Simple Trussrod Slotting Template
I made this template because I am trying to do one piece headstocks with no wings on my new necks. I use the type of scarf joint that goes 'through' the neck, so I need to have my headstock glued on before the trussrod slot is routed. On a standard table router or simple shaper setup the taper from the headstock to the body end of the neck needs to be equal so the slot will be routed straight while the neck is being passed along the cutter. A one piece headstock is wider than the actual neck shaft so that method wont work here.

This type of template requires a router that accepts template following guides (an oversized ring that mounts to the base of the router instead of a bearing of the same diameter on the bit itself). First get a large piece of plexiglass or similar material that is thick enough to clear the height of your template following guide. Then set up your router to cut a slot to match the outside diameter of one of your template guides. In my case I did a 1/2' slot to match a 1/2' OD guide. Setup a fence along one edge of the plexiglass for the router to ride against. I double stick taped a 36' straight edge ruler to the edge of mine. Then in a series of small passes with the router on slow (for plastics so you don't melt them too badly) route all the way through plexiglass. Make sure to run in the direction that moving forward will pull the router 'into' the fence. I went from left to right with the fence away from me. If you are uncomfortable about being able to stop the router at the end of the run you might want to set up a stop guide too.

To use the guide mark a center line on your neck blank as well as marks that represent the inside edges of you template, in my case 1/2' wide on center. Then align your template to the center of the neck and double stick tape it down. This might take a while to get good at so be patient. Make sure to provide the correct offset for the rear of the template to match the end of your truss rod. Now in a series of light passes you can route your slot using the correct sized cutter and depth for your specific truss rod. In my case the slot is 1/4' wide by 3/8' to match the double acting LMI trussrod.