3D Printed Candle Mold
Observations from printing and casting candles with 3D printed molds
The goal here was to design and make custom candles using 3D printed molds. I’ll share my setup and key learnings that I didn’t find elsewhere.
Setup
What I want: I wanted two-tone candles with the tones separated horizontally rather than vertically. This required a two-part overmolding process: mold and make one candle, then insert it into a second mold and pour the second candle around it.
Mold Design: I first designed the candle shape in 3D, then designed the mold using that shape. The mold consists of a cavity and a sealing pin. Once the wax sets, the sealing pin is removed and an ejector pin pushes the candle out.
Sealing Pin: In practice, I left a bit of space and used Teflon tape around the sealing pin because a plastic-to-plastic hard seal would be less reliable and harder to remove.
Sealing Pin Shape: Use a circular-ish sealing pin shape - complex shapes are much harder to seal with Teflon tape. It doesn’t have to be a perfect circle; the shape below worked fine.
Ejector Pin Surface Area: The ejector pin needs as large a surface area as possible; otherwise, it just indents the wax.
Mold Material: PLA and PETG were easier to work with. I tried TPU, but it was prone to air bubbles from moisture in the filament, which caused leaks. I could have dried the filament properly, but that seemed like more effort than it was worth.
Print Settings: Standard print settings will leak. To get a watertight mold, I increased the wall loops to 5 and used slight over-extrusion (a flow factor of 1.05 for PLA and 1.02 for PETG).
Couple images from the process:
Other Learnings
Wick Size: I was surprised by how much this matters - there’s more to candle making than I thought. There’s a subtle balance of wicking speed, material constituents, etc. I don’t fully understand it yet, but it was fun to get a glimpse into what’s going on behind the scenes in candle design.
Wax Additives: A hardening agent helps with mold release, improves shrinking, and makes the candle harder and easier to work with. I added 2% stearic acid by weight to my paraffin wax. Apparently this also improves opacity, fragrance retention, etc. Not really sure about the details on this. As I said, there’s more to candles than I thought!
Draft Angle: An 8-degree draft angle worked well for ejecting the candle. 2 degrees were too hard to eject.
Cooling Time is Critical: Wait for the wax to cool and shrink. Ejecting after three hours resulted in high ejection force even with 8 degree draft, launching the candle halfway across the room. After waiting overnight, it just needed a gentle tap.
Mold Release: I used a paintbrush to apply oil onto the 3D printed mold as a release agent.
Excess Wax: Don’t throw away wax drippings - they’re useful for repairing cosmetic defects like sink holes. I used a hot air gun to drip wax onto the problem area and fix it.
