It's fun to turn a 3d-printer into a plotter,
but alas only for simple stuff.
A given-away laser printer (that is, $0) and $25 laminator deliver 15 mil / 0.4 mm traces easily and consistently.
I very much doubt any pen can do that, even with proper mount - the rubber band will just ruin any accuracy and consistency, and even if the pen is hard fixed, the tip will still wobble, plus always imperfect levelling will mess with the track width.
This is true, that's why v2 of my mount uses a zip tie! That one works much better, and I don't really need 0.4mm traces for the quick PCBs I need. If I need tighter tolerances, I can make the PCB this way, see that it works, change the tolerance and send it to a fab.
A given-away laser printer (that is, $0) and $25 laminator deliver 15 mil / 0.4 mm traces easily and consistently.
I very much doubt any pen can do that, even with proper mount - the rubber band will just ruin any accuracy and consistency, and even if the pen is hard fixed, the tip will still wobble, plus always imperfect levelling will mess with the track width.