3MF is a file format for 3D printers with inbuilt DRM. Some slicers are not able to read 3MF files. Here is a way to convert such files to STL.
If you need to convert a 3MF file to STL format you may find that there is no really simple solution. I found this very useful blog post by Zebethyal that describes how the command line tool 3mf2stl by Charles Shapiro can be compiled on a Mac to convert 3MF files to STL format. The required steps in all brevity:
- Install Homebrew
Open terminal and type (all in one line)
ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)" < /dev/null 2> /dev/null
Hit return. Homebrew is downloaded and installed. - Install libzip
Type
brew install libzip
After hitting return, the libzip library will be installed. - Download 3mf2stl
Enter the following URL in your browser
https://github.com/lemgandi/3mf2stl
and download the 3mf2stl repository (green button to the right, download as ZIP).
Unzip the file to a directory, e.g.~/Documents/3mf2stl/ - Compile 3mf2stl
Change to this directory
cd ~/Documents/3mf2stl/
and type
make
Hit return. The code will be compiled.
If the compilation was successful you will have an executable named 3mf2stl in this directory.
Usage is ./3mf2stl -i <input_file.3mf> -o <output_file.stl>