Convert a Simple STL into a Body in Fusion 360

by | Jul 28, 2017 | 3D Printing, Fusion 360 | 0 comments

If you are interested in 3D printing and follow news on the subject, you will hear almost daily about advances in the sophistication and capabilities of hobby and semi-professional 3D printers. New 3D printing techniques and technologies, not to mention new 3D printing products, are being developed constantly. However, one of the most underrated advances in the consumer 3D printing market is the proliferation of 3D model repositories. Thingiverse, Youmagine, pinshape, GitHub, and Sketchfab are just a few of the dozens of different sites hosting 3D models for download.

These sites and many others are fantastic for downloading and printing models, as long as the models provided suit your needs. But what if you need to or want to edit the models? This seems like it should be easy; however, the major problem you will encounter is that the vast majority of 3D models online are provided in STL format. STL files can be downloaded and printed directly, but it can be difficult to edit these models in 3D CAD software like Fusion 360.

If you want to, for example, download a model from Thingiverse and edit it, you will need a way to convert the STL file into a form that the tools provided by your software can understand. This guide will show you how to convert simple STL files into solid bodies in Autodesk Fusion 360.

What is a “simple” STL file?

An STL file consists of a bunch of triangular surfaces joined together to create an object. The reason most 3D CAD programs cannot edit STL files the same way they edit models created directly in the software is because STL files have no internal structure. An STL file is simply a complex surface consisting of two-dimensional triangles.

In this STL file (thing:14702), you can see that the object is made from many triangular surfaces.

Therefore, in order to convert an STL into a solid body, Fusion 360 must build a solid object based on every triangle in the STL. This process becomes more and more difficult as the number of triangles in the STL increases. With complex STL files, if you follow the steps below, you will get an error in Fusion 360 that will essentially tell you that the STL file is too complex to convert to a body in any reasonable amount of time.

You may get this error at the end of the process below if the STL file you are using is too complex. In this case, there is a different guide for converting complex STL fies.

For the purposes of this guide, a simple STL file is one that does not trigger such errors. A different technique is required to convert complex STL files into a body. The more advanced conversion process is described in a different post.


Convert a Simple STL into a Body

As long as your STL file is not too complex, the procedure below will allow you to convert the STL into a body that can be edited in Fusion 360 using your normal editing tools in the Model workspace.

Import your STL into Fusion 360

First of all, the STL file will need to be imported into Fusion 360. If you’ve done this before, skip to the next step. Otherwise, in the upper-left corner of the Fusion 360 window, click the Upload button. Then, click the Select files button and navigate to the STL you wish to import.

upload button location

Upload an STL file using the Upload button.

After selecting the STL file you want to convert, click the Upload button, this time the one in the lower-right corner of the file upload window. Then, the STL file you selected will be imported into Fusion 360. The process can take a few minutes.

Click the Upload button after selecting your STL file.

Disable Design History

Normally Fusion 360 tracks all the edits you make to a model in a timeline at the bottom of the window. However, we actually cannot convert the STL file into a body while Fusion 360 is tracking history. Therefore, the history tracking functionality will need to be turned off.

In the upper-left corner of editing window you will find a browser feature tree. If you have used Fusion 360 much before, you are probably familiar with this feature tree. At the top level of the tree is the file name itself. If you right click on the file name, you will get a menu. To turn off history tracking, select Do not capture Design History.

turn off history

Turn off Design History by right clicking the file name in the feature tree.

When trying to turn off Device History, you may find that it is already disabled, in which case the option at the bottom of the menu will say “Capture Design History.” If this is the case, you will need to turn on history and then turn it off again.

Convert Mesh to BRep

Now the STL can be converted into an object. Looking in the feature tree again, if you expand the Bodies section, you will find an item called MeshBody1. The mesh body is the STL file. To convert the STL file, right click on the mesh body and select Mesh to BRep.

Mesh to BRep

Right click the MeshBody1 and choose Mesh to BRep

Depending on the complexity of your STL file, the conversion process can take quite some time. It may appear that Fusion 360 is frozen. Just be patient and the process will eventually complete.

At this point, you may get an error message basically saying that the STL file has too many faces to be feasibly converted into a solid body. If this is the case, you will need to follow the guide for converting complex STL files to solid bodies [post coming soon].

If the STL is too complex, you will get an error.

Combine Co-Planar Faces

At this point you have successfully converted your STL model into a solid body. However, you may notice that the solid body looks much like the STL; it has numerous triangular faces making up the body. We will want to clean up the model a bit by combining all of the co-planar triangular faces into a single face.

Fortunately this is very easy to do. Simply select one of the faces on a side of the model that you wish to simplify and press the delete key. Most of the surfaces on that side of the model should merge into a single surface. If there are still triangular faces left over, simply select more of the faces and press the delete key again.

Delete faces until all co-planar surfaces have been merged.