Robert Kirberich developed a Python script to convert two Gerber files into a .STL that is 3d printable. It also works with Eagle files. It outputs the files into OpenSCAD .scad files and you can work on them form that environment.
You can find all the software at: https://github.com/kirberich/gerber_to_scad
There is also a web application based on that software you can use freely: http://solder-stencil.me/
Project homepage: https://hackaday.io/project/9550-solder-stencilme
|Solder stencil 3d printed using Robert's software|
Here is a video tutorial on how to use soldering stencils by SparkFun to stencil an Arduino Pro PCB:
Instructables user rmd6502 made a detailed tutorial how to design a 3d printed soldering mask for your electronics projects. he goes from Eagle EPS to PDF format, then PDF to DXF and then uses OpenSCAD to get the final STL.
This is a neat way to save a bit of money when you order boards. Normally you pay an extra $25-50 for a solder stencil, either a silkscreen or a sheet of metal with holes where the solder paste needs to go
Detailed guide can be found at: