z axis drive question

I am in the process of building a Z axis for an X Y table I am converting into
a CNC router. I plan to use Artsoft mach2 software with Rutex servo amps to drive the system.

Can anyone give me any more info on the following:

I have a quality 25 mm thick ball nut screw cut to 5 tpi - I have a choice of rotary
encoders from 400 to 2000 steps per rev. I intend to drive the screw
direct from my DC servo motor shaft.

Not being that familiar with servo systems (the amps haven't arrived yet !) I am concerned
that when I turn the ball screw by hand, a mere fraction of a turn seems to move the ball nut a long way !
Can a DC servo system with my proposed setup resolve enough resolution to move the ball a few thou,
typically for fine, milling depth cuts for finishing etc.

Any info would be most appreciated

Rgds

Dave Fisher



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