Every once in a while someone brings in an acoustic instrument that somebody sat on. The latest one was an old 60′s Segova mandolin. Usually a neck breaks on an angle so that there is a decent amount of surface area for the two pieces to mate up with. That makes for a strong repair. Every so often a neck breaks like a pencil so there is almost no surface area to glue too . Most repairmen install splines to increase the strength of the break. To install splines you need to route two long 1/4″ or 1/8″ routes length-wise down the back of the neck, through the crack. Then inlay two 1/4″ pieces of hard wood into the routes. It can be very difficult making a jig that will route those lines straight, especially on a little mandolin neck.I’ve devised a way to fix a neck without having to do the spline thing. My method is quick to set up and comes out super strong. First I crazy glue the two parts of the neck together. This just holds the two pieces in place while I set it up in the jig. The jig consists of two thick pieces of wood mounted on either side of the neck to act as rails for the router to slide on.
Next I crazy glue a 1/4″ piece of wood to the back of the neck (see pic 1). This acts as a router template. The instrument is clamped to my bench that has a little shelf built into it…great for clamping a guitar face down. Next I mount the router on the rails and route out trenches on either side of the 1/4″ jig that I glued to the back of the neck. I use a top-side roller bit and roll the bit against the 1/4″ jig. My starting and stopping points are arbitrary. I kind of go by feel. I just take out about an inch of neck material on each side (see pic 2).
The next step is to carve 2 pieces of maple or oak inserts to fit into the routed sections. This is the hardest part but not so bad. I just keep taking off little amounts on my belt sander until they fit (see pic 3). I carve the pieces so they sit high out of the neck so I can take of the excess after they are glued in. Next I glue the pieces in with 5 minute epoxy to fill any gaps and carve off the excess using the rounded edge on my belt sander or just with a wood file.
After sanding the area it is ready to be sprayed, in this case I did a black “widows peek” like the old Gibson necks. It looks classic and it hides the work. Now all you have to do is avoid sitting on it and you should be just fine in the future!