determining stepper motor current

I have a Step 4 cnc machine for which I've built a new controller
based on L297/298 combo (as the original went up in smoke) I'm
having trouble determining the vref setting. The motors are marked
nanotek - munich 1.8deg/step 1.2ohm. '17' size and I think they were
originally set up for a max current of 0.8A. I am trying them at the
moment with vref=0.4v and with sense resistors of 0.5ohm , but the
motors do not have any of their original torque.

As I understand, I am effectivly setting the current as the peak
current which will be much less then the average current. I am wary
of increasing the current without any more data on the motors.

any suggestions will be appreciated.

alan