inch drill bit, some west system epox done.  It made the truss part of my first personal designed Mando easy.  Glad to have read this thread.....it confirmed I did the right thing.

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Rob Zamites

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## peter.coombe

My experience has been the same as Rolfe.  100 mandolins and mandolas made with CF in the neck, one has come back so a problem rate of 1%.  That one I see regularly, and after a re-levelling the neck has remained straight, and that was about 5 years ago.  The customer uses heavy strings and plays it hard.  I think a lot of hoo ha is talked about with CF.  Yes a truss rod will allow neck adjustments (how often do you adjust a trussrod? - probably never), but a truss rod is likely to make it more likely you will need the adjustment, and in some cases even a neck replacement.  Some customers are misinformed, and I can put that right, others are just plain stubborn.  The stubborn ones go away, which is probably a good thing for me since they are probably stubborn about other things as well.  I have only ever used a truss rod once, in a longer scale mandola, and in that case I considered it to be necessary because of the longer neck.

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Rob Zamites

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## Rick Turner

I'm an early adopter of using carbon fiber, and I've remained a believer now for 33 years, though I use the stuff differently than I did at first.  For longer necks, I do like the ability to adjust, but for short ones like mandolin necks, I think we can put just the right relief into the neck, fingerboard, and fret tops and simply be done with it.  And besides all that, I believe that CF makes necks "sound" better.  The necks are stiffer and more neutral tonally, and they suck less energy out of the strings.  Just my opinion...

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Rob Zamites

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## Nick Triesch

When this topic came up a few years ago I went to the "eye candy section"  of the Cafe and was blown away by all the super builders that use the adjustable truss rod.  Really,  check it out.  Rick you just crack me up!   Yep it's terrible how all the energy has sucked out of all those Nuggett,  Apitius, Gibson, and so on mandolins!!! My old Gibson Snakehead sounds so wonderful the energy must have sucked the other way on that one.    Nick

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## Michael Lewis

Many makers follow tradition because that is what the market demands.  It just has to have a red spruce top, or varnish, or a truss rod, or whatever the current fad is.    I use red spruce because it is easier to sell than sitka spruce, though it doesn't necessarily sound any better.  I also use engelmann, sitka, and redwood as I see fit.  

Peter Coomb's remark is right on, neck with a truss rod will more likely need adjustment than a neck with CF reinforcement, if installed properly.  Over the years I have made 100+ mandolins,  only a handful with adjustable truss rods, the majority with CF reinforcement, and a few with square steel tubing and of all these I have never had to adjust a CF reinforced neck but have had a few problems with the adjustable ones.

I'm considering adding an adjustable rod to my future necks due to the market bias, even though I know it will mean a heavier neck, a weaker headstock, and a few more problems to deal with down the road.  It makes me feel like I'm selling out to my better judgement, but it will help sales.  You want chrome reversed Waverlys?  Tuned and balanced inlays?  Ported, polished, and turbo charged tuner buttons?  Hey, I'm yer guy. :Cool:

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## kestrel

"Yep it's terrible how all the energy has sucked out of all those Nuggett, Apitius, Gibson, and so on mandolins!!!"

And, who's to know they wouldn't sound _even better_ with CF instead of the truss rod? Hmmmmmm.

Great conversation, but I've got a third fret dot to tune on the mandola that's under way.  :Grin: 

Gene

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## Dave Cohen

I've seen numerous mandolins in my shop for setup/repair by now.  I've seen vintage mandolins without truss rods, and vintage mandolins with truss rods.  For the former, some had perfectly straight necks, while others had severely bowed necks.  For the latter, the same was true.  For those vintage mandolins with severly bowed necks and truss rods, adjustment worked in some cases, but didn't work in other cases; either the rods were adjusted as far as they would go, or the neck wood was just too inhomogeneous for the rod to eliminate all of the the humps and dips.

Of the newer mandolins that I have seen in for repair, some had remained acceptably straight without adjustment, and some needed adjustment.  Of those that needed adjustment, the rod did the job acceptably for some, while others retained humps and dips no matter what was done with the rod.

All of the above points to significant variation in the properties of neck woods, even within the same species of wood.  The remedy is either to select the wood based on measurements of Young's moduli, or employ some method of stiffening.  If a luthier can not afford to reject more than half of his neck wood supply, that leaves the stiffening methods.  I first used two parallel 1/8"x3/8" CF rods just under the fingerboard.  The necks on most of my mandolins build with that system stayed straight, with the exception of one or two that moved a bit more than I would have liked.  I have since changed to a different configuration of the CF that has been perfect so far.  On F mandolins, I use both CF reinforcement and a truss rod, simply because I think that many people expect a truss rod on an F.  On the other hand, if a customer specifically wanted an F mandolin with only CF neck reinforcement (i.e., no truss rod), I would be happy to build it that way.  I am confident, on the basis of experience with all of my other mandolins, that a CF reinforced neck will remain stable and straight.

http://www.Cohenmando.com

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## D.E.Williams

I'm not a mandolin expert by any means, but my gut tells me that Rick is dead right (once again, as usual).  I've eliminated the trussrod from my F5 design, and feel confident that I can build the right amount of relief into the FB and make the neck itself very very stiff.  I've used CF rods in my guitars for years, and believe they help make the neck play more evenly (tonally) along the whole length of the FB than without them.

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## Steevarino

Well, since I am up against a new batch of necks for my flat "Traveler" mandolins, I might  try one or two with CF instead of a steel adjustable truss rod.  It's a shorter neck than most of you guys are using, so CF might even be overkill.  I have used 1/8" X 1/2" CF as a back-strip on many of my pickguards for years, so I always have that size around the shop.  If I taper it off a bit before it approaches the peghead, do you Users of the Carbon Fiber Clan think that is an appropriate cross-section of this stuff?  My thought would be to run an 1/8" groove in the neck, perpendicular to the fretboard surface, and mount it that way.

Probably overkill, but as my friend Van Hohe say, "Anything worth doing is worth OVER-doing".

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## amowry

I use a bigger piece (1/4" by 1/2"), but it's probably overkill. It's partly why I'm so confident about it, though. The material is light enough that I can use a lot and still have it be lighter than a single-action rod. I run it as low as possible in the neck, and continue it into the headstock. 

I agree with Rick about less energy loss with stiffer necks. I don't see any reason to expend energy on moving the neck when our main goal is to transfer that energy to the bridge.

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## kestrel

Steve -

I was using 3/16 x 1/4" bars in my mandolins, but am concentrating on mandolas, now, and have switched to the 1/8 x 1/2" that you're talking about. With both, I run my channel all the way through my tenon, and straight out into the peghead, cutting the angle on the bar to the flat of the top peghead surface, under the head plate. I figure that adds strength to the potentially weaker area at the angle from the nut. Guess I couldn't do that if I weren't using a head plate. 

Gene

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## Rolfe

I used to use 1/4" X 1/2" but found that to be overkill and have been using 1/4" X 3/8" for quite some time.  The bar extends from the headstock out into the fingerboard support block, but the bar is cut down to about 1/3 of its depth in the support block section.

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## Hans

I use a truss rod. It's worth it to have a tiny amount of adjustability to me.

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## Steevarino

Well, there you go Hans.  I was all ready to go over to the Dark Side, and you hauled me back.  

Nah, I'll probably still give CF a shot.  What the heck, I already have it, and this batch of Flatties I am nearly drowning in is one big Cluster-Flotchie of experimentation anyway...

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## Rick Turner

Rolfe, good on that.  It's how I build my acoustic guitars and I dado the CF up into the fingerboard as well as down into the neck.  No, you wouldn't want to try to remove the fingerboard, but I'll be dead in 40 years and I won't care.

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Rob Zamites

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## John Bertotti

No point to make just adding my 1911 vega bowlback neck has a slight bow at normal mando tention, nothing major. Down tuned a full step it is a almost perfect neck. Age and years of constant tention, I'm sure where the cause. No truss rod no gf and still a good neck almost 100 years later. My new mando, still in the womb, will have gf and I am every bit as confident of will be a good player 100 years down the road.

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## D.E.Williams

> rolfe, good on that.  It's how i build my acoustic guitars and i dado the cf up into the fingerboard as well as down into the neck.  No, you wouldn't want to try to remove the fingerboard, but i'll be dead in 40 years and i won't care.


roflol....

 :Laughing:  :Laughing:  :Laughing:  :Laughing:  :Laughing:

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## Steevarino

Or, maybe:

nrofd  

(not rolling on floor dead)

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## oldwave maker

I use 1/4x3/8 cf in 12-fret-to-the-crosspiece oval holer necks, adjustable steel in everything else. Sometimes chunky necks (made from really hard red maple seasoned as a blank for a year or more) resist the persuasions of 3/16 mild steel in spite of our best intentions.....

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## mandozilla

My mando has CF. It's over 26 years old and the neck is perfect.  :Grin: 

 :Mandosmiley:

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## Nolan

I hear truss rods work better in flat sawn necks....

