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7 Free STL Editors + How to Edit and Repair STL Files

Picture of Frederik Bedrich
by Frederik Bedrich
October 14, 2017

7 Free STL Editors + How to Edit and Repair STL Files

How to edit and repair an STL file with 7 free STL editors: FreeCAD, SketchUp, Blender, Meshmixer, Meshlab, 3D Slash and SculptGL.

How do I edit STL files? That is something any 3D printer owner sooner or later wonders. After all: Ready-made STL files are fine. But what if an STL file you downloaded lacks some features, is damaged or you need only a part of it? That’s when you need an STL editor.

Don’t miss: STL Viewer - 20 Best Free STL File Viewer Tools

Editing STL files can be done in two different types of modeling software:
On the one hand, there is CAD software (Computer Aided Design). It’s tailored for construction, provides exact measurements and solid modeling. These tools were not made for 3D printing in the first place. In CAD software, circles, for example, are “real” circles; in 3D printing – and in STL files for 3D printing – circles are represented as polygons. So CAD tools cannot show their full strength when editing STL files. Nevertheless, they can be used for working with STL files. Three of the four tools we present in this article are true CAD tools: FreeCAD, SketchUp, and Blender.

On the other hand, there are mesh editing tools such as MeshMixer and MeshLab. They are designed for modeling, animation, and objects represented by a 2D surface. That means: These objects have just a shell and no filling. This may cause paper-thin walls, which can’t be 3D printed, if the object is not solidified (which, however, can easily be done in tools such as Meshmixer). In fact, mesh editors are excellent tools when it comes to editing STL files.

1

Free STL Editors FreeCAD

FreeCAD is an open source and free to use CAD software. It offers many different tools for construction, like Drafts, Drawings, and Design features. You can download FreeCAD for free from the FreeCAD project website. Simply select the correct version for your OS and install.

A serious limitation: FreeCAD has some problems with intercepting structures and may mess up the mesh when it contains intercepting edges!

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

  1. Open FreeCAD and create a new document by clicking on File > New.
  2. Click File > Import and select the object you want to modify. FreeCAD can open other mesh formats such as OBJ and AST as well.

  3. Change your workbench to Part.
  4. Select the imported object in the Model window.

  5. Now click on Part > Create shape from mesh. This will split up the imported object into many small triangles. You can adjust the precision of tessellation, but 0.10 is perfectly fine for most objects. If the number gets smaller, it will take longer to convert the object.
  6. You can now delete or hide the imported mesh. This will show you the shape of your imported object consisting of many triangles.

  7. Click Advanced utility to create shapes and select Solid from shell. Now click on any triangle forming your imported object and then on Create. You will not notice anything because the shape is overlapping the solid. Click Close to finish.
  8. Next, delete or hide the old shape. You now have a solid object of your mesh file ready for editing.

Step 2: Edit STL file

  1. Switch your workbench to Part Design.
  2. Click on any face you want to add or remove material, so it shines green.
  3. Now click Create Sketch.

  4. Create a shape you want to extrude or cut into using the tools for drawing a circle, rectangle or lines.
  5. Click on Close to confirm the sketch. If you want to edit the sketch, double-click it in the model tree.

  6. Now select a feature you want to apply. You can use the Pad tool to extrude or the Pocket tool to cut elements.

Of course, there are many more features and tools to use. If you want to learn more about FreeCAD, visit this tutorial!

Step 3: STL Repair

FreeCAD  features an extensive mesh repair tool:

  1. Select Meshes > Analyze > Evaluate & repair mesh.
  2. In case 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.

The pros and cons of using FreeCAD

When using FreeCAD as an STL editor, you really notice its purpose. It is a CAD program to create exact and models for mechanical use, not for modeling. This is great when you want to construct technical objects. Sculpting a model in FreeCAD is very difficult; as FreeCAD lacks a free move-around 3D view, sculpting is nearly impossible.

2

Free STL Editors SketchUp

SketchUp – formerly Google SketchUp – is a full-blown 3D modeling software that is now owned by architectural company Trimble Buildings. SketchUp is available as a commercial version called SketchUp Pro and as the free SketchUp Make edition. By installing different plugins, you can adjust SketchUp up to your personal preference. You can download the free SketchUpMake edition from their official website.

Step 1: Install the STL plugin in SketchUp

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. Now log in with your Google account.
  3. Search for SketchUp STL. Select it and click install.

Step 2: Open STL file

When you have the plugin installed go to File > Import… and set the file type to STL files. Browse for the object you want to open and import it.

Step 3: Edit STL file

  1. Use the Eraser to remove the edges of the triangles, 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.

Step 3: STL Repair

In order for your STL file to be 3D printable, you have to check it for manifold vertices and other hitches. SketchUp offers no STL repair out of the box. However, you can choose from a number of free and commercial plugins that will do the job nicely.

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

Another great plugin you should try is called Cleanup. It allows you to get rid of superfluous or hidden geometry.

