board_width = 78.0;
board_length = 90.0;
case_depth = 10.0;
wall_thickness = 2.0;
board_thickness = 1.0;
column_side = 4.0;

union ()
{
  difference ()
  {
    cube (size = [board_length,
                  board_width,
                  case_depth + wall_thickness]);
    translate (v = [wall_thickness,
                    wall_thickness,
                    wall_thickness])
    {
      cube (size = [board_length - 2 * wall_thickness,
                    board_width - 2 * wall_thickness,
                    case_depth]);
    }
  }
  translate (v = [wall_thickness,
                  wall_thickness,
                  wall_thickness])
  {
    cube (size = [column_side,
                  column_side,
                  case_depth]);
  }
  translate (v = [wall_thickness,
                  board_width - wall_thickness - column_side,
                  wall_thickness])
  {
    cube (size = [column_side,
                  column_side,
                  case_depth]);
  }
  translate (v = [board_length - wall_thickness - column_side,
                  wall_thickness,
                  wall_thickness])
  {
    cube (size = [column_side,
                  column_side,
                  case_depth]);
  }
  translate (v = [board_length - wall_thickness - column_side,
                  board_width - wall_thickness - column_side,
                  wall_thickness])
  {
    cube (size = [column_side,
                  column_side,
                  case_depth]);
  }
}