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## Nick Triesch

Truss rods?  Gibson, Poe, Gilchrist ,Red Diamond,  Brentrup,  Nugget,  Apitius,  Collings, Weber, Kimble, Daley  just for starters!   I'm not saying that CF is not a good thing.  It's just that the very best in the world use truss rods.   It's just not tradition....these mandolins sound wonderful.     Nick

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## Dave Cohen

NTriesch, for one thing, you already posted to that effect earlier in this thread.  For another, the reasoning ain't so good.  There are certainly wonderful mandolins by great makers made with truss rods.  There are also lots of good, fair, mediocre, poor, and lousy mandolins made with truss rods.  Same can be said for CF reinforcement.  The method of neck adjustment/reinforcement doesn't have to do with the sound quality of a mandolin as much as it has to do with playability, feel, balance, and long-term stability.  Among builders, there are adherents of truss rods, adherents of CF and other non-adjustable reinforcement, some who use both truss rods and non-adjustable methods in different mandolins, and some who use both truss rods and CF in the same instrument.

Mandolins tend to be head-heavy instruments.  For me, that tips the scales against truss rods.  For others, ymmv.  Differences in sound quality between the different neck reinforcement methods are currently small if they exist at all.  A neck/headstock/tuning machines assembly would have to be made a whole lot stiffer and lighter than is possible with existing methods to unambiguously test any hypotheses about differences in sound quality due to neck mass and stiffness.

http://www.Cohenmando.com

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## Rick Turner

Where you really hear the effect of CF reinforcement is in electric bass necks.  I use both CF and an adjustable rod in most of my basses, and the CF really smooths out response and helps tame dead notes and wolf tones.   I also hear the difference and feel it in acoustic guitar necks, and I wouldn't make a 12 string guitar without CF these days.

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## Nick Triesch

Dave,  my 86 year old Gibson is light as a feather, the neck is super straight and it sounds like a Snakehead should....fantastic.  I grew up with cool guitars and mandolins.   I just would like to be able to tweek it if the instrument  ever needed it.  I have owned instruments where the maker said that the neck would  "never warp or bow".  We all know that is not true. How bout this...sometimes a maker may set up his or her mandolin with just the amount of relief that they think is right.  Many players like myself will get the mandolin or guitar home and set it up to play and feel like we like it to play and feel.  Usually after the adjustment you will not need to touch it for several years.  And if you need to it will only be a very tiny tweek.   I want to make the tweek for $ 3000 to $10,000 bucks!   That's all I'm saying.  Holy Smokes!    Nick

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## mandozilla

Maybe if Orville or Lloyd had CF available they would have used it!?...I'm just sayin'...  :Laughing: 

 :Mandosmiley:

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## labraid

One thing that has not been mentioned is the compression that a neck is under. An adjustable truss rod can either compress itself, or belly up or down a neck (two-way). What it cannot do is _resist_ compression. With those 150lbs of compression slapped on the neck, the wood removed for a truss slot is not fighting the compression... neither is the truss rod; you get more compression on the wood that _is_ there. An unreinforced neck, or a neck with CF, is fighting that compression, and keeping your instrument in better tune the while... 

Man, self perpetuating fallacies are my bane in life. Why is it so often we dance around the truth but dive into the fire..... I guess fire's cool and all.

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## Nick Triesch

Maybe someday Dudenbostel and Nugget mandolins will use CF instead of an adjustable truss rod.

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## french guy

just a question for CF afficionados 
what type of glue do you use between carbon fiber and neck wood?
personnaly I've used sometimes titebond glue , sometimes superglue , but I want to know what is your choice .

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## Rolfe

Epoxy.  Since I am installing the neck along with the truss bar, epoxy is used for it all.  I used to AMR epoxy, but it has gotten outrageously expensive.  Smith's All Wood epoxy (from LMI) now since it is slow-curing and gives lots of working time.

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## kestrel

Smith's All Wood epoxy, also.

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## Rick Turner

Thick superglue or WEST epoxy.

But that ain't how Bill done it...

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## Michael Lewis

I use West Systems epoxy too because it gets harder and will less creep less than the Smith stuff.  I haven't tried the CA gel but it would work well.  CA is recommended for use with CF material by the CF manufacturer.

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## Rolfe

> I use West Systems epoxy too because it gets harder and will less creep less than the Smith stuff.  I haven't tried the CA gel but it would work well.  CA is recommended for use with CF material by the CF manufacturer.


What mix do you use with the West System?  AMR gets rock hard, which is why I liked it, but, as I said, it got way too expensive.

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## Rick Turner

We use enough WEST epoxy to buy the gallon cans of the resin and the quart cans of the hardeners; we keep both the fast and slow hardeners on hand.  They have metering dispensing pumps, so the proportions are automatic...you just carefully pump equal squirts of each part, A and B.   You can also adjust the speed of the cure by mixing the fast and slow hardeners.   

I like WEST because it's available locally at the chandler's, they have a range of products, and it's just so convenient being able to pump the proportions.  Add to that that it's great adhesive, and that's all I need to know.  The yacht racing crowd loves the stuff, and those boats are quite the test.

I use the same stuff for pore filling and sealing open pored woods like rosewood, walnut, and California sycamore prior to finish, and I may try it on closed pored woods as well.  It wets nicely and used as a sealer or pre-sealer, it helps to literally glue the finish to the wood.

Take care not to get it on your skin, wear breathing protection, etc.  Allergic reactions to epoxies are not uncommon, and they are really a drag.

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## David Newton

Don't make fun, but I use JB Weld. It sets up real hard.

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## first string

> Maybe someday Dudenbostel and Nugget mandolins will use CF instead of an adjustable truss rod.


A lot of the builders who have weighed in on the side of CF in this discussion are right up there with those guys. They might not command quite the same prices, but that is largely because they have dared to part with tradition. The sad truth is that the bluegrass world (which is the primary market for mandolins) tends to be a little stodgy. Building a Loar replica is probably the most monetarily rewarding use of a luthier's time. Thankfully some have tried to at least subtly push the envelope sonically, and aesthetically, despite the inevitable resistance. You may prefer a traditional instrument. More power to you. That doesn't invalidate anything that has been said about the properties of CF.

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## papawhisky

I never expected my question to generate such a great thread, and I have learned a lot.  No question that F models are about tradition, and truss rods are part of that.  As I understand it, they have a function.  The need for that function may be increased by the wood removed to accomodate them. But that was an innovation a hundred years ago.  I suspect that when the Gibson company filed for the truss rod patent nearly a century ago that there were critics of the new fangled device.
My vote is for innovation where it fits in the tradition.  My CF reinforced mandolin should arrive next week.

Papawhisky

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## mandozilla

If a person's mandolin has CF and no truss rod but wanted to maintain that traditional look, I suppose he/she could attach a truss rod cover to the headstock and no one would be the wiser.  :Grin: 

 :Mandosmiley:

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## Nick Triesch

The best mandolins I have ever played had adjustable truss rods.  Who knows,  maybe in a few years CF will be the rod of choice in a mandolin.  But I think there will always be those who want a Loar type instrument that can be adjusted.  I still think most players are old school .  I owned a Martin 000 21 that the company
 said never needed adjustment.  But I could shoot arrows off it if I wanted to.  Thats how warped it was.  It needed hundreds of dollars to make it right.   A CF neck mandolin may never need an adsjustrment...but if it ever did,  you are just out of luck.  With a Weber or Collings for instance,  you just pop it right back into place.  Takes just a couple of minutes.  We all know how great mandolins with truss rods can sound, and how easy it is to adjust them,  why would you not want a mandolin built with a quality adjustable truss rod?   Why would you want to take away a way to fine tune adjust an expensive mandolin?       Nick

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## David Houchens

I finally decided to give cf a try. I just threw a wild chery A model in the next batch of mandolins. I decided to try a few new things on this one. Try and keep it for a while and see how they work.I glued in two 1/8 x 3/8 cf rods in the neck blank. I'm also gonna give the Simminoff neck joint a try. Never done anything but dovetail joints before. I'll keep an eye on it.

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## Dave Cohen

NTriesch, at the 2006 CMSA convention in Louisville, two mandolins with CF reinforced necks and no truss rods took first and second place in a blind listening test against numerous other mandolins, all with truss rods.  The test was jointly conducted by the CMSA and First Quality Musical Supply.  Does that mean that mandolins with CF reinforced necks sound better than mandolins with truss rod necks?  Absolutely not.  The test cited is only an _anecdote_.  Same is true for all of the anecdotes you have cited in your posts in this thread.  Unless you have conducted experiments with quantitative measurements and controls, you can make all the claims you want about truss rods and they will amount to nothing.  The listening test which I cited above also did not not involve any quantitative measurements, and there were no controls, so it, too, is nothing more than an anecdote.  I cited it to make this point.

So (a) how many high quality mandolins with CF reinforcement/no truss rod necks have you listened to?  And (b) How many mandolin necks with truss rods (beside your own mandolins) have you adjusted?

My point is not that mandolins with CF-reinforced necks sound better than mandolins with truss rod necks.  I am not claiming to know the answer to that.  My point is that you are not making your case.  To the contrary, you are probably damaging your own case.

Bryce, if you put the 1/8"x3/8" CF rods directly under the fingerboard, you may not have enough reinforcement.  The rods need to be set deeper in the neck, and get deeper as the neck gets deeper.  I used the two parallel 1/8"x3/8" rods oriented vertically early on.  Most of those necks did remain straight, but a few moved more than I liked.

http://www.Cohenmando.com

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## labraid

Re: placement: has anyone mathematically determined where the neutral axis is in a mando or guitar neck? Anyone got any diagrams? Numbers?

