Mold Box Maker: 3D Print a Box for Silicone Molds
Open a 3D model and get a box to print round it for pouring silicone: plain, fitted to the shape, or in two parts.
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Your model is opened by this page and never uploaded. The mold is built here, in WebAssembly.
Making a silicone mold starts with a box to pour the silicone into, round the master you want to copy. Open your master's STL, OBJ or GLB and this builds the box for it, ready to print, with as much silicone round the model and over its top as you ask for, and works out how much silicone to mix, in millilitres and grams.
Three kinds. A box: four walls and a floor, the simplest to print. A fitted box: walls that follow the outline of the model seen from above, a set distance out, which on a tall or odd-shaped master can save half the silicone. And a two-part mold, for a casting that has to come out of a closed mold: a lower and an upper frame that stack on corner pins, a parting board between them cut to the model's cross-section at the height you choose, with cones that become keys so the two silicone halves line up, and a pour spout to glue on top of the master.
Turn the model a quarter at a time to stand it the best way up, pull the parts apart to see how they fit, and download each part as an STL. Everything is worked out in this page, in WebAssembly: your model is never uploaded.
How to use it
- Open your master model. It is never uploaded.
- Choose a box, a fitted box or a two-part mold, and turn the model to stand it the best way up.
- Set how much silicone goes round and over it, and the wall and floor of the box.
- Download each part as an STL and print it. The silicone to mix is shown above the parts.
Questions
Which kind of mold box should I choose?
A box for a master with a flat side to stand on: you glue it to the floor and pour over it, and the mold opens where it stood. A fitted box for the same, when the model is tall or irregular and silicone is expensive. A two-part mold when the casting has no flat side to pour into, or has to be cast closed: the spout is the way in.
How much silicone round the model?
Ten millimetres is a good start for small and medium parts: thinner and the mold tears or bulges when it is filled, much thicker and it wastes silicone. Large parts want more, and a mold strapped or boxed when it is cast can do with less.
How is the silicone worked out?
It is the space inside the box up to the silicone over the top of the model, less the model's own volume and the spout's. For a two-part mold it is given for each half, since they are poured one at a time. Multiply by your silicone's density, about 1.1 g/ml for most, to weigh it out.
How do I use the two-part mold?
Glue the spout to the highest point of the master. Stand the lower frame on the table, push the master into the parting board's hole so the board sits on the lower frame, put the upper frame on top, and pour the first half. When it has cured, turn it over, take off the lower frame and the board, put a release agent on the silicone, put the lower frame back as the walls, and pour the second half.
What clearance should parts have?
0.3 mm suits most FDM printers: it is the gap round the pins and round the model in the parting board. A tighter printer can go to 0.15; if the pins will not go in, raise it.
Is my model uploaded?
No. The page reads the file and builds the mold in this tab, and is served with a security policy that forbids it from opening any network connection.
Your data stays on your device
Everything above runs inside your browser as WebAssembly compiled from Rust. Nothing you type is uploaded, logged or stored on a server. You can load this page once, go offline, and it still works.
This page makes no requests at all, to anywhere. That is not a promise in the copy: it is a Content-Security-Policy header your browser enforces, and connect-src on it is none. Open the network tab and watch nothing happen.