2.Add strength and style with splines
Splines in a mitered box corner provide eyecatching detail and significantly strengthen the joint. To cut either straight or dovetailed splines, build the jig above, then cut the slots [Photos A–D]. Dovetail splines provide the illusion of dovetailed corners. The same jig works for cutting this joint [Photos E–H]. Prepare stock 1∕16" thicker than the bit diameter for splines and for testing setups.
Install a 1∕4" spiral bit in the router table, place the box in the jig, and set the height of the router bit (3∕8" here, for these 3∕4"-thick box sides). The 1∕4" plywood backer prevents chipout on the exit side of the cut.
Center the bit in the slot in the jig’s base, and lock the router-table fence against it.