Molding and Casting — Beeswax Candle Molds

I designed a two-part 3D printed mold in Fusion 360 that will be used to cast the silicone mold. The design process started with the candle shape I wanted to create.

Design Approach

I designed the candle shapes I wanted — four candles in a row. Then I created a negative mold by cutting those shapes out of a solid block. This creates the cavity where the silicone will be poured.

Two-Part Mold with Alignment Features

The mold consists of two halves that fit together precisely:

• Alignment Arches: One side has long arches that protrude, and the other side has matching grooves. The arches sit inside the grooves to ensure perfect alignment between the two halves.
• Center Clamping Hole: I added a cylindrical hole through the center of both halves. This allows me to clamp the two halves together tightly during the silicone pour. The cylinder shape creates a hole in the silicone mold (not a solid post), which is intentional for the design.
• Precision Fit: The alignment system ensures the two halves line up perfectly every time, which is critical for creating a clean silicone mold without seams or misalignment.

3D Printing Settings for Smooth Finish

Since the silicone will pick up every detail from the 3D printed surface, I needed the smoothest possible finish. Each half took about 20 hours to print due to the precision settings:

• Printer: Bambu A1
• Quality Setting: High Precision mode — finer layer heights mean smoother surfaces and less visible layer lines
• Wall Thickness: Increased wall thickness for structural rigidity and to ensure the two halves align properly
• Why Precision Matters: Every layer line on the 3D print will transfer to the silicone mold, and then to the final wax candles. The finer the print, the less post-processing (sanding and filling) is needed.

Even with high-precision printing, I still needed to fill and sand the 3D printed molds to eliminate any remaining layer lines before casting the silicone. The smoother the 3D printed surface, the smoother the silicone mold will be, and the better the final candles will look.

Mold Clamping Solution

I originally planned to design a 3D printed clamping box to hold the two silicone mold halves together during the wax pour, but the mold is too large to fit a holder on my printer bed and it would have taken an extremely long time to print. This is something I may revisit in the future, but for now I decided to lightly clamp the two mold halves together between two wood boards instead — a simpler solution that worked well enough to test the molds before fully committing to a printed clamping mechanism.

After printing the mold halves on the Bambu A1 using High Precision mode (each half took about 20 hours), I spent a significant amount of time sanding them by hand to achieve a smooth surface finish that wouldn't show the 3D printing toolpath.

Sanding Process

I worked through progressively finer grits of sandpaper to remove the layer lines:

1. 220 grit: First pass to knock down the visible layer lines and rough texture from the print
2. 330 grit: Second pass to smooth out the scratches left by the 220 grit
3. 440 grit: Final pass to achieve a very nice, smooth finish ready for silicone casting

This was a time-consuming process, but it's critical — every imperfection on the 3D printed surface transfers directly to the silicone mold, and then to every candle cast from it. The time spent sanding pays off in the quality of every future cast.

With the master mold printed and sanded smooth, I poured the silicone and left it to cure overnight.

Silicone Casting Process

1. Prepare the Master: Applied mold release to the sanded 3D printed master to prevent the silicone from bonding to it.
2. Mix & Pour the Silicone: Mixed the two-part silicone and poured it into the mold cavities, then left it to cure overnight.
3. Demold: The next day, I removed the cured silicone molds from the 3D printed masters.

Two Different Silicone Batches — Lessons Learned

When I demolded the silicone, I noticed that the two mold halves had noticeably different textures and properties. This happened because I used a different container of silicone mixture for each half:

• Hazy/Clear Mold: One half has a hazy appearance with parts that look clear. This silicone came out much softer and more flexible.
• Solid Blue Mold: The other half has a consistent, solid blue color. This one is firmer and more rigid.

For candle making, I prefer the solid blue silicone — it's more durable, holds its shape better when clamped together, and should be more resistant to the heat of molten beeswax over repeated use. The softer, hazy silicone would likely deform more easily and may not last as many casting cycles.

Second Attempt — Remaking the Failed Mold

Since the softer, hazy mold wasn't going to work well for candle making, I remade it using the correct silicone. However, the second pour didn't come out perfect either:

• Patchy Surface: Some sections of the new mold have a patchy, uneven texture rather than the smooth consistent finish I was hoping for.
• Shape Issues: The mold didn't capture the perfect shape of the 3D printed master in all areas.
• Twisted Alignment Groove: One section of the alignment grooves (used to line up the two mold halves) appears to be twisted. This is likely because someone tried to remove the mold from the master before the silicone was fully cured, which deformed the still-soft silicone.

Rather than remaking the mold a third time, I decided to just go with the first two mold halves I had — the solid blue one and the patchy second attempt. They weren't perfect, but they were good enough to test the full wax casting process. Patience is key with silicone — pulling it out early saves a few hours but ruins the whole cast.

Safety Notes

• Work in a well-ventilated area
• Wear gloves and safety glasses
• Review the Safety Data Sheet (SDS) for your specific silicone product
• Some silicones are inhibited by sulfur, latex, or certain 3D printing resins — check compatibility

Before casting, I needed to render (melt and filter) the raw beeswax from my hives. Raw beeswax contains debris, propolis, and other impurities that need to be filtered out.

