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Repair STL Files-3 Free STL Repair Software

How to Repair STL Files-3 Free STL Repair Software Tools

The days of manual mesh programming are long behind us, and to measure up to the demands of the digital age, engineers and designers have found solace in STL files. STL is a file format widely used for 3D printing, computer-aided manufacturing, and rapid prototyping. The file describes the surface of 3D objects without representing the texture, color, and other Cad attributes.

Despite all of its good intentions, it can be frustrating when you do everything, but your 3D models don’t print. Due to its design, STL files should have a consistent wall thickness for proper printing optimization. Hence, when the file is not watertight, your model won’t print. As a result, most designers come out with defects in their models. When this occurs, you need to repair your STL file with a software tool.

When an STL file is broken, it is not uncommon for the slicer software not to pick the error. Sometimes, the software will print on the error and cause you to waste time and resources; At other times, online printing services can flag your upload as too large due to a broken or bloated STL file. Whichever the case, you need to repair the file to achieve a printable version.

There are several SLT repair tools, each with distinct advantages and exciting features. However, the repair tools' general design is to help you identify the problem and solve it for successful prints. Not just this, but most of the repair tools are free; hence, available to anyone. Some popular repair tools include Netfabb, 3D builder, 3D tools, Blender, Meshlab, Meshmixer, and several other tools.

We shall explore the first three options as they are among the best free STL repair software tools.

Netfabb - STL Repair Software

Netfabb is a handy Autodesk tool for repairing STL files. The software is designed to reduce build error and streamline workflow for a more significant result. Thanks to its design, you can create models and maximize the number of parts to include in your build. Apart from this, you can convert and import different models from several CAD applications. It also lets you work with mesh repair functions and customized support to improve your production processes.

Netfabb used to be available for Linux, macOS, and Windows before Autodesk who limited access to windows acquired it. However, you can download older versions that support the use on MAC and Linux devices. After downloading and registering, you will get 30 days’ free trial, after which access is restricted to the basic version. Nevertheless, there are still enough functions and features to help you correct your files.

How to import the STL file?

The first step after launching Netfabb is to click on File and Open Part from the Menu. A settings panel displays different options that let you import an STL file. However, you can use the default function and select Add Parts. A bold red exclamation mark appears at the bottom right corner of a defective STL file to indicate a repair need. Hence, if there is no big red exclamation mark, you can’t print the file since it is OK.

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How to fix the error?

The repair tool is located above the toolbar and is depicted by a red cross icon. When you choose the repair tool, the software creates a model copy and applies the changes to the copy to avoid altering your original model. On the left side of the toolbar, locate the repair panel, and check for model features. For example, the repair panel informs you if the mesh is oriented correctly, watertight, and how many holes the model has. Apart from this, it indicates the number of triangles that are not oriented like their close relatives and the number of border edges present in the model.

Click Run Repair Script on the Repair Panel and choose Default Repair from the popup panel. However, it is not uncommon for Default Repair to fail to fix the error. If this occurs, select Execute on Extended Repair to repair the file. If the repair is successful, the repair panel will indicate a closed mesh and orientate it by displaying two green checkmarks.

After repairing the file, right-click on the copy you created earlier to apply the repair. Alternatively, locate the Parts menu on the top left panel and select Apply Part repair. Before applying the changes, the software will ask if you want to compare the original and the copy to identify differences. If there is none, you can replace the old model. After this, check to ensure the exclamation mark is no longer present as it indicates the file is OK.

From the top menu, click on file and export the part you’ve repaired. You can save in a different format; however, we recommend you rename the file correctly.

3D Builder

3D builder is versatile, user-friendly, and considerably easy to use for Windows users. The builder is handy for automatically detecting errors and repairing STL files. Unlike Netfabb, it is preinstalled on Windows 10, so you don’t need to go through the hassle of a fresh installation. Use the search box to locate it and run the application.

Import the file to repair

After opening the builder, select Load Objects to choose the file you want to repair. After loading the object, it will materialize on the work plane. However, although the project will be loaded, it is not the same as importing. Besides loading it, choose Import Model from the top menu bar to approve file importation.

Follow up importation

After importing your file, the builder will display a popup to reflect defects in the model. When there is indeed an error, the popup will tell you that “one or more objects are invalidly defined.” Then, it will ask you to Click Here to repair the object. Apart from the popup, a red line underlines the model to signify a defect. In contrast, where there is no popup or red line, a blue outline means there is no problem with your file, and can proceed with printing.

If the software shows the error message, the builder will automatically repair your STL file when you select the Click Here command. After the repair, the red line will change into blue and form an outline around the object.

Save your repair

After repairing, click on Menu and select Save As to save and download your model. Although the builder pairs your file with a default output, you can change it into any format you want. Not just this, but you should rename the file to reflect the repair and avoid confusion with your original file.

Microsoft 3D Tools

Like the 3D builder, the Microsoft 3D repair tool is available on Windows and not on Linux and Mac. However, you can try out other repair tools like meshmixer, a more powerful STL file repair tool. On the downside, it requires considerable knowledge for a significant result. On the other hand, Microsoft 3D tools is easy to use and is often described as a one-click repair tool.

Interestingly, Microsoft 3D tools is available as a browser-based alternative for Mac and Linux users. Hence, you can use the tool by signing into your Microsoft Account via the cloud service. Unlike the two we have reviewed earlier, the Microsoft 3D tool is the easiest to use. Thanks to its simple and minimalist user interface, you can repair your file with ease. 

The tool has an option that lets you upload your STL file for repair and download the repaired file. Simple as it sounds; Upload, Repair, and Download. The three functions are clearly displayed on the page, so there is no chance of missing it.

However, although well-meaning, you can only download the repaired file in a 3MF format. Hence, the corrected file will only work on slicers that can process 3MF files. Alternatively, you can repair the file as 3MF and use another software to convert the format into an STL file. If anything, it is the easiest to use STL file repair tool of the three.


It can be challenging to work around a broken, damaged, or bloated STL file. However, free STL repair software tools are handy for correcting the errors and making your files printable. Unlike the paid versions, the free tools boast of equal efficiency without letting down on quality. More importantly, we recommend running your file through a repair software tool before printing it to save time correcting errors and save cost.

We have examined three of the best free STL repair software tools; however, there are other automatic and free solutions for repairing STL files. The ones we have discussed are simple to use, versatile, and have a user-friendly interface. Apart from this, they provide control over the repair process. You can try each solution until you find the one you are comfortable with, since each has tailored features and benefits. Nonetheless, each is designed to offer impressive STL repair solutions.

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