I am always on the lookout for ideas to make more hand-cranked wooden toys. I saw a video on Facebook, and one of the toys was a plastic hand-cranked windmill, with plastic gears. I decided to modify this concept, and adapt it to a wooden toy model.
I designed my wood model version using Sketchup. For the gear design, I used GearDXF program, that I previously downloaded to my computer.
I had to refresh my memory on gear design. You want the mating gears to have the same diametral pitch [# teeth/pitch dia.]. After checking my previous wood toy projects that used spur gearing, I selected a diametral pitch of 7. In Sketchup, I got an idea of the pitch diameter I wanted for each gear. Then using the GearDXF program, I selected the closest gear design that had a diametral pitch of 7, and the even number of teeth that go me the closest to my target pitch diameter.
For the initial design, I selected a 12x12" base using standard 3/4" wood. I will probably try this out when I build it, then increase or decrease it depending on how stable it is.
Using Sketchup, I printed out full scale paper drawings of each gear. I then white Elmer glued them to the red oak blanks. Then I cut them on the scroll saw. When done, I used a wet rag to wash the white paper and glue from the finished gear.
On previous wood gear projects, I learned that you must add 1/16 to an 1/8" on to the theoretical distance between gears. This is because of the stack up of tolerances (run-out between shaft hole and gear face, errors in cutting the teeth, etc).
I made a pine piece and first tried 1/16 inch extra. This did not work...........so I tried adding an 1/8"........and it worked ok.
I used blue masking tape to keep the gear attached to its 3/8" dowel shaft, and made sure the gears worked ok.
For the propellor, or fan blade, I already had a 16" diameter fan blade made up..........from a whirligig project. I used a hand coping saw to shorten to diameter from 16 inches to 12 inches. To try it out, I put small screws in the end of the 3/8" dowels, to keep them from rotating. It seemed to work fine!
I decided to use a mortise and tenon joint...........to join these 2 pieces. I used the tenoning jig on the table saw to cut the tenon on the bottom end of the vertical main pole.
On my other wood hand-cranked toys, I usually use a 3/8" diameter wood dowel, installed into a rotating wheel. As you turn the crank, the 3/8" dowel must slip in your hand.
On old hand cranked tools, like grinders or drill presses, the handle rotates with respect to the wheel, meaning the handle stays fixed in your hand..........which is easier and more comfortable. I decided to try to figure out how to do this on this toy.
This design works very well. The only issue is that a handle with a 1.5" diameter is little large for children's hands. It might be possible to reduce the handle diameter, if you scale the whole design down from using a 3/8" dowel to a 1/4" dowel. So .25/.375 = 67%............so 67% of 1.5" handle diameter = 1 inch. I may have to try this on a future hand-cranked model.
I used water based yellow dye for the top windmill blade spacer........and green colored dye for the handle. I gave them 2 coats of dye, then 2 rounds of polyurethane and 220 grit sanding. I wanted the handle nice and smooth since your hand rubs on the handle.
I used Golden Oak oil based stain on the oak parts, then 2 rounds of 220 grit sanding and antique flat polyurethane.
To speed up drying times, I put the parts in the oven at 120F for maybe 15 minute cycles. If you go longer than 15 minutes, the polyurethane may bubble on you.
I made a Youtube video to show this model in action.
This was a fun model to design and build. It has been a couple years since I designed and cut wood gears, and I had forgotten that the diametral pitch of the gears in the drive-train must be the same number. I did remember you have to increase the distance between gears slightly due to tolerance stack-ups.........and trial and error testing arrived at a 1/8" increase for the gears to work nicely.
The grandchildren should have fun with this one. I also display and let kids operate all my wood toys at an annual summer celebration in Marsh Park in Fairbury. The adults have just as much fun as the children!
Whenever I build a new toy, I have grandson Caleb test it..........unfortunately it failed "the Caleb test". One of the gears came loose from it's 3/8" shaft that I glued it to. I took it home and dowelled each gear to its shaft using 3/16" wood dowels and glue. Hopefully it will pass the 2nd Caleb test :)