Many guitar manufacturers use a bolted-on neck on their acoustic guitars. The neck is fastened through the upper block using two bolts that fit into two threated inserts which are screwed into the front of the neck heel.
Martin Guitars use a bolted-on neck on their D1 models. You can see the threaded insert on the tenon. The neck is still glued in but the bolt acts as a clamp during gluing.
Some manufacturers (e.g. Taylor Guitars) simply use a butt joint and two screws and depend on that. It seems to work but a mortise and tenon configuration will have more strengh. The neck-to-body joint is basically the same as in "Guitarmaking" by Cumpiano/Natelson. As the upper part of the neck heel is always pressed against the body by the string tension I find that one screw should be sufficient.
The neck-to-body connection consists of a threaded insert in the lower part of the neck-tenon and a screw that goes through a hole in the upper block. This insert has a coarse thread on the outside and a fine thread on the inside. This kind of insert is easy to find in Europe.
After setting the neckangle and fitting the heel edges tight to the body the position of the threaded insert on the tenon is marked with the help of a brad point drill bit. Then the insert hole is drilled with a diameter of approximatly 90% of the insert diameter. A drill press with its table twisted to 90 degrees and the neck clamped upright to it is advisable for this operation. After the hole is drilled turn a short (app. 2" long) threaded rod into the insert and secure it by two nuts. Put the assembly into the drillpress chuck and turn the insert into the neck tenon by hand. Since the thread is in end grain it is advisable to put some superglue on the insert.
The bolt is inserted through the soundhole and fastened - a simple, easy to make and strong joint.
Using knock down hardware like the one shown above avoids threading anything into end grain. Look at William Cumpianos web site for this stronger and better solution.