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Hey all
Been digging around I can't find a good breakdown on how to actually build a CF neck. And I don't mean skinning a wooden neck with CF. I own one Moses neck but I really don't want to saw it in half to find out I understand how to work with CF and have used it to a small amount in boat building so I understand the processes but... without a actual design to look at it's a little hard to see what to actually build... I know some are hollow but I'm not that hot on the idea really anyway.. what thoughts you oh forumites?
Do you actually want to make the whole neck from carbon fiber? When I took the MIMF mandolin making class a few years back, we used carbon fiber beams in the (maple) neck, in place of or in addition to a truss rod. Rectangular cross sections were preferred, with the short side exposed under the fingerboard, and the long dimension going deep into the neck. For a guitar or bass they would probably be in addition to, instead of in place of, a truss rod. The MIMF bass we auctioned off not long ago had a truss rod and carbon fiber rods that sat to either side of it.
You make a neck out of wood first, then you take a mold of it, then you make the cf neck inside the mold. If you don't want it to be hollow, you fill it with anything you like.
Marko Ursin wrote:You make a neck out of wood first, then you take a mold of it, then you make the cf neck inside the mold. If you don't want it to be hollow, you fill it with anything you like.
That is one way, but the more common approach is to route a couple of slots in the neck on either side of the truss rod and glue in store-bought rectangular epoxy-carbon bars. They don't need to be very big to stiffen up the neck. I like to use bars that are .090" thick and 1/4" high. Those are definitely on the small side but they add some strength to the neck without making it too stiff to adjust with the truss rod.
Another approach that I have used (like in the previously mentioned MIMF bass) was to rout slots and then place loose carbon tow (bundle of parallel carbon fibers) that are saturated in wet epoxy into the slots and cast them in place. This is not a common approach but I don't think I was the first to use it. It also does not provide as much strength as the store-bought bars, so I would not recommend it for a first guitar.
Guys, he's asking how to make a CF neck, not reinforce a regular neck with CF.
First, you do NOT want a solid CF neck. It would be one heavy sucker!! CF has similar, though a bit higher, specific gravity as ebony, so if you can imagine what a solid ebony neck would weigh, there's your answer. It would also be one expensive neck.... A hollow CF neck would be lightweight, but it would be pretty tricky to do; as well, any hollow sections of an instrument will be prone to having their own resonances, and that could lead to all sorts of sound/tone, and even feedback, problems.
What you really want to do is carve a neck from a lightweight wood(cedar, spruce, balsa[maybe], etc....), then "skin" it with CF for strength and appearance. If your skin is thick enough, you could possibly use dense foam instead of wood, but then you're left with the problem of how to afix a fretboard on top of it, so foam is very likely a bad idea, unless you're willing to make the fretboard of CF also, but you'll be on your own when it comes time to slot and fret it.....
So, in the end, you really don't have much choice but to skin a wooden neck. There's a reason that those who do that, do that.
Edit: just as I was going to hit "submit", I had a thought. If you were to completely skin the foam-cored neck, meaning CF at the fretboard's surface also, then you could epoxy a regular wood fretboard in place, or...! Using a lightweight but fairly hard an stiff wood(fir comes to mind, but a good dense spruce might be good too) as its core, you could also do a CF "skinned" fretboard!
Marko Ursin wrote:You make a neck out of wood first, then you take a mold of it, then you make the cf neck inside the mold. If you don't want it to be hollow, you fill it with anything you like.
I'd say again that this is the only way to make a cf neck if you do not want to skin anything with cf. I have no clue about the material thicknesses or anything. Trial may be the best way to find out.
I didn't want to go that route on my cf/wood composite bass and skinned a very lightweight core (that would not be even nearly strong enough to hold the string tension) with 1,5mm cf layer. Worked out great. No hollow resonances and no need to make a mold for one-off instrument.
You might want to look at torsion box design as that's essentially what a hollow neck is. If you want a hollow neck (Modulus necks are hollow last i checked), you can make an EPS (expanded polystyrene) foam core, wrap it with CF cloth and vacuum bag it using an epoxy matrix and melt out the EPS with a drop of acetone or styrene.
You can also start with a smooth, tapered mandrel shaped like the neck core, treat it with mold release agent, wrap it in CF tow, vacuum bag it with resin and slide it off your mandrel once cured. Alternatively you can use layers of continuous woven CF tube "sock" that will conform to the neck taper and headstock shape. That would be my preferred choice for strength and durability.
I know a guy who did an entirely CF guitar. But he bought a trashed Washburn and pulled a mold off of it, then vacuum bagged the CF into the resulting mold.
Regarding Moses necks - just spent some time poking about on their site. Reads like they actually build out of graphite, not CF. Rather like doing a cast resin/epoxy thing.
I'd leverage boat building - use another neck as a mold, pull a carbon/foam/carbon sandwich off of it. Or, shape the neck out of blue foam and skin with a few layers of carbon. Given that the back of the neck is in tension, and carbon loves tension...run one of uni lengthwise, top with a 45 degree bias layer, then another of regular weave set lengthwise. The result would be strong enough to stand on.
