I learned a lot trying to use adapters from Aliexpress and eventually got them working after some modifications, but up to now I couldn't find any good quality refill pens which I could use with them. So I will go back to that later on.
For most of my works created using self build plotter I used Stabilo point 88 pens, so I wanted to have an adapter for them. Of course the easiest way to do that was to design and 3D print one.
I'm using a trial and error route to get the dimensions just right for tight pen fit as well as position and diameter of the ring (which are crucial for automatic grip to work). Some work needs to be done to make it work every time, but I'm getting closer.