Step 4: Export as STL file

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

The pros and cons of using SketchUp

SketchUp is easy to use, runs smoothly and has all the tools to create a 3D model. However, it is missing some key features of an STL editor for example for creating a solid object or for translating the triangle mesh of an STL file to squares which are easier to edit.

3

Free STL Editors Blender

Blender is an another great free program to either create models for printing, games or video clips. It contains many useful tools for example various algorithms for smoothening or interpreting a surface. It is also very easy to import and prepare STL files for modeling. However it will take some time to getting used to Blender, and due to its huge amount of different tools and commands, it can be quite obscure. It also requires a powerful PC to display some models, especially if you subdivide the model into many smaller tiles.

You can download the software from the Blender project website.

Step 1: Open STL file

  1. Delete the cube by hovering with your mouse above it and pressing the Del button.

  2. Click on 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 mode. You can now see all the edges your model is made of.

  2. Then 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.

    Free STL editors: Use the search option to acces commands quickly.

  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 plane, Cube or Sphere to add them to your model. Free STL editors: Extrude
  7. The Extrude command extrudes an area.
  8. Use the Boolean command to cut or merge one form with another.

Visit this tutorial to learn how to create a 3D map in Blender.

Step 3: STL Repair

Apart from STL import, Blender offers a native STL repair tool.

  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.
  3. Blender’s 3D Print Toolbox allows you to address all the issues that might cause your STL file to print incorrectly. The most pressing are:
    Overhangs that require support structure when printing with FDM and other techniques.
    Wall-thickness indicates areas that cannot be printed because they are too thin.
    Manifolds confound 3D printers with identical edges directly on top of each other.
  4. You can either check for all these issues by pressing Check All.
  5. On the bottom of the toolbox appears a list of errors you can cycle through.
  6. To repair vertices and edges press Isolated.
  7. To make your mesh manifold press Make Manifold.

Step 4: Export as STL file

To export your object go to File > Export > Stl.

The pros and cons of using Blender

Blender is a great STL editor if you want to create high poly models. It offers many tools to sculpt and work out fine details in models. However, it takes a while to getting used to working with Blender and as already said: When having a high poly object, it will require a lot of computing power.

4

Free STL Editors MeshMixer

MeshMixer is a free mesh editing program which you can download from AutoDesk’s website. It is very easy to edit STL files and also has a built-in slicer tool. This means you can send the edited model directly to your 3D printer to print it. If you want to learn how to prepare, repair or check your object for 3D printing with MeshMixer, visit this tutorial.

Step 1: Open STL file

  1. To import an STL file simply click on Import and browse for your object.

    Free STL editors: Make your object solid.

  2. Click on Edit > Make solid.

Step 2: Edit STL file

  1. You can now use Select to mark parts of your model.
  2. Press Del to remove marked tiles.
  3. Use Meshmix to open different forms.
    Free STL editors: Insert different forms and combine them with the Sculpt tool.
    Insert different forms and combine them with the Sculpt tool.

    You can access more models by switching from basic forms to for example arms or legs. Drag and drop the object you want to insert. Use the different colored arrows to move or rotate to model. Use the little square in the middle of the arrows to scale the model.

  4. Click on Sculpt to either smoothen or extrude different regions of the model.

Step 3: STL Repair and Preparation for 3D Printing

  1. In the sidebar, select Print. Here you find a comprehensive selection of  tools that can help you prepare your STL file for 3D printing:
  2. First, select your 3D Printer from the drop-down list.  The most common models on the market are on that list. Otherwise, you can add your  3D printer manually. Refer to your 3D printer’s manual for the specs.
  3. To repair your mesh select Repair Selected.
    This little tool will automatically fix all holes, non-manifold vertices, etc.
    Also, you can hollow your mesh to use less material.
    And you can adjust the minimum wall thickness.
  4. If you want to generate a support structure for your STL file, select Add  Support. Adapt the settings to your 3D printer’s requirements and click Generate Support and then Done.
  5. Once you are satisfied with the state of your mesh, click Send to Printer.

Step 4: Export as STL file

To export your object go to File > Export and select the.Stl file format.

The pros and cons of using MeshMixer

MeshMixer is one of the best tools to edit your STL files. It takes all occurring problems like the paper-thin walls into account. Working with MeshMixer as an STL editor is easy and useful if you just want to resize your model or change something.

5

Free STL Editors MeshLab

MeshLab is a free open source program that allows you to view or merge, transform or repair STL, PLY, STL, OFF, OBJ, 3DS and many other file types as well as point clouds. You can download MeshLab for free from the Sourceforge project website.

Step 1: Open STL file

To open a supported mesh file go to File > Import Mesh and browse for your model.

Step 2: Edit STL file

MeshLab does not have the tools to create new vertices or objects. However, it is a great tool to combine two meshes of a 3D scan. You can also remove parts of the mesh and repair holes in the model.

Free STL editors: In the Task bar you can find many usefull tools.
In the Task bar you can find many useful tools.

