When cutting mortises, you can go a lot of different ways: you can drill holes and then clean out the waste with chisels; you can make a jig that allows you to cut the mortise with your router and a straight cutting bit; you can also choose from quite a few jigs, specialty tools, and gadgets on the market. One of these gadgets, the Mortise Pal looks like a workable solution, if you can afford it.
To use the Mortise Pal just mark out your center lines for your mortise. Once you have the lines, center the jig with the tool’s alignment marks. Attach one of the plastic templates that corresponds to the mortise size you want. Then just route away with a spiral upcutting bit until you get to your desired depth.
The kit consists of the main jig, four templates, a wrench, centering pin, and a router bushing. The Mortise Pal will only work with routers that are 2-1/2 HP or less.
List price is about $200, but you can buy it for $175 on the manufacturer’s web site. It looks like a neat jig, but the cost seems high enough to me that I would just make my own jigs.