Although laser cutter machines are still quite expensive, you can find now a cheap service in some Maker Space. The wood mechanisms always fascinated me, and I passed a lot of time when I was a child sawing plywood with a coping saw. Now that spare time is not much anymore I like to design and cut wood parts with laser machine.
This time I decided to make some gears, which would take long time if I had to cut them with the coping saw, and assemble a toy to give to my young nephew as birthday present. I'm sure he will like the moving parts.
Step 1: Gears Software
To design a gear is not simple at all, but we don't need to go deep in detail this time. Fortunately a very functional software can help us. It's also freeware and very simple to use. Just visit the website and download it: GearDXF.
After installing it you can give a try to see how the image of the gear change with different parameters. We are interested for now only in two parameters: the Diametral Pitch and the number of teeth. If you multiply these two values expressed in inches you obtain the measure of the Pitch Diameter i.e. the distance between centers of two adjacent gears. Quite simple, isn't it?
I decided to use for my wood toy a Diametral Pitch of 10 and 22 as number of teeth (12 in some images of the software). You can of course use different parameters, just be sure to use always the same Diametral Pitch for all your gears. As Bore Hole Diameter use a right measure corresponding to the screws you want to use.
Step 2: Export .dxf
Select "metric" measure unit and save the .dxf file clicking the icon on top left of the window.
Now open the gear which is now in millimeters in your CAD software and add a circle centered in the hole, with a diameter equal to the Pitch diameter you read in the GearDXF software. You will need this circle to set the right distance between gears.
Step 3: Side by Side
Now place gears side by side keeping half a millimeter or more (depending by the dimension of the gear) between the two circles. This will avoid tedious friction due to imperfection of the cut or a center not exactly centered.
Step 4: Arrange All the Gears
With the same principle of before go on copying the gears in CAD and placing one adjacent to each other in the shape you prefer. I opted for a typical square with 9 identical gears, but you can change the project as you wish. After placing all the gears draw a rectangle around them. You see that I left the circles and I added an inner rectangle to be engraved as ornament.
Step 5: Lasercut
In some Makerspace (like WeMake in Milan where I made it) you can lasercut your plywood panels in a friendly and professional atmosphere. You can use a 60x90 cm or a bigger 90x120 plane lasercut machine, which is also more powerful.
I cut my nine gears and the base following instructions for that machine. It took not more than half an hour.
You can of course print your gears on a paper sheet and then glue it on a plywood board to cut it with a jigsaw. In this case I suggest you to design bigger teeth so they will be easier to cut.
Step 6: Some Metalware
You only need a set of ten screws and ten or twenty washers. Use double washer if you want that gears will roll more freely.
Step 7: Work on Details
If you want a better looking mechanism you probably can etch a seat for the screw heads, with a special drill bit you can see in the picture.
Step 8: Assembling
Time to assemble the toy. Pay attention that screws don't exit from bottom of the board. Use a gimlet to make an hole on one gear and attach an handle to it. This handle should be a small pipe which roll freely around the long screw, so that the child can rotate the gear easily.
Also you can add some rubber feet so the base will stay firm on the table meanwhile you rotate the gears.
Step 9: Ready!
The toy is now ready to be wrapped and given as present! I'm sure someone will enjoy looking at all nine gears moving together.