Brian,
Are you saying that there's a difference between Graphite and CF? I see the terms used interchangeably when talking about structural elements. I don't think Moses is building necks from pencil lead. They use a pre-cast, internal "W" shaped spar that's surrounded by an epoxy matrix.
David - I think Moses is building from graphite in an epoxy matrix. IE powdered graphite (or carbon) cast in resin. Generally, people think of CF as fabric or threads, thus the "fiber" part of the name (what Marko used on his bass). While technically they are both the same material at heart, there is a vast structural and construction difference between powder in epoxy and epoxy impregnated fabric.
The resin construct will have strength in compression and torsion due to the solid 3D nature - but the strength is from the resin - there aren't continuous fibers running along it to carry load. On the other hand, the fabric has strength in tension when stiffened by epoxy; compression and torsion only if layered really thick or made into a beam/box form using a spacer or sandwich layup. The strength is in the fabric (warp and weft) - more resin actually doesn't help because the overall carbon density goes down. That's why high strength stuff is build from vacuum forming, resin infusion in an autoclave, or using pre-impregnated fabric.
Also why there are different kinds of fabric - pure "oomph" comes from uni-directional stuff. All the fibers run one direction - no strength at all on the 90, but really strong along the axis.
I read that, and mostly went "yah, yah..." It reads like a primer on "what is carbon fiber" - what they don't say is "how do we build necks out of the stuff?"
As you say, they could be using a CF (as fabric) W formed via a mold or something as the core. That gives you a geometrically stiff shape once the epoxy kicks in the fabric. Then surround the thing with epoxy mixed with some thickener to turn it into a neck shape.
I doubt the necks are hollow, and doubt they are completely CF - enough pure carbon fiber to form a neck ~0.85 inches thick gets pretty heavy. (and expensive...)
That's what I'm saying. I have photos of sawn-through neck cross-sections from Steven Mosher which i'd post but they aren't mine so I'd have to email them to you. I've know Steven for 20 years and have had many discussion over the years with him regarding the various construction methods he's tried. I feel pretty confident about this but I'd be happy to invite him to join us here if you have questions.
He doesn't use fabric however but unidirectional tow fiber that gets stretched and resin cast between metal plates. Those sheets are sawn up into strips and then fabricated into a variety structural components around with the matrix is poured. Some of the headstocks are hollow but the necks generally aren't.
Ah so. Gotcha. Most people (me, among others) think of carbon fiber construction as inherently hollow - the strength lies in the outer skin, so the only thickness you need is bend resistance (keeping it in column). He can use uni fabric because he doesn't really need strength across the width - the load is longitudnal, where the uni runs. The idea of using an epoxy matrix to fill out a non-structural shape around uni fiber is somewhat unique - we tend to use a lighter fairing material, or fill with foam and lightly skin that.
So really, the graphite powder thing is a red herring - doesn't really matter what you impregnate the resin with, the core structure is the uni fiber. Everything else is just making it the right shape to hold on to.
All this makes me wonder about making a CF neck, just for giggles. Not hard to do (I've got rolls of fabric, epoxy, and vacuum forming gear) - the challenge is making it with the right relief already in the neck. It's not going to bend much once it cures. Suppose you could just sand some relief back into it. May have to experiment with truss rod-like things to see if it can impact the overall curve.
Neat stuff! I like where this is all going, THANKS! I have stuff to go on interms of where to go If I want to... I have used graphite powder mixed with epoxy before but not in instrument building, it is really easy to do but jut like adding anything to resin that can act as a thickener you have to get your amounts down.
Marko Ursin wrote:You make a neck out of wood first, then you take a mold of it, then you make the cf neck inside the mold. If you don't want it to be hollow, you fill it with anything you like.
That is one way, but the more common approach is to route a couple of slots in the neck on either side of the truss rod and glue in store-bought rectangular epoxy-carbon bars. They don't need to be very big to stiffen up the neck. I like to use bars that are .090" thick and 1/4" high. Those are definitely on the small side but they add some strength to the neck without making it too stiff to adjust with the truss rod.
Another approach that I have used (like in the previously mentioned MIMF bass) was to rout slots and then place loose carbon tow (bundle of parallel carbon fibers) that are saturated in wet epoxy into the slots and cast them in place. This is not a common approach but I don't think I was the first to use it. It also does not provide as much strength as the store-bought bars, so I would not recommend it for a first guitar.
Do you have any particular place to purchase these bars?
Also I wanted to know if anybody has used carbon fiber bars to add strength to the neck say from fret 12 or 14 down into the body of the guitar in a neck tru design to allow for very thin neck all access joint with added strength.
I have a lot of experience on how "not" to do things.
I like to use the .256 round tubes sold by "Into The Wind" kite supply. You need a round bit to install them, and I place the routes in the neck and in the underside of the fingerboard. I like them, very light and just the right amount of stiffness.
I understand how to work with CF and have used it to a small amount in boat building so I understand the processes but... without a actual design to look at it's a little hard to see what to actually build... I know some are hollow but I'm not that hot on the idea really anyway.. what thoughts you oh forumites?