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## barry k

Hey, I have a thought, might end all discussion.  Get a carbon fiber block big enough to obtain a neck blank, then walla....solved the warping , weight, adjustablity, filler and tone problem all in one swoop. And didnt have to chop down a tree either. Might just work ???

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## Nick Triesch

Dave,  I don't think I am damaging my case at all.   What case?  Most of us mandolin players have mandolins with adjustable truss rods.  That's the case.    If you few guys want to build expensive mandolins with CF that you cannot adjust any warp or bow out then have at it.  I have not done any experiments on mandolins or guitars.  I have adjusted several guitars and mandolins in my life with great results.    I grew up with terrible, cheap instruments because we didn't have a lot of cash.  So now in my life I have some pretty cool instruments and I demand that they are set up (by me) to play like glass.  The adjustable truss rod and good set up combined helps me do this.     Thats all.  I myself  (and many others)  will never buy a mandolin without an adjustable truss rod.  How bout this....what ever floats your boat?   Nick

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## labraid

Nick, I think your point is made. We're jazzing CF now, not who sells more mandolins for the most and why. It's immaterial.

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## MnRoss

I have a friend up here in Mn. with a "High Buck" CF truss rod mando built by a famous builder. Minnesota has pretty extream climate swings both in temp and humidty. There are times during the year his mando is unplayable. Sure in the perfect climate of his house it's fine but gigs up here in the winter can really,  how should I say this "test the best of fine acoustic instruments". I adjust my truss rod twice a year and keep a good action, he switches to guitar for gigs when his mando is unplayable and just leaves the mando at home. It's not that the neck bends it's just the fact that the whole instrument moves around is what I think. I can compinsate and adj but he can't although this year he is going to build a new lower saddle and try that during the winter he says. It's going to be silly low and almost nothing at all so should be fun to see what happens. 

I'm just saying that in some conditions it's nice to have that adj option and here in Minnesota I'm glad I do. My house I keep just fine temp and humidity but I play a lot of gigs that tend not to have those conditions. Nothing worse than having your e string bottom out on the frets in the 1st set because the room/hall you are playing in is so dry. I like to have the adjustment and after seeing and playing my buddies "5 figure" cf truss mando in conditions like we live in it would be hard for me to own something that I couldn't adjust.  This is just my opinion and it has to do with where I live and playing gigs all the time in places that I can't control the humidity and temp during the winter.

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## Michael Lewis

Well, that is a common example of misinformation regarding 'adjustable" necks.  The adjustability (truss rod) is to set the RELIEF, not the action.  The action is set by raising or lowering the saddle.  The truss rod does effect the action, but it is not there to do anything but set the relief.

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## Dave Cohen

Barry, a solid CF composite neck would be very heavy.  The CF composites have a density greater than ebony.  The all CF composite instruments made thus far have had a molded hollow neck.

What hasn't been mentioned so far is that it is possible for a CF/reinforced neck to bend if the reinforcement is not sufficient or is not done properly.  The tension from the strings acts on the overall stiffness of the neck.  So if a particularly soft piece of maple is used for a neck, just throwing some CF at it may not effect enough stiffening to resist the string tension.  The shape of a neck + fingerboard puts the neutral axis pretty close to the glue seam between the neck and fingerboard.  But just placing the CF or truss rod immediately below the neutral axis is not enough.  The maximum stiffening in the case of CF, or the maximum adjustability in the case of a truss rod, is obtained by getting the rod or reinforcement (whichever is the case) as far below the neutral axis as is possible.

To amplify Michael's point, the greatest amount of movement in an instrument occurs in the plates.  When the relative humidity is low, arched plates will sink a bit, hence the motivation for an adjustable bridge.  The dimensional change comes largely from cross-grain shrinking.  The shrinking of woods along the grain is minimal.  If a neck moves, it is usually in response to string tension, as the shrinking along the grain is minimal.  Left that way long enough, the deformation in the neck becomes permanent, as the wood cells "creep" past each other.

Sometimes truss rods are able to do their intended job, and at other times, they aren't.  That's why Stew-Mac sells a truss rod repair kit.  Truss rods can get maxxed out, the threads can strip, and other problem can (and do) occur.  Adjusting a few rods on your own instruments is not enough experience.  When repair is part of your living, you become less confident about the adjustment capabilities of truss rods.  As I have already said several times, sometimes they work well, and sometimes they don't.

http://www.Cohenmando.com

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## labraid

I still have a beef with the neutral axis assumptions... I may be wrong, but that it is solely a function of profile seems a bit off. The compression forces down are so much greater than the vector pulling perpendicular from the nut, this would shift the neutral axis sufficiently far back in the neck to put most of the neck in compression, and only a small portion in tension. Any takers? Any math?

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## Dave Cohen

The location of the neutral axis is not solely a function of profile.  It is _influenced_ by the profile, but also depends on ther elastic modulus of the neck material itself, the modulus of the fingerboard, and the "wedging" action of the frets.  That kind of calculation can be done, but to me, it is not worth the time.  I think you would find that much of the neck below the fingerboard is in tension, but the tension is a lot greater much deeper in the neck than it is just below the fingerboard.  It is enough for me to know that I get the greatest stiffening by placing the CF composite bars as far below the neutral axis as possible, and hence as deep in the neck as possible.  As I already said, the same applies to the capacity of a truss rod to adjust the neck's curvature.  The deeper the rod is located in the neck, the more easily it will adjust.  Look, if the part of the neck where the truss rod is located were not in tension, the truss rod would not work.  What the truss rod does in effect is bring back the tension that is lost as the wood cells move past each other when the neck begins to take a "permanent" set.

http://www.Cohenmando.com

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## John Bertotti

So then isn't the neck join also a function of the amount of tension the neck will feel? I would think the dovetail would be more secure placing a bit more tension in the deep part of the neck but a mortise and tenon maybe might give a bit? I'm not math man so I am just guessing but in my reality at the moment it makes sense!  :Popcorn:

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## labraid

My argument is as follows:



where the red are force vectors and the blue is the neutral axis in each case.

> The deeper the rod is located in the neck, the more easily it will adjust.

This is true, but I believe the neutral axis can change in an adjusted versus an unadjusted neck, and this is why a compression rod works. In effect, by its use you eliminate the neutral axis by keeping the rear of the neck in _as much_ compression as the fret side. Simply neutralizing or equalizing forces. The further away from the median zone (not a true neutral axis, but a _relative_, inferred one), the more this compression force torques around that central point, making it more efficient..

> if the part of the neck where the truss rod is located were not in tension, the truss rod would not work.

Respectfully, I do not think that is necessarily true. One area/zone may appear to be in _relative_ tension, but in effect it only needs to be in lesser compression to do that: you could bend a solid rod, for example, by simply compressing one edge more than the other with a *perfectly* _in-line_ force, but in this example the whole rod will be under compression (though varying amounts, thus!) and that bend will still occur.

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## Dave Cohen

Brian, that just ain't right.  The neutral axis of a given beam relative to its own dimensions doesn't change with a change in tension.  Nor does it change with a change in the location of the forces acting on it  The amount of shear changes, but the neutral axis doesn't.  The location of the neutral axis is a function of the cross section, moduli, and homogeneity of the beam itself.

John, first, a dovetail joint - pin plus tail - is a kind of mortise and tenon.  Second, regarding a straight mortise and tenon "giving": if it does, then your neck joint is in trouble.  If a straight mortise and tenon joint is secure and the glue doesn't creep, then it is not going to result in any change in tension.  Btw, when old dovetail joints fail, it is sometimes because of shrinking of the wood in the joint.  I recently reset an old Guild guitar neck that needed about 0.020" of shims total to make the joint tight again.  The self-locking aspect of a dovetail joint was just about gone.  The part of the tail (tenon) nearest the back plate was just about coming out of the mortise by itself when the guitar was brought to me.  With the shims in place, the joint was once again self-locking.

http://www.Cohenmando.com

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## markishandsome

"Usually after the adjustment you will not need to touch it for several years. And if you need to it will only be a very tiny tweek. I want to make the tweek for $ 3000 to $10,000 bucks!"

I don't know, if i spent 10 grand on an instrument I don't think it would bother me to have to throw down an additional hundred IF it needed to be tweaked by a professional several years later.  Frequently played instruments need fretwork every several years anyway.  Even the finest instruments require periodic maintenance.  Would you refuse to buy a new car if it didn't have an transmission you could personally disassemble with an allen wrench?

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## labraid

Compressing a piece of foam in my shop vise proved my point to be true. A 2"x2" cross-section of homogenous foam 150mm long (~6") was cinched at a lower extreme edge (compression face), and the vise tightened. The 150mm tension-face mark was measured at the beginning, during, and at the end of compressing the block of foam over 1/2" in the vise. At first it appeared you were correct, the 150mm dimension became 151mm. Still, a mighty small gain, but there was an outward bow in that dimension, which when flattened out by pressing with a straightedge, put the dimension back at 150mm. One side compressed 1/2", the other not at all. Illustrating precisely my drawing at center.

I did something similar with a taller piece of foam putting all of my weight on one edge. That edge compressed the other bowed. When the bow was pushed back into place though, simulating actual rigidity in the perpendicular direction as a mando neck has for all practical purposes, the edge with my weight was compressed, and the other would not flex/expand/what-have you. This was easily visible without measurement, and I encourage others to try it.

