But, I normally use phenolic resin single sided stock of various thickness, and don't have to mount and align the stock twice. It seems too hard to find "Double-Sided" FR1, FR2 or CEM :( Also ...
What did you try (include command-line arguments): Uh, using the pcb2gcodeGUI frontend: pcb2gcode --output-dir=/home/kljhgv/CNC/PROJECTS --metric=true --metricoutput ...