Reduction Ratios

Hi Group,
I am in the process of setting up the 24 volt servos on a 36" lathe.
I'm using a Hitachi 2.1 amp, 500 pulse/rev encoder, 3/16" diameter
shaft servo for the X axis. The Z axis servo is much larger with a 1/2
inch shaft & 1000 pulses/rev encoder but with no other specs available.
I've heard that servos run at about 3:1 reduction but this doesn't
allow for different pitch ballscrews. Can anyone tell me the distance
the tool should move per revolution of the servo ? ( or how many
revolutions/mm )
Thanks,
Glen