Here’s another video on how to cut a perfect mortise using a plunge router – this one’s from Fine Woodworking. The video shows you how to make a mortising jig that guarantees perfect mortises and can be used over and over. The jig is easy to build and works beautifully. To define the mortise’s start and stop points, a length of T-track has been set into the long beam that serves as the bearing surface for the router.
Plunge and fixed base routers both have a place in the workshop, and each one is best suited to specific routing tasks. Basically, use a plunge router when you want to rout in the middle of the workpiece or when making a stopped cut that doesn’t go all the way to the edge of the workpiece e.g. a mortise; use a fixed base router when you are not making a stopped cut and routing the edge of the workpiece.