Lay your board flat. Draw a line across the board that is parallel with the 13-inch edge, and 1 inch away from it. Draw another line across the board that is parallel with the 13-inch edge, but 1 inch away from the opposite 13-inch edge.
Draw 12 lines across the board that are perpendicular to the first two lines, and space them 1 inch apart. The two outside lines should be ½ inch from the 6-inch edges.
Drill 24 holes that are ½ inch deep where the lines intersect.
Place a dab of glue that is about a cubic-quarter-centimeter inside each hole, and insert the dowels into the holes. Wipe any excess glue with your damp cloth. Let the glue dry according to instructions.