Hollow or cup-shaped parts: suction effect and drain holes

Symptom

Hollow or bowl-shaped parts get holes or ruptures in their walls, separated layers or parts that come loose; sometimes resin splashes when peeling or liquid resin stays trapped inside.

Likely causes, from most to least likely

1. A cavity open towards the film traps air or resin; as the build plate lifts, a vacuum forms and the wall caves in or bursts (suction cup effect).
2. The part is hollowed but has no drain holes, or they are too small.
3. The cavity walls are too thin to withstand the pressure difference.

Checks to tell which one it is

• In the slicer, look for cavities whose opening faces the film (upwards in the view, away from the build plate); some slicers highlight them.
• Check that the hollowed part has at least two drain holes.
• See whether the rupture is right on the cavity wall.

Before you start

Uncured resin irritates skin and eyes: wear nitrile gloves and safety glasses, ventilate the room and do not look at the UV light. Before taking anything apart or cleaning it, switch the printer off and unplug it, unless a step says otherwise. If in any doubt, stop and ask a professional.

Step-by-step fix

1. Reorient the part

   Rotate the part so the cavity opening faces the build plate rather than the film (downwards in the slicer view), or tilt it; Formlabs gives 5 to 15 degrees. Then generate the supports again.

   Check: In the preview, no cavity is closed against the film any more.

   If that does not fix it: Add drain holes.

2. Add drain holes

   If you hollow the part, add at least two drain holes so air and resin can escape. As a guide, Phrozen recommends holes of 3 mm or more near the base; the minimum varies from printer to printer.

   Check: When washing the part, the resin inside flows out through the holes.

   If that does not fix it: Make the walls thicker.

3. Thicken the walls or fill the cavity

   Increase the thickness of hollow walls or fill small cavities. As a guide, Phrozen gives walls of at least 1.5 mm on small parts and 2 mm on large ones.

   Check: The wall does not cave in or break on the next print.

   If that does not fix it: Clean the vat and check the supports.

4. Clean the vat after a rupture

   Wearing nitrile gloves, remove the pieces and filter the resin before printing again: a suction cup can splash resin or damage the vat.

   Check: No pieces are left in the vat and the film is intact.

   If that does not fix it: If the film is damaged, follow the resin leak and torn film sheet.

Prevention

• Before printing, look for cavities in the preview and point them towards the build plate or tilt them.
• Every hollowed part gets at least two drain holes.

Still not fixed?

Tell usi3d's AI about your case: choose your printer, describe what you see and add photos if you like. It proposes checks step by step, with their sources.

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Printers it applies to

Any resin (MSLA/SLA) 3D printer, from any brand.

Official sources

This guide summarises the official documentation linked here:

• Preventing suction cups in PreForm · Formlabs
• Cupping blowout · Formlabs
• Hollowing · Prusa Research
• Why Did the Model Not Print While the Supports Printed? · Phrozen