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Stabalizing a Neck with a 12th Fret Kink Using Carbon Fiber Threads

W

wewing

Sep 19, 2011
28
10
#1
I have a 2008 rosewood board J neck that has a slight rise at the 14/15th fret. I am thinking about using clamps and some heat to bring it back flat(shouldn't take much) and then use Bruce's suggestion of milling/routing a 3/16-1/4" slot in the back of the neck and laying in some carbon fiber thread. I don't even plan on laying in a wood filler strip, I would simply fill the slot with epoxy, making sure the fibers are well below the neck surface.
Has anyone else repaired a neck using this method that could share some tips and insight?
 
#3
I am using carbon fiber TOW threads(2/12K or 4/6K) as well as epoxy. My plan it to run the slot mid heel to the 6th fret. I have done a little more searching in here in the TB forum and I may be able to reduce the slot with to 1/8" as the threads are fairly small in diameter
 
#5
It looks like the preferred epoxy is West Systems 105/206. Not sure if hardware slow cure or woodcraft supply system three T-88 would be an acceptable substitution or not.
Another question is is a channel 1/8WX1/4D enough space to bury 4 strands of 6K TOW fiber(no filler strip being used)? I've never used my BP to mill a slot in wood but it will surely work, I will just have to make sure the the oil in the head doesn't contaminate the slot.
 
#6
Yes, I have done what you are planning, although I milled the slot 1/4" wide to match the existing skunk stripe, and capped it with a matching piece of wood. But yes, you could mill a narrower slot down the center of the skunk stripe, and fill it with the TOW and black-tinted epoxy. Mill the slot neatly, and you get a neat black line.

A 6K TOW strand, saturated and lightly twisted, is only about 1/16" diameter. So, yes, four will easily fit into a 1/8" x 1/4" deep slot. Four strands into a 1/8" x 1/8" deep slot would probably fit, but might be a little messy getting them in there. Actually, two 6K strands in a 1/8" x 1/8" slot would be plenty of strength, particularly if it's right at the back surface of the neck. I've never actually measured the tensile breaking strength of 6K TOW, but it's in the thousands of pounds range. Carbon fiber TOW is about 5 times the tensile strength of steel.

My favorite epoxy is West Systems, mostly because I've been using it for 25 years. System 3's T-88 is also an excellent similar type of epoxy. Hardware store epoxies that are long-cure, like 24 hours, are probably okay. Don't use any of the quick-cure (5 minutes, 1 hour) type epoxies for this. They are too thick and rubbery. You want a fairly low-viscosity epoxy that will soak into the TOW and dry hard.

A tip: My favorite pigment for making epoxy black is Smooth-On's So-Strong Black Colorant. A teeny drop makes West Systems epoxy jet black.

Milling the slot in a milling machine isn't hard. Use a normal end mill, normal cutting speeds. The key thing is getting the neck clamped down solidly so it doesn't chatter or jump. You've seen my fixture that I used in the MusicMan truss rod replacement thread? Simple to build and makes things easier.

Replacing The Truss Rod In A Skunk Stripe MusicMan Neck
 
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#7
Bruce, Thanks for the reply. I have been looking over your postings on the subject this morning and you have contributed a vast amount of knowledge on the subject. I will fixture up some scraps in my mill and see how maple/oak machines. The slower I can turn the end mill the less likely I will have an oil issue. I have a router table as well, but if the mill works so much the better, less noise and dust.
I will make a copy of your milling machine jig. Thanks for the link I hadn't found that thread.
I assume when I fixture the neck and lay in the CF I want to use the truss rod to pull it as near flat a possible?
 
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#8
wewing said:
I assume when I fixture the neck and lay in the CF I want to use the truss rod to pull it as near flat a possible?
Click to expand...

No need to do that. The truss rod and the curvature of the outboard portion of the neck have nothing to do with the surgery for correcting a 12th fret kink. Leave the truss rod alone. After you get the reinforcement in, then you'll need to check out the frets and see if they need a leveling touchup.

I have a lot of old machines that drip oil, like some of my giant old drill presses. When I need to use them on a bare wood instrument part, I'll often use some clear packing tape and Saran Wrap to protect the wood from drips. Get the neck set up in your holding fixture, then run a strip of clear packing tape down either side of the skunk stripe.
 
#10
If you will please indulge me with one last quick question.

