Essential Router-Table Jigs: Miter-Angle SledSee how a simple sled with a hinged base makes it easy to cut stopped grooves at an angle
This sled makes it easy to cut the slots needed to hold a hidden spline in a miter joint. You can make it from plywood or MDF, with the two leaves of the jig held together with inexpensive hinges. Screws in the two uprights hold the hinged leaf at the desired angle. Make the jig long enough to hold a range of sizes, and attach hold-down blocks as needed.