Graphite Neck Laminates; Tell Me Your Experiences.

[westhemann]

it says in the instructions that you can do that...although it is talking about solvent based thinners...(same thing)and it just says the bond will be a bit weaker.

i am sure it would be minimal though...i bet it would hold up perfectly

[tirapop]

GBT,

Laminating the composite perpendicular to the fingerboard would add stiffness to the neck, resisting string tension. It's not the most efficient way to add stiffness, but, it does. To resist bending, you want as much material on the top and bottom as you can (think of an I-beam). The taller the beam is, the stiffer it is.

For a rectangle, the area moment of inertia (a measure of geometric stiffness) is width X (height cubed)/12. You can see that adding height is more efficient than adding width to increasing stiffness. The material in the middle doesn't add much to the stiffness. If the height were one, eighty percent of the height (0.8) would add only half (0.8^3 = .512) of the total stiffness. Again, that's why I-beams look like I-beams.

If the laminations are through the thickness of the neck, taller than what a precured carbon reinforcing rod is, it can be made as stiff or stiffer than the rod.

[westhemann]

To resist bending, you want as much material on the top and bottom as you can (think of an I-beam). The taller the beam is, the stiffer it is.

i am not sure you realize that this sounds like a contradiction...i am sure you know what you are talking about though...your further explanation shows that you are correct.

picture an I beam from the end view...the top and bottom of the I are the "flanges"...the middle of the I is the "web".

the web is what gives the beam it's up and down stiffness,and the flanges stiffen it up side to side.

this is how i make a living.installing the iron that the engineers and architects dream up.

[tirapop]

Hey Wes,

I make my living as a structural analyst. I get to say how big the I-beams are.

When you stand on a I-beam, that's supported on it's ends or cantilevered, your weight puts a perpendicular load on the beam. It's called the shear load. That load is carried in the web of the I-beam.

Your weight also will put a bending load on the beam, called the bending moment. The bending load puts a compression load on the top of the beam and a tension load on the bottom. Picture the beam sagging. The length of the curve on the top of the beam is shorter than the length of the curve on the bottom. The top is getting squished and the bottom stretched.

The transition from squished to stretched is continuous through the height of the beam and somewhere in the middle of the beam, it's neither squished nor stretched. So, at the top and the bottom of the beam, that material is getting stretched/squished the most. Adding more material there resists those stretching/squishing loads. That makes the beam stiffer.

Think about a truss bridge. There's a lot of air where the web of an equivalent I-beam would be. The beams at the top and bottom of the truss are doing most of the work in resisting the bending moment from vehicles crossing the bridge.

In a guitar neck, there's no shear load. The bending moment comes from string tension. The strings are reacted by compression in the neck, along its length, and a bending moment. The most efficient use of graphite to stiffen a neck would be to put it on the surfaces that are getting stretched/squished the most. A layer under the fretboard and a layer on the back of the neck would be stiffer than equal amounts of carbon in a carbon rod or a through thickness laminate.

[GodBlessTexas]

GBT,

Laminating the composite perpendicular to the fingerboard would add stiffness to the neck, resisting string tension.  It's not the most efficient way to add stiffness, but, it does.  To resist bending, you want as much material on the top and bottom as you can (think of an I-beam).  The taller the beam is, the stiffer it is.

Given that laminated (meaning infused with resin) carbon fiber cloth in a flat sheet has all of it's strength on the flat surface, wouldn't it be ideal to laminate it parallel to the fretboard? I guess it depends on what aspect of the neck you're trying to stiffen. To get some bearings on orientation, let's assume you're holding the guitar strapped to you as if you were playing it. If you use carbon fiber in the traditional way that guitar necks are built, with the material running perpendicualr to the fretboard, then the support will help keep the neck from twisting or being bent up towards the cieling or down towards the floor. But it won't provide strenth to keep the neck from being pulled towards the body along the strings. Of course, it will provide increased strenght along that axis if it is laminated thick enough. That is one of the reasons why rods are used so frequently.

