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| Tips for installing carbon fiber rods? https://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=46877 |
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| Author: | Linus [ Mon Dec 21, 2015 10:57 am ] |
| Post subject: | Tips for installing carbon fiber rods? |
I'm getting ready to install carbon fiber rods along side 2-way truss rods. The rods are 0.2" from Stewmac. Do I install them the entire length (including into the dovetail tenon?) or stop once I reach the heel? I'm planning on using epoxy. And tips and pics would be helpful. 
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| Author: | Alan Carruth [ Mon Dec 21, 2015 11:11 am ] |
| Post subject: | Re: Tips for installing carbon fiber rods? |
CF rods right under the fingerboard aren't doing as much good as they might. Dave Hurd showed that that's the 'center of moment' of the neck; the place where there's no tension or compression, but only shear loads. Carbon fiber itself is strong in tension or compression, but in shear what you're mostly loading is the epoxy matrix, and that's not nearly as strong. Basically, the deeper into the neck you put the rod the more of the load it's taking it tension, and the more stiffness it is likely to add. Of course, when you do that you're requiring the truss rod to do more work when you adjust it, so that gets harder. With that straight grained mahogany I wonder if you need the extra stiffness. A couple of years ago I made a 12-string out of claro walnut that was supplied by the customer. I found a nice piece of black walnut for the neck with figure that matched pretty well. That was a mistake. Curly wood has low long-grain stiffness, and on a 12 with a 14 fret neck it was not stiff enough: it pulled up even with the aluminum channel truss rod maxed out. I had to remove the fingerboard, swap in a steel channel rod, and add a couple of CF rods on the side to get the stiffness up to snuff. It still takes a lot of oomph to adjust it, but so far, so good. |
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| Author: | WudWerkr [ Mon Dec 21, 2015 11:21 am ] |
| Post subject: | Re: Tips for installing carbon fiber rods? |
Agree with the above , not sure that they are even needed . |
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| Author: | Linus [ Mon Dec 21, 2015 1:42 pm ] |
| Post subject: | Re: Tips for installing carbon fiber rods? |
Thanks, I'll take that into consideration. But for those that used them, can you describe your install? |
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| Author: | SteveSmith [ Mon Dec 21, 2015 1:59 pm ] |
| Post subject: | Re: Tips for installing carbon fiber rods? |
I've done several this way. I used two 3/8" x 1/8" solid CF rods each spaced 1/8" from the truss-rod channel just under the finger board. I ran them from the end of the neck (mortise/tenon joint) at one end and the other end ran into the headstock where the ends of the CF were trimmed at an angle. Rods were installed with epoxy. They make the neck noticeably stiffer and I would recommend a two-way trussrod (which is what you appear to have) because the strings may not pull the relief you need although I have not had that problem. |
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| Author: | Stuart Gort [ Mon Dec 21, 2015 2:42 pm ] |
| Post subject: | Re: Tips for installing carbon fiber rods? |
A typical sandwich core construction uses carbon fiber VERY efficiently....since carbon fiber's profound strength occurs when it's put into direct tension. Bend a 2x4 over your knee. The layers nearest outside of the bend are more in direct tension than anywhere else. The layers nearest the inside of the bend are more in compression than anywhere else. In the middle, the fibers are neither in tension or compression...and are essentially useless for bending strength EXCEPT that they keep the inner and outer layers suspended...away from each other. In a sandwich core construction...foam or some other exotic material is placed between the two surface layers of carbon fiber for the SOLE purpose of keeping the two layers apart. The lighter the better...as long as it has enough compression strength to keep the outer layers apart when bending loads occur. When this is applied to the structure of a guitar neck it become obvious that with these bars being sold....really only the top edge and the bottom edge are doing us any good...and that the more fiber we can put at the OUTSIDE of the "sandwich" the more efficient it will be toward your purpose. The slots would be difficult to make...and the rods are impossible to obtain in the perfect, right shape...but two strips of carbon about .05" x .2" that were inserted in a flat orientation into a groove that went ALMOST through the back of the neck....and then two more strips measuring .05" x .2" set flat into the FRETBOARD directly above the other two pieces.....THAT would be efficient...and possibly many times stiffer than just plopping two rods into a groove. |
