This instructable will show you a technique of casting known as lost foam casting, to create aluminum gears. The gears in this instructable do not have any real purpose other than decoration, but with more time and patience, you could create gears for actual use on something. Please vote and favorite!
Step 1: Watch the Video
I made a full tutorial on creating these gears. I recommend watching it, as it goes a little faster than reading this instructable, and goes into further detail.
Step 2: Templates
For this project, I use Matthias Wandel's gear generator to make templates for my gears. The generator is made for creating wood gears but it worked just fine for my purposes. The site is very simple to use and is totally free. After I made a set of gears, I printed them out on normal printer paper and glued them with glue stick onto some flat pieces of polystyrene foam.
Step 3: Cutting Foam
After the glue is dried, I went and cut out the gears with my homemade hot-wire foam cutter (Instructable coming soon!). Make sure to follow the lines as close as you can, so the gears fit together.
Step 4: Casting
To begin the casting process, I first sifted out a bunch of dirt to a get really fine particle soil. I then mixed in some motor oil to help the soil clump together and buried the foam gears in it. I used a steel baking tin to hold the dirt in, so that if any aluminum spilled out, it wouldn't ruin the container. When I buried the foam, I held a glue stick on it and later pulled it out to act as a chimney for the liquid to flow down. Be careful to not cave in the chimney. After your mold is set, you can start the fire, I used wood as my fuel but coal or charcoal would be much better. To get the fine hot enough to melt aluminum, a fan is needed to blow on the fire to supply it with lots of oxygen. Once the fire was started, I turned on the fan and put in my crucible. The crucible is the container that hold the aluminum while it is melting. My crucible is made of the bottom of a steel propane canister, but any steel cup or container will often work. I used aluminum pop cans as the main source of aluminum. Once it was completely liquid, I carefully poured it into the mold chimneys and waited for it to cool.
Make sure while doing this, that you have all the necessary safety equipment at all times. This includes: face shield, fire proof gloves, long handled pliers/tongs and a fire extinguisher.
Step 5: Filing/Finishing
After I pulled my gears out of the mold, they looked very rough and uneven. Since these gears aren't going to be held or touched very much, I won't need to polish them as much as my Aluminium Handled Knife, but I still want them to look better than coming straight out of the molds. I first clamped the gears in the vise and cut off the bit of aluminium that filled the chimney. For the first gear, I used a normal hacksaw, but it took a very long time so for the second round, I used a Sawzall with a metal cutting blade. Then I flipped the gears in the vise and used an angle grinder to grind the faces down to a more silvery finish. After that, I used a drill to cut out the holes that had been filled in the casting process. Finally, I used an assortment of metal files to fine tune the teeth and sprockets of the gear. In the end, I could have spent a lot more time on them but I didn't have a use for them, so for now, they will stay rough.
When I cast the gears, the larger one didn't fully take shape and ended up not having several teeth. To solve this problem, I used IFixit, a kind of putty-like epoxy, and sculpted the teeth by hand. It actually turned out very well and worked better than I had hoped.