By binding I was meaning that the screw may not be the same all along the length such that when the nut has very little play it will get harder to turn in a few spots.
With the stepper motor removed you should be able to turn the screw rather easily. Using your thumb and middle finger
to turn a nut you would need to exert a lot on a big nut to turn 100 in oz ( very rough example to relate in terms of in oz ).
With the screw free to turn you would adjust the nut and then turn the screw by hand and if you find a place where it gets
hard to turn to move the axis you need to see what is causing it. Sorry but kind of like telling someone how to tie their shoe laces.....
RICH