Crayon Gear System

I have enjoyed seeing several projects over the past few years where people melt down old crayons into fun new shapes and have always thought it would be fun to try. In this project, I wanted to extend this idea so that students could have fun repurposing their crayons while hopefully learning a little bit about engineering in the process. This instructable gives explicit instructions for how to mold and create a repurposed-crayon gear system you can use to teach youngsters about both gears and manufacturing.

• Crayons (old or new); about 3 crayons per gear
• Gear cookie cutter
• 1/2" dowel (cut into 1" pieces, one per gear)
• Scrap wood / board
• Oven
• Oven-safe bowl
• Glue (hot glue works well)
• Optional: cooking spray, utility knife, popsicle sticks, drill

Depending on how much time you want to dedicate to this project, you (and/or your students) can either design and 3D print your own gear mold (in a 3D modeling software like Tinkercad of Fusion360) or simply 3D print a read-made open-source "gear cookie cutter" (like the one found HERE on Thingiverse).

If you choose to go the "pre-made" route, you can simply 3D print the file attached here.

Gear tie-in: If you choose to have students design their own gears, this is a great opportunity to talk about different design elements of gears and/or how different-sized gears that are connected (1) need to have the same sized teeth and (2) will spin at different speeds!

For each gear you want to make, you will need the equivalent of 3 crayons to melt down. I wanted the gears in this project to be distinctly different colors, so I sorted my crayons into like colors first, but you could use any colors together if you are happy with a swirled or multicolor design.

Peel the crayons and break them into small pieces.

Manufacturing lesson tie-in: This is a great opportunity to talk to students about how plastic, rubber, etc. pellets are used in manufacturing, including how surface area impacts melting, etc.

After they are peeled, the crayons can be melted.

In an attempt to make this project with less mess, I attempted to melt the crayons in the microwave in a disposable cup at first, but this was largely unsuccessful and I ended up with a clump of semi-melted crayons in a scorched cup. I recommend finding an old bowl you don't mind scraping some wax off of later and going straight for the oven-melting approach.

For each gear, melt three crayons in an oven-safe bowl at 150F for approximately 10 minutes.

Even though this is a low temperature, the bowl will still be very hot, so make sure to use oven mitts when removing this from the oven - especially if you are working with younger children.

Manufacturing lesson tie-in: From here, you can discuss how molding requires us to melt down materials into a liquid plastic/rubber/metal/etc. before it can be used to form new shapes. HERE is a great reference video you can show students to help lead this discussion while the crayons are melting.

When the crayon wax has become liquid, pour the wax into the gear mold. You may need to use a disposable tool like a popsicle stick to help get all of the wax into the mold.

Let the wax cool in the mold for at least 30 minutes (or for 10 minutes in the fridge).

Once cool, gently press the gear out of the mold. I used the eraser end of a pencil to press gently around the edges to remove mine. If you have any buildup around the edges of your gears, you may want to clean it up with a utility knife before moving on.

Molding tips: While many crayon molding projects use silicon or flexible molds, these 3D-printed gear molds are rigid, which makes it more challenging to remove the gear shape from the mold. Don't stress if your first attempt turns out like mine (the red one shown above). You can always just remelt the crayon bits and try again! After my third try, I found that spraying the mold with a very light coating of cooking spray helps it slide out of the mold with much more ease. Make sure not to overapply the cooking spray, however, or your crayons will become slimy and smeary.

Now that you know how to mold one gear, you can repeat steps 2-4 until you have created as many gears as you want. For this project, I made four gears.

Once all your gears are printed, lay them out on whatever board you plan to attach them to. I used a scrap I had layout around from an old project, so feel free to grab whatever you have that works. A strong piece of cardboard could be substituted in for the wood here as well.

Making sure the teeth are interlocking, trace the holes inside the gears so you will know where to attach your axles/dowels. You can glue the small dowel pieces directly to the wood/cardboard or, as I did, you can drill out a hole so the dowel/axle can slide all the way into the wood. I prefer this method so that the dowel can be glued in place on the back of the board, away from where the gears will be spinning.

Once you have attached your dowels, simply slide the gears onto your system to complete your design. When you turn one, the rest should turn!

Gear tie-in: The final product should transmit the rotational force from one gear all the way through the gear system to the final gear. This project is a great way to introduce the idea of transmitting motion using gears to students!