Swap out the table saw blade for a dado blade and cut dados ¼” deep and ¼” from the back of the 1x3 red oak board.
Miter the board ends on a 45 degree angle. Lengths to suit your required frame size. Sand smooth and ease any sharp edges.
Cut the back panel. For this I used ¼” MDF to get a smooth matte black painted finish. The straight cuts can be made with a track saw and should be ½” longer and wider than the inside dimensions of your frame (to slide into the dado).
Finish the frame as desired. Since I was building a pool cue rack I added some counterbored holes at the bottom to accept the bottom of the cue. A peroxide and lye solution to bleach the red oak before applying a polyurethane finish.
Assemble the top to the sides of the frame with some wood glue or instant adhesive and pin nails.
Slide the back into the dados and install the bottom of the frame with some wood glue or instant adhesive and pin nails.
Install whatever you are framing to the backing and attach to the wall studs or drywall anchors.
I also used the same process to frame the pool rules and triangle holder.