To make this joint, you'll rout the dovetail slot first, then cut and size the dovetail to fit. For the slot you'll need a handheld router and the dado jig shown below. In addition to a 5⁄8 " guide bushing, you'll need a 1⁄4 " spiral downcut bit for clean cuts (a 1⁄4 " straight bit will also work) and a 1⁄2 " dovetail bit. We chose a 7° dovetail bit because it leaves a thicker, stronger "neck" on the dovetail than a 14° bit would. You will shape the dovetail on a router table. For testing the router-table setup, prepare a panel the same thickness and about the same width as the project panels to be dovetailed.
Lay out; then rout
You will cut the dovetail slot in two operations. First, to reduce the load on the dovetail bit, remove most of the waste with the spiral downcut bit. Then switch to the dovetail bit to complete shaping the slot. Because the dovetail slot tapers from bottom to top, the inside edges of the jig do not align with the top edges of the slot, photo below. To reposition the jig accurately for each operation, use the jig to draw layout lines on your workpieces to define both sides of the slots. Install the bushing and spiral downcut bit, and set the bit's cutting depth to 1⁄16 " less than the final depth of the slot. Clamp the jig along the layout lines and rout across the panel. Rout each slot with this setup.