Less expensive carbon fiber reinforcement

[eadbass]

thanks a lot for your detailed answer @Bruce Johnson .
I think what's fooled me is the fact that we usually measure neck relief at around 7-8-9th fret so I thought the area where the truss-rod has the maximum action was around there, but it makes sense that the maximum string load is nearer the nut so the truss-rod compensation should act mainly there.

 

[eadbass]

hello @Bruce Johnson, I have another noob question.
I read threads where you explain how to apply the back strap technique to an existing fender style neck with skunk stripe. I'd like to try it, but maybe you can confirm I understood the process correctly :
- mill out the whole width of the skunk strip from 5th or 6th fret to the heel. Is a 1/4" depth safe to avoid being too near to the truss rod?
- I'm not familiar with TOW carbon, but I assume it's like a flat wire, and the stiffness is across its width/the largest dimension (that's why it's possible to wrap it on a bobin across its depth).
So I need to lay in epoxy 2 strands of 12K TOW or 4 strands of 6K TOW (maybe 6K is easiest to handle for a noob like me?) with the width of the TOW perpendicular to the fretboard so the stiffness is from fretboard to the back of the neck direction and not from side to side.
- Let cure the epoxy
- If enough room remains above the epoxy/TOW carbon fibers, fill with a fine strip of wood glued with epoxy? Then sand and try to refinish?
Or maybe easiest to fill the slot with a mix of epoxy and powder of the skunk strip when it was milled out?

Thank you for you help

 

[T_Bone_TL]

I'm not familiar with TOW carbon, but I assume it's like a flat wire, and the stiffness is across its width/the largest dimension (that's why it's possible to wrap it on a bobin across its depth).
So I need to lay in epoxy 2 strands of 12K TOW or 4 strands of 6K TOW (maybe 6K is easiest to handle for a noob like me?) with the width of the TOW perpendicular to the fretboard so the stiffness is from fretboard to the back of the neck direction and not from side to side.
- Let cure the epoxy
- If enough room remains above the epoxy/TOW carbon fibers, fill with a fine strip of wood glued with epoxy?

TOW is not stiff at all. It's a "ribbon" of very fine fibers, barely held in a ribbon shape by a tiny bit of resin, and can be deformed into any convenient shape to fit your slot.

The high strength is longitudinal, pulling specfically (tension) and stiffness only happens when you epoxy it into place.

Your wood strip is best applied while gluing the TOW in place, as it will help to clamp the whole business into place. Epoxy, TOW, possibly more epoxy, pre-cut wood strip, clamps.

Alternatively you could epoxy it right to the outside surface without removing any wood (probably best to try on scrap to see if you like that look.) Loud and proud rather than trying to hide.

 

[Bruce Johnson]

TOW is not stiff at all. It's a "ribbon" of very fine fibers, barely held in a ribbon shape by a tiny bit of resin, and can be deformed into any convenient shape to fit your slot.

The high strength is longitudinal, pulling specfically (tension) and stiffness only happens when you epoxy it into place.

Your wood strip is best applied while gluing the TOW in place, as it will help to clamp the whole business into place. Epoxy, TOW, possibly more epoxy, pre-cut wood strip, clamps.

Alternatively you could epoxy it right to the outside surface without removing any wood (probably best to try on scrap to see if you like that look.) Loud and proud rather than trying to hide.

Thanks for answering, T_Bone_TL; that's what I would have said.

 

[dwizum]

Think of tow as yarn. It's basically yarn made from carbon fibers all oriented in the same direction. The stiffness and strength comes from gluing it into a finished shape with a rigid epoxy or other adhesive.

Carbon fibers are not stiff on their own - the magic of carbon fibers is the way they resist tension and compression. Think of grabbing a carbon fiber by it's two ends and trying to stretch it - it will resist stretching much better than most materials. A single carbon fiber is very flexible and easy to bend, but it is very difficult to stretch it.

The stiffness of a carbon part (i.e. a carbon rod or bar) comes from gluing thousands of fibers together all oriented the same. When you do that, the glue creates a rigid matrix around the fibers, such that when you try to bend the bar or rod, your attempt to deform it is translated into tension on some of the fibers - and since they resist tension so well, the material is very stiff.

 

[Jon Clegg]

Here's a pic of CF TOW 'in the wild' fresh off the spool and ready to go into the slot, as you can see it's just a bunch of parallel fibers.

 

[T_Bone_TL]

Warms the cockles of my heart to see those little spools out in the wide wild world being useful.

 

[Jon Clegg]

Warms the cockles of my heart to see those little spools out in the wide wild world being useful.

I'm wondering how many basses I'll have to build to use it all

 

[eadbass]

thank you everybody for your answers, it's clearer for me now!
So i's possible to lay the TOW flat in epoxy in the slot or to deform it so it fills it the best as possible.

I have just an extra question : on a modern fender precision neck (says 0.820" 1st fret and 0.870" 12th fret thickness) what is the thickness of the skunk stripe? Is milling out 1/4" of the skunk stripe safe to leave enough of it under the truss rod and to have enough room to put the TOW fibers then a piece of new skunk stripe?

