Gray-B-Gon wind-powered evapotron for graywater disposal

Step 24 Propeller: pick mounting points and cut blades

Materials:

• trial blade.
• bike wheel with pulley wheel mounted.
• aluminum sheet, enough for five 9"x12" or 8"x12" pieces. A roll of aluminum flashing, available at hardware and building supply stores, is a good thickness.
• medium-grit emery cloth.
• black mini zip ties.

Clamp your wheel upright, with the pulley wheel facing you, and think of the pulley side as the back face of the propeller. Position your trial blade like the annotated blade below. With one thumb or finger, press the blade against the spoke crossing ("first mounting point."). The crucial spoke is the one running down from the left -- it cages the blade within the spoke line.

Find a second point on the blade to press, farther out, that will encourage a curve that makes the blade arch out in the front at about 30 to 45 degrees. (The "second mounting point."). 

If this layout doesn't work on your wheel, it may be due to an unusual spoke pattern.  Try the mirror image, or find another shape or position that does work. Cut a new trial blade if necessary.

Press the trial blade into the spokes. Mark the blade with a dot at each side of the spoke crossing and at each side of the second point. Drill 1/8" holes at the dots.  From the front, slip a zip tie through a hole, around the spoke and back through the other hole, and cinch it up. After zip-tying two points, you may find you need a third point anchored to get the shape you want. 

Look the blade over. The curve and angle may be okay, but the blade may be too long, or not long enough, or the back edge may be sneaking past the spoke line. Use the marking pen to show the needed changes, sever the zip ties, and cut and drill a new and improved blade shape.

Once you're satisfied, use the blade as a template to draw eight more shapes, and cut them out. (Or seven more, for a 32-spoke wheel.) Smooth all the edges with emery cloth, so your propeller won't draw blood.