Free tool
GLB Mold Generator
Turn a watertight GLB into a two-part mold block, right in your browser. Everything runs locally — the model is never uploaded, and there are no accounts, AI calls, or credits involved.
Needs a fully watertight input mesh. A basic 2-part cavity block split on a flat plane — no draft angles, alignment pins, or shrinkage compensation.
Mold generation needs a fully closed solid. Patch open holes first with the free GLB mesh repair tool.
Open the mesh repair tool → · Convert OBJ to STL →Why use this GLB mold generator
100% private
The mold block is generated entirely on your device inside a Web Worker. There is no upload endpoint on this page — the file never touches a server.
Completely free
No account, no card, no credits. Generate as many mold blanks as you want.
Real CSG, not an approximation
Uses manifold-3d — the same robust boolean-geometry library that powers ManifoldCAD — to subtract your model from a solid block and split it into two halves.
Adjustable wall margin
Pick how much material surrounds your model, from 5% to 50% of its largest dimension.
Three export formats per half
Each half downloads as .glb (Blender), .obj (almost any 3D tool), and .stl (ready to slice) — six files in total.
Honest about limits
This makes a basic two-part cavity block split on a flat plane. No draft angles, no alignment pins or registration keys, and no shrinkage compensation — those need dedicated mold-design software.
Frequently asked questions about the GLB mold generator
Is my GLB file uploaded anywhere?
No. The mold block is generated locally in a browser Web Worker. This page has no upload endpoint — nothing leaves your device.
Why did it say my mesh is not watertight?
Mold generation needs a fully closed, manifold solid to subtract from a block — an open hole makes the boolean operation ambiguous. Use the free GLB mesh repair tool to patch open holes, then upload the repaired .glb here.
How does the split work?
The tool builds a solid block around your model, subtracts the model to leave a cavity, then splits that cavity block in half on a horizontal plane through the middle of your model’s bounding box. There is no option yet to choose a different parting plane or add draft angles.
What wall margin should I use?
Higher percentages mean a thicker, sturdier mold block around a smaller model; lower percentages save material on a larger one. 20% is a reasonable starting point — increase it if the walls look thin relative to your model’s size.
Is this ready for injection molding or silicone casting?
It is a starting block, not a manufacturing-ready design. It has no draft angles (needed to release a part cleanly), no alignment features to keep the two halves registered, and no shrinkage compensation. Treat it as a base to refine in CAD software for anything beyond casual prototyping.
Sculptly converts a single image into a real GLB, OBJ, or STL mesh in two to four minutes.
Try Sculptly →What the mold block is, step by step
It welds the GLB’s vertices, checks for a closed solid, and builds a rectangular block around the bounding box. The wall margin (5 to 50 percent, default 20) is a percentage of the model’s longest dimension, added on every side (a 100 mm model at 20 percent gets 20 mm on every side). The model is subtracted from the block to leave a cavity, and the block is cut in two at the middle of the model’s height. The boolean work runs in a Web Worker on your device using manifold-3d.
You get six files: a bottom and a top half, each as .glb, .obj and .stl. The GLB stays Y up in metres. The OBJ and STL are rotated to Z up and scaled to millimetres.
How it differs from slicer or CAD molds
Some slicers have a negative-part feature that can carve a cavity by hand. This page does the block, subtract and split in one step and gives you the halves as files. CAD programs add draft angles, a parting line that follows the part, registration keys, pour gates and vents. Treat the output as a starting block, not a finished tool.
When the flat split is the wrong choice
The cut is a horizontal plane through the middle of the bounding box, in the file’s up direction. It suits shapes widest near mid-height, such as a bottle or a bowl. A handle, an arm or any undercut along the up direction can trap the cast part in one half. Rotate the model in your editor before uploading to choose the cut axis. There is no pour hole or air vent; cut those in afterwards.
More questions about this tool
Which format should I use for each half?
STL for slicing, OBJ for other tools, and GLB for Blender or a viewer. STL and OBJ are in millimetres, Z up.
How do I print the two halves?
Print each half cut face up, so the cavity opens upward and needs fewer supports. The top half arrives cut face down; flip it 180 degrees in your slicer.
Why is the cavity exactly the size of my model?
No clearance or shrinkage allowance is added. Many casting materials shrink a little as they cure, so scale the model first if yours needs room.
How big will the printed mold be?
The block is the model plus twice the margin on each axis, with the GLB’s metres converted to millimetres.
Will it keep my model’s colours or textures?
No. The halves are plain geometry with a single grey material.
Related tools: patch holes so the model is watertight, estimate the cost of printing the two halves, and lighten a heavy STL before slicing.