 

[Bruce Johnson]

thank you everybody for your answers, it's clearer for me now!
So i's possible to lay the TOW flat in epoxy in the slot or to deform it so it fills it the best as possible.

I have just an extra question : on a modern fender precision neck (says 0.820" 1st fret and 0.870" 12th fret thickness) what is the thickness of the skunk stripe? Is milling out 1/4" of the skunk stripe safe to leave enough of it under the truss rod and to have enough room to put the TOW fibers then a piece of new skunk stripe?

Be careful! In the middle of the neck (around the 5th-6th fret) the skunk stripe on a Fender neck may be as thin as 1/8", although some models are more like 1/4" thick. From the 8th to the heel is all more than 1/4".

If you are routing or milling out the skunk stripe, do it in gentle passes of about 1/16" deep per pass. As you get into the 6th to 8th fret zone, go carefully to see how deep it is, and stop when you see some sparks. If you see the wood getting thin, you can cut the last bit of depth with a chisel.

Ideally, you'd like the carbon fiber TOW backstrap to run from the 5th fret back to the heel. But, if there isn't enough depth in the thickness of the skunk stripe, you can start it at the 7th-8th fret. It will still work and be effective in preventing stretch in the back of the neck.

To add a backstrap to an existing Fender neck, you should cut the skunk stripe away, 1/4" deep, extending the slot toward the center of the neck as far as you can, until you hit the truss rod. That will be somewhere between the 5th and 7th fret.

 

[eadbass]

thank you @Bruce Johnson , I think I better follow your advice to do gentle passes of 1/16" per pass, cause I assume it's better to leave a few thickness of the "old" skunk strip between the TOW fiber + epoxy and the truss rod so the epoxy doesn't fix on the truss rod.

 

[Tom0Blam0]

Sorry if this had been answered but I did not see this in the responses I'd read (I read the majority of the thread) would this TOW fiber + epoxy strategy work on repairing a twisted neck? Obvious once the twist was removed with heat, could you theoretically add channels for the fiber and epoxy and stop the twisting. Or would this be so stiff you'd get no bow in the neck?

 

[T_Bone_TL]

Sorry if this had been answered but I did not see this in the responses I'd read (I read the majority of the thread) would this TOW fiber + epoxy strategy work on repairing a twisted neck? Obvious once the twist was removed with heat, could you theoretically add channels for the fiber and epoxy and stop the twisting. Or would this be so stiff you'd get no bow in the neck?

See #46 which you must have missed.

 

[dwizum]

Sorry if this had been answered but I did not see this in the responses I'd read (I read the majority of the thread) would this TOW fiber + epoxy strategy work on repairing a twisted neck? Obvious once the twist was removed with heat, could you theoretically add channels for the fiber and epoxy and stop the twisting. Or would this be so stiff you'd get no bow in the neck?

The benefit of tow + epoxy is that you get ultimate control over the amount of stiffness you're adding. One strand of 6k or 12k tow is going to make a very small difference in stiffness. Ten or twenty strands will make a huge difference, probably more than a truss rod could overcome. You can alter the recipe to get exactly what you want anywhere in the middle, versus being stuck with predetermined pultruded bar sizes that have predetermined stiffnesses.

 

[Bruce Johnson]

Yes, the TOW bundles are very specific in how, where, and how much they reinforce the neck. If you put them in an X pattern underneath the fingerboard, like I described in Post #46, they will resist twisting, but add almost nothing to the stiffness in bending.

 

[Tom0Blam0]

See #46 which you must have missed.

Yeah I've got a 13 month old. It's not hard for me to get distracted reading these forums and lose my place! Thanks!

 

[T_Bone_TL]

So, I thought this might amuse and (perhaps) instruct, or demonstrate. It's not a bass. It's a classic dough mixer (CamCo - possibly a #12, or 12A or something like that) that (my analysis, without extensive research to fix the point in time) was cheapened to the point of failure probably in the 1970s - I see pictures of older ones that are solid aluminum frames (not clear if cast or forged) and this one is thinned down pot metal, as best I can tell from the way it cracked. Hopefully the "insert as thumbnail click to embiggen" feature is working.

First bodged on some JB Weld right on the cracked area while attempting to apply just the right about of force to get it back to the shape it should be.

4 sections of 24K TOW. Epoxied them down at one end, wait for cure, snug up, epoxy down other end, wait for cure, take up any remaining slack on one side of the center (wedging foam in there, basically), epoxy the other side, wait for cure, epoxy anything left bare. Will see how it holds up in use again soon. Should add a massive amount of reinforcement to the poor thing. Hopefully enough to overcome the poor design change to the cast part.

Each bundle crosses the center ridge of both legs it is on, which is pretty much the same idea as pushing it to the back of the neck on a bass - trying to get it as far as practical from the other face of the beam.

