Carbon Fiber Use In Lutherie

[Hesh1956]

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Recently I started using a bit of CF in my upper transverse braces and I will be very interested to see how the finished guitars sound. To my ear the tap tone is about the same if not slightly higher pitched in the UTB area.

I know that some ANZLFers have been using CF for a while now if not for some years now.

Lets see what folks are doing with CF and Lutherie and perhaps more importantly why?

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[Hesh1956]

Oh Rick and others using CF wanna weigh-in here and photos would be great too!

[Kim]

If your after giving the brace maximum strength Hesh, which is the only reason i would consider using CF in lutherie, you really want to be using 'unidirectional' CF glued to the 'bottom' surface of the brace/beam.

I will dig up a link to a relevant discussion.

Cheers

Kim
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[Kim]

Here ya go Hesh: viewtopic.php?t=1509&highlight=graphite


You may remember the old Maton rebuild i did a while back, it was that project which triggered the conversation at the above link. Here are some images to show what resulted with the 2mm thick unidirectional CF strip being glued to the bottom of the brace. This example is quite extreme and most defiantly overkill if the 1/4" square CF were included for a 'standard' guitar UTB, but a much needed addition which resolved the main problem in the original 'heelless' neck design of the F11. Anyhow i am sure you will get the idea.

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He's a link to that entire thread in case someone new is interested.

viewtopic.php?t=1903&postdays=0&postorder=asc&start=0


Cheers

Kim
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Last edited by Kim on Wed Dec 30, 2009 8:11 am; edited 1 time in total

[Hesh1956]

Thanks Kim!

Actually for my application here I am not after maximum strength. Instead I want to add more strength to the UTB but still have it flex slightly but retain some memory and return to it's neutral position. If a CF augmented guitar brace did not move at all we would not have a very responsive instrument.

What I wanted to see here were the diverse uses for CF in Lutherie. I know that Rick uses a lot of CF in his very cool guitars.

[Craig]

This should be an interesting thread Hesh as I'm sure a lot of us are finding more applications to improve the instrument.

First up is a foot I put on my headblock . I could only have this 1/2" thick because of my adjustable neck hardware. Not much strength , so I put in three 5mm. C.F. tubes which extend right through the headblock and foot . I like the tubes as they add no extra weight :
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After fixing these in place ,I capped the end of the foot with a piece of mahogany and Rosewood racing stripes to hide the tube ends ( and make it play faster Laughing ) This pic also shows my two 8mm. tubes I have running through the heel to help with any flex.
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These 8mm. tubes go right through the heel and meet up with the neck shaft C.F. rectangular sections ( 3 mm. X 9 mm. ) You'll also note these neck shaft reinforcements are splayed
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This pic shows my back brace closest to the heel .In my case , I capped it with a 3mm. X 1 mm. Carbon Fibre strip ( the 'Neutral Axis' thing ) This, to hopefully limit headblock rotational forces .
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Craig Lawrence

[Kim]

I don't believe there is any 'benefit' in having any amount of movement what so ever in the UTB and in fact will happily go on record as stating that any movement at the upper transfer brace (UTB) will only sink string energy into the upper bout and neck block thus reducing the effectiveness of the lower bout which, in my opinion is the area of the instrument that is the very essence of a responsive guitar.

Cheers

Kim
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[Kim]

Great work Craig, impeccable and innovative as usual.

Must ask, with the capping you have placed on the back brace, would not the CF have been more effective placed on the 'bottom' of the brace given that, if memory serves, it is most efficient at adding strength to a beam when placed to resist tensile force?

Cheers

Kim
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[Craig]

My thoughts too Kim regarding rigidity in that area. As you can see by my above pics , I have reinforced the neck shaft , heel , headblock and back brace area to be fairly rigid . This, to my thinking, should promote a sustaining string . Other areas , such as the remaining back braces , I have not reinforced as I want some movement there
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Craig Lawrence

Last edited by Craig on Wed Dec 30, 2009 8:52 am; edited 1 time in total

[Craig]

( doublepost cock-up )
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Craig Lawrence

[Craig]

Kim wrote:
Great work Craig, impeccable and innovative as usual.

Must ask, with the capping you have placed on the back brace, would not the CF have been more effective placed on the 'bottom' of the brace given that, if memory serves, it is most efficient at adding strength to a beam when placed to resist tensile force?

Cheers

Kim

In a word , 'No ' Think of the I beam . The back plate becomes one end of the beam's flat section and the C.F. capping becomes the other. i.e. the Neutral axis principle.
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Craig Lawrence

[Kim]

Yes Craig i can clearly see where you are heading with this an must say that i like the lay out very much.

