Materials and Tools:
Hod Rod Adjustable Truss Rod with 4 mm hex nut (Available from Steward MacDonald)
Table Saw: -or-
Set The Truss Rod:
Although the truss rod itself has a PVC cushion to prevent rattling, we need to address rattling issues at the nut end of the truss rod. To eliminate rattling problems at the nut, apply a small amount of silicone bathtub sealer in the slot at the double nuts, then press the rod as deeply into the slot as possible. Use only enough silicone for minimal squeeze-out. A spot or two along the double rods can also be cushioned by a little sealer.
Keep Glue Out Of The Truss Rod Channel:
I want to really stress that when you glue you fretboard to the guitar neck, we want to keep any of that glue from reaching the truss rod, thus inhibiting it’s ability to easily adjust back bow or forward bow out of the neck.
The easiest way to do this is to place a piece of masking tape down the center of the neck, for the entire distance of the channel. Be sure to center this tape on the slot. Spread your glue on the surface of the neck using a notched glue spreader and now remove the masking tape.
You can now proceed with gluing the fretboard down to the neck without having not to worry about glue dripping into the truss rod slot.
GLS Tip: Another way to prevent glue from flowing into the truss rod channel, cut the channel just a bit deeper (about 1 mm). This will allow you to install a 1 mm strip of wood that is sized to wedge in the channel. This way you can spread glue over the entire surface of the fretboard and not have to worry about glue at all. The wood strip stays in place while you glue the fretboard.
Adjustment of the Rod:
After the glue has dried thoroughly, the rod can be tested and used with care. Turn the nut clockwise to correct an upbow, and counterclockwise to correct backbow. As with any truss rod, if you encounter excessive resistance, the neck should first be eased into a corrective bend with clamps. The rod can then be adjusted.