We have one more thing to do to the neck before we can build our truss rod. We need a spot for the anchor to fit into. I drill two small holes about 1/4" deep or so on either side of the truss rod channel, near the headstock.
I then use a small chisel and hammer to clean out a spot for the anchor to fit into. It doesn't have to be pretty, just functional.
With that done we can now start building the truss rod itself. I build my rods out of 3/16" cold rolled steel rods from Home Depot or Lowes. They come in 36" lengths, which is enough for two rods. I prefer cold rolled as it's stronger, and I'd rather the truss rod nut get stripped and fail than the rod itself. The anchor is made from 1/8" thick, 1/2" wide steel bar, also from Home Depot or Lowes.
I cut a small length of the steel bar, about 3/8" long, and put in in my drill press vise. Using the drill bit included with a 10-32 tap set, I drill a centered hole in the steel.
I then swap the bit out to the tap and thread the inside of the hole.
The rod is then tightened into the vice, and threaded with a 10-32 die.
I aim to get about 1/4" of threads on the anchor side of the rod.
The anchor is then screwed onto the rod, and I use a hammer to peen the end of the rod around the anchor.
I then take the rod over to the grinding wheel to grind the anchor down so that it will fit in the slot on the neck. I round off the edges, and grind the thickness of it down so it isn't much thicker than the rod, so it fits nicely into its slot.
I test fit the rod in the anchor slot and channel, and mark with a pencil about 1/4" inward from the heel end.
I cut the rod at this mark, and thread it about an inch deep. I sprayed a little WD-40 in the die as I was threading it, to help it cut the threads better. They still aren't too pretty, but they will do.
The last thing to do to the rod is to cover it from the anchor down to the threads. I wrap it with teflon plumbers tape, but you could also use heat shrink tubing. This is so it doesn't get glued to the neck itself. It also helps to fill the channel up more, preventing the rod from rattling around.