Smoothing STL files made in Sketchup with Blender for 3D printing

In This Article:

A Word About SketchUp

Sketchup is one of our favorite 3D modeling tools here at Airwolf.  It is easy to learn, easy to use, and is capable of some incredible detail.  However, Sketchup is primarily a surface modeler.  In other words, objects are first drawn as surfaces and then must later be connected to form solid objects (for 3D printing).   When drawing free-form objects, this leaves us with visible “polygons” as shown in the automotive application below:

smoothing stl model from sketchup

A Neat Tip for Smoothing STL Files

In Sketchup, using the Window>Soften Edges feature smooths the edges on the sports car:

smoothing stl file with blender

However, this is only visual.  In other words, by softening the edges you have not smoothed the underlying CAD model, you have only altered the way the model appears on your screen.  Here is how the STL of the model appears in Cura (make sure and use Netfabb to clean your model first):

smoothing stl file

To achieve a smoother model (and a smoother 3D printed car), adding more polygons to the existing model in Sketchup  can help (and more than double your modeling time), but the surface  will still not be smooth.

The Answer is Blender

Blender is a powerful, free, and open source program that enables you to effectively “subdivide” (into multiple polygons) and smooth your model to achieve the desired 3D printed surface finish.

First, the STL file is imported into Blender (refer to this helpful video by Blender guru Shapespeare to properly configure Blender for 3D modeling):

how to smoothing stl

Second, open Edit Mode to display the polygons from the STL file:

smooth your stl file with blender

While Blender has many modeling features, this tutorial is focused on modifying the underlying STL file for smooth 3D printing (rather than optimizing for renderings, etc.).  The Blender Wiki has a great discussion on three different forms of mesh smoothing.

Our first editing operation is to press “Alt-J” to convert the triangles in the above STL file to rectangles or “quads.”  Quads are required for a good subdivision surface.  They enable us to more precisely control the subdivisions and smoothing of the model:

smooth polygons in your stl file

Once we have the quads, we need to break the model down into more polygons to set up the model for a smoothing operation.  On a model of this size, subdividing the model 3 times strikes a good balance between quality and disk space usage (Tools>Add:Subdivide – enter “3” for the Number of Cuts):

smooth polygons in your model

Now we can start smoothing the polygons in the model.  For this model, smoothing the vertices 3 times seems to work well.  Too much smoothing and the model will start distorting (Tools>Deform:Smooth Vertex – enter “3” in the lower smoothing screen):


Export the resultant STL file and open up in your host software.  Finally, we have an appropriately smoothed STL file worthy of printing on our Airwolf 3D printer!