The 8 Best Free STL Editors to Edit and Repair STL Files

Fusion 360 is a full 3D CAD software by Autodesk. It is built to be a professional CAD solution and is an industry favorite. Even so, the interface is easy to navigate and has a nice selection of advanced tools, so it is a perfect solution for beginners and experts alike. While it technically is a paid service, you can get a year or more free with a student or hobbyist license.

• Price: Free for the first year
• OS Compatibility: Windows, Mac

Opening STL Files

First and foremost, you will need to install Fusion 360 on your computer, create an account, and get your license or free trial. You’ll need to log in to access the program’s interface. Once you’ve done that, you can import an STL file of your choice.

1. Choose File -> Open from the toolbar.
   
2. Click Open from my computer…
   
   
3. Select the desired STL from the file explorer.
   
4. Click Open. Your STL file will appear in the workspace after.
   

(The STL used in this article is 3D Printable Pliers by Fernando Jerez.)

Editing STL Files

Fusion 360 has a number of surface and mesh editing tools. Which tools you select depends on what you are trying to edit in the model. You can scale, slice, remesh, reduce, and much more using the tools under the Modify toolbar in the Solid, Surface, and Mesh tabs. You can even open additional STL files and merge them or use the shape tools available in Fusion 360 to add to the current STL.

Repairing STL Files

To repair an STL file, you can use any number of mesh editing tools shown in the previous step, depending on the issue. Fusion 360 usually lets you know there is an issue with your file when you import it, so it’s easy to diagnose. Fusion 360 also has a repair tool that automatically fixes errors and issues with the mesh as well.

1. Go to Form -> Utilities and select Repair Body.
   
2. Choose a tolerance (the default is 0.01mm) in the dialog box that appears.
   
3. Click OK to run the tool.

Export STL File

Once you’ve finished editing or repairing your STL file, you can export them.

1. Choose File -> Export from the main toolbar
   
2. Name your file and select STL from the Type dropdown.
   
3. Choose a destination for your file. It will default to the location you imported it from unless you choose somewhere different.
   
4. Click OK to start the export. The job status pop-up will show you the progress of your export.
   

FreeCAD is an open-source CAD software capable of creating and editing complex 3D models. Since it supports the STL file format, it is a great STL editor for 3D printing purposes. It has an easy-to-use visual interface for beginners, as well as built-in Python support for more advanced users.

• Price: Free
• OS Compatibility: Windows, Mac, Linux

Opening STL Files

You will first need to install FreeCAD on your computer and open it.

1. Go to File > Open. Or you can select File > New Document and File > Import.
   
2. Select the STL file you want to open.
   
3. Click Open to bring the model into the workspace.
   

Editing STL Files

To edit STL files in FreeCAD, it’s best to convert it to a mesh first.

1. Tab over to the Part workspace.
   
2. Select Face > Create shape from mesh.
   
3. Set the tolerance. The default is 1, but you can go down to 0.1 for more complex geometry.
   
4. This converts the model to a mesh and allows you to use more tools in the program to manipulate it.
   
5. Use the tools under Part > Part and Part Design > Part Design dropdowns to make changes to the STL file or use the sketch function to sketch and extrude shapes to add to the existing mesh.
   

Repairing STL Files

It is easy to repair STL files in FreeCAD thanks to its built-in repair tool.

1. Tab over to the Mesh Design workspace.
   
2. Go to Meshes > Analyze > Evaluate and repair mesh.
   
3. Check the boxes for all the diagnostic tests you want FreeCAD to run.
   
4. Press Analyze to run the tests. If it shows any issues, you can select the Repair button next to the problem and it will automatically correct it.
   

Exporting STL Files

1. Go to File > Export in the main toolbar.
   
2. Name your file, select STL as your file type, and choose where to save it. Press Save to finish the process.
   

MeshMixer is a free STL editor designed for combining, splicing, and otherwise remixing files for 3D printing. It also has tools to easily repair STL files to fix things like wall thickness, holes, and other issues that would lead your 3D printing projects to fail.

