This Instructable describes how to create a wax candle from a computer generated design using a 3D printed mold. The key here is that instead of creating a typical “clamshell” style mold with two or more halves with a cavity inside, this method creates the outside skin of the mold which is then torn off after pouring the wax. The advantage is that you can cast more complex shapes relatively quickly without designing a complicated multi-part mold. The disadvantage is that the mold is not re-usable, but this method could be used to make one-off custom candles (with personalized messages cast into the wax for example) or to verify how the candle looks and burns before making a solid mold to make multiple copies.
Step 1: Create Model
Begin by creating a 3D model in your favorite CAD software, or downloading one from an online source such as Thingiverse or GrabCad. I will be using this Tornado from thingiverse. The point is to make a thin walled model that will be easy to tear away after pouring the wax. The “Shell” command is common in several CAD programs and is used to hollow out a solid model to create a thin walled part. Adjusting your printer settings and or the model itself so that the print is composed of a single string of filament will make it easy to tear away. After you save your model as an STL file, load it into your G-Code generating program such as ReplicatorG (for Makerbot, etc) or Slic3r and create the tool-path.
Step 2: Print Mold
Load the printing code for your mold into the 3D printer and begin printing. If this is the first time printing a new design it may have some imperfections. Once the mold is finished printing, examine it for potential leak points. Since the mold is thin walled, there may be breaks in the print which you can seal instead of re-printing the entire part. Printing slower, adding additional shells or setting a thicker print height layer may help eliminate leaks. However, if you still get breaks in your mold, it is easy to seal them up. ABS cement works well, you can find it in the plumbing section of your hardware store (near the black ABS plumbing pipe parts). You can also make your own by dissolving some ABS filament with acetone or use something else to seal up the gaps such as modeling clay.
If you do not have a 3D printer there are plenty of 3D printing services online that you can search for like shapeways or quickparts, although these tend to use higher quality printers and are thus more expensive.
Step 3: Gather Tools
You can buy candle making kits, different types of raw wax or melt down existing candles to cast in your mold. If you don't buy a kit, you will need to get a set of wicks separately. You should use a dedicated pot to melt the wax down to not contaminate your cooking pots. Additionally, you should have a secondary container like another pot or tupperware in which to set your mold while pouring, so that if anything spills out or breaks, you dont get a huge puddle of wax all over the counter.
Step 4: Prepare Mold
If your mold has an open bottom like this tornado, you will need to seal it before pouring the wax. An easy way to do this is to soften up some wax (just enough to be pliable) in the pot and press it into the mold. After it has cooled, you can use a toothpick to punch a hole through the wax for the wick. If the wick has a metal ring at the base like the one shown, you can dip it into melted wax before pulling all the way through in order to have it stick better.
To secure the loose end of the wick, poke a small hole in a piece of tape and feed the wick through the hole. Then secure the tape to the top of the mold so that the wick is positioned where you want it.
Step 5: Melt and Pour Wax
Once the wick is installed in the mold it's time to pour the rest of the wax. Place the raw wax or candles you are melting down into your pot and begin heating slowly on the stove. Once the wax begins to melt turn the heat down. The hotter you get the wax initially the longer it will take to cool and set. While the wax begins to melt, set your mold into a secondary container to catch any spills. It may help to tape the mold in place to avoid it tipping over.
Once the wax is melted its a simple matter of pouring into the mold, but you can experiment with various techniques to get different results. For example you could melt different colors and pour them in seperatly or at the same time to get various color patterns in the candle. To get discreet color layers, you should wait until each layer begins to harden before pouring the next one. You can also add various incense or flowers while pouring to suspend them in the candle.
Step 6: Allow to Cool
After pouring the wax you need to wait for it to cool and harden. You will see the wax start to skin over and get hard. The best way is probably to let it cool naturally on the counter but you can try sticking the mold in your fridge or freezer or add ice packs to the side of the mold while you are pouring the wax to help cool it faster and prevent leaks. This can however lead to bumpy surface finishes as things cool at different rates and may not be desireable. Experiment to find a good cooling startegy.
Step 7: De-Mold the Candle
After the candle has cooled sufficently, it's time to tear away the mold. Since the mold was mold was printed with extruded plastic filament, you can simply unwind it strand by strand.Using some smallnail clippers or wire cutters, cut into the the mold and begin peeling off the plastic. Once you get to the end you will have your finished candle!
Once you are done peeling off the plastic, you can add finishing touches by dipping the candle in more wax, heating up sections of it with a torch to get drip effects or keep it the way it is.
Step 8: Conclusion
The tornado shown here is a fairly straight forward design and could have been made with a conventional two part "clamshell" cavity mold but the method can be used on more complex interwoven geometry like the attached image. There are plenty of variations and techniques you can try with this method, and if you mess up simply melt down the candle and print a new mold!
Finally, since this method is good for creating oddly shaped candles, it's important to make sure they do not topple over as they burn and the mass of the candle shifts so be sure to use a candle holder which holds the candle securely.