\'mort-әs\ n: a hole cut in a piece of wood into which another piece fits to form a joint.
\'ten-әn\ n: the shaped end of one piece of wood that fits into the hole in another piece and thus joins the two pieces together.
The topic of Weber's mortise-and-tenon neck joints comes up periodically and we hope that this will be helpful. In general, there have been three types of neck joints used for instrument construction: the dovetail, the mortise and tenon and the bolt-on. The reinforced mortise-and-tenon neck joint that we use is often, incorrectly, associated with bolt-on necks.
The dovetail and the mortise and tenon are fitted and glued joints. They maximize surface contact between the neck and the body of the instrument and both are very stable joints, when done well. After the glue dries, they are not adjustable or easily replaced. True bolt-on necks are very different and are not designed to be glued. A bolt-on neck may be removed or replaced by simply taking out the bolts and lifting the neck off.
When we started Weber Fine Acoustic Instruments, we were not locked into any specific tradition, so we could choose or invent whatever design elements we felt were best for our instruments. We prefer the structural strength and simplicity of the reinforced mortise-and-tenon joint. Our neck joint gives our instruments a tight, strong, and stable fit at the heel and body with very consistent neck angles on all three relevant planes.
The tenon is a simple rectangle the height of our ribs and extension block (1 3/4-inches tall), nearly an inch long and a 1/2-inch thick. The matching mortise is also a simple rectangle. It has very large wood-to-wood contact areas and we get a strong, glued joint, on six matching surfaces. Four sides of the tendon and two wings that transition the neck to the body. This gives the greatest structural strength perpendicular to the force of the strings. The large height and length of the tenon also gives the joint great resistance to lateral and twisting forces. The screws, that we use, go through the head block and into barrel nut inserted in the tenon. They clamp the neck against the body until the glue dries and give mechanical support to the mortise-and-tenon joint after the glue has set.
Since two of the three relevant neck angles are determined by two vertical cuts, perpendicular to the body and parallel to the center-line of the instrument, we really only have to focus our adjustments on the primary neck angle. We use two screws so that we can do fairly minute adjustments to that neck angle before the glue dries. All of the design parameters of our mandolin body are dependent on these neck angles. The top graduations, brace dimensions, and bridge height are optimized to a specific angle. If that angle varies from our intended specifications the tonal qualities of our instruments will be changed. The mortise-and-tenon joint is ideal for keeping these angles consistent.