No matter how carefully I cut miter joints for frames, I often end up with a slight gap in one or more of the corners.
To hide them, I made a jig to rout a recess over the joints that accepts an inlaid piece of contrasting wood. This hides the gap, looks great, and adds strength.
To a piece of ¾” plywood, I screwed (not glued) two extra-long parallel guides spaced to fit the base of my trim router. Then I marked the centerline on the plywood between the guides, as well as the inside edge of each guide.
After removing the guides, I laid out and cut a 90° notch connecting the edge lines and centerline. Then I reattached the guides with glue and screws.
To use the guide, clamp it to each frame corner and use a straight bit to rout a shallow groove over the miter joint. Cut wood inlays to fit the grooves, then glue them into place and sand them flush.
