Re: Advice needed?.

It sounds like several things are going on here.

I didn't do the math but with the pitch screws you have, I suspect it
going to take a lot of Motor RPM's to get the IPS you want. As you
know, as speed goes up on a stepper, torque goes down. You may be a
victim of the dreaded torque/speed curve! Reducing the belt ratio
might well make this worse.

There is also the issue of lead screw "whip". Long small lead screws
when turned at high rates tend to distort and increase the lead screw
frictional forces and decrease the efficiency. Commercial ball screw
catalogs have pages of charts giving max RPM for a given diameter of
screw.

The raw efficiency of an acme type screw is real low to begin with so
you may need 3 times the amount of torque to get the same foot/pounds
(cm/kg) as with a ball screw type. Of course your finer pitch gives
more force but at the expense of speed (IPS)

You might want to check your mechanical items as well. Binding in
the lead screws or their mountings, poor screw lubrication, binding
or excess friction in the gantry mechanism can all add up to heavy
losses.

The reason the guys were asking about voltages was to see if your
instanteous current pulses were enough to get the total amount of the
rated torque from your motors.

Disconnect your gantry from its screws and slide it by hand. Does it
bind or is it hard to push. I should glide easily along the track.

Rather than using 700 oz steppers you might want to consider using
servo motors with the stepper-to-servo drives from Gecko (320 and
340). Servo motors will turn higher RPM's and maintain torque across
a wider range.

Just one man's opinion.