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Tutorial 6 Min Read New Feature

Hollow Any STL and Place Drainage Holes in Seconds

2.5 mm
Hollowing & Drainage

Shell + auto-placed drainage ports — entirely in your browser

A 1 m bust printed solid swallows kilos of filament you do not need. Hollowing turns it into a thin shell that prints in a fraction of the time, with a fraction of the material.

The MegaSlicer Pro Hollowing & Drainage tool shells any STL and drops the drainage holes that resin and trapped-air pockets need — all in your browser, no install required.

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Step 1: Drop the STL

Open the tool and drag your model onto the canvas. The viewer auto-fits the model and reports the original triangle count and bounding box, so you know what you are working with before any modification runs.

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Step 2: Pick a Wall Thickness

The Wall Thickness slider runs from 1 to 8 mm. There is a sweet spot for each printing technology:

FDM Sculptures

2.5–3.5 mm. Thick enough that the shell will not collapse mid-print, thin enough that you save 60–75% of the original solid volume.

Resin Prints

1.5–2 mm. Cured resin is stiffer than cooled FDM plastic, so a thinner shell holds up just fine and saves even more material.

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Step 3: Add Drainage Holes

Set Drainage Holes to 2–6 and pick a hole diameter (4–8 mm covers most cases). Two placement modes are available:

  • Lowest Faces (auto) — the tool finds the geometry's lowest points and drops holes there, so resin or trapped air can escape naturally.
  • Bottom Grid — a regular pattern under a flat base. Pick this for figurines that sit on a plinth or any model with a clearly flat bottom.

Pro Tip — Section View

Toggle Section to slice the preview in half. You will see the actual interior cavity and the ports cut through the wall, which makes it easy to spot pockets that did not get a drain. Pockets with no drainage trap resin or hot air and ruin a print.

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Step 4: Export and Slice

Hit Export Hollow STL. The tool reports the volume saved as a percentage of the original solid — a 1 kg solid model often becomes 250–300 g once shelled.

Load the result into your slicer with 0% infill (the tool already replaced the interior with empty space) and a single perimeter equal to your chosen wall thickness. Anything more is wasted material.

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Pairs Well With

Hollowing is the first stage of an end-to-end large-print workflow:

  1. Hollow the model with the tool above to drop 60–75% of its mass.
  2. Run the result through the Orientation Optimizer to find a stance that minimises supports against the new shell.
  3. Send the oriented STL to Slicer Pro to chop it into printable segments with alignment keys.

Hollow Your Next Print Now

Drop an STL into the tool and watch the volume drop by two thirds. Drainage holes included.

Open Hollowing Tool Slice After Hollowing

100% browser-based STL in, hollowed STL out