The neck as it is has a slight visible and measurable kink, but with a setup to Fender spec doesn't have any buzz until you get above the 15th fret, if you dig in. So would you lay in the CF as the neck is now or try to pull some of the kink out prior. I am leaning towards working on it as is and deal with the high frets as a separate issue. Probably pull the neck and let it "relax" for a week or so while I am gathering supplies and building my jig.

I also see that my local Woodcraft supply carries System Three general purpose resin which has a viscosity more in line with the West 105 resin. So I will give it a try. The T-88(glue) looked like it would require some effort to thoroughly wet all the fibers due to it's much higher viscosity.

Thanks again.
 
#11
wewing said:
If you will please indulge me with one last quick question.

The neck as it is has a slight visible and measurable kink, but with a setup to Fender spec doesn't have any buzz until you get above the 15th fret, if you dig in. So would you lay in the CF as the neck is now or try to pull some of the kink out prior. I am leaning towards working on it as is and deal with the high frets as a separate issue. Probably pull the neck and let it "relax" for a week or so while I am gathering supplies and building my jig.

I also see that my local Woodcraft supply carries System Three general purpose resin which has a viscosity more in line with the West 105 resin. So I will give it a try. The T-88(glue) looked like it would require some effort to thoroughly wet all the fibers due to it's much higher viscosity.

Thanks again.
Click to expand...

Putting in the carbon fiber strap on the back will stop the bending of the kink, wherever it happens to be at that time. Putting in the strap won't, by itself, pull the kink straight. It just stops it from getting worse.

If the kink isn't too bad, if it looks like you could fix it by just leveling the high end frets, then you could go ahead and put the strap in now. Then level the frets.

If the kink is more serious, where you would have to pull the frets and re-machine the fingerboard, then straightening it first could save you some work. Apply clamps and gentle heat to get it pretty close to straight. Then put in the strap. Then clean it up leveling the frets.
 
#12
Thanks Bruce. The kink isn't to the point where the board needs to be planed. The last four frets have plenty of height so they can be brought down no problem. I may try clamping it just to see how straight I can get it.
 
#13
I used clamps and some mild heat over the weekend to remove a slight kink at the 14th fret, it turned out almost perfect. The heat really dried out the wood and it took me several days to re-hydrate it. I will give it a few more days to stabalize.

I just finished the neck fixture today and will mill the slot to lay in the carbon fiber TOW this weekend.

My fixture is patterned off the one Bruce built, I went cheap and used a 2x4 instead of Baltic plywood. It won't have long term stability like plywood but should work fine.



Neck Jig 1.JPG
Neck Jig 3.JPG
 
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#15
Bruce Johnson said:
Looks good! That will be strong enough. The important thing is the cleats. You don't want the neck to kick sideways.

Life is so much better with a milling machine. Everyone should own one.
Click to expand...
Can't that be done with a compound slide milling table and the correct bit in a drill press?
Nevermind; a quick google search snuffed out THAT idea.
 
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#16
Bruce Johnson said:
Looks good! That will be strong enough. The important thing is the cleats. You don't want the neck to kick sideways.

Life is so much better with a milling machine. Everyone should own one.
Click to expand...

Thanks Bruce. The cleats are hard maple and fit up against the neck very snug.

When milling the slot should I try to maintain a 3/16 depth the full length (6th fret to mid heel)? I am planning on leveling(more or less. see my comment later on playing with this a little bit) the tapered portion of the back and milling the slot parallel to the taper then level the heel and cut that slot 3/16 deep. I will play with the level of the tapered portion of the neck to put the intersection of the two slots at about the body/neck joint point
 
#17
You can make the slot follow the back surface, then tip the fixture to go level on the heel. If you want to be elegant about it. But it's not really necessary. Starting at 3/16" depth at the 5th and just going straight back, parallel to the fingerboard, will be fine too. It'll end up at about 5/16" deep through the heel. Fill it with a couple of strands of TOW and some black epoxy, and it will be permanently strapped.
 
#18
sissy kathy said:
Can't that be done with a compound slide milling table and the correct bit in a drill press?
Nevermind; a quick google search snuffed out THAT idea.
Click to expand...

Yeah those compound milling tables on a drill press can be used for little hobby things, but not a job like this.

If you don't have a milling machine, then this job is best done with a router and fixture. Basically make up a holding fixture like wewing has made to hold the neck steady. Add a pair of wood strips to guide the collar on the base of the router down the straight line.
 

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