Step 1
Clamp the birdhouse upside down in the vise. Center the birdhouse on the 12 inch by 12 inch square of wood. Hammer nails through the bottom of the wood square into the walls of the birdhouse to secure the house to the board.
Step 2
Measure 6 inches from each corner toward the center of each edge of the board. Make a mark at these points, which will be in the center of the edges. This will create four equal points, one in the center of each edge.
Step 3
Draw a line from the pencil mark on the right edge to the mark on the left edge. Draw a line from the mark on the top edge to the mark on the bottom edge. This will create a crossed design, with the pencil marks crossing at the exact center of the wood.
Step 4
Place the floor flange over the crossed pencil marks, using the marks to center the flange. Situate the flange so that the screw holes all line up on pencil marks, if you have a flange with four screw holes. If your flange has three holes, line up one hole on a mark and think of it as 12 on a clock. Set the other two holes so that they mark 4 and 8 on a clock.
Step 5
Screw the flange securely to the bottom of the board. Make sure that the flange doesn't move during this process, to keep it in the center of the board.
Step 6
Turn the board and birdhouse right side up. Slip the center of the flange hole over the top of the post to install your birdhouse.