Now back to the first example: when the foam was held straight up in the vise, and I pushed perpendicularly against it, it was easy to see how much it moved, 100mm became 102mm easily. It is the bowing action, the flexing which creates the neutral axis you're describing, just like in my left-most drawing. _That_ neutral axis never moves if the force remains purely perpendicular, and it _factors in_ with component vectors, but it is not the be-all, end all. Take any material which is restrained from bowing (for practical purposes this is the mandolin neck in question), compress it at an extreme edge, one edge gets shorter, the other doesn't move. If I had another force vector in the drawing above, this time pressing at actual center of the neck and not at an end, where would the neutral axis be then, the axis which you've say never changes position within a cross section? It would be "undefined", because there is none possible.

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## David Houchens

Dave, I didn't cut the groove for the cf parallel to the back. I guess I should have. I did however cut the groove 1/2" deep and used a cover strip as I usually do for a 3/16" adjustable rod. So its not quite at the fingerboard. BOUT AN 1/8" DOWN. My neck is only .640" at first fret(not counting the fingerboard), with a V shape so I wouldn't want to lower that end much more. it only leaves me with .140" of wood in the thickest place. Is there a tearout factor if you get the cf too close to the back. How close too the back would you recommend as being safe? I have seen older banjo necks that had split under 2nd-3rd frets. Don't know if too much tension on the adjustable rod caused this or not.  If I do another, I do believe it would make sense to lower the heel end to be parallel with the back of the neck. Its about .740" at the 8th fret, so I could lower that end about .100" or so.
Also, I placed the two 1/8"x3/8" bars side by side. Would they be any stronger spaced apart a little?

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## Rick Turner

Brian, are you trying to say that a compression rod eliminates the neutral axis?

In a bending structure there is always a neutral axis as the force on one side of the beam, be it compression or tension, tries to overcome the force on the other.   If you put too much compression on the beam, it will rupture and buckle, but you've still got a neutral axis in there 'til you simply crush it.

Dave quite rightly has pointed out that a material like CF, which is at it's very best in resisting tension, does the most good ounce for ounce as far away from the string tension as possible.   That's why in my first patent (1978) for a graphite neck, I made the neck a hollow CF shell...a tube.   CF also happens to be pretty good in compression, and can be improved by adding carbon nanotubes to the epoxy that sticks the whole mess together.  

In practice, we often use CF in less than perfect ways which are, perhaps more practical.   The stuff is so good and so versatile that using CF rods as we do, even when part of the rods are in the neutral axis, the result is really good.  I like the combination of CF and wood because I like the feel of a wood neck, and I like being able to change widths, depths, and shapes to suit various customers.   With a fully molded CF neck you are locked into a particular shape, and tooling is prohibitively expensive for custom instruments.  Combine the best of both worlds, and you've really got something.   And you can put a truss rod in a neck with CF if you want to...

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## Nick Triesch

Mark....I think it could cost a lot more than a hundred bucks if your non truss rod neck needed an adjustment.   But forget all that....I really like Ricks idea of using both....CF with an adjustable truss rod.  If you have to have the CF installed.   Nick

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## labraid

My physics may not be up to PhD snuff, but my understanding of the neutral axis as I learned it some 12 years ago was that it was the plane within a solid where the wood was neither in distortional compression nor in distortional tension, rather it is a plane separating these two distortioning forces. If a some rigid material were pressed in a vise until it compressed 1/16", there would in fact be no neutral axis -- it would be under pure compression -- there is no tension in the wood, because tension is a distortional force and requires displacement. Tension of wood net compressed in a vise is negative, therefore there is no divide between compression and tension, therefore no neutral axis.

I know a guy who once overlooked gluing in his CF rod, rod which was directly beneath the fretboard. He went and strung up his new octave and heard these creaking sounds from within the neck. The neck was bowed up into exagerrated relief. Now tell me, why was the CF inside the neck creaking past the neck wood? Was it creaking one way on the top of the rod and one way on the bottom of the rod?? because that is where the CF was, directly on the "accepted" neutral axis.. No, the wood that gave way and caused that "big relief" was wood missing from the CF slot -- it was compressing around it and the CF wasn't taking up the fight. The neck wood was shrinking right over that CF rod...

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## Rick Turner

Brian, I'm not going to get into a pissing contest over engineering semantics here.  You build 'em your way, I'll build 'em mine.   You understand 'em your way, I'll understand 'em mine.   But I have yet to see a neck that is entirely in compression...and I don't expect I ever will unless it's got strings on the back of the neck as well as the front.

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## labraid

It's unfair to say I'm trying to win a pissing contest by arguing my point, IMHO.

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## Dave Cohen

Brian, first, foam is a really terrible model for a beam made of an elastic solid - like, say, wood or a CF composite beam.   Wood and CF composite bars are also very anisotropic, whereas your foam is pretty isotropic (means properties are the same in all directions).  And with foam, the moduli in all directions are so small compared to wood or CF composite that you get all kinds of distortions that render your experiments wacky.  Second, "proof" lies entirely in the domains of mathematics and logic.  Scientists never claim to "prove" anything.

Bryce, you can mill your slots for the CF to follow the plane of the back of the neck by gluing a sacrificial piece of wood or something to the area of the nut.  I glue a little sacrificial piece of wood to the nut area with CA, then just chisel it off after I am done cutting the slots.  Measure the thicknesses your neck will be at the first and eighth frets, subtract out the thickness at the first fret and you have a triangle.  Calculate the sin or cos or tan function of the angle at the nut, and use substitution to figure out how much the back of the neck drops over the length from nut to the end of the neck nearest the heel.  By similar triangles, that will also be the thickness of the little sacrificial piece that you temporarily glue on at the nut.  Works well, and makes a big difference.

http://www.Cohenmando.com

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## labraid

I swear, ISTJ, you remind me soooooooooo much of my paps. That's part compliment, but the man isn't worth arguing with, cause he'll always find a technicality to completely divert the argument to where he knows he'll win, away from where he isn't sure. 
Nothing was solved today then. You haven't won the point without some sort of well, anything more than that... I'm not letting you off. See you at CMSA (bring paper)

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## Nick Triesch

Hey, I found 3 more makers that use the truss rod.....Monteleone, Paganoni, Zeidler.   I will buy a mandolin with the adjustable truss rod!

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## labraid

The status quo is such, Nick, that it doesn't need folks to defend it.

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## peter.coombe

I have been away from this thread for a while and I think my earlier statement that some customers are just stubborn has been well illustrated.

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## Rick Turner

Like I said, it's not either/or unless you make it that way.  You can wear a belt with your suspenders if you like...

All I know is that CF is really wonderful stuff, and for me, it makes for better sounding instruments by helping drive more energy into the body as the neck robs less energy from the strings.  

And I do use both a dual acting truss rod and CF in my guitar necks...

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## mandozilla

:Grin: Oops!...My Bone! 
 :Mandosmiley:

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## mandozilla

"Can't we all just get along?"  :Crying: 

Now if someone could make an adjustable truss rod out of CF...Hmm... :Laughing: 

Say, do fiddles have neck reinforcement of any kind? Or don't they need it?  :Confused: 



 :Mandosmiley:

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## Stephanie Reiser

Say, do fiddles have neck reinforcement of any kind? Or don't they need it?  :Confused: 



 :Mandosmiley: [/QUOTE]

_No, and no._

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## markishandsome

"I think it could cost a lot more than a hundred bucks if your non truss rod neck needed an adjustment. "

Maybe, but not much.  While the instrument is in for a routine refret, the board is replaned to correct the relief.  A common procedure, even on truss-rodded instruments.  An additional couple hundred bucks on top of the base cost of the refret.  Still only a few percent of a 10k purchase price (ie less than sales tax).  Not something I'd like to have to do very often, but if I had that much money to be spending on instruments, i wouldn't consider it a big deal.  If i spent 10K on a dog, i'd still have to buy its food.  

Violin necks don't usually have any reinforcement.  They have an enormously thick fingerboard and a very stubby neck.  If the relief needs to be tweaked, it's carved into the fingerboard (just like a mandolin  :Smile:  ).

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## Dave Cohen

Brian, I'm not trying to win anything, nor am I trying to divert the discussion away from whatever it is. Your understanding of beam statics is just crazy.  I'd like to help you out.

Remember that physical Laws are constructs that have never been observed to be violated.  That doesn't mean that they can't _ever_ be violated.  Nothing save falsifiability is doctrine in science.  Everything in principle must be falsifiable.  But if one ever does come up with evidence for overturning a Law, (s)he had better be ready with some mighty good data and explanations.  Now to the point.  Your understanding of beams and neutral axes violates Laws.  I really appreciate the spirit of your foam experiment.  I wish that more people would think analytically and empirically like that.  But, you have to take your analyses to the next level.  Whenever we investigate a problem, we go to the literature both _before_ and _after_ doing our experiments.  Before, we have to ask things like "what is the current thinking on this?" and "Do I have reason to think that the current thought is wrong?...or right?...".  After, we have to ask things like "What could I have done wrong here?" and "Are there artifacts?" and How will others criticise my hypotheses and work?", and most important, "How do my results either fit with or contrast with whatever is currently accepted?".  That is one of the reasons why we have anonymous peer review; it automatically initiates some of those questions.  And last, you have to thoroughly understand existing formalism in order to be prepared to topple it.

