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Hi, guys. I'm having problems with a truss rod i recently installed. It's a standard one way compression rod, like the one that comes in a Fender. I took it out of a strat neck, and it was working fine in that neck. However, i've installed it in the neck of my current build, and it's acting weird.
OK, a little background. I installed this rod in the neck, but it is not dead center of the neck. It's off about 1/8th" toward the bass side at the nut(where adjustment is made). I took a wrench and tightened it because i was trying to see if the truss rod being slightly off center at the nut would cause the neck to warp or twist when it was adjusted(fretboard is not installed ). Imagine my surprise when instead of producing a back bow, the rod is producing relief.
Here's the rod.

and here it is installed.

The way I understand how the compression rod works(on a basic level), the rod is installed deep enough in the neck to be closer to the back of the neck and farther away from the fretboard. When the rod is tightened, because it is closer to the back of the neck than the fretboard it compresses the wood in the back of the neck, thus causing a corrective backbow to the neck. The only thing I can think of is that, because the fretboard is not installed, there is less wood between the rod and the face of the neck blank than there is between the rod and the back of the uncarved neck blank. Therefore, once the fretboard is installed and the back of the neck is shaped it should produce the correct back bow, instead of relief.
Someone tell me that will happen, please. Otherwise, I'm at a loss to explain what's going on.

_________________
Mike

The only thing nescessary for evil to thrive is for good men to do nothing.

Well I can't tell from the picures, how deep you have cut your slot but it need to be deeper in the centre so the rod is in a curve and it needs a spline glued over it to hold it in that position.
Without the spline the rod will pull straight and compress the top surface rather than the back of the neck

Thanks, Jeff. Yes, it has a spline over it.
As for the curved channel, according to my research there are three ways to go. You can go with a curved rod, or you can install the rod so that it is deeper on one end than the other, or you can use a straight channel, as long as the rod is close enough to the back of the neck. Both will work fine, according to my info. I chose the third method.
If you look on Frank Ford's site, you'll see a cross section of a Gibson rod.
http://www.frets.com/FRETSPages/Musician/GenSetup/TrussRods/TrussRodAdj/tradj.html
You'll notice that rod is mounted in a straight channel, as were many others, and they work just fine. The curved rod simply makes the rod more efficient, giving it sort of a head start, if you will, and making the adjustment range larger. But you do not have to use a curved channel. As long as the rod is close enough to the back of the neck, it will compress(shorten) the wood fibers in the back of the neck and result in a corrective back bow.
This has been discussed before in the guitar building forum here, but I can't find the discussions.
Here is another discussion on this topic.
http://www.mylespaul.com/forums/luthiers-corner/77789-must-compression-truss-rod-channel-have-arch.html
Here's one from the OLF archives.
http://www.luthiersforum.com/forum/viewtopic.php?f=10102&t=4422&hilit=+straight+truss+rod+channel
Anyway, thank you for replying. After considerable thought, i believe my first hypothesis is right. After I install the fretboard and carve the back of the neck, i believe the rod will work as it's supposed to.

_________________
Mike

The only thing nescessary for evil to thrive is for good men to do nothing.

If the rod works opposite to what it should it is in my opinion installed up side down.

Fred

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Fred Tellier
http://www.fetellierguitars.com
Facebook page http://www.facebook.com/pages/FE-Tellier-Guitars/163451547003866

Thanks, Fred. That was my first thought. But i don't know how you could install a compression rod upside down. It's simply a 3/16" rod with a threaded nut on one end and an anchor on the other. In fact, if you look at LMI's version, they replace the anchor with a bend in the rod. I really cannot see any way you could install the rod upside down. Again, i really think it comes down to the fact that the rod is installed in an uncarved neck blank with no fretboard installed. There is more wood underneath the rod(back of the neck) than on the top(1/8" thick spline), so the compression is working against the spline and the face of the neck blank, instead of against the back of the neck. I really think it's gonna be alright. We shall find out. If I have to remove the fretboard and start over, so be it. live and learn. But I really think it's gonna be fine.

_________________
Mike

The only thing nescessary for evil to thrive is for good men to do nothing.

UPDATE. The rod is now functioning properly. I looked closely at the neck, and found that when i installed the spline it was slightly long. The washer under the adjusting nut was resting on the spline alone, and not on the cheeks of the truss rod access cutout, which are cut out to either side of the spline to allow room for the washer. When I adjusted the rod, it was bearing on the 1/8" spline only, simply compressing it and nothing else. I took a sharp chisel and cleaned up the access channel, and now all is well. The rod now produces the proper back bow required. Thanks for all of your help and suggestions.

_________________
Mike

The only thing nescessary for evil to thrive is for good men to do nothing.