How To Fix an .STL File That Won’t Open

In the 3D printing world, few things are more frustrating than an .STL file that refuses to open. Fortunately, you can take some practical and straightforward steps to remedy this problem.

To fix an .STL file that won’t open, follow these steps:

1. Choose your .STL repair software.
2. Import the .STL file in the repair tool.
3. Pull up repair options or scripts.
4. Use basic or auto mesh repair actions (if available).
5. Use advanced mesh repair actions (if available).
6. Export the repaired file.

In this article, I’ll provide a more detailed explanation of how to repair your corrupted STL model file. So, let’s look at the steps together and fix that file!

1. Choose Your .STL Repair Software

There are several repair tools available for .STL files. Let’s look at some of the more popular options:

• MeshLab. MeshLab is a free and open-source 3D modeling tool with several mesh repair features. According to ECU Libraries, MeshLab is a more advanced and difficult-to-master program. If you’re new to 3D modeling and printing, it might be a good idea to start with a less complicated, more beginner-friendly tool.
• Netfabb. There are several versions of Netfabb available, with a free version among them (as Slic3r Manual explains.) Since free versions are available with specific settings and walkthroughs for beginners and advanced users, this tool is a good option for all experience levels.
• Meshmixer. Created by Autodesk, Meshmixer has many repair features (both basic and advanced) available. However, it is not a free program. There’s a temporary free trial for download, but this tool might not be a long-term solution if the price is a concern.

2. Import the .STL File in the Repair Tool

Once you’ve selected which repair tool to use, the next step is to import the broken .STL file into the software. This process will vary slightly from program to program but should be easy to find within the program’s menu bar. 

After you’ve imported the file, you can start the repair process.

3. Pull Up Repair Options or Scripts

Again, this step will differ depending on which program you’re using. However, all of the software tools I’ve mentioned display obvious repair options buttons and tabs, so pulling up your options or scripts should be straightforward.

Programs will also differ in whether they provide “options” for repairing your STL file or if they provide “scripts.” As FormLabs points out, MeshLab uses scripts.

Both choices essentially function the same, so which terminology the tool uses won’t be a problem when following the rest of this guide.

4. Use Basic or Auto Mesh Repair Actions (if Available)

All three of the programs I’ve covered have several STL file repair options, ranging from basic and automatic choices to more advanced or manual features.

Netfabb and Meshmixer provide automatic STL repair functions, while MeshLab offers basic mesh filters. 

.STL File Auto Repair Options

Meshmixer and Netfabb use the following automatic repair options:

• Extended Repair (Netfabb). Extended repair is a checkbox that you’ll see upon importing your STL file. This option will fix most errors and allow the software to make quick and automated 3D model repairs for you.
• Auto Repair All (Meshmixer). Found under the “Inspector” tool (as described by Meshmixer’s FAQ page), this will, like Netfabb’s Extended Repair, correct the most common STL corruption issues. 

Using Basic MeshLab Filters

While MeshLab doesn’t use the same automatic repair scripts as the two tools mentioned above, it does have some easy-to-use 3D mesh filters that you can try. These include:

• Remove Duplicated Faces. This tool eliminates unnecessary or duplicated vertices.
• Select Self Intersecting Faces. This feature will select any intersecting triangles found in the model.
• Close Holes. The Close Holes feature removes holes in the model, which can also cause issues with an STL file.
• Compute Geometric Measures. This tool helps you track down where the errors in the model are, making them easier to repair.

5. Use Advanced Mesh Repair Actions (if Available)

The three tools I’m covering all provide advanced repair options for your 3D model, but there are a couple of caveats to note.

Netfabb’s free versions do not include some of the more advanced repair tools that its paid version does.

Suppose you try the automatic and basic repairs, and your STL file still won’t open. In that case, you might have to either choose a different program or upgrade to a more advanced, paid Netfabb version.

Manual .STL File Repair Options

Here are a couple of the manual 3D model repair tools offered by Netfabb and Meshmixer:

• Optimization Utility (Netfabb). This tool will allow you to restructure your model for the most optimal printing layout.
• Bridge tool (Meshmixer). Using the Bridge tool, you can manually fill and fix holes that the Auto Repair function missed during execution.

Using Advanced MeshLab Filters

In addition to its basic mesh filters, MeshLab also offers several advanced filters. These filters might be able to fix up your STL, so let’s take a look:

• Merge Close Vertices. This feature reduces triangles in the model to prevent corruption and large file sizes.
• Split into Connected Components. This tool detects unattached model parts for either removal or attachment. 
• Remeshing, Simplification, and Construction. These features determine your mesh’s faces and restructure the model to fit this number.

The advantage of MeshLab becomes more apparent with these advanced filters. 

While more straightforward and user-friendly programs might not have as many options to choose from, power users will find MeshLab’s detailed manual repair tools refreshing.

6. Export the Repaired File

Once you’ve repaired the errors in your STL file, the only remaining step is to export the new, corrected file.

This step will be slightly different depending on which tool you use. Under Netfabb, for example, you’ll choose “Export part -> As STL” to export the new 3D file. 

However, the option should be easy to find regardless of the software. If you can’t find it, there are plenty of user guides and discussion boards available for all of the three tools I’ve covered that should help you out.

Final Thoughts

Broken and nonfunctional .STL files are a common, frustrating problem when working with 3D modeling. 

That said, there are a few simple steps to follow that will, in most cases, correct the most common errors:

1. Find and install an .STL file repair tool.
2. Import the broken file into the software and open up the repair options.
3. Use either automatic or advanced repair options to fix the defective 3D model.
4. Export the new file.