As far as I-beams go, I'm not quite sure how applicable it is to the construction of guitar necks. Of all the graphite/carbon fiber reinforced necks I've seen, they fall into two categories:

Wood necks reinforced with carbon rods - the most common, probably because it's easy to do and requires about as much work as putting a truss rod in a neck.

Wood necks reinforced with an outer overlay of carbon fiber - Parket guitars, though actually the entire back of the body and neck is overlayed in one piece of cloth. The best solution in my opinion because it protects the neck from warping and twisting because the cloth is oriented on axis.

If the laminations are through the thickness of the neck, taller than what a precured carbon reinforcing rod is, it can be made as stiff or stiffer than the rod.

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No arguments there. But the rod has the advantage of providing stiffness parallel and perpendicular to the fretboard. A laminated sheet will only provide support along the weave of the cloth.

Remember the Alamo, and God Bless Texas...

Edited August 9, 2005 by GodBlessTexas

[GodBlessTexas]

In a guitar neck, there's no shear load.  The bending moment comes from string tension.  The strings are reacted by compression in the neck, along its length, and a bending moment.  The most efficient use of graphite to stiffen a neck would be to put it on the surfaces that are getting stretched/squished the most.  A layer under the fretboard and a layer on the back of the neck would be stiffer than equal amounts of carbon in a carbon rod or a through thickness laminate.

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That's exactly what I was saying. You want the carbon fiber to run parallel to the fretboard. If you use it like you would in a traditional wood laminated neck, it runs perpendicular to the fretboard.

Remember the Alamo, and God Bless Texas...

[westhemann]

the point is moot ...you are talking some serious hoodoo to get that carbon laminate on the rounded back of that neck..all for absolutely no reason,since the wood is strong enough without any carbon laminates of any sort already,and more than strong enough with the vertical laminate or the inserted rods.

but you and i both know that the web of the beam in most standard beam sizes supports the majority of the downward pressure...the top and bottom flanges only(well not ONLY...but that is the majority of it) keep the web from twisting sideways under the load...just like bridging does for joists.

by the way,when every engineer i ever met or did work for sent us in to beef up an existing beam with plate steel for an increased downward load,they had us beef up the web,not the flange.i have installed rolled steel into the corner of the web and flange...but i really think rolled steel is not dependant so much on positioning.but of course we are meant to install all of that as close to top or bottom of the beam,but it is for beefing up the web load.

same reason we ALWAYS run angle with uneven sides(6" by 4" for example) with the long side down...it supports more weight that way..

When you stand on a I-beam, that's supported on it's ends or cantilevered, your weight puts a perpendicular load on the beam. It's called the shear load. That load is carried in the web of the I-beam.

oops..i just caught this...that is exactly what i was saying...nevermind,we are on the same page..i think we are just confusing each other with terminology.(at least that was my problem)

but yes,i am familiar with shear load and cantilevered beams and all of this...i am the guy with the drawings down on the ground telling all my men what they say,with occasional epithets and screaming things like "get the m***** f**** up there.." and "you're not going to THINK it up there..!"

most people don't realize it,but you have to have a seriously big brain(so to speak) to read those drawings and get a comprehensive mental picture of what the building will look like...don't get me wrong...i have met foremen and superintendants who just kind of muddled through...but believe me when i say i have a complete working knowledge of the building methods of my craft.most ironworking foremen are very sharp,even though they don't talk like it...you just get used to speaking the language simply enough for your incompetant hands to understand you...(especially when most of mine don't speak english as their primary language)

[fryovanni]

Wes,

but yes,i am familiar with shear load and cantilevered beams and all of this...i am the guy with the drawings down on the ground telling all my men what they say,with occasional epithets and screaming things like "get the m***** f**** up there.." and "you're not going to THINK it up there..!"

most people don't realize it,but you have to have a seriously big brain(so to speak) to read those drawings and get a comprehensive mental picture of what the building will look like...don't get me wrong...i have met foremen and superintendants who just kind of muddled through...but believe me when i say i have a complete working knowledge of the building methods of my craft.most ironworking foremen are very sharp,even though they don't talk like it...you just get used to speaking the language simply enough for your incompetant hands to understand you...(especially when most of mine don't speak english as their primary language)

Dude, You kill me

An Ironworker with a BIG BRAIN, not just the hardest working fools on site. CHEERS!

