Introduction: The Magic Propeller
OK, this is a silly one, and I even have to admit you can find a few toys like this on the internet. A site for teachers describes how to make one using a pencil. But I feel entitled posting this Instructable because I can remember when my dad made one for us kids roughly 60 years ago. My brother and I were completely baffled how he would rub a little dowel on a notched stick and the little wooden propeller at the end would start spinning, and then he would say, "stop and go the other way," and without the slightest perceptible change in anything he was doing, the propeller would obey. And of course we would try and try and fail.
Naturally there was a trick, and for those who have not seen this toy, I will reveal the trick at the end of this Instructable.
You need a few little pieces of scrap wood -- almost any kind will do, and a small brad.
Step 1: Step One
I used my table saw to rip a piece of pine to about 5/16th inch square, and cut it to about 12 inches in length.
Starting about three inches from one end, and continuing to about one inch from the other end, I marked one edge, using pencil, with 1/4 inch intervals.
Then, using a small, fairly coarse, square file, I filed notches in one edge.
Since folks are going to be rubbing this stick like crazy, it needs a very good sanding including rounding the edges slightly.
Step 2: Step Two
The propeller is another little piece of wood -- I used a little scrap of maple since it is nice and hard and the hole will likely remain true and clean after drilling. But I bet a little piece of Masonite or Plexiglas would also work fine. Even a soft wood like pine should be OK if you make a nice clean hole and get rid of any little fibers.
The one I cut out is a full 1/8 inch thick, and is 2 3/4 inches long X 5/8 inch wide. These dimensions are not critical.
It is important to drill the hole in the exact center to prevent the propeller from being out-of-balance. I used a #48 drill from my numbered drill set. I did not measure the drill with a caliper, but it is probably about 1/16th inch in diameter. You should use a larger drill or countersink plus a bit of sandpaper to clean-up the edges of the hole -- it must be nice and clean to allow easy rotation. It is a very loose fit on the brad that attaches the propeller to the notched stick.
Step 3: Step Three
I bet the hardest part of this project is finding the perfect little nail to attach the propeller to the notched stick. In spite of a huge collection of nails and screws in my shop, this little baby was elusive. It is about 3/4 inch long, and very thin.
You just drive the nail straight through the hole in the propeller into the end of the notched shaft. Sure, go ahead and try to center the nail on that tiny end, and while you're at it try to get the little devil to go in straight. Good luck! I had to bend mine straight after nailing, but don't tell anyone.
For the rubbing stick, I was looking around for a piece of 1/4 inch dowel, but I only found a few scraps of 3/8 inch material. I cut a piece to about six inches long, smoothed-up the ends, and that seems to work fine.
Step 4: Step Four (secret)
OK, here is the big secret. Please do not not ask me to explain why this works. For all I know, it really IS magic. In the photo, please note carefully the positions of the fingers when holding the dowel. When rubbing the stick, the index finger (if you are right handed) will be riding up and down on the left side of the notched shaft. Your middle finger will be riding up and down on the right side of the shaft. When you rub the notched stick, if you continuously hold your middle finger against the edge of the shaft (with no pressure from the index finger), the propeller will rotate to the right. If you hold your index finger against the shaft while rubbing, the propeller rotates to the left. No one sees your tiny shift in position to reverse rotation because it continues to sound the same and they are all watching that ridiculous obedient propeller! Have Fun!!
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