Squeeze and snap! That’s all it takes to assemble this CNC-routed box. Th e
joint’s flexibility comes from a series of slots that allow the hooked tenons to be
compressed, so they slide into the mortises. When released, the tenons spring
back into position, locking the parts together. While not as rigid as a glued joint,
the assembled spring joints are surprisingly stiff . And you can enjoy assembling
and disassembling the box as oft en as you like.
The key to making this joint fit well—neither too tight nor too loose—depends
on several things. Th e primary factors are the spacing, length and number of
the slots as well as the tolerances between the tenons and mortises. Th e springjointed
front and back are also 1/8" taller than the mortised ends. This small difference
in height keeps the hooked tenons slightly compressed aft er assembly,
which adds additional stiffness to the joint. Th e type of wood and the thickness
of the parts also affect the joint’s flexibility.
Accommodating all these variables can be a bit of a challenge —I made eight
prototypes before I found a fit that I liked. But similar to mastering hand-cut
dovetails or mortise and tenon joints, the time spent working out a solution for
this box was a very satisfying learning experience.
The slots become part of the box’s design and variations are almost unlimited.
However, I kept the shape and arrangement of the slots for this box simple in
order to show how the parts are made. Plans and tips for routing this box can be
found at AmericanWoodworker.com/CNC.