Tiny Online Tools
Why hollowing is worth doing
A solid resin print is mostly wasted material. A 60 mm bust can hold 40 cm³ of resin; the same bust with a 2 mm wall holds about 10 cm³ and prints with far less suction force on the FEP, less shrinkage stress and a much lower chance of cracking as it cures. On FDM, hollowing a thick part before slicing gives you a genuine cavity instead of relying on infill percentage.
How this tool does it
Hollowing cannot be done on the triangles themselves. The inner wall is the surface at a fixed distance inside the outer one, and that surface almost never has the same shape: thin features vanish, separate lobes merge, sharp inside corners round off. Pushing every facet along its normal produces self-intersecting garbage on anything that is not convex.
So the tool does what resin slicers do. It samples the signed distance to your surface on a regular grid, extracts the isosurface at minus your wall thickness, flips its winding to face into the cavity, and appends it to the original outer mesh. Everything runs in your browser — the model is never uploaded.
What that means in practice
- The inner wall is resampled on a grid, so wall accuracy is about one grid cell. The tool prints the cell size next to the result.
- The outer surface is never touched. The outside of the part is exactly the triangles you gave it.
- Hollowing only means something on a closed model. On an open one, "inside" is undefined and the result cannot be trusted — repair it first.
- Features thinner than twice the wall thickness stay solid. That is correct, not a bug.
Then drill drain holes
A hollow resin model with no way out traps uncured resin. It can blow a hole through the wall as pressure builds, or cure into a heavy blob later. Always add at least two drain holes — one to drain, one to let air in — before you print.