Here is a post that shows how to build a demonstration “CNC” machine with cardboard, paper clips, an Arduino controller and three small servo motors. For students that know nothing about how a CNC machine works this really provides a great way to safely understand the basic components in a “Hand On” manner.
He also shows how to do it as a manual machine with no Arduino or servo motors (The student gets to be the computer and motors)
Here is his full Youtube site