achievement : design and make a DIY 2 sided PCB for a Arduino (Mega) Shield.
result : done - nearly perfect : 1 broken trace to fill and one to cut (design error) - seems perfectly aligned.
personal note : and it’s really my first diy PCB ever ! And it worked at first try, no miss during the transfer or etching. 2 good hour of zen concentration and it’s easy (really) :D
other note : thanks @xuv for the laser printer, used to make a mask for the etching: it can also print circuit finally ;)
publication note : this will probably be published in gpl when finished … with some pure-data patches too.
 and now I'm wondering how to make pcb plates other way ... as this method (industrial pcb chemicaly etched on place) does'nt seems to be the most ecological, economical and sustainable way to produce circuit in the long run : a lot of waste for some small traces ...
ha yes ... I thought about that but my CNC is for big dimensions (like meters, not millimeters) and ... I have in mind to or adapt a 3D printer to put a drill instead of extruder, or make another one in plywood ...
but making the plates in the first place is a problem still ... ;)