Also I should define my earlier statement re; any movement at the UTB being a negative toward accomplishing a responsive guitar.

Should a builder have already countered the rotational force of string tension via buttress bracing back to the waist etc, then i concede that the upper bout certainly can be explored as a way of increasing the effective sound production area of the top. Failing that, it is my opinion that any movement or flex of the top at the UTB will at best 'reduce' the responsiveness of the guitar, and at worst indicate a lack of structural integrity.

Cheers

Kim
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[Kim]

Craig wrote:

In a word , 'No ' Laughing Think of the I beam . The back plate becomes one end of the beam's flat section and the C.F. capping becomes the other. i.e. the Neutral axis principle.

Fair enough, just keep'in you on your toes smarty pants
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[Hesh1956]

Craig you do some of the most beautiful work that I have ever seen!
Kim yes but.... there are many examples of approaches and some notable builders who buy into the idea that the top real estate north of the UTB has potential to add value to the sound of a guitar.

There are builders who either won't use a Popsicle brace or folks that make a living removing them from Martins believing that this frees up this area above the UTB to produce sound.

When I look at the approach that emphasizes massive structure instead of say a simple UTB I would suspect that the huge increase in mass acts as an energy sink providing no value to the performance of the overall system.

Another way to say that is that heavy ass guitars usually...., not always...., sound like shit - to me....

Anyway who cares - I just wanted to see the various uses that ANZLFers use CF for....

[Kim]

Hesh1956 wrote:

Kim yes but.... there are many examples of approaches and some notable builders who buy into the idea that the top real estate north of the UTB has potential to add value to the sound of a guitar.

There are builders who either won't use a Popsicle brace or folks that make a living removing them from Martins believing that this frees up this area above the UTB to produce sound.

Yes i know Hesh, but given enough time i'm sure they will eventually wake up to themselves.
Cheers

Kim
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[Hesh1956]

[Dominic]

Kim, your analysis sounds right to me. A strip of CF on the bottom of the brace would help control the back and stop it from over bending, forming a tighter back radius. Since the brace is glued to cross grain on the back that area would be relatively more susceptible to movement/swelling which would put the bottom of the spruce brace (I beam) under tension, letting the back dip and the head block tip in. String tension would act this way constantly.

CF strips on both top and bottom of the brace would offer more support and create a CF I beam held apart by spruce. This would resist both over bending and flattening of the back.

Hesho’s arrangement would do something similar but there is much less CF resisting tension on the bottom and top and more in the neutral middle where its function is far less effective.
Lovely work Craig btw.
Cheers
Dom
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[Rick Turner]

I refrain from gluing CF directly cross grain on the backs because I want there to be a slight allowance for wood movement. Gluing CF to the tops of the braces only makes them as strong as you could possibly want. As pre a previous thread, I also glue CF to the top of the center seam reinforcement cross grain strip (either cedar or spruce).

Then there are the CF flying buttresses, neck stiffeners, reverse kerfing topping, and binding that I've done on various acoustic guitars. It all works well.

BTW the comments re. vertical laminations in braces are true...much of the CF is wasted by being in the neutral axis of movement. For maximum efficiency (not always the rule...), you want the highest modulus materials to be at the maximum surfaces of tension or compression..."I" beam style, tubular construction style, or stressed skin panel style. This is basic structural engineering.
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[jeffhigh]

I do not use CF inside the box on my builds. dont see the need for my style of build (Stauffer style neck joint with floating fingerboard).
I do however use a A frame arrangement of bracing from the neck block but glued to the top not isolated.
I am not saying there are not gains to be made by using CF, but when deciding on any reinforcement it would be worth considering the following aspects
-For every action(force) there is an equal and opposite reaction
So the neck pushes on the top and the bridge pushes back in the opposite way The force has to find it's way between these locations.
You can't just put a prop from the top of the neck block to the back at the waist (i Know you do it differently ricK) and think you are dissipating the force there.
-Look at failures (your own and other people's) and analyse them when working out what you need to reinforce. But don't just beef up something because it has failed when the glue has let go from exposure to heat or though impact. Personally I am moving to Hide glue for heat resistance.
-Weight is not the only enemy, excessive stiffness in the wrong place can also kill sound
- the major structural problem with a guitar top is the big hole between bridge and neck, you have to provide a force path around it whether it be using attached bracing or flying butresses

ps I do agree with Rick on not putting CF crossgrain directly on the wood of the back.