 

[Bruce Johnson]

So, I thought this might amuse and (perhaps) instruct, or demonstrate. It's not a bass. It's a classic dough mixer (CamCo - possibly a #12, or 12A or something like that) that (my analysis, without extensive research to fix the point in time) was cheapened to the point of failure probably in the 1970s - I see pictures of older ones that are solid aluminum frames (not clear if cast or forged) and this one is thinned down pot metal, as best I can tell from the way it cracked. Hopefully the "insert as thumbnail click to embiggen" feature is working.

First bodged on some JB Weld right on the cracked area while attempting to apply just the right about of force to get it back to the shape it should be.

4 sections of 24K TOW. Epoxied them down at one end, wait for cure, snug up, epoxy down other end, wait for cure, take up any remaining slack on one side of the center (wedging foam in there, basically), epoxy the other side, wait for cure, epoxy anything left bare. Will see how it holds up in use again soon. Should add a massive amount of reinforcement to the poor thing. Hopefully enough to overcome the poor design change to the cast part.

Each bundle crosses the center ridge of both legs it is on, which is pretty much the same idea as pushing it to the back of the neck on a bass - trying to get it as far as practical from the other face of the beam.

View attachment 4833009 View attachment 4833011 View attachment 4833012

Yes, nice job! That's a good example of the use of carbon fiber TOW to reinforce things. Think of them as steel cables that you are installing like guy wires on a tall pole. The TOW needs to be anchored tightly at both ends, and needs to be in tension along the path that you want to stop the movement. TOW doesn't help much at all in compression, bending or twist. It has to be put in tension, like a cable or a rope. In tension, TOW doesn't stretch or move, at all.

I use TOW and epoxy for repairing all kinds of things in my shop.

 

[MovinTarget]

So I'm going to take this to the ludicrous level (and I'm sorry!)

Could I laminate Heavy Duty carboard in 2.5 inch wide strips while adding epoxy impregnated strips of 12k CF cloth every 1/2" or so to manufacture a board that could serve as a lightweight one piece neck and body (i.e. through neck)? To be clear, I mean that the open edges of the carboard would ultimately be the "face" of the board.

After the initial lamination or perhaps during, I would try to get the carboard somewhat if not completely saturated as well so that there is some durability, but it would be great to to that after most of the "routing" is done.

Though it might be a good idea to work it out to have the criss-cross along the expected neck area... Could still route a truss rod channel afterwards...

Once shaped, simply enclose it in more CF fiber + epoxy.

Madness? Would it end up heavy with epoxy, ensure enough is used?

 

[Bruce Johnson]

So I'm going to take this to the ludicrous level (and I'm sorry!)

Could I laminate Heavy Duty carboard in 2.5 inch wide strips while adding epoxy impregnated strips of 12k CF cloth every 1/2" or so to manufacture a board that could serve as a lightweight one piece neck and body (i.e. through neck)? To be clear, I mean that the open edges of the carboard would ultimately be the "face" of the board.

After the initial lamination or perhaps during, I would try to get the carboard somewhat if not completely saturated as well so that there is some durability, but it would be great to to that after most of the "routing" is done.

Though it might be a good idea to work it out to have the criss-cross along the expected neck area... Could still route a truss rod channel afterwards...

Once shaped, simply enclose it in more CF fiber + epoxy.

Madness? Would it end up heavy with epoxy, ensure enough is used?

Well, I wouldn't call it Madness, but you are getting into the building of Composite structures. Composites are just that: soft filler material, very strong fibers or cloth, and lots of resin to stick it all together. That's how airplane wings and race car chassis are built these days. Done right, you can make very strong structures.

But....An important thing to understand is that composite structures are quite heavy....per cubic inch. They work in airplanes and race cars because the composites are very strong, so they make the wings and chassis as very thin structures. Almost like sheet metal, hollow and thin. Designed very carefully for the loads. That's how they get the very high strength to weight ratio.

If you built up a bass neck as a solid laminated composite beam, it would be about 100x as strong as it needs to be....and about 3x as heavy as a wood neck. A big block of plastic is surprisingly heavy. And expensive.

A wood bass neck, built well, has plenty of strength and stability for the loads it sees. If you want to build a composite neck to handle those loads and be around the same weight, it needs to be a hollow thin-walled structure. Not a solid composite beam.

My buddy Jon Wilson is building composite/carbon fiber versions of his GuitarViols. He forms the back of the neck in a mold, with layups of carbon fiber cloth and resin. It's a hollow shell, quite thin walled. He makes up a fancy fingerboard, casting it from high-strength epoxy...with the frets built-in! Then the fingerboard gets glued onto the neck shell. The neck is hollow, very strong and stable, and about the weight of wood. That's one way to build a composite neck.

Other folks, like Marco (MPU here on Luthier's Corner) start by carving a wood core from a soft, lightweight wood. Then they put a wrap of carbon fiber cloth and resin on the outside of the wood. The composite layer is thin, but it takes almost all of the load. The center wood core is just there to hold the cloth in shape. That's another way to build a composite neck.

And there are other ways too. Building around a foam core that gets melted out. Building up a laminate of light weight wood strips and carbon fiber cloth and TOW ribbons. They are all about minimizing the quantity of resin and carbon fiber in the neck, to keep the weight reasonable.