Here's a router based mortise jig I made from info on the great www. I did a search on this site and didn't find anything like it, so thought I would post it. I Like the way it works, and being shop made it's cheap.
The jig clamps to your bench, the work clamps to the jig, and router is guided by an edge guide running in a track, heres and over all pic.
The work clamps to the face of the jig. I am using shop made clamps. This jig is good for table leg mortises that are not necessarily centered. Mount the one leg from left side, and to cut the opposing mortise in the adjacent leg, mount it from the right side, no adjustment of the router is required, you do to need change the stops. There is a registration pencil line in the center just align the end of the work to it
The router is guided by an edge guide running in a track and the length of the mortise is controlled by stops in a T track.
You only need to mark the the center of the mortise and the beginning and end. Then adjust the edge guide to center the bit on the line and adjust the stops to align the start and stop points. Mount the end of the work aligned with the registration mark on the jig body. Repeated mortises can be be cut without further marking or adjustment.
The main 3x3 needs to be square, thats the only critical part. Except for the T track it is all scrap wood, including the 3x3 that is glued up from 3/4 popular. I have cut 1 1/2 in. table legs and 3 in. bed posts with it. It does work really nice.