In your case, you can find some starting places in Fletcher & Rossing's "The Physics of Musical Instruments" (2nd Edition) in section 2.15, pp 58-60.  A text on statics would be the next place to look.  Maybe Pap has one?

Btw, are you in Cape Breton yet?  & if so, do you like it?  House hunting?

http://www.Cohenmando.com

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## Nick Triesch

I don't think I am being stubborn Peter,  Heck,  I'm just going along with the great masters of mandolin construction.  Come on,  that alone has to say something.  Most of those guys have been building for many years.  They have it wired!  They know what works for them.  And they also do not want their mandolins to come back to the shop.   I say keep up the good work and keep on building your experiments.   Nick

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## man dough nollij

I've been following this thread from a distance, intrigued by the heat generated. I'm far from a builder (not even close...), but I have kind of a tinkerer/engineer mentality so I often follow these threads.

I'm curious about something... Maybe Rick and Dr. Dave and others can chime in on this. I've heard lots of stories where luthiers removed the fingerboard with an iron, using the heat to loosen the hide glue that holds it on.

If you put a CF tube or rod in the neck and used epoxy to hold it all together, wouldn't that greatly complicate any future repairs? I couldn't bear the idea of whackin' the whole neck off of a nice custom mandolin, steaming the neck joint apart and building a whole neck from the joint up, just to replace a fretboard. Wouldn't epoxy create that scenario? Hmm?

 :Confused:  :Chicken:  :Confused:

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## j. condino

Rough crowd out there in mandolin world for this thread....

I sure wish Peter Mix would add a few comments on carbon fiber and mandolin necks. As a musician, luthier, and engineering grad school dropout, I'll add that that I can agree with and find value in almost all of the comments posted here. 

Given the fact that I can use anything commercially available or that I need to custom fabricate to stiffen the neck of my personal mandolin, my preference is for non-adjustable carbon fiber. Field testing them from the bottom of the Grand Canyon in August to the Himalaya in the winter, they've always sounded better and held up better for me. 

Most builders I know are generally very accommodating to whoever writes the final check; if you prefer an adjustable Gibson style rod, that's what they will build for you. If you really want it, I know one mandolin nerd who will even cut funny holes all over the sides and paint the thing green for you...

j.
www.condino.com

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## Rolfe

> I've heard lots of stories where luthiers removed the fingerboard with an iron, using the heat to loosen the hide glue that holds it on.
> 
> If you put a CF tube or rod in the neck and used epoxy to hold it all together, wouldn't that greatly complicate any future repairs? I couldn't bear the idea of whackin' the whole neck off of a nice custom mandolin, steaming the neck joint apart and building a whole neck from the joint up, just to replace a fretboard. Wouldn't epoxy create that scenario? Hmm?


I use epoxy as my primary building glue; so, not only is the neck/truss bar installed with epoxy, the fingerboard goes on with it too.  Removing the fingerboard with heat works just as well with epoxy.  You heat the knife or wedge used to pry the fingerboard up; you don't heat the whole fingerboard.  We just recently removed the fingerboard of one of my mandolins built ten years ago without harming the fingerboard, the inlays, the binding, the neck, or anything.  We had pulled the frets already, so when we reinstalled it, we leveled it, refretted, and away it went---nice and original.  There is a myth out there about epoxied parts not being repairable.  I will say that it is CHEAPER for me to whack off the whole neck (after salvaging fingerboard and parts) and put on a new one than trying to undo the truss bar system, but I've had to do that only once in my career.

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## labraid

If there was any heat it is the result of frictions and not an open flame. Dave's a friend, we just like to grill each other from time to time. He gets me, I get him. All good fun.........

My position on the topic is that the church, in this case, does not want to prove what it believes. I'm happy to continue building necks "glass" flat with approaches to CF that are very mainstream, with only small doubts, perhaps, that the mainstream is 100% spot on in its theory. Still, my results are consistent with other CF users because that is an area I do not wish to take risks in. I may be wrong in my theories, but as Socrates said, "the univestigated life, et caetera, et caetera". Building is my addiction... Questioning, my nature. I'm pretty confident that's the right way to go, and will result in deeper understanding in the long run. Afterall, one does not _truly_ know who they are, until they know who they are not. Same goes for building I think. Get the disease into the sunlight, it'll cure faster than under a wet bandage.

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## Dave Cohen

Glues let go when the "glass transition temperature" is reached.  For hot hide glue, that is up around 400-450 degrees F.  For epoxy, it is down around 200 degrees F, and it is slightly lower for PVA glues such as TiteBond. Quite a number of luthiers are now using epoxy for gluing fingerboards.  Fingerboards glued with epoxy are easily removed by removing the frets and heating with a household iron.  I removed an epoxy-glued fingerboard from an archtop guitar a while back  That guitar neck has CF reinforcement _and_ a truss rod.  The fingerboard came up cleanly, and the rest of the neck was unharmed.

Actually, you need heat _plus_ moisture to separate hot hide glue seams.  Hot hide glue seams do come apart cleanly, but not without quite a bit of effort.

http://www.Cohenmando.com

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## Rick Turner

Another epoxy user who has no problem taking fingerboards off with heat.  They come off cleanly, easily, and with no fuss or muss.  I don't even always take out the frets to do it.  

The great thing about epoxy is that it doesn't induce water into the wood, and so glue lines stay nice and stable.  

With regard to fix it or replace it...folks who only repair tend to be very leery of replacing necks.  Those of us who build may often find it easier, cheaper, and better to simply replace a broken neck.  Making necks just isn't that big a deal if you do it all the time.

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## Rick Turner

Oh, one more thing...there are epoxies that cure with heat and can handle up to 500 degrees F before they let go.  These are used in aerospace for satellite parts which are cured in autoclaves.  The first carbon fiber necks were done with hi temperature epoxies because the parts were made at Ford Aerospace in Sunnyvale, CA, and that's what they had.  The materials cured at 350 F.

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## John Bertotti

Oh. No you didn't! I see it now, mando magic and superior tone acheived through baking your tone woods! I have to call OldWave now! Bill just has to bake mando!  :Disbelief:  :Disbelief:

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## Rick Turner

I froze a Derrington/Gibson F-5 once; I sent it to a company in LA that does cryogenic treatment of (usually) metals.  Had that sucker taken down to minus 360 F for 72 hours.  The binding didn't like it at all... The mando was in the white and had been left under Charlie's bench when he left for a few years in the late 1980s.  Since I was el queso grande of Gibson Labs West, I could raid the factory for bits and pieces.  This was supposedly due to be a factory second, and I made well sure of it!

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## Rick Turner

Oh, the Kulesh Mastertone banjo tone rings that we cryo-treated came out great, and now that has become kind of a fairly normal thing to do to high end tone rings.  I still have one of the rings that Rich Sr. made for me.  Just have to build a banjo someday.

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## j. condino

"El queso grande", your are my favorite! Nobody else around here has been brave enough to ship out a Derrington F5 to Walt Disney in LA for the weekend.

j.
www.condino.com

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## Rick Turner

I guess I'd better not tell Frank Wakefield about it...

Actually, I'd gotten into cryo treating of strings in the mid 1980s with my old pal Lowell (Banana) Levinger now of Players' Vintage Instruments fame and a guy who has a couple of nice Loars and a pile of Loar ViviTones.  We dabbled in a little mail order cryo treated string business for a little while.   We were having Tom Vinci make the strings for us, and then we were sending them out for treatment.  This is one of those things that I maybe should have patented, but didn't.  Now, of course, there are several companies offering cryo-treated strings with Dean Markley being the most obvious.  

So when I wound up doing R&D for Gibson, circa '88 and '89, I was quite happy to try just about anything...and did...that being the era of Jim Triggs and Greg Rich in the Gibson Custom Shop...  It did get a bit crazy at times...

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## labraid

I've done a bit of reading and my conclusion is that the opponents of my theory are quite incorrect in their assumptions. 

Dave and Rick are correct on one point: the neutral axis does not move, only because it is theoretical and based on everything Dave said it was -- profile, MOE, etc. However they are both wrong in stating that this neutral axis does not undergo net compression from the state of no string tension to a state *of* string tension. It _does in fact compress_ under this load. I was wrong in calling this a shift in the neutral axis, it is nothing more than a net change in the length along a plane due to external forces, and my drawing showing little or no change in the compression at the back of the neck still holds true, only it does not represent the neutral axis, it represents stability between state changes, non-movement. The area of the cross section nearest the fretboard is subject to the most compression in a neck's profile, purely as a result of the component force vector parallel to the fretboard face, and therefore the most net shrinkage. A CF rod installed under no string tension (obviously) and then later compressed under string tension, _is in fact subject to net compressive forces_, and purely so in almost any arrangement within the neck, but even moreso nearest the fretboard. Whatever happens after equilization of forces during stringing, happens around the centroid, the neutral axis. But from a state of no strings to strings, that rod's very first job is to fight compression. 
That's all I meant to say from the getgo............ and you can quote me on it.

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## Rick Turner

And what if you put the carbon fiber rod at the back of the neck?  Do you still think it's under compression?

You just don't get it...

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## Robbie McHone

:Popcorn:

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## Rick Turner

OK, here's another way to understand it...

