The DWG format is a closed source binary file format that is not directly supported by FreeCAD. It requires an external 3rd party file converter to first convert then import the conversion into FreeCAD for use.
The Teigha Converter is a small freely available utility that allows to convert between several versions of DWG and DXF files. FreeCAD can use it to offer DWG import and export, by converting DWG files to the DXF format under the hood,then using its standard DXF importer to import the file contents. The restrictions of the DXF importer apply.
On all platforms, only by installing the appropriate package from https://www.opendesign.com/guestfiles/teigha_file_converter . After installation, if the utility is not found automatically by FreeCAD, you might need to set the path to the converter executable manually. Change workbench to "Draft", than in the menu Edit -> Preferences -> Import/Export -> DWG and fill "Path to Teigha File Converter" appropriately.
For more detailed instruction see this tutorial.
The program may be used with the command line interface or the graphical interface. Be sure to convert the dwg-files to an ASCII-Format.
Command Line Format is:
Example for Linux
TeighaFileConverter "/home/dwg-data" "/home/dxf-data" "ACAD2010" "DXF" "0" "1" "test.dwg" The second number (audit) needs to be 1 otherwise it fails
Example for Windows
"C:\Program Files\ODA\Teigha File Converter 3.08.2\TeighaFileConverter.exe" "Path-To-Input-Directory" "Path-To-Output-Directory" "ACAD2010" "DXF" "0" "1" "Name-Of-A-Test-File.dwg"
There is a free commercial program called Draft Sight (http://www.3ds.com/products-services/draftsight/overview/) that can import most DWG files and can save and export in formats that are friendly to FreeCAD. Draftsight runs on
A free registration is required for activation of the program.
There is also DoubleCAD XT (http://www.doublecad.com/DoubleCAD/DoubleCAD-XT-v5) . The program is free for personal and commercial use. It requires a free sign-up to receive an activation code via E-Mail. This Program is windows-only.
Exporting your AutoCAD files in a more FreeCAD friendly format, like DXF R12 or R14, SVG, and if version supports it, IGES. All are better alternatives to the DWG format when using FreeCAD.
It is important to know that, contrarily to popular belief, there is no difference between the contents of a file saved in DWG or DXF formats, provided it is the same version (ex. DWG 2014 vs. DXF 2014). Both formats are maintained by Autodesk, and they both support exactly the same features. The difference is that DWG is closed (machine-encoded) while DXF is open.
Simply put, stop accepting work done in DWG format. In practice, this is often easier said than done. Still, it would not be bad practice for users and supporters of FreeCAD to avoid and reject the DWG format whenever possible.