3 Ways You Can Repair Your Files for Free

How to edit and repair an STL file with 3 free STL editors: FreeCAD, SketchUp, Blender

Repairing STL files is an important step towards creating a perfect 3D model for printing. Here are 3 free tools you can download and use, if you haven’t already. You can download them at these addresses for BlenderFreeCAD and SketchUp.


Blender is a great tool to work on high poly models with intricate details, but it requires high computing power. It is very easy to import and prepare STL files for modelling. However it will take some time to get used to Blender, and because of its huge number of different tools and commands, it can be quite obscure.

Step 1: Open STL file

File > Import > STL

  1. Delete the cube by hovering with your mouse above it and pressing the Del button.
  2. Click File > Import > STL, browse for the file you want to open and import it.

Step 2: Edit STL file

  1. Switch from Object to Edit You can now see all the edges your model.
  2. Hit Alt L to select all elements so the model shines orange. You can also select individual points, edges or planes by right-clicking them.
  3. To convert the triangles to rectangles, use Alt J.
  4. You can now change the number of tiles the model is made of by either searching for Subdivide or Un-Subdivide.
  5. Use the three different selection options Vertexes, Edge or Face select to extrude, move or delete parts of the model.
  6. Search for different shapes such as Add planeCube or Sphere to add them to your model.
  7. The Extrude command extrudes an area.
  8. Use the Boolean command to cut or merge one form with another.

Extrude area with the Extrude command.

Step 3: STL Repair

  1. Activate the 3D Print Toolbox: File > User Preferences > Add-Ons > Mesh: 3D Print Toolbox.
  2. You can access the toolbox now in the left sidebar. 

Step 4: Export as STL file

To export your object, go to File > Export > STL.



Open source and free, FreeCAD offers many tools for construction. It is also a tool for mechanical models and technical objects, not sculpting. There is no freely movable 3D view. Be careful, if your model has intercepting edges, it may mess up your mesh.

Step 1: Open STL file and convert it to solid model

3. Change your workbench to part

  1. Create a new document by clicking on File > New.
  2. Click File > Import and select the object you want to modify. FreeCAD can also open other mesh formats such as OBJ and AST.
  3. Change your workbench to Part.
  4. Select the imported object in the Model window.
  5. Go to Part > Create shape from mesh. 0.10 tessellation is fine for most models.
  6. Now you can delete/hide the imported mesh.
  7. Click Advanced utility to create shapes and select Solid from shell. Now click on any triangle forming your imported object and then Create. Don’t worry if you see nothing – the shape is overlapping the solid. Click Close to finish.
  8. Now delete or hide the old shape. You now have a solid object of your mesh file ready for editing.

5. Create shape from mesh

7. Advanced utility > Solid from Shell > Create

Step 2: Edit STL file

Create Sketch

  1. Now switch your workbench to Part Design.
  2. Select a face you want to add or remove material.
  3. Click Create Sketch to Create a shape you want to extrude or cut into using the tools for drawing a circle, rectangle or lines.
  4. Click Close to confirm the sketch. To edit the sketch, double-click it in the model tree.
  5. Now select a feature you want to apply. You can use the Pad tool to extrude or the Pocket tool to cut elements.

6. Pad to extrude, Pocket to cut

Step 3: STL Repair

1. Meshes > Analyze > Evaluate & repair mesh

  1. Select Meshes > Analyze > Evaluate & repair mesh.
  2. If you know what defects your mesh has, select the appropriate item in the list and then click Analyze. Otherwise, choose All above tests together and then click Analyze.
  3. After the analysis is complete, click Repair.

Step 4: Export as STL file

To export your object as an STL file again, select the last feature in the model tree.  Then click on File > Export and select Mesh formats.


SketchUp is a full-blown architectural modelling software with many plugins. It is easy to use, runs smoothly and has all the tools to create a 3D model. However, it has missing key features of an STL file editor, such as creating a solid object or for translating the triangle mesh of an STL file to squares which are easier to edit.

Step 0: Install the STL plugin in SketchUp (if your SketchUp does not have the plugin)

To import STL files in SketchUp Make you need to install a plugin first (this plugin is already installed in the Pro edition).

  1. Start SketchUp and click on Window > Extension Warehouse.
  2. Log in with your Google account.
  3. Search for SketchUp STL and install the extension.

Step 1: Open STL file

Go to File > Import… and set the file type to STL files. Browse for the object you want to open and import it.

Step 2: Edit STL file

  1. Use the Eraser to remove the triangle edges, so you end up with a rectangle to extrude. You can also use the Pencil or one of its shapes to create new sketches to extrude.
  2. When you have created new sketches, you can use the Push/Pull feature to extrude or cut through the model.
  3. Use the Move tool to drag edges or vertices.
  4. You can create a reference line by orbiting over a point or surface and then move to the actual point where you want to start or end.

2. Pull to extrude and Push with your mouse to cut.

Step 3: STL Repair

  1. Install the Solid Inspector Plugin from the Warehouse.
  2. Select your mesh, then press the Solid Inspector button in the toolbar. Solid Inspector displays a list of errors that prevent your mesh from being solid manifold.
  3. Use Tab (Shift Tab) to cycle through and zoom to the errors in your STL file.
  4. To automatically fix these errors, click on the Fix or Fix All buttons in the list.

Step 4: Export as STL file

To export your model go to File > Export and select the .stl file format.

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