Truss rods work in tension.  Tightening the nut applies more tension to the rod just like tuning up strings apply more tension to the strings.  Yes, the tension on the rod applies compression to the neck, but it's doing so through the force of tension.  You are balancing the tension of strings with the tension of the truss rod, and your neutral axis is in compression.  But there's still a neutral axis...the balance point between the forces in opposition.  Think of the neutral axis as being like a fulcrum point.

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## labraid

Rick, you're not trying here. My illustration is quite clear: the back of the neck _is in tension_ due to the vector of pure bending moment. I'm admitting, you guys are right on this part man. But what you're not taking into consideration is the state change from no strings to strings. You're acting as if that neutral axis were made out of kryptonite, that it were physically incapable of being compressed from one state to another of equilibrium. This is just simply not the case. What you have is that once that rod under the fretboard is under compression, it is then subject to any tensions around the neutral axis, the bending moment. But only when you factor the first part in. 
Yes it is under tension when placed in the back of the neck! It is infuriating that you neither seem to read what I've written, or ask questions on points I may be being unclear on! My argument is that there are two components and as far as I can tell you're only seeing one. The neck first undergoes net compression, and this is why that first G string drops down two steps when you put the rest of the strings on, the fretboard remaining flat the while. If the neck were only subject to the forces you are saying it is, if you strapped 150 lbs pulling *away* from the nut, you'd have massive bending around the neutral axis, and massive relief as a result -- the back of the neck under intense tension and the front of the neck in intense compression. But the 150lbs is split into two things. One of the above, the other which is not being considered because you are forgetting "to put the strings on"..

You would do well not to cast off other's thoughts without any numbers or justification in the future. You can't reason your way out of this with reputation. If I'm wrong about the strings adding net compression, then please show me why. A piece of wood in pure, net compression in a vise retains its neutral axis through the compression where, let's say, the block shrinks 1/64". The neutral axis has shrunk 1/64" in this case! Any residual bending moments placed on it after that, revolve purely around the neutral axis.

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## labraid

we co-posted, but Rick, I already admitted the neutral axis. ?

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## Jim Hilburn

I think this is a great discussion, and I get a little lost in the science of trussrods, but to me the issue of string tension is about the back of the neck stretching as much as the fingerboard area compressing. This is where the entire neck is weakest and wants to give way to the upward pull of the strings. With a traditional adjustable rod the point is to counteract the string force within the neck and relieve the stress on the back of the neck.
So if your going to use CF exclusively it makes sense to me to do it like A. Mowry and install a big stiff bar in the center of the neck which will allow you to get it deeper in the neck than with a pair of bars on either side. That seems to be how CF is used in conjunction with an adjustable.

To Nick. When mandolins started to be popular through bluegrass and it became apparent that there were very few options for buying a good mandolin, the pioneers of the small builder market almost exclusively modeled their instruments on the Loar which included the adjustable. 
But in the meantime in the guitar building world, while some stuck with tradition ( actually, tradition in the steel string would lead to a steel t-bar) there was and explosion of innovation, and Rick was right there in the thick of it.
Alternate materials and methods have slowly been working their way into mandolin construction, but there are plenty of adjustables to be had. You've named many of them. But there are plenty of examples of CF necks that have stood the test of time.

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## Rick Turner

At this point, we just may be arguing on the same side of the engineering, but looking at it from two different points of view.  

If you take the strings off of a mandolin with a truss rod, is the fingerboard now in tension...being stretched?  You betcha...  And probably the neutral axis has moved because its location is dependent on the forces acting on the beam.

So maybe we don't have a problem, Houston...or Cape Breton...or Dave.

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## Dave Cohen

Brain, I swear I'm gonna charge you a consultancy fee for teaching you physics, since I ain't gettin' paid for the time I have to put into these posts.

You are overlooking something huge, namely the anisotropy of both wood and CF composites.  A crystalline metal is isotropic, meaning that its' properties are the same in all directions.  Composite materials like wood and CF are enormously anisotropic.  Along the direction of the fibers, the MOEs are extremely high - multiple megapascals.  At the atomic level, closest packed metallic crystals are pretty uniform in all directions.  To be compressed, the atoms have to be pushed closer together; to be stretched, the atoms have to be pulled farther apart.  What resists the atoms being pushed closer together is repulsion between the nuclei; what resists the atoms being pulled farther apart are the various types of attractive forces between atoms - electron-nuclei attractions, Van der Waal's attractions, etc.  Now, even with an isotropic material like a metal, if the shape is long and thin, like a beam or an instrument neck, the sum of the forces in the long dimension is much greater than in the other dimensions.  Add in the anisotropy of wood and CF, and the forces are overwhelmingly greater in the long dimension.

You were getting warmer with your first diagram.  That the moduli are so high in the long dimensions means that the resistance to pushing the atoms closer together or pulling them farther apart in that direction is very great.  Wood and CF composites very effectively push back against the long blue vector in your first diagram.  But the little red component vector in your first diagram is the one that does the bending, since the moduli are much, much lower in that direction.  And once you have bending, you have a neutral axis, and the atoms above the neutral axis in the beam or neck are pushed closer together, and the atoms below the neutral axis are pulled farther apart.  Hence, you have shear from compressing above the n.a., and shear from stretching below the n.a.  Ergo, the material above the n.a. has to be in compression, and the material below the n.a. has to be in tension.  When we make necks from the traditional materials at hand, we are attempting to resist the shear almost entirely with the high longitudinal M.O.E.s of those materials, since the M.O.E.s in the other directions are so much lower.

Btw, no "assumptions" here. The formalism of the statics and dynamics of beams goes back over a hundred years that I know of.  The technology for good laboratory measurements is not as old, but still goes back, what, seven decades or so?

http;//www.Cohenmando.com

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## labraid

Dave, that's not a problem. I will gladly offer you a couple pints of German suds! 

But you owe me some back, now *I* need a beer!

I think we are in agreement, as Rick said. You reiterated and restated a number of things I just put forth, either because I did not say them in the scientifically proper way, or what I don't know. But I just agreed with what you wrote, Rick says we're in agreement. Could we get a: 

<handshake>

You may not agree that there is _as_ much value placing a truss rod directly under the fretboard, but I think I have presented a fair argument that at the very least could inspire the more mathematical, computer-inclined person to actually simulate some of these things. Not only forces once the instrument is happily strung, but the before and after as well. Which materials are taking the most stress, and where. It seems just crazy that we're battling this out over the cloud of uncertainty we all agree is there -- and it is a cloud without testing and numbers. Would not an article of this nature create some stir in a future Guild journal? The world needs these numbers....

ps, I did not overlook all you said, the diagram is purely a description of forces and how I estimated they would have effect. Estimates have their role in many theory applications.

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## Dave Cohen

Suds are good.   :Smile:   Btw, you didn't give your early impression(s) of Cape Breton.  Find a house yet?

http://www.Cohenmando.com

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## labraid

Will be arriving shortly! My better half is there, so by default, as they say: "home is where the heart is."

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## amowry

I love Cape Breton! Good music.

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## mandozilla

> But there are plenty of examples of CF necks that have stood the test of time.


27 years on mine and still straight and true.  :Grin: 

 :Mandosmiley:

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## roundel325

Informative thread guys.  I'll add that in my personal experience and it also depends on the neck wood density and dimensions.  I have a Morris A4 (longneck hybrid) that has a very slim neck with a non-adjustable steel rod in it.  It is dead flat unstrung, but under string tension the neck bows considerably.  Enough that it is impossible to dial in an action as low as I would like without buzzing at the upper frets.  With j74s it's a serious problem.  j73s are more manageable, but far from perfect.  By comparison, and my teens A1 stays dead flat with j74s with no reinforcement at all (beefy, short neck).

My take-away is that if you like slender necks and heavier strings, you may want the ability to tweak the neck relief.  Especially if you intend to experiment with different string gauges.  With beefier or shorter necks, it may not be an issue.

I ordered my new mando with an adjustable rod.  It should be here soon!

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## Nick Triesch

Jim,  when Porsche switched from air cooled motors to water cooled I was not upset like many other sports car fans.  I knew the new motors would have more power and run cleaner for many years to come.  It was a better idea.  But as for the great mandolins from the masters I feel the adjustable truss rod is a very good idea that has stood the test of time.   Like my old Gibson A type that is 86 years old and still very straight and many the truss rod mandolins after it,  the truss rod is time tested.  Really,  I think CF is fine,  just not for me.  I want the option to adjust.   We all know that the truss works.  We all know that CF in the neck probably works very well.   I always get comments on my instruments on how easy they play and how straight the necks are.   I bet if you were to do a study,  most mandolin players would want the ability to adjust.  Because most players I know set up mandolins to play just like they want.  I understand the truss rod is not for adjusting action but it does so anyway,  Nick

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## labraid

You know what else is time tested. War. Yeah, you know those diplomatic French, trying to talk stuff out and all, look where it got them in WWII. 
Slavery. Hey, work for free, why not? They built one rich nation, why not others?
Hey, maybe CF will be time tested one day. Then we can count it among the great time tested things of history. 
Your arguments are priceless Nick.

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## kestrel

Price-less.

