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Generating mold…
splicestl/mold is a free in-browser tool that generates 3D-printable mold boxes from STL master models. Drop in your master, pick a casting material (silicone, resin, plaster, or wax), and download a two-part mold ready to print and pour. Everything runs locally — your files are never uploaded.
The most common workflow: print the rigid mold box on a regular FDM or resin printer, pour liquid silicone into the cavity around your master, let it cure, then peel the printed box off. The resulting silicone mold becomes your production tool for resin casting, plaster casting, concrete casting, wax masters for investment casting, or any other pour-and-demold material.
Print the box, pour platinum-cure silicone (e.g. Smooth-On Mold Star 30), then use the cured silicone mold to cast clear or pigmented epoxy/UV resin parts. Default preset: 5 mm wall, 1 mm clearance.
Print the mold box and pour resin directly — for low-detail parts where peeling a rigid mold off works (release agent required). Default preset: 3 mm wall, 0.5 mm clearance.
Print thick-walled mold boxes for pourable concrete, plaster, or hydrostone. The mold is rigid enough to hold heavy slurry without flexing. Default preset: 4 mm wall, 1 mm clearance, large pour spout.
Print the mold box, pour wax, then use the wax in a lost-wax investment casting process for metal parts. Default preset: 4 mm wall, 0.8 mm clearance, accounts for wax shrinkage.
You don't print silicone directly — silicone needs specialized casting equipment. What you DO print is the mold box (the rigid outer shell). After printing, pour liquid silicone into the box around your master model. Once cured, peel the printed box off and the silicone mold is your finished casting tool. splicestl/mold generates these printable boxes.
Any standard FDM printer (Bambu, Prusa, Ender, Voron, etc.) handles mold boxes well — PLA or PETG work fine. For very smooth interior cavities (where surface finish on the finished casting matters), a resin printer gives sharper detail. The default mold box wall thicknesses (3-5 mm) print cleanly on a 0.4 mm nozzle.
Generate a two-part mold from your master in splicestl/mold, print both halves in PLA (or PETG for warmer pours), spray with mold release, clamp the halves together with your master inside, pour silicone through the pour spout, let cure 24h, separate halves, demold silicone. The alignment keys ensure the halves register precisely so the silicone seam is invisible.
5 mm wall is the default and works for most silicone pours up to 200 ml. For larger pours (>500 ml) or thicker pot life materials, go to 7-8 mm. For thin, low-viscosity silicones (Smooth-On Body Double, etc.), 3-4 mm is fine. The clearance setting (default 1 mm) adds space between master and inner wall so the silicone has somewhere to flow.
Lost PLA casting is using a printed PLA part as a sacrificial master that gets burned out during metal casting. Print the PLA shape, invest it in plaster (or ceramic shell), heat to burn out the PLA leaving a void, then pour molten aluminum, brass, or other metal into the void. splicestl/mold isn't directly for lost PLA casting — that uses the printed part itself as the master, not as a mold box. But the same casting workflow benefits from clean 3D-printed masters.
No. splicestl/mold runs entirely in your browser. All boolean operations, mesh splitting, and STL export happen client-side using JavaScript + WebAssembly (Manifold). The only network traffic is loading the page itself.
splicestl cuts large 3D models into printable pieces with press-fit joinery — so you can print a model that's larger than your build plate. splicestl/mold (this tool) generates a separate mold box around your model, so you can pour silicone/resin/plaster/wax casts of it. Different problems, same underlying engine.