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| Author: | Stuart Gort [ Mon Dec 21, 2015 2:53 pm ] |
| Post subject: | Re: Tips for installing carbon fiber rods? |
...and....the stiffer you make the neck, the more stress will be required for a truss rod to straighten out anything that needs straightening....so test that thoroughly (in a groove) before you glue it up...a good bit of advice whether you use carbon fiber re-reinforcement or not. |
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| Author: | Terence Kennedy [ Mon Dec 21, 2015 3:28 pm ] |
| Post subject: | Re: Tips for installing carbon fiber rods? |
When I started using them I stopped them at the nut and the level of the body joint. Later I started running them across into the headstock. It seemed like those necks are stiffer. I also use two 1/8 X 3/8 bars 1/8" on either side of the truss rod. One caveat, if you are doing a slothead stop them short of the string ramps or else you will expose a small corner of carbon. Next time I do a neck I'll do a deflection test before and after installation. I've been using them for 11 years and for some reason never thought of doing that. I will say the necks with carbon did not pull into as much relief as the ones before I started using it. Both had a typical 1/4" LMI/Allied/Blanchard style two way rod. |
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| Author: | WudWerkr [ Mon Dec 21, 2015 5:02 pm ] |
| Post subject: | Re: Tips for installing carbon fiber rods? |
Bend a 2x4 over your knee. I wanna seeeeeeee that !!!!!!!! 
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| Author: | SteveSmith [ Mon Dec 21, 2015 5:10 pm ] |
| Post subject: | Re: Tips for installing carbon fiber rods? |
Stuart, I'm an engineer and you'll get no argument from me. Definitely inefficient but the two 1/8" x 3/8" rods do stiffen up the neck noticeably and the extension into the peghead acts as a spline to increase the strength of that joint as well (I do one-piece necks). That said, I'm not trying to advocate that they are a necessary addition for steel strings and I don't use them on necks made from well-quartered mahogany, for example. |
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| Author: | Stuart Gort [ Mon Dec 21, 2015 9:00 pm ] |
| Post subject: | Re: Tips for installing carbon fiber rods? |
WudWerkr wrote: Bend a 2x4 over your knee. I wanna seeeeeeee that !!!!!!!! Hey...I didn't say how MUCH to bend it. If you want to SEE it bend....you'll have to look pretty close. 
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| Author: | DannyV [ Tue Dec 22, 2015 9:29 am ] |
| Post subject: | Re: Tips for installing carbon fiber rods? |
I should have taken a picture. Just did one. I use a laminate trimmer that came with an edge guide. Makita router in this case. Route a 1/8" slot 1/8" outboard of each side of the truss rod. Bit of eposxy in the slots. Insert rods. Press in and get rid of any epoxy squeeze out . Cover with wax paper. I have a thick and true Maple block that I use for a caul. The whole shebang takes about 15 minutes. I cheap out a bit. I buy 4' rods and cut them into 1' pieces. Probably if I lived a little closer to Dragonplate I would use more. |
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| Author: | Terence Kennedy [ Tue Dec 22, 2015 1:01 pm ] |
| Post subject: | Re: Tips for installing carbon fiber rods? |
A good way to clamp them that I think Tony Karol posted here a while back is to cover with wax paper and lay a 1/8" dowel or brass rod over the slot that the bar is in and use spring clamps. It helps of the bar is just slightly below the fretboard surface. I usually mask off the slot before the epoxy to avoid getting squeeze out all over the wood. The masking tape had already been removed in the picture below. 
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| Author: | SteveSmith [ Tue Dec 22, 2015 1:10 pm ] |
| Post subject: | Re: Tips for installing carbon fiber rods? |
+1 on the masking tape - makes cleanup a snap. |
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