into a CNC machine: tinkernut stepper motor on the linear slide: 18 degree step, or 20 step per revolution each revolution is around 3 mm, 3 / 20 , = 0.15 mm linearly per step from hypertextbook CD track is 1.6 um track to track distance, seems to be quite good from repairfaq and here three beam optical pickup system: Arduino and DVD Bipolar Mini Stepper Motor driven by a L293D Arduino next next from homofacien: plotter CDROM