This lesson will complete the frame of the boards.
Measure the distance between the two side frames. This will be the measurement of the end pieces. Make sure you measure this correctly, too large can be trimmed down, but too short will be waste.
Make sure to flush up the end piece with the plywood and not the side piece. It’s common that the sides can be longer but these will be trimmed down with a router or sander later.
Predrill and countersink the first screw from the plywood, into the end piece.
Then predrill and countersink the two screws from the side piece into the end.