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I’m first-time installing solid rectangular carbon fiber, in an OM neck build, truss rod is already installed (and capped).

I’m not sure where to start (or stop) the channel on the tenon end:
Do you avoid the tenon, and route outside of it? That places the carbon further from the center of the neck (and closer to the bottom).

Or do you start the channel at the headstock end and stop it short of tenon? That would allow me to locate the channel closer to the truss rod and further from the bottom of the neck.

The neck M&T has two reinforcement strips of hard maple running up and down on the tenon.

I have .200” .250 rods in hand, and now questioning if those are too robust in size/ stiffness.

So many trade-offs…. I'm probably over-analyzing again.

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Measure Twice,

Karl Borum

Cubed rule of stiffness applies to CF as well. The extra width is nothing compared to extra height.

If that were my neck, I would not use the CF size mentioned. I would want taller, thinner ones. I would use the tablesaw to cut a channel on either side of the tenon out through the face of the headstock. I would stop the cf bars at the spot before the tenon sticks out so as to not mess with the tenons geometry.

First time I tried 1/4" rods. They didn't do much. After that I went to 1/8" x 3/8" rectangular bars. The necks were noticeably stiffer. After a few of those I decided the carbon fiber was not needed and have not used it since. If you wish to use them I would also recommend the taller stock.

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Steve Smith
"Music is what feelings sound like"

I've use carbon fiber rods one time in an archtop neck with a floating fretboard extension. I was concerned about the joint for the extension and wanted to add the rods for strength. If I recall they were 1/4 wide by 3/16 tall. At the head end I ran them under the head plate for a little additional security.



In retrospect the neck is almost too stiff. Acoustic light guage strings (12's) barely pulls 2 or 3 thousands of relief. If I was to do it again I would probably drop the height of the rods

1/8” x 3/8” for me. End before the tenon and carried across the headstock. I end before the tenon because I install before the tenon is routed and I don’t want to damage router bits hitting the bars. Just fill the slots with wood in that area.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Thanks for the replies, they were helpful.

Since I had the .200x.250 on hand, I used it, cutting the channels on router table with a 5mm upcut bit. then a .015" tape shim for about .015" oversized width. Cut the grove thru the headstock, marked the angle on the rod with a marking knife, then profiled the angle on the belt sander. Cut the channels + .020" deep to allow for a wood cap. Plugged the mortise end of the channel with a stop block to keep the rod imbedded, and away from the heel cheeks.

Adhesion test with fish glue, CA and TIte Bond. Adhesion rating "F", they all just popped off.
Used epoxy with sandpaper-abraded and cleaned rods and capped the channel.

I had a thermal runaway with the epoxy at about 4 minutes after mixing (an interesting story for another time) but finished the glue up with seconds to spare.

Thanks again for all the good information!

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Measure Twice,

Karl Borum

I've alway heard slow set high strength epoxy was the glue to use on CF. I didn't cap mine and sanding it was filthy.

When I use CF I just glue it in the slot a bit below the surface of the blank. It gets filled mostly with epoxy squeeze out anyway. No wood filler on top. There is plenty of room for a final flat sanding w/o hitting the CF. Still plenty of surface area to glue down the FB too.

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Brian R, Wood Mechanic
N8ZED

I do the same.

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It's not what you don't know that hurts you, it's what you do know that's wrong.