Modify STL 3D printing files with FreeCAD

There are many free STL files are available on the internet to 3D print useful objects at home. There are times when we want to make some adjustments to them to better fit our need or 3D printing equipment. If the STL file describes an object that is larger than the maximum dimensions your printer can produce, you can print the object in two or more pieces and glue them together. There are glues on the market that can make as strong bonds as the materials themselves they are attaching together.

There are free applications that can open and edit STL files, one of them is the open source FreeCAD.

Download FreeCAD from

Open and edit STL files in FreeCAD

Import an STL file into FreeCAD

  1. Start FreeCAD and create a new document with File > New,
  2. In the menu select File > Import and navigate to the mesh file you want to modify. FreeCAD can open STL, OBJ, and AST mesh files.
  3. In the dropdown select the Part workbench,
  4. In the Model window select the imported mesh,
  5. In the menu select Part > Create shape from mesh
  6. The default 0.10 tolerance is usually fine for most of the objects we 3D print, click OK,
  7. Delete the imported mesh in the Model window. Right-click the name of the imported mesh and select Delete,
  8. Convert the shapes to solid. In the toolbar click the Advanced Utilities icon,
  9. In the Tasks window select Solid from shell
  10. Click one triangle on the object,
  11. Click the Create button. You will not notice any change because the solid overlaps the shape.
  12. Click the Close button in the Tasks window,
  13. Delete the shape. In the Model window right-click the name of the shape and select Delete. We have converted the mesh to solid, ready to be edited.

Edit the solid model in FreeCAD

  1. To add or remove parts, open the Part Design workbench,
  2. Select the Solid in the Model window, so the object turns green,
  3. In the Part Design menu select Create Sketch
  4. Select the plane you want to draw and click OK,
  5. Draw lines, circles, rectangles that we will extrude to add or subtract them from the object. Don’t worry if the sketch is not at the correct elevation, we will move the sketch to the correct elevation later.
  6. To print a portion of a too large object, draw lines and trim them at the location where you want to separate the object into multiple parts.
  7. To close and save the sketch click the Close Sketch icon in the tool bar.
  8. To continue to edit the sketch, double click it in the Model window.

To change the elevation of a sketch

  1. Select a face on the solid the move the sketch to,
  2. In the Part Design menu select Map sketch to face
  3. Select the sketch in the drop-down list and click OK,
  4. The sketch opens. You can continue the editing of it, or just close it.



Import STL mesh files into Autodesk Inventor

Import and export STL mesh files

To enable Autodesk Inventor to open and save .stl files add the STL Import and STL Export add-ins to Adobe Inventor. .stl files are used to transfer 3D print designs between computers. You can download most of them for free from the Internet.

  1. In the Tools menu open the Add-in Manager
  2. On the Translators tab select the STL Import and STL Export translators.

To be able to edit the STL mesh files

install the Mesh Enabler add-in

Download the Autodesk Inventor Mesh Enabler

  1. Navigate to the Autodesk app store at
  2. Sign in with your Autodesk account
  3. Search for Mesh Enabler
  4. Click the Download button

Install the Autodesk Inventor Mesh Enabler

  1. Double click the downloaded AutodeskMeshEnabler.msi file and complete the installation
  2. Start Autodesk Inventor
  3. In the Tools menu select the Add-in Manager
  4. On the Applications tab select Autodesk Mesh Enabler
  5. Select the Load Automatically checkbox
  6. Click OK

To convert an STL mesh file to a solid model

  1. Start Autodesk Inventor
  2. Open the STL mesh file
  3. In the browser right-click the MeshFeature1 element and select Convert to Base Feature
  4. In the dialog box select the output you need and click OK.

    1. Solid/Surfaces: Converts the selected mesh features to multi-solids or individual surfaces. To create solids, the mesh features must form closed meshes.
    2. Composite: Converts the selected mesh features to a single composite feature.
    3. Delete Original: Deletes the selected mesh features after conversion.

Set the default project location

Inventor saves the new projects in your document folder. To set a different default location

  1. In the Tools menu select Application Options
  2. On the File tab click the yellow folder icon next to Project folder and set the desired location.

To save the solid model as an STL 3D mesh

  1. Open the Inventor Parts (.ipt) or Inventor Assembly (.iam) file in Autodesk Inventor,
  2. Click the Inventor icon in the upper left corner,
  3. Click the small arrow next to Save As,
  4. In the submenu select Save Copy As,
  5. In the Save as type dropdown select STL Files,
  6. Enter a name for the file and click Options…,
  7. Select Source Units to make sure the size of the mesh is identical to the objects in the Inventor document,
  8. Click OK to close the Options window,
  9. Click Save to write the file to the disk.