Peace, Rich

[tirapop]

Howdy GBT, howdy Wes,

GBT, like I said a thru thickness laminate (perpendicular to the fretboard) isn't the most efficient way to stiffen the neck, but, it does stiffen the neck. Notice the orientation of the carbon rod (example 1) in this stewmac diagram:

What thegarehanman proposes is to make that carbon rod taller (stiffer to string induced bending) and narrower (maybe less stiff, depending on the thickness). Remember increased height increase stiffness by its cube, much faster than you lose it by reducing thickness.

If you have a flexible steel ruler, you can do the quick science experiment at home. Orient the ruler the way the laminate would be (perpendicular to the fretboard, parallel to the floor). Now, try bending it the way the strings would, making the corners on the edge furthest from you move together. Stiff, eh? You might be able to get the compression side to buckle (bow out of the way). But, laminated in wood, it wouldn't buckle and would be stiffer still.

Wes, you can wet lay-up carbon to the back of a guitar neck pretty easily.

A couple of carbon DIY fab links: making a graphite tube (makes wrapping a guitar neck look easy); making a graphite spar for a model airplane (notice for the wing bending loads they make the flanges graphite and use foam for the web); making motorcycle parts

The idea isn't to make a stronger neck, just a stiffer (more stable) neck.

I appreciate the guys who can take drawings and make them into hard parts. Analysts just check to make sure things are strong enough. You can blame designers for making thing difficult or impossible to build.

thegarehanman, have you seen what the polished edge of a graphite laminate looks like? They aren't pretty, like the face of the laminate, that's shiny and looks like woven silk. The edges of the laminate look matte and you see the ends of fibers and lengths of fiber weaving over and under those fibers perpendicular to the edge. Thin glueline or not, they probably won't enhance the appearance of the neck, when you take a close look.

[SwedishLuthier]

About the I-beams: The flanges in an I-beam isn't there to stop the beam from twisting. It is the flanges that give the beam the strength. The web is only there to separate the flanges!!! That’s a fact. Try the steel rule experiment with the ruler orientated parallel with the imaginary fret board. Not much support, eh?

This shows that the use of square graphite rods embedded in the middle of the neck, example 3 in the pic, actually doesn’t do much to support the neck against the string pull. What it actually does is to help prevent the neck from bending up or down (in playing position)!!! It might also help prevent twisting a little bit.

The best way (for me and you, more about that later) to laminate a thin graphite sheet into a neck is between strips of wood and let the sheet go all the way thru the neck (I’m speaking structural strength, not the best look) much like old arch tops some time have thin laminates of ebony running down the centre line of the neck.

Actually the ideal way, structurally, to use reinforcement a neck is to glue a thin sheet to the back of the neck and a thin sheet just under the fretboard. Now the neck wood will act as the web in the I-beam, and the reinforcement sheets will act as the flanges. But that would look like crap. That is why company like Modulus cap the entire back of their necks in graphite.

Conclusion:

To support the neck against string pull, glue graphite sheets between wood laminates.

To support the neck from bending/twisting use graphite rods embedded in the neck.

Peter

Edited August 10, 2005 by SwedishLuthier

[westhemann]

Wes,

but yes,i am familiar with shear load and cantilevered beams and all of this...i am the guy with the drawings down on the ground telling all my men what they say,with occasional epithets and screaming things like "get the m***** f**** up there.." and "you're not going to THINK it up there..!"

most people don't realize it,but you have to have a seriously big brain(so to speak) to read those drawings and get a comprehensive mental picture of what the building will look like...don't get me wrong...i have met foremen and superintendants who just kind of muddled through...but believe me when i say i have a complete working knowledge of the building methods of my craft.most ironworking foremen are very sharp,even though they don't talk like it...you just get used to speaking the language simply enough for your incompetant hands to understand you...(especially when most of mine don't speak english as their primary language)

Dude, You kill me

An Ironworker with a BIG BRAIN, not just the hardest working fools on site. CHEERS!

