Next you need to rout the grooves that will accept the dowels in the side panels. Keep in mind throughout this step that the left and right panels are not identical - one is left handed and one is right handed. To avoid a mistake, clearly mark where you want the grooves to go so you don't make the all-too-common mistake of making either two left or two right sides.

Using a router and a straight router bit that has the same diameter as the dowel you will be using, rout some grooves about as deep as half of the thickness of the panels. So for example, if you panels were 3/4" (2cm) thick, rout the groove about 3/8" (1cm) deep. We made a couple of passes on the router table to achieve the desired depth: routing to the full depth puts undue strain on the router and the bit. You can also do this with a free router, but your guide will be slightly more difficult to set up. If the dowels do not fit into the grooves, you can sand the ends of the dowels to the proper size; its easier to resize the dowel than it is to resize the grooves. Note that we will be cutting the dowels to size after assembly.