I used an Instant Pot as a double boiler to safely melt the wax. The setup:

• Water Bath: Fill the Instant Pot with water (about 2–3 inches)
• Glass Jar: Place a heat-safe glass jar filled with raw beeswax in the water
• Rag Filter: Place a clean rag or cheesecloth on top of the jar to filter out debris as the wax melts
• Low Heat: Set the Instant Pot to "Keep Warm" or low heat — never melt wax over direct high heat as it's flammable

As the wax melts, it passes through the rag filter, leaving behind debris and impurities. The clean, filtered wax collects in the jar and can then be poured into molds.

I've processed a good amount of beeswax using this method and it came out really well — clean, golden, and ready for casting once the silicone mold is finalized.

Safety Notes

• Never melt wax over direct high heat — it's flammable above 400°F (200°C)
• Always use a double boiler or water bath method
• Keep a thermometer handy to monitor temperature (ideal: 145–150°F / 63–65°C)
• Work in a well-ventilated area

With the silicone mold complete and the beeswax rendered, it was time to cast candles. I decided not to 3D print the clamping mechanism since it wouldn't have fit on my printer bed and would have taken an extremely long time — something I may revisit in the future. Instead, I lightly clamped the two silicone mold halves together between two wood boards, which worked well enough to test the molds before fully committing to a printed solution.

Preparing the Wicks

Before threading the wicks through the molds, I lightly coated them in melted beeswax. Pre-waxing the wick helps it burn better and more consistently — the wax coating primes the cotton fibers so the candle lights easily and maintains a steady flame.

Melting & Pouring

I heated the beeswax the same way as before — using the Instant Pot pressure cooker as a water bath with the wax in a glass jar. Once the wax was fully melted, I poured it into the clamped silicone molds.

Casting Results — Lessons Learned

I cast three candles, and each one taught me something:

• First candle: Came out pretty good. However, the wax shrank as it cooled due to thermal contraction, so I needed to go back and top off the mold with additional melted wax.
• Second candle: I underestimated the amount of wax I needed, so I had to melt more wax mid-pour. This created a visible line where the second pour met the first — the second layer is a slightly lighter color since it was a separate batch.
• Third candle: The wax spilled out the bottom of the mold. This is where a 3D printed clamping mechanism would really help — the wood board clamp didn't seal the mold halves tightly enough to prevent leaking on this one.

Demolding & Results

After letting the candles fully cool, I removed them from the silicone molds and they looked pretty good. You can obviously see where I had to make the second pour of wax on the one candle since it's a slightly lighter color, but overall I'm happy with how they turned out. I cut the wick strings to length and they were ready to test.

Burn Test

I tested one of the candles and it burned perfectly — steady flame, clean burn, and that great natural beeswax smell. It's not the greatest looking candle, but the function is there and I'm sure there are improvements to make with more practice.

Potential Improvements

• 3D printed clamping mechanism: Would seal the mold halves more tightly and prevent wax from leaking out the bottom. This is the biggest improvement I'd make.
• Taller pouring section: Making the top of the candle mold cavity a bit taller would account for thermal shrinkage — when the wax contracts, it won't affect the final candle shape since the extra height acts as a reservoir.
• Pour temperature control: The temperature I pour the wax at could be a really important variable that I didn't closely monitor. Pouring too hot or too cool likely affects surface finish, shrinkage, and air bubbles.
• Single continuous pour: Having enough wax melted ahead of time to fill all molds in one pour would avoid the visible color difference from separate batches.

Why Mold Casting Instead of Dipping?

Traditional pillar candles like the ones I made are usually made by repeatedly dipping the wick into melted wax, building up layers over many dips. I wanted to try a faster method using silicone molds, and I'm happy with the result. It's a great way to use up extra beeswax from my beehives, and the molds are reusable for many future candles.

For the group assignment, we compared different mold fabrication methods and reviewed safety data sheets for each material used. McKinnon made a star-shaped mold using both 3D printing (Bambu A1) and CNC milling (Carvera into machinable wax), casting silicone directly into both. I did a two-part silicone molding process — 3D printing a master, casting silicone from it, then casting beeswax candles from the silicone mold.

Comparison of Mold-Making Methods

	3D Printed Mold (Direct)	CNC Milled Wax Mold	Two-Part Silicone Mold (from 3D Print)
Process	3D print mold → pour silicone directly	CNC mill wax → pour silicone directly	3D print master → cast silicone mold → cast beeswax from silicone
Stages	1 stage	1 stage	2 stages (master + silicone mold)
Detail	Sharp angles, fine detail	Corners rounded by bit diameter	Sharp detail — silicone captures everything from the sanded master
Surface Finish	Layer lines visible — needs XTC-3D coating	Smooth directly off the machine	Smooth — sanding the master (220→330→440 grit) transfers to silicone
Reusability	Reusable for silicone casting	Reusable for silicone casting	Silicone mold reusable for hundreds of wax casts
Casting Material	Silicone	Silicone	Beeswax (can't go directly in PLA — wax melts at same temp PLA softens)
Best For	Complex shapes, quick turnaround	Simple shapes, smooth finish without post-processing	Heat-sensitive casting materials, production runs, multi-part molds

The two-part silicone molding process takes more time upfront but is the only option when the casting material (like beeswax) can't go directly into a 3D printed or milled mold. For direct silicone casting, the group preferred 3D printing for sharper detail — CNC milling wins on surface finish straight off the machine but is limited to simpler geometry.

Full group documentation: Charlotte Lab — Week 13 Group Assignment