For a 2 way or 1 way truss rod? Here's one for a single action rod channel (like in teles and strats) from one of the guys over at TDPRI - http://www.tdpri.com/forum/tele-home-de ... lates.html.
For a 2 way rod that inserts under the fretboard, I simply use double-sided tape to attach my neck to my work table. Then I clamp a 3' level to my table so that it runs parallel to the center line on the neck. I set it just far enough away so that my router bit lines up with my center line and rides against the level as a fence.
I take small bites and do successive passes to reach my final depth, checking the depth after each pass to make sure I'm not going too deep for my truss rod.
Here's the rod I use
After routing the channel for the main rod, I've had to do a couple of different things for the adjustment nut slot. With the first rod of this type that I used, the nut was smaller than the rod, so I put in a smaller bit, readjusted my fence, and routed the slot for the nut. The difference in channel sizes kept the rod from sliding out of the headstock end. With the second rod I used, the nut was the same size as the main rod, so I had to go back and glue in a wooden stop between the rod and nut to keep the rod from sliding up.
