Manifolded Edges – How to Check if Your Model is Watertight and Ready to 3D Print

So you have a nifty model that you want to 3D print.  You may have designed it yourself, or  maybe you are doing a favor for a friend, or perhaps you downloaded the STL file from Thingiverse.   However, when you went to slice the STL file to generate your gCode, an error came up.  The answer is that in order to 3D print the model well, it needs to be completely manifold or “watertight.”

What is manifold?  Think of it in these terms, if you were to fill the walls of your model with water would you have any leaks?  Non-manifolded edges would cause leaks in your model.  Non-manifolded edges are parts of the model where the dots have not been connected to create a solid.  A line, or even a plane, does not have dimensions in three separate directions (X,Y,Z) that are necessary for printing.  This is a common occurrence during the design phase when two components are “connected” in the computer aided design software.  Sometimes the two components appear to be connected on the screen, but in reality, the seams between the two objects have not been joined.  Either that, or in some cases you may have components of the model that overlap one another, confusing the slicing engine.

Here is how to check to see if objects are actually ready to 3D print.

We use a neat tool called MeshLab.  Here is a link: (this depends on Python 27 which you have already downloaded for using Pronterface).

1.  Install the software using the installation instruction provided on the site.

2.  Start a new empty project.

3.  To see if there are any non-manifolded edges first import the STL file in MeshLab

3.  Then on the drop down menu for “render” select “show non manif edges”

4.  Use the mouse to rotate the object around.  If the object is not watertight, then the non-manifolded edges will light up a bright color.  You can open the file in SketchUp and correct the model to close up the openings and try again.

in Working With 3D Models