A loose guitar neck has been successfully, strongly, steadily and reliably repaired by carefully positioning a thin and long woodscrew. Machine screw can also be used.
The assembly of the guitar neck to the guitar body is very unstable considering the possibility for a hit and the constant pressure of the strings on the neck.
A similar problem has steadily been rectified by a simple long woodscrew with an important preparation for this by drilling a hole with a specific diameter.
Similar applies to the lower bridge of the guitar when originally glued. Glued bridges are unstable. Although woodscrews and a wooden plank instead of nuts can be used, machine screws and a wooden / metal / plastic plank inside the guitar body is preferable.
The neck was glued to a plank inside the guitar body with the side veneer of the guitar body positioned between the neck butt and the plank. Screwing a woodscrew directly may break the notch of the neck butt or the whole neck butt. This is why a hole was drilled through the neck butt and the plank with an electric drill. The diameter of the hole was such as to allow for reliable support of the woodscrew but large enough to prevent breaking of the neck butt. As a rough guidance, the hole was similar to the diameter of the core of the woodscrew which is the diameter of the screw minus double the length of the woodscrew thread. Then the woodscrew was carefully screwed in the middle of the hole without bending. A thin woodscrew with a length of approximately 3" was used with a corresponding washer.
For a better performance a long and thin machine screw, a top and a bottom washer, a lock washer and a nut can be used with. The hole through the neck butt and the plank must be larger than but very close to the diameter of the machine screw so the machine screw goes tightly through or may even need to be slightly screwed into the hole.
A hook for a guitar strap may be put on the screw.
By Steven Stanley Bayeswww.Steven-Stanley-Bayes.com