Peace, Rich

←

i said ironworking FOREMEN are generally pretty sharp...your average ironworker is dumb as a brick and almost as dumb as a brick mason

tirapop...i worry that a graphite skin would need to be finished to be safe...is it not graphite in which they say it is dangerous to sand?i know stewmac warns against shapiing the carbon fibre rods

This shows that the use of square graphite rods embedded in the middle of the neck, example 3 in the pic, actually doesn’t do much to support the neck against the string pull. What it actually does is to help prevent the neck from bending up or down (in playing position)!!! It might also help prevent twisting a little bit.

that is the silliest use of theory i have ever heard

just install the rods as reccomended by stewmac and the manufacturers..good grief

[fryovanni]

Wes,

i said ironworking FOREMEN are generally pretty sharp...your average ironworker is dumb as a brick and almost as dumb as a brick mason

I just got a kick out of the "Big Brain". Just had a pic in my head of a guy with a very large hardhat. No put down tward Iron workers, especially the ones packing tools. Seems like most General Superintendents on large projects have a background in iron work. What do I know though... I am an Electricial.

Peace, Rich

[nollock]

I would have though part of the reason for using an I beam is that it has good a strength to weight ratio? But as carbon fiber is lighter than wood the weight is irelivant, so it jsut becomes a case of what is strongest and most convenient. For example an inch square rod will be stronger than a similar size I beam, easier to use, and make little differance in terms of weight.

imho

chris

[westhemann]

well...beam construction has nothing to do with guitars,so debating beam strength is probably way off topic.

but in a guitar neck of course the whole point is to counter string tension,and add stability...and that is what the rods do,regardless of which diagram you follow on the stewmac page.

[tirapop]

I-beams have flanges to increase their bending strength and to keep the compression flange from buckling. When you need strength/stiffness in the other direction, you go to an H-beam (wider flanges) or a box section.

Swedish, like I said, beam web is there to carry shear loads. If you have pure bending, then yes, it's just there to separate the flanges.

The squat carbon rods in examples 3 & 4 are probably short to maintain some edge distance to the back of the neck. No, they aren't the most efficient, for resisting string tension. But, the do resist twist. Twisting forces are smaller than the string tension forces. That's probably why the rods are set so far apart from each other, compared to example 2, to provide more leverage to resist twist. The truss rod is there to adjust for bowing from string tension.

Yes, Wes, you need to use some care when finishing graphite... but, there are a lot of conventional guitar building materials that require as much caution. Check out that link on DIY carbon motorcycle parts. Much of the finishing is troweling on more epoxy to fill pinholes and build up a smooth surface. They're just sanding epoxy, not fibers. Depending on how you capped a neck with carbon, you could do it in such a way that you weren't removing any fiber.

[SwedishLuthier]

This shows that the use of square graphite rods embedded in the middle of the neck, example 3 in the pic, actually doesn’t do much to support the neck against the string pull. What it actually does is to help prevent the neck from bending up or down (in playing position)!!! It might also help prevent twisting a little bit.

that is the silliest use of theory i have ever heard

just install the rods as reccomended by stewmac and the manufacturers..good grief

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[westhemann]

If you want good resistance to bending, you need to place the material that shall withstand the bending as FAR away as possible from the centre line of the construction.

this is not practical....they are placed under the fretboard because that is the most practical way to do it,and it adds just the stiffness needed,no more,no less...it isn't an engine hoist after all,it is a guitar neck

or thin laminates between wood, going all the way trough the neck.

hmmm...much like the web of a beam?i thought you said that was bogus?just a few posts ago you were arguing that was not "efficient".

look,let's get PRACTICAL with the guitar building.and PRACTICALLY speaking,ALL of those reinforcement diagrams increase stiffness in every direction more than the wood they replace.that is,once again,their purpose.

tirapop has some good suggestions about the carbon fibre "skin",or "exoskeleton"..i think that may be worth doing.

by the way,ever hear of T plate?it is a member which supports loads in which there is no bottom flange at all,the web supports the great majority of the load.

but back on topic...like i said,all of those diagrams show ways to increase stiffness in the neck,and none of them are meant to support the neck from the pull of gravity in playing position,like you suggest

[Mr.Churchyard]

I have another question. I was thinking to build a neckthrough from the ground up. Would the use of carbon fiber neck rods eliminate the need for laminating the neck and allow me to build it from one maple piece? Or can I scrape that idea?

