Tiny Online Tools
Why a hollow resin print needs holes
Hollowing a model traps a sealed pocket of liquid resin inside it. Nothing about the print removes that resin: it stays in the cavity, it is heavy, it is still reactive, and as the plate lifts through each layer the pressure difference across a sealed shell has to go somewhere. It usually goes through the thinnest wall. Even when the part survives, weeks later the trapped resin can cure, expand and split the model open.
Two holes solve it. One lets the resin run out, the other lets air in behind it — the same reason a jerry can has a vent. A single hole drains slowly, or glugs and stops.
How this tool places them
Suggested finds the lowest point of down-facing surface in each cell of a coarse grid across the model, sorts them by height and keeps the lowest few that are far enough apart. That is where resin actually pools — which, on a part tilted for printing, is rarely the bottom of the bounding box.
Manual is a click on the model in the viewport. The tool raycasts against the mesh, takes the hit point and the surface normal there, and drills either perpendicular to the surface or straight along the vertical axis, whichever you choose.
It is a real boolean
The holes are cut with a CSG subtraction, not drawn on top. The exported STL, PLY, OBJ, GLB, OFF or Draco file genuinely has holes through it, and the triangle count and enclosed volume both change to prove it. Everything runs in your browser; the model is never uploaded.
Practical advice
- Under about 2 mm rarely drains modern 4K and 8K resin reliably. 3 mm is a safe default.
- Put them where they will be hidden — under a base, inside a socket, along a seam — or somewhere easy to fill and sand afterwards.
- The model has to be hollow first. Drilling a solid model makes a blind pit, not a drain. The tool reports the shell count and how much of the drill's path was actually material, so you can see which one you have.
- Always check the result in your slicer before printing.