160x160mm grid. pictured here in black and pink PLA. The pieces are http://www.thingiverse.com/thing:34017 scaled up 5XPretty simple. Print the board_edges.stl in the color of your choice, and two sets of board-squares.stl in two colors. Lightly sand the squares until they pressure fit in the grid. I then had a slightly bowed board due to the pressure, so I let my printer bed heat up, carefully took off the hot glass and set the assembled board on the metal plate, then set the glass on top, with a weight until it straightened out.