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## Nick Triesch

This thread has obviously generated a bunch of interest.  Folks will read all this stuff and will use it to buy their mandolins now and in the future.   It's all really about to tweek or not not tweek?  That is the Question.   I want to tweek!    I just got home from work and I will grab my Weber and a hot cup of coffee and work on the Butch song,    "Black Mountain Aire".    Almost got it wired!   Nick

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## Rick Turner

I wouldn't buy an instrument weighing the decision heavily one way or another based on this thread.  I think that if an instrument is built by a good maker, either system will work; there are just trade-offs.  I would buy an instrument based on liking the tone as the top criterion, then go to playability and how I feel it's likely to stay stable...or not.  I'm after results in a new instrument, not stories.  If I want stories, I'll get a vintage instrument with lots of ghosts in it.  Back stories about the why and wherefore are great, and I certainly sell instruments with that in mind, but tone is king and trumps all else.

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## amowry

I think it's been illustrated here that there's more to it than the question of adjustability. If that were the only issue I'd choose adjustability in a second. However, for me, the advantages of CF outweigh adjustability. Different strokes...

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## Michael Lewis

Well stated, Andrew.

Whether a neck is reinforced with  CF or an adjustable rod does not necessarily mean it will be a good neck.  As always, it depends on HOW it is arranged.  I have done set ups on some Pac rim imports and from a domestic maker that the truss rods were absolutely useless.  Rods either glued and locked in their slots or set too high in the neck beam.  I have also seen CF reinforced necks that flexed too much due to the fact that the CF was either too small or not placed strategically.  The more flexible the neck the more critical the reinforcement.  The design parameters set forth by tradition usually work well enough, but there exceptions.  Some necks warp, twist, or bow regardless of the adjustable truss rod.  

Flat top guitars are still being made in the traditional design that will guarantee the neck will need to be reset at some point in the future.   Rick Turner makes acoustic guitars that probably will not need that procedure because he has designed the instruments to resist the typical forces and deformations.    Tradition has it's place, but remember, what now is Tradition was at one time the new kid on the block.

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## Rick Turner

Thanks for the mention, Michael.  Actually, you can "reset" the neck on my guitars in about ten seconds, and that's if you fumble with the Allen wrench.  The neck angle is totally adjustable, and that is the means for adjusting action, which in turn means you don't have to mess with the bridge saddle height.

And I've got carbon fiber assisted back braces, and carbon fiber flying buttresses, and two 1/8" x 1/2" CF rods in the neck, ............and an adjustable two way action truss rod.

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## labraid

That's some mighty reinforcement, Rick.

To add to what Michael said, there is also a question of how you treat the rod at installation. Was the surface properly readied, is the adhesive the right one, was it simply laid in a bed of glue leaving a thick glue line, or was it clamped to maximize squeezeout.

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## j. condino

Michael:

'Careful about giving away trade secrets....Martin neck resets are a nice reliable source of regular income for anybody that works on guitars; almost as reliable as old Kay basses, which get a lot of carbon fiber retrofits under the fingerboards! 

j.
www.condino.com

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## Rick Turner

Given that there are close to a million and a half Martins out there, I don't think luthiers will be out of the reset biz anytime soon!

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## labraid

You know, I keep laughing to myself, something in all this really is very funny. I mean, this whole CF rod placement thing being unresolved still. I mean, I'm not just an obsessive fool... The anecdotal evidence of aforementioned dude, whose lack of secured CF rod in the slot, placed directly on the "accepted" neutral axis under the fingerboard, and the neck that bowed like mad? No one else mentally juggling that? Something that flies in the face of everything we take for granted in our CF work, and... that's it? 
My last ditch effort........

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## labraid

Ok, I have a plan. I'll present my hypothesis and the method I intend to use in testing this.... If it sounds to others like it would prove things one way or another, I'll go ahead with it. Give me a few days...... We're in the middle of a freakin' move, God I must be insane.

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## Rick Turner

I don't have a problem with his having had a problem.  He used the stuff all wrong, so of course he had a problem...   I don't see anything out of line with what Dave and I have been saying.  Put CF in the neutral axis, and it won't do much except take up space.  Put it at the very back of the neck, and it won't stretch.  Make a fingerboard out of it (my patent assigned to Gibson from 1989...) and it is pretty darned good in compression.  Add one or more CF webs to that (also in that patent), and you've got what I call a structural fingerboard, and yes, some of the CF is in the neutral axis in that structure which is what I do now.  But it wouldn't be cost effective to do anything much different.   With my guitars, the structural fingerboard is so stiff and stable that the neck could be practically anything.  Also it puts stability and predictability right were you need it...supporting the frets.  It's all about the fret tops when it comes to playability.  That conical or cylindrical surface line with a gentle relief curve is what we're going for.  Anything at all that stabilizes that is a good thing.

We're picking nits here with worrying too much about the neutral axis.  There is one, it's there in any neck.  I'd worry more about the fret tops and the line they take, and I believe I do know how to control that.

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## labraid

> I don't see anything out of line with what Dave and I have been saying.

This is where the neutral axis _is_ worth picking nits on, IMO. Dr. Cohen recommends to all that they put the CF as deeply into the neck as possible, and not directly under the fingerboard. Why? Because under the fingerboard would be the neutral axis and therefore provide no net benefit to stability. My only problem with this recommendation is that I have seen the large amounts of CF that DC uses in his necks, and believe the man they are in fact very sturdy. The sad truth, though, is that DC could put his CF assembly almost anwhere, similar to what you say Rick, and it would have the very same effect -- he has essentially, and very wisely, hedged his bets. His recommendation to others, however, that if they were to use only one single rod alone, that it be buried very deeply in the neck... this recommendation, while not mal-intentioned, could be very harmful due to the fact that neither is DC using this configuration, but he admits, I believe, that he does not know where the neutral axis is with any detailed precision. Furthermore, no one person at this point is willing to gaurantee anyone else *that the NA is the most stable region* given the _non-bending_ forces which distort the NA. His recommendation of deep-setting one's CF is based not only on traditional compression rod technique, but also on an unverified _assumption_.... Yes an _assumption_ that deep down in the neck is the most instable region of the neck, an area which needs to be tamed more than any other in the profile. For one, though, a CF rod is not a compression rod, and two, the region of the neutral axis is not gauranteed any sort of stability outside of pure bending forces. Three, anecdotal evidence from an amateur builder's oversight (how many of us have had such a fortunate and telling error!) shows that a 1/8" wide x 3/8" tall cavity directly under the fretboard did not in fact contain any area of stability -- rather, and to the contrary, it was evidenced to contain an area significant in upholding the overall straightness of the neck. 
Does my argument seem to be taking on some sort of precision at this point?

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## Rick Turner

The reason for putting CF as close to the back of the neck as possible has nothing to do with what part of the neck is the most stable, it's because CF resists stretching better than just about any material known to man, and when a neck bends forward, the back of the neck is stretching.  That's why my original patent was for a hollow CF neck.  Putting a high modulus material as close as possible to the surface that is under tension is the most efficient use of the stuff.   I choose not to do that these days, but rather make a structural beam out of the fingerboard and CF that is quite stiff and strong enough for my purposes.  I know I'm not using the materials as efficiently as I could, but there are other reasons that override pure engineering here...like the ability to carve a wooden neck.

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## Dave Cohen

Brian, no assumptions whatsoever are involved.  As I said earlier, I have the math chops to do the calculation which you are talking about.  I choose not to spend any time on the calculation because I don't think that it would be a good use of my time at the moment.  Imo, it is not even that difficult a calculation.  All one would have to do is make a scale drawing of the neck cross section(s), and use numerical integration to determine the shearing moments.  Where the moment is zero, you are at the neutral axis.

"Stability" is not really the proper word for describing what happens when a neck bends.  If it bends into a position and stays there (at least for a while), it is at equilibrium; it has the lowest possible potential energy (save being able to return to straight), and it is as stable as it's gonna get (at least for a while).  When a neck bends under string tension, the material exactly on the neutral axis neither stretches nor compresses.  Go a tiny bit south of the neutral axis, i.e., toward the back of the neck, and the material there has to stretch.  That means that the fibers have to slide past each other in the lignin matrix.  Go further toward the back of the neck, and the material has to stretch more.  Go all the way the the back of the neck, and the fibers have to stretch the most.  The terminology is that the shear is greater the farther away from the neutral axis you get.  It also means that the restoring forces farthest away from the n.a. are the largest.  Same thing happens above the neutral axis, i.e., toward the fingerboard, except that the material has to compress instead of stretching.  Now, if you are gonna use some very high modulus material that is very resistant to stretching or compressing to reinforce the neck, you want to put it where the shear is greatest to get the greatest effect, and that would be all the way at the back of the neck.  There, you are supplying the greatest restoring forces possible to counter the shear forces.  Since we (a) don't want it to be visible, and (b) glue seam failure would risk catastrophic failure of the neck, we put it about 1/8" to 3/16" (ca 3-5 mm) up from the back of the neck.

Btw, no one is recommending that the reinforcement be at the n.a.  To the contrary, it should be as far from the n.a. as practically possible.  That is why I put my CF as far toward the back of the neck as possible, and Rick puts as much of his "structural fingerboard" as possible above the n.a.  Once again, those are not assumptions at all.  Another thing; I am using two 1/8"x3/8" CF composite rods in my necks, which is less than some recommend.  I just configure them differently to get as much stiffening as possible.

