In the current issue of Popular Woodworking magazine (August 2008), Senior Editor Robert W. Lang used two jigs on the bookcase shelves to cut the dados and to create the twin mortises for shelves’ through tenons.
The first jig, shown in “Router Jigs Part 1,” walks through making a dado jig to accomodate any shelf thickness. Bob uses a straight router bit with a top-mount bearing to cut the dados. You can use the steps shown to produce a perfect fit for any dado joint, regardless of shelf thickness.
The second jig, shown in “Router Jigs Part 2,” is quite innovative in how it’s built. Bob uses several pieces of 1/2″-thick Baltic birch plywood and a pin nailer to construct this jig. From there, he’s just a drill and router away from a simple tenon-routing setup. This is a great technique!