Christophe,

The english for your "plastic rings" is grommets. You might qualify that by "Rubber grommets" or "Plastic grommets" but usually just grommets is enough.
Nice post as we have come to expect. A year or back I converted an old 3D printer to a laser engraver and just used the motor control 0 to 10 V PWM signal to control the laser power.