[westhemann]

you can build itfrom one piece regardless..the graphite rods are merely insurance against future neck problems

[Mr.Churchyard]

you can build itfrom one piece regardless..the graphite rods are merely insurance against future neck problems

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Really? All the neck-throughs I was looking at had laminates for stability... That is reassuring, thank you.

[jnewman]

Wes, stiffness is measured in terms of bending moment (I). Calculate the bending moment for an I-beam, then calculate the bending moment for just the beam's web. The bending moment for the I-beam is often more than an order of magnitude higher.

The reason that you always end up reinforcing the web of an I-beam is NOT to make the I-beam stiffer. It'll make it a little stiffer, but only a very small amount. The reason you reinforce the web of the I-beam is because the mode of failure for an I-beam under bending moment is primarily buckling in the web. You're increasing the failure strength of the I-beam, not (at least not to a significant extent) it's stiffness. There's a BIG difference, and in this case, we're more interested in the bending moment (stiffness) than the failure strength. Guitar necks bend a little bit under string load, they don't break under string load.

The more cross-sectional area there is the farther away from the axis of flexure, the greater the bending moment - i.e. you can increase bending moment by moving the cross-sectional area away from the axis of flexure, by increasing the cross-sectional area at a given distance from the cross-sectional area, or both.

To sum up: the reason for using a T-beam with a long web, an piece of angle with the long side in the plane of the load, or reinforcing the web of an I-beam, is to allow it to support more load without failure in a direction perpindicular to that of the load, not to keep it from flexing.

Take two I-beams. One has a web 8" high, one has a web 4" high. Both have the same mass per length. The 4" web I-beam may have a higher failure strength, but it will also flex more under load than the 8" web I-beam will.

You're comparing apples and oranges - tirapop is talking about how to increase stiffness (flexure per load), you're talking about how to increase ultimate strength (load to failure).

[westhemann]

you can build itfrom one piece regardless..the graphite rods are merely insurance against future neck problems

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Really? All the neck-throughs I was looking at had laminates for stability... That is reassuring, thank you.

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most people use laminates because it is easier to rip and flip a flatsawn piece than it is to find a good quartersawn piece.

carvin makes all of their neck throughs one piece

[westhemann]

Wes, stiffness is measured in terms of bending moment (I). Calculate the bending moment for an I-beam, then calculate the bending moment for just the beam's web. The bending moment for the I-beam is often more than an order of magnitude higher.

The reason that you always end up reinforcing the web of an I-beam is NOT to make the I-beam stiffer. It'll make it a little stiffer, but only a very small amount. The reason you reinforce the web of the I-beam is because the mode of failure for an I-beam under bending moment is primarily buckling in the web. You're increasing the failure strength of the I-beam, not (at least not to a significant extent) it's stiffness. There's a BIG difference, and in this case, we're more interested in the bending moment (stiffness) than the failure strength. Guitar necks bend a little bit under string load, they don't break under string load.

The more cross-sectional area there is the farther away from the axis of flexure, the greater the bending moment - i.e. you can increase bending moment by moving the cross-sectional area away from the axis of flexure, by increasing the cross-sectional area at a given distance from the cross-sectional area, or both.

To sum up: the reason for using a T-beam with a long web, an piece of angle with the long side in the plane of the load, or reinforcing the web of an I-beam, is to allow it to support more load without failure in a direction perpindicular to that of the load, not to keep it from flexing.

Take two I-beams. One has a web 8" high, one has a web 4" high. Both have the same mass per length. The 4" web I-beam may have a higher failure strength, but it will also flex more under load than the 8" web I-beam will.

You're comparing apples and oranges - tirapop is talking about how to increase stiffness (flexure per load), you're talking about how to increase ultimate strength (load to failure).

