Available in Pro and Premium versions
A very common problem in resin 3D printing that causes frequent failure, especially with the hollowed models: It’s the suction cup effect.
You probably know the experience of the glass upside down in a tank of water that keeps the air when it is immersed or that keeps the water when it is almost out of the water. Of course, the classic suction cup in the water sits on the bottom of the bathtub. This is precisely what can happen with your 3D prints in many cases.
When your 3D model has been hollowed out, areas that don’t have a drain hole act like suction cups when moving the build plate up and down, because of these suction cups, large forces can be applied to your 3D prints that can cause parts of the model to break off, cause degenerate holes, tear the model of the supports, and more.
To make matters worse, you can also have areas where liquid resin gets trapped, which can also cause prints to burst over time and spill resin everywhere.
To avoid this problem, it is advisable to add holes as close as possible to the starting point of the area with a cavity.
Be careful. This hole must have a minimum size to make the resin circulate as efficiently as possible, especially for resin with low viscosity. The bigger the holes and the more of them, the better.
(3-5mm is a good starting point for small to medium prints.)
Unfortunately, cavities are not always easy to find on a model due to the orientation or simply realizing that the positioning of a hole is not optimal.
That’s why the suction cup detection tool will help you better find these cavities and allow you to find the best place for your hollowing holes.
Attention! The tool does not tell you if the holes are large enough for an unconstrained flow of your resin.
The Suction Cup detection tool is located in the Hollowing tool, Holes tab, in the Prepare Workspace.
The tool allows you to analyze any 3D model, hollowed out in 3D or not, as cavities and suction cups can appear everywhere. However, the tool is currently incompatible with 2D hollowing.
To detect cavities:
- Select the object(s) to be inspected.
- Click on the Search button. Depending on the selection, you will get Search Selected or Search All.
- After a few moments, you will get the result as shown in the image below: three cavities have been detected and are highlighted in yellow.
- The camera will focus on the current cavity by clicking the Show button. Using the right and left arrows from the interface, you can move from one cavity to another if the model has more than one. Note that some cavities might be very small.
Important note on cavity dimensions #
Lychee Slicer detects cavities of a minimum size. Your model may have many more small cavities than displayed. However, the software ignores them entirely because they are considered insignificant and will not impact your 3D print.
It is, therefore, possible that small cavities are detected by analyzing your exported files with an application like (the excellent) UVTools. It will, of course, be possible to correct them in this software, but we consider that it is not necessary.
Fixing suction cups #
Before considering the different solutions to fix suction cup effects, it may be essential to ask whether the hollowing is necessary. Often, it may be tempting to do this to save resin. This makes sense on a large model, but on a small model, it may result in a negligible saving of resin (a few milliliters) which may cause printing problems.
There are two main solutions to correct the suction cups:
Adding drain holes #
The best way to eliminate a suction cup is to add at least one drain hole using the “Hole” function. As mentioned in the introduction of this documentation, this hole must be:
- Positioned as close as possible to the starting point of the hollowing area. Otherwise, all hollowed parts under the model will always be considered a suction cup.
- Have a minimum diameter of 3mm. The bigger your holes are, the more you will limit the deformation or suction cup risk. If your model is large with a very large hollowed area, the volumes of resin displaced during the movement of the build plate and the immersion of your printed model in the resin will be significant. Consequently, the forces applied to your 3D print will remain very high and barely attenuated by a too-small hole. Do not hesitate to position several holes.
Using Hollowing Blockers #
If certain areas are more difficult to access or a drain hole simply cannot be placed, you can use the Hollowing Blockers found in the Hollowing tool. This tool allows you to prevent 3D hollowing locally and, therefore, the suction effect that could result from it.
Please note that the Hollowing Blockers only work if 3D hollowing has been performed within Lychee Slicer and if this hollowing is still dynamic.
Analyze (again) your model #
Whatever your 3D scene is, make it a habit to analyze it, even if it seems evident to you that your model does not have suction cups. It has happened to the most experienced users, with prints failing due to unintentionally ignored suction cups (including your humble editor, who has missed a few beautiful yet obvious ones…)
Then, don’t forget that after a modification is applied to your 3D model, whether changing the thickness, adding holes, or Hollowing Blockers, you must analyze your 3D model again. This step is not automatic.
The suction cup detection tool can save you the frustration of missed prints. Make use of it, and always restart it before exporting your print!