The downside of MeshMixer is that Autodesk has discontinued all support for it, so it is difficult to find an installer for any systems besides Windows and the software may stop working on newer computers as it ages. They have integrated most of MeshMixer’s features into Fusion 360, so if you aren’t able to install a copy of MeshMixer, that is your best alternative.

• Price: Free
• OS Compatibility: Windows

Opening STL Files

Install the MeshMixer software onto your computer if you have not already done so.

1. Select Import from the home menu.
   
2. Choose your STL file of choice and press Open.
   
3. Your file should now be in your workspace.
   

Editing STL Files

MeshMixer has several types of tools to build and edit STL files. They have an extensive library of built-in polygon objects that you can add or subtract from your existing mesh.

There are also basic shapes that can be stamped into the mesh’s surface with the Stamp Tool.

Meshmixer also has a rudimentary set of sculpting tools that can serve as a quick and easy way to add details to or deform the mesh.

Repairing STL Files

MeshMixer’s STL repair features are where it becomes one of the best free STL editors to have for 3D printing. It has several tools made specifically to repair STL objects including an automatic STL repair function.

1. Go to the Analyze tab to access the various repair tools. To automatically diagnose and fix errors on the STL file’s surface, choose Inspector.
   
2. You can choose one possible mesh issue to diagnose and repair or you can simply choose Auto Repair All to analyze and fix all categories at once.
   
3. The other tool you will likely use regularly from the Analyze menu is the Thickness tool. This helps you adjust the thickness of the mesh’s surfaces and set a minimum wall thickness to prevent fragile printed objects and other failed 3D printing attempts.
   

Exporting STL Files

1. To export your object, choose Export from the side menu.
   
2. Name your file, choose a destination for it, and set the file type to STL. Click Save to export your STL.
   

MeshLab is a free mesh editing software that is designed to optimize a pre-downloaded STL file. While you can technically build a mesh file from scratch, the interface is not well suited for it. MeshLab, like MeshMixer, is more suited to edit or repair STL files than produce them.

• Price: Free
• OS Compatibility: Windows, Mac, Linux

Opening STL Files

1. Select File > Import Mesh from the main toolbar.
   
2. Choose your STL file. Click Open.
   
3. If you haven’t saved your pre-open preferences, this dialog box will pop up. This cleans up your vertices, but you can deselect it to do it manually later if you’d like. Press OK.
   
4. Your STL file should now appear in your workspace.
   

Editing STL Files

MeshLab has several tools to edit STL files depending on your needs. You can add new shapes to your mesh or use any of the many tools in the Filters menu to change the mesh as needed.

Repairing STL Files

While MeshLab doesn’t have a tool to automatically diagnose issues in your mesh, it does have several repair features.

1. Go to Filters > Selection > Select All to select the entire object.
   
2. Choose one of the many options from Filters > Cleaning and Repairing that addresses the issue your mesh has.
   

Exporting STL Files

1. Go to File > Export Mesh As.
   
2. Select STL as your file type, choose your save destination, name your file, and click Save.
   

Tinkercad is an in-browser computer aided design software. It started as a way to teach absolute beginners the basics of CAD, but it has evolved to serve as one of the most popular basic free STL editors for 3D printing enthusiasts looking for a simple design solution.

• Price: Free
• OS Compatibility: Web-Based

Opening STL Files

1. Choose Create new design to open a blank project.
   
2. Select Import to add an outside mesh file.
   
3. Choose your STL file and press Open.
   
4. You can make changes to the scale and dimensions of the file before it loads into the workspace.
   
5. Click Import to load your model into the workspace.
   

Editing STL Files

TinkerCAD lets you merge any of its impressive number of different shapes to your object, so you can easily add elements to your model. You can also change the dimensions and scaling within the program as well.

Repairing STL Files

TinkerCAD doesn’t have any dedicated tools to repair STL files, so you are limited on the types of mesh repair you can do. Usually any fixes done in TinkerCAD consist of filling holes or pieces that aren’t needed or changing the size of the object in some way.

