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this is a 70s guild that had a poorly repaired headstock break . Why they used screws was beyond me as they caused more damage than the original break. So the initial plan was to make a fixture to hold the neck and headstock secure while I could machine in some splines to stabilize it . The headstock is 15 degrees and you will see in the picture rails to set the edge of the fretboard on so it is true to the headstock. I don't want to have things out of kilter.

Once the fixture was made I secured the guitar and milled 2 small splines to hold things so I can do the serious machining

once the glue set I could start with the actual splines. The first one was set up the center of the neck and into the head stock this now had good wood to good wood connection and I can not start machining out the bad and replace with solid wood.

so the last thing I did today was to work the side of the neck and cut into the headstock. This now ties the neck and headstock together. In all of this I am using tite bond. Mechanical things lick screws are useless as they will work loose over time. The strength is in the glue joint itself. Here you can see the last spline is sizeable compared to the first 3 as they are there so I can start the actual machining of the damaged area. There was so much cross grain break and the original repair caused even more damage from the screws coming loose the just tearing up the end of the neck and headstock area around the truss rod.
The key here is to get nice friendly friction joints. I want to gently push them in and allow the glue ample dry time I will reshape the neck as I go along.

I like the stabilization fixture. I used the two spline approach to repair a newer Epiphone Dot neck (335). It worked great. Without question, holding everything in position while doing the work would have made things a lot easier. Thanks for another helpful post!

A novice question John - are you using a milling machine (is that what it's called?) or is it a drill press?

it is a mill drill it is close to a milling machine you can use an X y table in the drill press

Today I finished the spline work , each spline was put in with a specific task in mind. The longer splines tie into the neck barrel , the the shorter splines strengthen where I removed damaged wood and the old repair that had superglue and epoxy .
Some people were asking me why I didn't use epoxy and the reason for that is , if I need to go back I cannot reverse epoxy. If I need to gap fill I would use it but my splines fit tight and tite bond is plenty strong for this job. In each case I created a sufficient glue surface area for strength and worked it so that the glue is in the best plane for the force applied. I don't want the joint to be in a plane that is pulling it apart. So if I do have a joint with this I also have a side joint for more strength.
Now once this is all cleaned up and sanded to shape I will place 2 veneers , one on top and one on the back and these will add a lot of strength and make the repair contiguous .
You will also note that the truss rod screw was covered in the beginning with shrink tubing so no glue gets into the threads. You will also see that the head plate veneer was now removed , and all the bad wood is gone.

Nice work, a thinking man's repair, must of spent more time setting up things than the actual repair.

Bruce,

done a few but yes the actuall repair is about 2 hr thinking 16 LOL