Almost every child has made a paper pinwheel in school at some point. Kids are fascinated by the way they can make the blades turn by blowing on it. However, a paper pinwheel cannot stand up to a strong wind. For this, you must bulk up the pinwheel design into a windmill. For the windmill blades to hold up, you must make them out of strong cardboard instead of thin paper. It may take slightly more work, but it will be worth it for a stronger construction.
Draw a perfect square on some strong cardboard. Use a ruler to get the lines straight, and use a protractor if necessary to get the corners exactly 90 degrees. Cut out the cardboard square with a utility or craft knife. Use the straight edge of the ruler as a guide.
Draw two diagonal lines from opposite corners of the square. They should cross exactly in the middle of the square.
Cut along the diagonals from each corner 2/3 of the way toward the middle. Now you have a square with four flaps.
Bend one of the sides of one of the flaps to the middle of the square where the lines cross. Pull it so it covers the center point. Do not allow any creases to form in the flap. It should curve, not crease.
Bend the same side of the next flap toward the center and cover the point of the first flap. Repeat this procedure for the other two corner. Only one side of each flap should be bent. All of the points in the middle should overlap and cover the center point.
Push a brass paper brad through all the layers of the cardboard at the middle point of the square. Spread the prongs of the brad on the back of the square to secure the flaps in place. Now you have windmill blades made of strong cardboard.
Use a sheet of strong cardboard that is also flexible. Because you will be bending the cardboard into windmill blades, do not use corrugated cardboard. Corrugated cardboard tends to crease. Rather, thick poster board or another flexible type of cardboard is best.
If you fasten the windmill blades to a mount, make sure there is a large bead or other item between the cardboard and the mount so that the blades turn freely.
Make a windmill with more blades by using a different geometric shape. For example, to make a six-bladed windmill, draw a regular hexagon instead of a square.