You need a lot of mortises, but you don't own a mortising attachment for your drill press. And you don't want to spend hours chopping the mortises by hand.

Here's a solution: Use a plunge router with these simple jigs, and you can cut mortises as fast as you can rout them. Glue and nail together two jigs as shown in Step 1. Make them about 4'' longer than your router base plus the length of the mortise.

Turn the jigs so the stops face in opposite directions, and loosely position them in a bench vise or Workmate. Slide the board to be mortised between the jigs, with the centerline of the mortise as shown in Step 2. Align the two stops so that the distance from the mortise centerline to each stop measures half the length of the mortise plus half the width of your router base minus half the diameter of your bit.

Tighten the vise or Workmate, extend the mortise centerline across the supports, and tack each stop to the opposite support. Attach an edge guide to your router, center the bit on the workpiece, then rout the mortise. The centerline markings on the supports enable you to quickly align the next workpiece.
—Ronan Cambridge, Ottawa, Ont., Canada