I don't think you want to mount the encoders onto the ballscrews.
Your servos have a 4:1 reduction and the ballscrews are 5 TPI.
The system may break out into oscillation because of the backlash
between your reduction/ballscrews/motor.
Your following error will be way more than the Gecko's can handle.
They are great drives but sadly they have one shortcoming, and it
is a big one. The following error is permanently set at 128 encoder
counts. Not good.
There is not a single servo drive currently on the market that takes
step and direction and is capable of driving large servos reliably. Rutex and
CNC Teknix are both having serious troubles with their drives and are
in the redesign process.
Gecko has the short coming I mention above.
I am using small 12.5 in-lb Baldor servos with 1000 line encoders
driving a series 1 BP mill with 4:1 reduction between motor and
ballscrew. I am using Gecko drives and they are probably the best
currently out their until CNC Teknix and Rutex get their drives
redesigned. I have constant problems with my drives going into
error state due to the small following error. The only solution is
to keep my drive rates low. I use 80 IPM rapids when my motor is
perfectly capable of driving my table at almost 200 IPM.
Granite devices is the best drive available if you can deal with a
12.5A peak current for your motor.
http://www.granitedevices.fi/Most of us need 20A or better for our larger machine tools.
Best luck,
Scott