Glossary · Setting
Drain holes
A small hole in a hollow-printed resin part. Liquid resin drains from the inside through it, and air can flow in.
Explained in more detail
Large resin models are often hollowed out, which saves resin and weight. A closed cavity, however, traps liquid resin and air. Drain holes let the resin drain out, let air escape and let the washing liquid flush through the inside during washing. Formlabs gives 3.5 mm as the recommended minimum diameter and advises one hole as close to the build platform as possible and at least one more, with correspondingly more for several shell-shaped areas. Without drain holes, liquid resin stays trapped in the part, and trapped air can trigger the suction cup effect.
Where does the term come from?
Drain holes let the resin run out. The second hole, through which air flows in, is also called a vent hole.
In practice
- Place the holes in the slicer after hollowing. Resin slicers such as Chitubox, Lychee and PreForm have a dedicated function for this.
- One hole should be as close as possible to the build plate, as Formlabs recommends. Place the second at a spot where it does not disturb visually or functionally.
- Formlabs recommends a diameter of at least 3.5 mm.
- Rinse the inside thoroughly when washing, and let the resin and washing liquid drain out completely before the part is dried and post-cured.
Not to be confused
Parts printed solid do not need drain holes. They belong with hollowed models and shapes with closed cavities.
Frequently asked questions
Do I need drain holes for every resin print?
No, only for hollow parts or shapes that form a closed cavity or a shell. Solid parts do not need any.
How big should a drain hole be?
Formlabs recommends a diameter of at least 3.5 mm. Other manufacturers give no uniform values, so check the guidance of your slicer and resin.