A two-part mold takes 4 steps. First upload the figure as an STL to kingscutter.com and pick the material you will cast. Then adjust the seal and the air vent, and download both halves ready to print in PETG. The two-part mold generator (TWO_PART_BOX_MOLD) works out the cavity, the pour channel, the air vent and the alignment keys with no manual modeling.
What is a two-part mold and what is it for?
A two-part mold is a rigid box cut in half that, once closed, encloses a cavity shaped exactly like the piece you want to reproduce. You pour the liquid material through the mold mouth, wait for it to cure and open both halves to release the finished piece.
A two-part mold is used to cast wax, resin, soap and plaster. Its advantage over an open mold is that the piece stays enclosed on every side. That is why it handles full-volume figures, such as a chess pawn or a sphere. An open mold would cast those shapes in halves and glue them afterwards.
Demand for molded pieces follows the growth of creative baking and handmade craft. The global cookie market is projected at USD 30.6 billion for 2025, with a compound annual growth rate of 4.1% through 2032 (Research and Markets, 2025). In the home segment, 37% of home bakers report cookies, brownies or bars as their top-selling product (Better Baker Club, 2022).
How do you make a two-part mold with a 3D printer?
Short answer: in the kingscutter.com designer you upload the figure as an STL, pick the casting material and download 2 STL files: left half and right half. Both are printed in PETG, a rigid plastic that carries the weight of the poured material and does not warp with curing heat.
The whole design takes about 10 minutes and print time depends on the box size. There is no need to model in Blender or draw the pour channel: the generator places it according to the chosen material and the pouring axis.
Step 1 â Upload the figure as an STL or use a built-in example
The generator accepts your own STL file: a scanned figure, a piece from your catalog or an STL made in another program. The file is re-sent to the geometry engine on every parameter change, so the mold always reflects the latest version of the figure.
If you do not have a file yet, the designer includes 3 example figures to test with: pawn, sphere and diamond. All 3 show how the cavity, the pour channel and the alignment keys come out before you commit to a long print.
Step 2 â Pick the material you will cast
Material is the highest-impact setting, because it changes 4 values at once: pour hole, fit clearance, air vent and wall thickness. The designer ships presets for wax, resin, soap and plaster.
The generator also estimates how many milliliters fit in the cavity. That number tells you how much material to prepare, and it prevents 2 expensive mistakes: running short mid-pour or mixing twice as much as you need and throwing it away.
Step 3 â Adjust the seal, the clamp and the air vent
The seal between halves is either a tongue or a set of pins. Clamping is either rubber bands or none at all, for molds that stay closed under their own weight.
The air vent opens when the material traps air. Resin, which is more fluid, needs a 2 mm vent; wax and soap pour with no vent. Every control carries a label in the interface language, so there is no guesswork about what each field does.
Step 4 â Download both halves and print
The output is 2 separate STL files, plus an Explode view in the viewer that shows how the halves fit when closed. Check that view before printing: if the figure has thin parts touching the box wall, thicken them and generate again.
Printing is standard FDM. Each half works under compression while the material cures, so a high infill and thick PETG walls pay off. Scale is set as a percentage in the designer: 100% keeps the figure at its original size.
Two-part mold generator data and measurements
The values below come from the real kingscutter.com generator, verified in the designer code in October 2026. They are not estimates: they are the numbers the mold applies by default.
| Mold setting | Default value | What it is for |
|---|---|---|
| Box wall (boxWallMm) | 5 mm | Rigidity of each half during the pour. |
| Fit clearance (boxFitClearanceMm) | 0.2 mm | Capillary channel that lets air escape. |
| Pour hole (boxPourHoleDMm) | 8 mm | Inlet for the liquid material. |
| Air vent (boxAirVentDMm) | 0 mm | Air outlet; resin uses 2 mm. |
| Seal between halves | Tongue or pins | Exact alignment when the mold closes. |
| Clamping | Bands or none | Keeps both halves together while pouring. |
| Pry pockets (boxPryPockets) | Enabled | Open the mold without hitting the piece. |
| Scale (boxScalePct) | 100% | Final size of the piece. |
| Orientation (boxOrientation) | Z up | Most stable pouring axis. |
The mold also lets you shift the pour channel along the X and Y axes. That matters when the figure is not symmetric and the highest point is not at the center of the box.
Which materials can you cast and how much do you need?
The table below summarizes the presets per material. Density is the figure that turns milliliters into grams of mix.
| Casting material | Pour hole | Clearance | Air vent | Wall | Density |
|---|---|---|---|---|---|
| Wax | 8 mm | 0.2 mm | 0 mm | 5 mm | 0.9 g/ml |
| Resin | 8 mm | 0.15 mm | 2 mm | 5 mm | 1.1 g/ml |
| Soap | 10 mm | 0.2 mm | 0 mm | 5 mm | 1.0 g/ml |
| Plaster | 12 mm | 0.25 mm | 0 mm | 7 mm | 1.6 g/ml |
A practical example: a 100 ml cavity needs 160 g of plaster, 110 g of resin, 100 g of soap or 90 g of wax. With the mold estimate and a kitchen scale, the pour lands right the first time with no leftover mix.
How do you avoid flash and misalignment between the two halves?
In our workshop we measured the classic weak spot of a printed mold. If the band groove is subtracted right on the box face, the halves end up with an open edge and the slicer can reject the part. The generator corrects the outline so the cut is always transversal and each half closes as a watertight solid.
The fit clearance serves a second purpose: it leaves a capillary channel that lets air escape without opening visible flash. With resin that value drops to 0.15 mm because the material is more fluid, and with plaster it rises to 0.25 mm because the mix is thicker.
Pry pockets are the third support. They let you insert a flat screwdriver or a wedge and open the mold without hitting the piece, which is the most common cause of breakage during demolding.
How is it different from a one-piece open mold?
The open mold, the one in the custom silicone mold guide, is a single piece with the cavity facing up: you pour, let it cure and demold by flipping it over. The two-part mold is a box that opens in two and allows figures closed at the top, with its own pour channel and air vent.
Choose an open mold for flat pieces, decorative plaques and one-sided pours. Choose a two-part mold for full-volume figures: candles, soaps, resin pieces and replicas of an existing figure.
Sources and standards
The technical data in this guide rests on verifiable official sources:
- eCFR 21 CFR 177.1315 â PET and PETG as base polymers suitable for food contact.
- eCFR 21 CFR 177.2600 â rubber and silicone articles for repeated food contact.
- EFSA â food contact materials.
- Wikipedia â Molding (process) â definition of casting and split molds.
- Research and Markets â Cookies: Global Strategic Business Report.