Oh, and another thing:  "non-bending" forces do not distort the n.a.  The neutral axis is a construct that exists solely because of bending.  All it is is the dividing line between where the shear results in compression and where it results in tension, i.e., where the shear is zero.

http://www.Cohenmando.com

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## amowry

While I don't have the ability to determine where the neutral axis is, I've always put my CF as far back in the neck as possible because it makes intuitive sense to me. We have the ebony fretboard at the front of the neck, which to me represents a structure that is fairly resistant to compression. If I'm going to put another reinforcing structure in the neck, it makes sense to me to put it as far back as possible, so I'm in a sense making the beam as thick as possible. I think the back of the neck is in tension, but even if the whole neck were in compression, it still makes sense to me to have the CF as far back as possible.

Say, just for the sake of argument, that the maple in the neck has no structural role at all, and is just there for filler. If you have a neck whose strength comes mostly from a fretboard and a CF bar, wouldn't you want those to be as far apart as possible? I know that's an oversimplification, but in my simple mind it seems quite clear, and holds true regardless of the location of the neutral axis.

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## labraid

Well, my method is going to be: 
5 identical maple rods, each 4 parts maple in cross sectional height and 1 part ebony -- loosely but constantly mimicking a neck profile. A critical section of each profile will be removed, first from the top 1/5, the ebony, second, 1/5 below the ebony, and so on until piece number 5 will have a section removed from its back. Each will be strung up with identically tuned and equal length sections of musical wire on both front and back faces. A steel cable simulating regular string tension will then be applied, each piece in turn and identically so. Dimensional change will be measured by how much each wire changes pitch -- shrinkage indicated by a drop in pitch, elongation by a rise. Deflection will be measured by the space between test surface and steel straight-edge at direct center of the piece.
Consistent with what I have been advocating, it is my belief that the piece 4 (1 being where ebony from the face is removed, 5 being where back wood was removed) will show the least forward deflection of the 5, illustrating that compression forces in a neck outweight tensions caused by bending, and also that the implied location of the neutral axis in relation to the voids (where CF rod would usually go) is less a factor in neck stability than currently taken for granted. Lastly, we will be able to actually hear and measure which faces will show net elongation, and which will show net compression. Here it is my belief that top strings in general will lower in pitch more than bottom strings will rise. Again, I believe piece number 4 will come out with the lowest disparity between pitch changes.

At least I have a reason to go and buy a nice table saw now.

ps, I'll need at least three months.

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## Rick Turner

Andrew, you are absolutely correct.

I have CF probably in the neutral axis just because it's convenient.  I dado 1/8" x 1/2" CF rods up into the fingerboard about 3/32"...just below where the fret slots are.  When I'm really on a trip, I don't use normal wood for the fingerboard; I use "PakkaWood" or "Diamond Wood"...laminated birch veneers impregnated with phenolic resin.  The compressive strength is pretty impressive on that stuff.  The CF rods are then dadoed a bit more than 3/8" down into the neck, so I suspect they pass through the neutral axis, but what the heck, there they are.  Then I have a two way truss rod between the CF bars.  Belt and suspenders.  No problems with the necks...even in the Antarctic climate.

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## labraid

Alright, here's a visual of the conundrum, does anyone else see a problem with the figure on the right?

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## Rick Turner

What I see is that you're trying to show us that the side of the beam closest to the load of the weight and the side farthest away are both in compression, and I'm not buying it.  That's not how things bend.  You're on this compression/compression kick, but it doesn't matter how you apply the load, if you're bending a beam, one side is in compression, one side is in tension.  This is absolutely classic engineering.

Try using an archery bow for your example...

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## labraid

Well... I guess I am wrong on this one. What can I say?......

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## Dfyngravity

I have been following this thread for the beginning and it all seems very interesting. I have been thinking about a few things, but I am not sure if they have any effect or not or if the theory holds any water what so ever. 

It seems to me that the closer you get the strings to run parallel with the neck, the less you have to worry about the neck bending. Also, the shorter the neck is the less you have to worry about it bending. 

Taking that into consideration, a new mandolin such as a classical mandolin like a bowlback that uses lighter strings, has a shorter neck, and typically lower action with the strings running closer to parallel will be less likely to have neck that bows forward.

So by using this theory, a typical bluegrass mandolin that has heavier gauge strings, a longer neck and action that is further away from being parallel to the neck, the neck is more likely to want to bow forward.

Does any of this make sense or have any value? If so, I would think you would want to not worry so much whether or not to use a truss rod vs. CF and try to minimize the effects of the string tension on the neck. For instance, if having the strings running closer to parallel with help relief tension on the neck, then you could increase the neck angle slightly. This would allow to you keep the same bridge height but the strings would closer to parallel to the neck and the action would be lower. But I am not too sure what you would do with the length of the neck. 

Anyways, these are just some things that popped in my head when I was reading though the thread. They are probably way off but I figured I would ask and see, since there seems to be a few here that have a lot more knowledge than I do.

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## Dave Cohen

Brian, no need for me to pile on now.  I can see where you misled yourself, though.  One thing is that you left out the little red vectors from your earlier diagram.  The resultant force is the sum of the (red _and_ blue) component vectors, which will point away from the top of the neck.  That is, it will point up off the fingerboard.  The other thing is that the origination of the vectors is at the top of the neck - actually above it, at the top of the nut and over the fingerboard - and on the basis of vector algebra, you can't claim that the force vector is doing the same thing at the back of the neck.... or anywhere but at the top of the nut, for that matter.  Sorry that I didn't think to point that out earlier.

http;//www.Cohenmando.com

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## Michael Lewis

Well folks, this has been an entertaining, educational, and enjoyable  session.  Thanks Brian, Dave, Rick, Andrew, and others (you too) for the lively discourse.

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## Joel Spaulding

Brian , Dave and Rick;

As usual you have individually and collectively informed, educated and entertained throughout this thread.  :Grin: 

Any time you three want to discuss this and similar issues until the wee hours of the AM, let me know and I'll cook and provide ample quantities of stout, pale ale or beverage of choice. Sorry I can't fly all of you to KY ( I guess that's _all y'all_. ) 

Brian - Cape Bretton is a pretty magical but somewhat remote locale - hope to return for another visit someday. Best of luck with your move.

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## J.Sloan

Thought I would bring this post back to life only to ask one simple question. For those with experience with CF necks, do you feel that it is crucial to use epoxy for gluing in carbon fiber rods, or would it be ok to use tightbond? I realize that epoxy is stronger, but once the rod & filler stick is glued in and covered, the CF doesn't bend anyway. I've always used epoxy in the few mandolin CF necks that I have made....but the stuff is so messy. I got into the habit off taping off the neck just in case of any spills or runoff. Maybe I could take a large hole syringe and slowly squeeze it in. But, if I can get the same results with wood glue....well...you know. I'm all ears and stand corrected if epoxy is supreme in this question. Up until now, it's all I have used anyway.  Thanks!

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## Dave Cohen

I'm not sure that epoxy is much stronger for bonding wood to wood than are yellow AR glues such as Tightbond.  On the other hand, the CF composite bars used for neck stiffening are usually CF/_epoxy_ composite, or sometimes CF/polyester composite.  The surface often needs to be made _bondable_ by roughening the surface w/ sandpaper.  Otherwise, no type of glue will stick to it for very long.  Once the surface of the CF composite bar is made bondable, epoxy is the closest chemically to the composition of the stuff in the CF composite bars that holds the CF fibers together.    I don't know if Tightbond will work in your application or not, but my first guess is that it will not work as well as epoxy. Tightbond is sold as a wood glue; it needs the somewhat porous surfaces of wood to be effective.

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J.Sloan

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## fscotte

I make my channel so tight that titebond is fine.  I have to literally use a clamp to push my CF rod in after I put down a layer of glue.  If your channel isn't so tight fitting then maybe a gap filling glue like epoxy would be better suited.  It's likely one of those things that wouldn't rear its ugly head until 80 years later anyway.

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J.Sloan

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## John Kelly

On the three necks I have done with CF reinforcement I have used Titebond, making sure the channel for the CF has been routed to a tight fit (as fscotte says above) and the filler strip is clamped down really firmly while the glue is drying.  I wrap the CF rod in masking tape too before inserting it into the slot.  No problems so far but we are only talking about a couple of years or so, so I do not know long-term results.  The steel rods I used before the CF have been in existence for around 12 years now on the first instruments I built and it's only on a bouzouki that I have used an adjustable rod - not on mandolin or octave.

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J.Sloan

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## bpatrick

Does anyone see a problem with using (2) !/8" x 1/2" carbon fiber rods glued together in the same channel instead of (1) 1/4" x 1/2" rod?

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## Tavy

> Does anyone see a problem with using (2) !/8" x 1/2" carbon fiber rods glued together in the same channel instead of (1) 1/4" x 1/2" rod?


No, that's what I use.  Just make sure that they're a tight mechanical fit in the channel in addition to being well glued in.

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## J.Sloan

I'm going with 2-- 1/4" carbon fiber rods for my current F4 build. I put them close enough together to not hinder the fingerboard profile once it's tapered down(1 1/8" nut) but I only did this because it's my first mahogany neck and it's a much softer wood than the red maple that I usually use for F5 and A5 mandolins. Hopefully, this will keep any future twisting from happening as well. 

sloanmandolins.com

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