How to merge two meshes:

  1. To combine two meshes load both models.
  2. Click on Show Layers. Select the models in the scene.
  3. To transform, rotate or scale an object, first select it in the Layer menu and then click on Manipulator Tools.
  4. You can now press T to select the Transform option, R to rotate the model and S to start scaling.
  5. The direction you are looking at the model determines the coordinate system you are working in. Simply drag and drop the arrows to move or scale the model in one direction. Turn the circle around the object to rotate it. When you want to rotate your view, press Escape, and when you have the desired view on the object press Escape again to continue transforming. Press Enter to confirm the placement.

    Free STL editors: Use Flatten Visible Layers to merge two objects.

  6. When you have put all the parts in place, right-click on any part of your combined mesh and click on Flatten Visible Layers. Check the first three boxes and click on Apply.

How to delete a section of a model:

  1. To delete a part of the mesh click on Select Face in a rectangular region.
  2. Then click Delete the Current Selected Face and Vertices.

How to repair your object or search for holes:

  1. Click on Fill Hole. You model has to be manifold for this option.
  2. A window will pop up and show you all the holes in the model. You can now select the holes you want to fill. They will shine green when selected. Click on Fill and then on Accept to finish.

Step 3: STL Repair

  1. To check if your STL file is watertight select  Filters > Quality Measures and Computations > Compute Geometric Measures. You should see a volume for your file or an error report in the dialog on the right side.
  2. In case your STL file is not watertight, select  Filters > Cleaning and Repairing > Merge Close Vertices, click Apply.
    Select Filters > Cleaning and Repairing > Remove Duplicate Faces, click Apply.
    Select Filters > Cleaning and Repairing > Remove Duplicated Vertices.
  3. Check your STL file again.

Step 4: Export as STL file

To export the model go to File > Export Mesh.

The pros and cons of using MeshLab

Even if MeshLab does not offer the option to create new objects, it is a great STL editor to combine or repair a mesh. Using MeshLab is a great and easy way to combine the mesh of a 3D scan or just to create new models by merging them.

6

Free STL Editors 3D Slash

3D Slash is a free and easy to use 3D modeling software that lets you create models using a simple building-block concept similar to Minecraft. You can download 3D Slash for free or even access the free STL editor on your browser.

Don’t miss:

Step 1: Open STL file

To open an STL file go to Start a new model and choose From a 3D file. You can browse for your file on the hard drive or drag and drop it into the browser.

Step 2: Edit STL file

The mesh has automatically been converted into a pixelated object that can be edited with 3D Slash.

    1. Select your tool in the upper left corner of the viewport. You can choose from a number of tools to add to and subtract from the mesh cubes in various sizes:
    • Hammer: remove cubes.
    • Trowel: rebuild cubes.
    • Chisel: remove slices of cubes.
    • Wall: rebuild slices of cubes.
    • Drill: remove everything inside the limits selected.

You can add various primitives to the scene to get started with a new project.

    • Adjust the size of the cubes with the palette on the left side of the viewport.

Step 3: Export as STL file

  1. To export the mesh select the floppy disk icon in the upper right corner.
  2. Choose Save as STL file.

The pros and cons of using 3D Slash

3D Slash will be especially gratifying for hobbyists who occasionally want to create their 3D designs without having to master the mysterious lore of conventional 3D modeling software.  If you are a beginner with aspirations of going pro one day, you will be better off with a traditional free STL editor like TinkerCAD.

7

Free STL Editors SculptGL

SculptGL is a free 3D sculpting tool. Unlike its professional cousins, like ZBrush, SculptGL includes only the basic tools necessary and allows you to give you a sense of the sculpting workflow – all in the comfort of your web browser.

One serious flaw is that this program can occasionally produce non-manifold vertices.

Step #1: Open STL file

  1. Click Scene > Clear Scene to delete the default primitive.
  2. Load your STL file by choosing File (import/export) > Add (obj, sgl, ply, stl).

Step #2: Edit STL file

Define the big features of your mesh (arms, heads, limbs) with a large tool. Move to smaller brushes for details.

  1. Adjust the tool size in the Sculpting & Painting toolbar under Radius.
  2. The names of the tools are self-explanatory.
  3. To save time you can activate the Symmetry button. This allows you sculpt one-half of the mesh, while the other half mirrors your changes.

When you realize that the STL file’s surface is degrading or you wish to add smaller details you should increase the resolution. There are two options:

  1. Subdivide the mesh: select Topology > Multiresolution  > Subdivide.
  2. Or, Remesh it by selecting a resolution at Topology > Voxel Remeshing > Resolution, then clicking Remesh.

Step #3 Export as STL file

  1. Click File (import/export) > Save stl.

The pros and cons of using Sculpt GL

SculptGL is a great way to get started in 3D sculpting. For anyone curious about 3D sculpting, this is the best free STL editor, to begin with. But once you try ZBrush or Mudbox, you realize what else is possible with this fascinating approach to STL editing.

(Image: Pixabay)

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