Project 14658EZ:

Keyed Miter Jig

A flat miter joint that is simply butted and glued together will have little strength, so it is generally advisable to add reinforcement, usually with some sort of spline. The keyed miter is a variation of the splined joint that is both strong and attractive - and with this simple jig, it becomes surprisingly easy to make. Although it can be made somewhat

larger or smaller, the jig we show is sized to accept a fairly wide range of mitered frames.