It all depends on what type of truss rod you have. So... What type of truss rod do you have and what store did you buy it from (because that changes things too)
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Don't hold me to this, but I believe that type of rod needs a channel that's deaper in the middle than at the ends. As long as you have at least 1/8" (or even a bit less) below the route, you should be safe. Then again, I've only installed double action TRs so you may want to wait for Cord .
"The most important thing is to learn how to play the guitar before you get 50,000 dollars worth of complicated gear" -Slash

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For a compression rod you want it to be as deep in the neck as possible. You need to have at least 1/8? of wood behind the rod when the neck it carved. If you don?t then you run the risk of having the neck split. So how deep you put the trussrod depends on how thick you want your neck.

As far as the curved trussrod channel goes? I?m not sure how warmoth makes their compression rods. Some people make them so that they are bowed and some don?t just look at it from the side. If it bows down in the middle then your need to have the truss rod slot accommodate the bow. There is an easy way to do this but I don?t want to explain it if I don?t have to so check your trussrod and get back to us if you need more info.
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I wrote Warmoth and asked them about it:

"If you're routing from the back of the neck, yes. It should be deeper
at the headstock and heel ends and shallower in the middle."

But I was going to route from the front of the neck, so basically deeper in the middle and shallower on the ends.

CorduroyEW, if you could give me help and instructions on this it would be great.
The easiest way to explain this is with a pic so here is my paint drawing.

You need to rout a channel that is all the same depth. Then make a strip of wood that fits perfectly into the channel that you routed.

Not that you have the strip you need to use trace lay the trussrod over the strip and trace the curve of the truss rod onto the strip. Now you have your line so that you can carve the contour of the trussrod out the piece of wood.

After you have that piece done you need to make another strip that will fit over the top of the truss rod and also follows the truss rods contour.

When you are ready to install everything glue the bottom piece into the neck then after the glue is dry put your trussrod in and lay the top strip over everything. Sand the top strip so that it is level with the rest of the trussrod and then glue the fretboard on.

This is the best way to do it if the trussrod has a significant curve to it. If it just has a tiny bit of curve then you might want to just hollow the middle of the routed neck with a rat tail file and then only use the strip over the top if your neck is thicker than 1/2" at it's thinnest point without the fretboard.
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Oh... If it looks flat then you could get away with just a flat routing, but to make it work better then just clear a little extra material out of the middle with a file.
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