Woodcraft Magazine - Table-Sawn Splines - Downloadable Technique

Miters are among the most common joints in woodworking because they provide an attractive way to join two pieces at almost any angle. The only problem is that a basic miter is nothing more than a butt joint. It's an inherently weak joint because you're gluing end grain to end grain. Adding a spline—a wooden strip fit into matching slots cut in both faces of the mitered parts—

turns a weak joint into one you can trust.