This is a gusset.

Joining two or more pieces together is an interesting endeavor.  Some joints, like dovetails or mortise and tenon joinery, have tremendous mechanical strength (especially when force would largely be applied in the direction of that mechanical strength).  Other joints, like rabbets and dadoes, offer greater strength than a simple butt joint, but nonetheless require some fasteners to achieve a durable connection.

But what about butt joints?  In theory, a face grain to face grain glue-up using a modern PVA glue with upwards of 3,000 psi in glue strength should do fine on its own.  Prudence dictates adding a metal fastener or two perpendicular to the mating surface to prevent the joint from sliding over time under normal force.  Forces are not uni-directional all the time, however.  And specific woods are not ideal for every application.

With a 4 sq. inch mating surface, the glue theoretically asserts 12,000 lbs of force at the glue line.

Take, for instance, the above-pictured “saw bench”.  Although patterned somewhat on the Schwarz design (plans are here), it is assuredly not a piece of shop equipment.  Made from Eastern White Pine, it’s instead a portable sitting bench for a buddy who is about have a child.  I like the design, as it’s easy to knock together in a leisurely day.  Plus, it’s so damned comfortable.

A proper Schwarz saw bench in the background.

Under no circumstances can this bench collapse with a baby in the picture.  So I added some gussets to stabilize the legs laterally.  I might not have done so in another, harder material.  In fact, had this been oak or ash, I might have instead just screwed twice into the face of the joint and put a third screw in from the bottom.  But pine splits with too many fasteners per square inch (even when pre-drilled).

So next time you need to stabilize a joint from forces in a direction other than the mechanical strength of the joint, consider adding a gusset.  It might just save a baby’s life.

JPG