Slaving A to X with Mach3 and Mechatronics Controller

I have just built a small Gantry router and am having problems with the X axis. I will post a picture of the router in the album shortly.

Some details-

Router built from 1/2 and 3/4" aluminum tooling plate. 42" X 16" X 6" work envelope. Linear ball bearings and Thompson ball screws/nuts on all axis. Motion seems to be very smooth and easy when moved by hand.

The steppers are 269oz from Xylotex. The controller is a 4 axis unit from Mechatronics. 24 volt power supply. Limit switchs installed. I am using a digital multimeter. VREF is adjusted to 4VDC.(Max reccomended vref is 5VDC). PFD voltage is adjusted to reccomended 2.5VDC.

Running Mach 3. With motor tuning set at 7878 steps per , 79.98 velocity , 20.182788 accelleration.

Y and Z axis perform very smoothly. X axis has A motor slaved to X. X axis motors seem to stall or don't move at all making high pitched buzzing noise. When X does move it seems to move slowly.

I don't understand what the PFD does and wonder if it needs adjustment???

Any insight on what I am doing wrong?

Thanks,

Jack