Hi Engblom, this has been covered a few times, maybe BrianQ can help you find it.
People add a truss rod in a cbg for the sake of keeping the neck from bowing too much? If you’re not building a full size 4 string Bass or a 6 string Guitar, on a 3string, I haven’t had the use for it yet?
I built a series of four 4-stringer for personal use. They all have truss rods to combat seasonal humidity changes here in Michigan, allowing me to always obtain the low action I prefer for my playing style.
Hi again, I tried BrianQ's suggestion [search] and found the previous post. I do not know if this is what one does to show it here. If not I tried.
Good luck Taff
There is one thing I wonder: if one does not have a router, could one make laminated neck and while gluing one would put the rod/bar between the wood pieces to get a tight fit?
Hi, if on a 3-4 string you can use three laminations and make the middle one of a hardwood, that would have the neck resist string tension. With a six string I would recommend a metal bar fitted as you suggest.