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everyone is a wannabe engineer these days.increasing "ultimate load" also increases stiffness as a byproduct.there is an overlapping of results...now stop with the off topic banter.I beams were brought up as an example and in reality there is not alot of correlation to guitar necks.

bottom line...graphite rods installed as per the diagrams shown increase stiffness!stop trying to sidetrack.that is what this topic is about...graphite rods and graphite laminates,not i beams,girders,joists,t plate,angle,bar stock,and of that b.s.

i deal in these materials and their erection every weekday of every damn year...and i don't come here to debate about them with every wannabe structural engineer enrolled in a college course.(tirapop excluded,he knows what he is going on about)

you know what?if you are so great at knowing all about steel strengths and load capabilities,then go to work doing it for a few years...then come talk to me about it.until then,leave me to my hobby of building guitars,because i don't want to sit here and argue with you about overlapping functions vs primary functions and which matters more to you in your head.

we are talking about PRACTICAL uses of these materials,a point which only tirapop seems to understand.

how do you others plan to put your "knowledge" and "theories' to work?how do you plan on adapting it to guitar neck construction?in what implementable manner do you propose to use your recently learned book smarts to further this discussion in a USEABLE manner?do you know?because i don't...

the only practical,implementable ideas to come out of this topic have been proposed by tirapop(graphite exoskeleton)and myself(use as directed...not even my idea...)

and also myka for finding the epoxy to laminate the graphite strips with.

have a nice day

[Gemleggat]

I have 2 carbon fibre rods to install in my first build. The main reason i wanted to use them was for future insurance. I was wondering if they would do much to resist compression forces that makes scale lenght shrink and necks go into the dreaded S shape in years to come. Anyone know much about this? I am using a hotrod between them. What sort of reliefs should i expect the neck to come up to with the truss rod loose? I know thats difficult to answer and is totally comparitive.

[jnewman]

Hey, guess what... that IS what I'm doing as work right now as an engineer in an engineering firm dealing with subsea structural elements.

Of course reinforcing the webbing will make a beam a bit stiffer - but not nearly as much stiffer as adding that material to the flanges. I'm not a "wannabe engineer," I AM an engineer.

I will agree with you that all this talk is pretty much the same thing as attempting to design a dinner table that will hold up a truck without falling down (i.e. far, far overdesigned), but if you're going for stiffness in the neck, and want it as stiff as possible, you want multiple laminates parallel to the fingerboard, which will result in a much stiffer neck. It will also let you use much less graphite, which will be both less expensive and (in my opinion) look better if you're leaving it exposed. I-beams are better than square bars because you can get away with a lot less material - ditto with, for example, two (or more) laminates parallel to the fretboard (the flanges of the I-beam) with a wood laminate between them (the web). The web only really matters as far as failure goes, and is obviously strong enough not to fail. The graphite laminates add tremendous stiffness (MUCH greater than the same amount of material perpindicular to the fretboard).

[EDIT] Although I didn't mention it originally, this idea taken to its logical extreme results in the graphite exoskeleton, which has, essentially, two laminates along the two outer surfaces (fretboard face and neck face) of the neck as far as possible from the center of the axis. This means that it is impossible to make the neck any stiffer without increasing the amount of material used - or, conversly, that for any given stiffness, this method uses the least graphite. There's a good reason Parker does things this way. They're one of the only major companies to use graphite reinforcement, and they DON'T do it with rods in the neck. I wonder why? [/EDIT]

What you're basically saying is "I have something that works alright for what I have so I'm not going to change it" - so why even use graphite at all, when wood works fine by itself? If you're going to attempt to design a stiff neck, you might as well design a really stiff neck that uses the minimum amount of expensive materials (i.e. a properly engineered graphite reinforced neck).

Furthermore, I don't think my comments ARE off topic. This topic is about graphite neck laminates and how to install them - and stiffness is the reason to install graphite laminates. There's been significant misunderstanding so far in this thread about what contributes to stiffness, and I was attempting to straighten a bit of it out.

If you're going to delete this post, go ahead - but at least read it first.

Edited August 12, 2005 by jnewman