The steel tape is like smooth. In the absence of a better, you can use two hacksaw blades.
The threaded rod must be of good steel ( stainless steel ), to give good accuracy.
The coupling between the motor and threaded rod, I do through a piece of polyurethane (red in the drawing). The engine vibration, the best way is to mount a motor driver that works in microsteps.
I use Picgoto:
http://es.groups.yahoo.com/group/Picgotogroup/
http://sites.google.com/site/picgoto/Manual
I added a new drawing in more detail:
http://marcosbaun.multiply.com/photo...eaded_rod_Disk