Stopped Dado Joint

What You Need
While a dado is easily made on a tablesaw, the best way to do a stopped dado is with a hand held router, preferably a plunge router, and a bottom cleaning bit the same width as the board that will go into the dado. For the shoulder, you could use several tools, including a handsaw, tablesaw, router or bandsaw. If you use a handsaw or bandsaw to cut the waste for the shoulder, you will need to trim it with a chisel.

Bottom cleaning bit

How to Make the Joint
To make the stopped dado, first determine exactly where the dado will go. Use another board as an edge guide, and clamp it down so that the edge of your router baseplate will be guided by it. You can set it up by eye or measure from the edge of the router bit to the edge of your baseplate and set the edge guide at that distance from the edge of the dado.

Once the guide is clamped in place, make a mark where the dado will stop, ¼" from the edge of your workpiece. Make sure you can see it while routing, otherwise you will need to clamp a stop in place to prevent you from routing straight through the board.

Rout the stopped dado in two passes, cutting half the depth in the first pass, then the full depth for the second pass. For each pass, stop when the bit reaches the mark you made earlier.

To make the shoulder on the workpiece that fits into the dado, mark the depth of the dado on the board and mark in ¼", plus half the width of the dado. This will provide enough clearance for the curve at the end of the stopped dado.

Cut the waste out with a bandsaw and then pare it down with a chisel, testing periodically until the joint fits without gaps.