Glossary · Failure pattern

3D printing

Suction cup effect (cupping)

A resin printing fault: a shell-shaped part sticks to the film like a suction cup. When lifting, a hole often tears in the wall.

Explained in more detail

In resin printing, every layer is peeled off the film in the bottom of the vat. If the opening of a hollow or cup-shaped part faces the film, air is trapped inside. When the platform is lifted, negative pressure builds up inside and pulls thin walls inwards. Formlabs describes the consequences: holes or large torn areas in the walls, rough surfaces inside the cup and resin splashes in the printer when the suction cup releases from the film. According to Formlabs, whether it happens depends on the resin, the size of the cup, its shape and the wall thickness. Small cups or thicker walls often print fine anyway.

Where does the term come from?

The name describes the picture: the shell adheres to the film like a suction cup on a tile. Formlabs calls the effect cupping in English, and the tearing open of the wall blowout.

In practice

• Orient the model so that no opening of a shell faces the film.
• Place drain holes in cavities and shells, as Formlabs recommends.
• According to Formlabs, PreForm marks such areas with the "Show Cups" function. In other slicers, you check the layers in the preview for closed rings.
• A large, ragged hole in a shell wall usually points to this effect, not to too short an exposure.

Not to be confused

The suction cup effect is not the same as a part that sticks to the film instead of the platform. There, adhesion to the film is too strong, usually because of levelling, bottom exposure or temperature.

Frequently asked questions

Why does my resin print have a large hole in the wall?

With hollow or cup-shaped parts, the suction cup effect is often the cause. Drain holes and an orientation in which no cup faces the film help.

Where do resin splashes in the printer come from?

Formlabs names it as a typical consequence of the suction cup effect: if the shell suddenly comes off the film, resin splashes.