How to build PVC windmill blades
Determine what size PVC pipe you need. This decision will be dependent on how large you want your windmill to be. To maintain structural integrity, the windmill blades should have a width-to-length ratio of somewhere around 1:5. For example, if you want your windmill blades to be 25 inches long, you should be working with PVC pipe that has a diameter of five inches. Each piece of PVC will provide two blades.
Draw a straight line down the PVC pipe using a pen. You will be using this line to cut the pipe in half. Use the measuring tape to determine the appropriate length for your windmill fans, and mark off that length.
Use your reciprocating saw to cut the pipe down to its proper length, and then cut the pipe in half. Each half of the pipe will be a separate windmill blade.
Lay the PVC pipe halves down and, using your measuring tape to ensure accuracy, mark off a line down the center of the pipe. We will call this the middle line. Also draw a line across the width of the pipe approximately one-tenth of the way up the pipe. For example, if your windmill blades will be 25 inches long, mark off 2.5 inches up from the bottom of the pipe. We will call this the base line, because it marks the base of the windmill blade.
Using the straight edge of your measuring tape, draw a diagonal line from the middle line at the very top of the pipe, to the base line at the bottom.
Use the reciprocating saw to cut along the diagonal line you have just drawn. This will shape your fan blades in a such a way as to increase their performance.
Use the electric drill to drill a hole in the center of the blade's base. This hole will be used to secure the blades to the windmill's axle. This is done by drilling a hole through the axle where each windmill blade will be placed, and attaching the blades by inserting a bolt through both the axle and the blade. The bolt is then secured by screwing a nut into place.
Use sandpaper to smooth out the rough edges of the PVC pipe. The smoother the edge of the blades, the better.