Dado joints have been used for centuries to build cabinets and bookshelves. Add this joint to your woodworking repertoire using a shop-made jig and router. With this setup, you'll perform precision cuts at varying widths every time.
A dado is a square-walled, flat-bottom channel cut across the grain of wood, that another piece of wood will fit into snugly. It's a simple joint but extremely effective. For example, when building a bookshelf using 19mm wood, you would cut a 19mm wide dado into the vertical piece for the shelf to fit into. The pieces are assembled using glue and screws.
The video above demonstrates how to setup your router, and use a simple jig and clamp to make dado cuts. The jig consists of two fences that keep the router enclosed along the entire length of your cut and maintain a consistent width. Dado joints are only effective when the two pieces of wood stock are aligned tightly together.
Router Joinery Basics: Dado [Woodworkers Journal]