[Below] Ever have one miter that doesn’t quite close? Here’s a trick I got from somewhere at some time.
[Below] Dab some wood glue on the open miter and work it in to the joint. Wipe off any excess, but don’t use water.
[Below] Go over the joint with your sander. A random orbit sander works best. The saw dust from the sanding fills the joint. Note: this won’t work on wide gaps unless you’re painting the piece.
-- Ni faru ion el ligno!