Exporting STL Files

1. Select the Export button.
   
2. Click the .STL button. It will automatically launch your download.
   

3DSlash is an easy, intuitive online STL editor. Instead of using traditional CAD software tools, they have easy-to-use tools that more closely resemble a game than a program to create or edit STLs. You typically start out with a cube in the program (but you can import your own models as well) and delete or add smaller cubes from the model’s surface in order to shape your model.

If you enjoy processes like building in Minecraft or using Legos, this is one of the best free STL editors to start learning modeling basics.

• Price: Free
• OS Compatibility: Web-Based

Opening STL FIles

1. In the create section, select From a 3D file.
   
2. Choose your STL file and click Open.
   
3. Your model should now be ready to use in your workspace.
   

Editing STL Files

To edit your STL file in 3DSlash, you have a few tools that should help.

1. Set the tool size from the left-hand side of the screen.
   
2. Choose your tool. You can use five different tools to edit your shape, all of which work off the idea of adding or removing cubes.
   
3. Use the tool to select the portion of the STL that you want to edit
   
4. Apply the modification
   

Repairing STL Files

3DSlash does not have an extensive mesh repair tool like other modeling software options. If you need basic tools to fill in a hole or other simple functions, you can use 3DSlash’s editing tools. Otherwise, you are better off choosing a different modeling software from the list.

Exporting STL Files

1. Choose the Apps icon to see the export options.
   
2. Select .STL and click the Download button. Your file will automatically be sent to your download queue.
   

SculptGL is a free web-based 3D sculpting program. Sculpting software like ZBrush and Mudbox are great solutions to quickly creating organic models, and while SculptGL only has the basic tools found in those other programs, it is still a quick and free way to edit your STL files.

• Price: Free
• OS Compatibility: Web-based

Opening STL Files

1. The program loads in a basic sphere automatically. Go to Scene > Delete Selection to remove it.
   
2. Go to Files (import/export) > Add (obj, sgl, ply, stl).
   
3. Select your STL file of choice and click Open.
   

Editing STL Files

Like other sculpting programs, SculptGL uses brushes to move or affect the topography of the mesh. Choose the one you need.

Click and drag your mouse along the area you want to be affected by the brush.

Repairing STL Files

SculptGL does not have mesh repair tools. If there are some issues with an organic model like a figurine or bust, you could most likely sculpt those away in the program, but sculpting is not a good method for highly technical models (like the plier model I’m using in this article).

Exporting STL Files

Go to Files (import/export) > Save .stl. Your file will automatically be sent to your download queue.

Blender is a free open-source program that goes far beyond STL editing. Like Autodesk Maya, it is a fully-equipped animation software. However, Blender goes a step further by incorporating a full sculpting environment into its interface as well. This allows you to do pretty much everything step of a complex modeling or animation workflow in one program. Blender is easily one of the best STL editor options available even with the steep learning curve for its UI.

• Price: Free
• OS Compatibility: Windows, Mac, Linux

Opening STL Files

1. Blender opens a new project with a cube on the workspace by default. Select it and either Right-Click > Delete or press X on your keyboard to delete it.
   
2. Go to File > Import > Stl (.stl).
   
3. Choose your STL file and press Import STL.
   

Editing STL Files

As we mentioned before, Blender is one of the most robust free mesh editing software options available. You can do traditional box modeling and sculpt within the program, so your options to edit STL files are only limited to your understanding of the many mesh editing tools in the software.

1. Switch from Object mode to Edit mode.
   
2. Tab across the different workspaces (Layout, Modeling, Sculpting, UV Mapping, etc.) to access all the different tools.

Repairing STL Files

Blender does have some built-in tools to analyze and repair STL files. Before you can use them, you must enable the 3D Print Toolkit add-on.

1. Go to Edit > Preferences. Choose Add-ons and make sure Mesh: 3D Print Toolbox is selected.
   
2. You should now have a 3D-Print tab on the right side of your workspace. Restart the program if you don’t see it.
   
3. Choose Check All to analyze your imported mesh.
   
4. If the program finds issues with your model, go to Mesh > Clean Up and choose the tools you need to repair it.
   

Exporting STL FIles

You can easily export your STL file from the 3D Print Toolbox. Choose your outgoing folder, select the STL file format, and click Export to save your model.