Create Rabbet Joints
Set aside the two side panels and locate the interior sides of the top and bottom pieces. Find the center lines of both the interior upper and interior lower panels and mark a 3/4” wide strip on each. Using a router or circular saw, notch out both laterals at a depth of 3/16" the entire width of the boards from front to back. This will create a “rabbet joint” – essentially, a U-shaped groove in the wood that will accept another piece of wood, cradling it, by locking it in on both flanks.
You are now ready to glue, nail and screw the four sides of the wine rack together. Try to use screws in areas that will not be visible.