[Kim]

jeffhigh wrote:

-Look at failures (your own and other people's) and analyse them when working out what you need to reinforce. But don't just beef up something because it has failed when the glue has let go from exposure to heat or though impact. Personally I am moving to Hide glue for heat resistance.
-Weight is not the only enemy, excessive stiffness in the wrong place can also kill sound
- the major structural problem with a guitar top is the big hole between bridge and neck, you have to provide a force path around it whether it be using attached bracing or flying butresses

Not sure if your reference re 'beef up' has to do with the images of the UTB i posted Jeff but i can assure you the "failure" of that Maton was the result of a design fault. More specifically the heelless neck and structurally compromised UTB used by Maton in construction. That instruments failure had absolutely nothing what so ever to do with glue, heat, or impact, quite simply that guitar was 'never' capable of withstanding the tension of steel strings from the day it was made and i say this simply because it was a cheap plywood classic that would barley hold form against nylon strings when Maton fitted the very same box structure with a steel string neck, tuners, and strings, and then released it upon the market.

Coupled with the reinforced rim linings, the UTB i put in place has been very affective in addressing these short comings. The guitar now has a surprisingly 'full' sound for such a thin body and is now completely rock solid in set up. I do agree that excessive weight and stiffness can be an issue sonically, but as you say, only when in the wrong place. I do not believe the UTB/neck block area of the top has the sonic value to warrant any concern in that regard. I also agree that the soundhole is a critical weak point of a traditionally braced instrument, but also believe that with the right approach, those very same forces that work to make a guitar top collapse, can be manipulated to help bring out the most response from the most sonically valuable areas of the top being directly behind, and radiating out from, the sides of the bridge.

I do note that CF is used by Greg Smallman and others in their lattice brace configurations. But it should also be remembered that this is a composite of CF and 'balsa wood' not spruce so i understand the need to stiffen these fine braces and also that the aim is to reduce mass in the lower bout. Like wise Ervin Somogyi and others use CF in the lower bout but i am yet to see CF used in that part of the top by a big name in lutherie. I have seen CF used vertically as Hesh has shown in a spruce "x" brace, but i am yet to understand why anyone would thing that would do anything but reduce the responsiveness of the top.

I know it is argued that CF allows you to make the 'X' brace smaller, but if the brace is spruce and you have glued on CF with epoxy, then just how much mass are you doing away with? My guess is that if you do the figures this is an exercise in expense and futility until you adopt Balsa as the core. Good discussion though. Cool

Cheers

Kim
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[Kim]

Kim wrote:

Should a builder have already countered the rotational force of string tension via buttress bracing back to the waist etc, then i concede that the upper bout certainly can be explored as a way of increasing the effective sound production area of the top. Kim

I missed the perfect opportunity in that statement to mention my good friend Dennis Leahy's "Angelina". Now this is an example of how the top can be freed up fro full exploitation without any CF at all.

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Here's more info if interested: http://www.luthiercom.org/phpBB3/viewto ... ine#p17679

Cheers

Kim
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[jeffhigh]

Definitely not a reference to your UTB Kim.
I agree and have always agreed that was a crook design to start with.
In most cases with conventional neck attachments the UTB is doing bugger all(as a beam) to support the neck against rotation.
What is happening in most cases is that the neck is trying to push a section of the top into the soundhole resisted only by the shear strength of the top along the edges of the fretboard and the glue joint of the utb to the top.
That is why I like some form or A frame brace to transfer the load to alongside the soundhole

[jeffhigh]

Of course Kim that arrangement with longitudinal bars just means that the area of the top between the bridge and the tailpiece will carry a proportion of the string load in tension (unless you are using a tailpiece)
Is that a good or a bad thing for sound, I don't know

[Kim]

No worries Jeff, i just wanted to make that point clear in case others were not aware of the shortcomings of the F11 Maton and why i deemed such a substantial (nice word for it ) brace necessary in that circumstance.. That said it should also be kept in mind that the was a 1973 release and certainly on the bottom rung of the price scale at just $70.00aud brand new Shocked

I will not speak for Dennis as I am hoping he will give his own thoughts in this discussion, but i will say that his design does use a tailpiece of sorts and all reports have people astounded at the volume and bass and overall tone of this guitar.

Cheers

Kim
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[Dave White]

Kim wrote:
I don't believe there is any 'benefit' in having any amount of movement what so ever in the UTB and in fact will happily go on record as stating that any movement at the upper transfer brace (UTB) will only sink string energy into the upper bout and neck block thus reducing the effectiveness of the lower bout which, in my opinion is the area of the instrument that is the very essence of a responsive guitar. Very Happy

Cheers

Kim

Kim,

Big statement there !! Some of us "flat earthers" believe that the upper bout is a very important, if subtle, part of the instruments sound potential - I think that Rick Turner is one too.

It's interesting to read of builders Damascene Conversions on this issue - here's one from Tim McKnight.

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