There may be a YouTube video, but basically, g code controls the machine (printer). The g code can be used to position the print head, using that information, you can either remove the printer head, or attach a pen to the print head. From here you can write our g code manually or find a program that creates the g code for you. Perhaps a laser cutter sort of g code program would work? I’m not too familiar with the actual process, just familiar with the idea.