Mortise and Tenon neck joint article: by Vern Brekke, Mandolin Café Forum
This topic seems to come up periodically and we hope that it will be helpful to add some additional information, about our instruments, to the discussion. 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 has not really been discussed but is often, incorrectly, associated with bolt-on necks or other types of mortise and tenon joints.
The dovetail and the mortise and tenon are fitted and glued joints when used on mandolins. They maximize surface contact between the neck and the body of the instrument and they 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. They 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 Sound To Earth, Ltd. we were not locked into any specific tradition. We could choose or invent whatever design elements we felt were best for our instruments. Most of us have worked with other neck joints in the past (I was responsible for adjusting the equipment that cut guitar dovetails at a previous job) and we prefer the structural strength and simplicity of the reinforced mortise and tenon joint that we designed and use. 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), that has its greatest structural strength perpendicular to the force of the strings. The large height and length of the tenon also gives the joint good resistance to lateral and twisting forces. The screws, that we use, go through the headblock and into barrel nut inserts in the tenon. The style of insert and the way that they are placed is unique to our “WEBER” instruments. They clamp the neck against the body until the glue dries and give mechanical support to the 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 our specific angle. If that angle varies from our intended specifications the tonal qualities of our instruments will be changed and we don’t like that. The mortise and tendon joint is ideal for keeping these angles consistent, from instrument to instrument, and that consistency is a primary reason that we use this style of joint. We also like the very tight fit that we get from the heel of the neck to the body of the instrument.
We do not believe that the mass or the weight of the screws will have any affect on the tone or balance of our instruments. The screws and inserts weigh less than 1/2 ounce. Our necks (peghead, veneer, tuners and fretboard) can vary in weight as much as 3/4 of an ounce - with a typical weight being 16 ounces. Wood is wood and the weight and density of it changes from piece to piece. With the average weight of our mandolins being 32 ounces, the screws represent an imperceptible fraction of the weight of the instrument. They are also located very near the actual center of balance of the instrument so their effect on the instruments balance is even further reduced. The shape of the neck and peghead; the type of tuners, and the style of tailpiece will have a noticeable effect on the balance and weight of the instrument. Our screws will not.
We feel that our reinforced mortise and tenon joint has many inherent advantages for our instruments and our customers and that it should not be misunderstood or confused with other neck joints.