Help with "Step Timing Calculator"

Looks like it isn't a preloaded nut, other than maybe having over-sized balls in it. It does look like it probably has been fiddled with, opening the possibility it might not have been reassembled properly.

How difficult is it to turn by hand? Ideally it should turn like an ordinary wheel bearing with a bit of pre-load on it. If it is really hard to turn you can remove the screws for the ball returns to let the balls fall out, then you should be able to work it loose and get it apart. (you will probably want to do this over a tray to catch the spilling fountain of balls). Just be warned these things can be virtual Pandora's boxes to try to get back together, especially when over-sized balls are involved, but if it is useless as is, what have you got to loose.

Sometimes a bit of stiff rubber hose or a wooden dowel approximately the same size as the minor diameter of the screw, can be used as a mandrel for removing/reinstalling the nut onto the screw. (I like the rubber hose because it can be slipped over the machined portion of the screw.)

One of the main places balls hang up is where they are picked up out of the screw and transition to the return tube. Then again when returning back into the screw. If these areas are badly worn the nut might not be salvageable.

you should be able to turn the nut by hand , up and down the shaft ,
it could be the balls are jammed because of lack of use ,or maintenance . can you see any old grease or rust ?
or the grease has solidified , are the usual causes .

the easy way to open them up , is to remove the ball return tubes , gently and carefully do this over a tray lined with an old towel or cloth ,
you can then carefully rotate the screw and the balls will rotate out hopefully . clean and refit the balls by coating the balls with grease as you pop each one back in , you'll need to get a few balls in before it starts to level off , so watch for and balls slipping out between the screw and the nut , then check movement and regrease
the last few balls can be a bit difficult , so having someone else to help with an extra pair of hands helps

if the nut moves freely bu hand then leave it alone , or try some light oil to free it off , you may find removing the grease nipple and rotating the nut will push the grease out
or add a few drops of light oil to free the grease and try to push as much of the old grease out as possible . and regrease

above all work over a tray and cloths ( guess how I know )

above all work over a tray and cloths ( guess how I know )

I hear the voice of experience. Oddly enough that's encouraging.

Thanks guys, it should be an interesting few days.

I was just wondering, the drawings I have seen of this precision ball nut all show bearings throughout the races and in the tubes, completely full of bearings.
I am shot a number of bearings, is that normal or has someone cracked this open and lost a hand full??

If more than one or two, I'd say the probability is quite high.

If you need to replace balls, be careful they must be very precisely sized.

as todd says be careful on size , the track should be just about full , if you jam an extra one in , you'll find it will lock up and not move
the balls do track along the slide and move around , so an odd one missing wont harm directly , although i'd say more than 2 missing could cause intermittent problems

If you need more balls. I'd suggest contacting the screw manufacturer. You will need the serial number from the nut and or maybe the screw. Usually these numbers are hand engraved on the nut somewhere. They should be able to tell you the size and probably supply you with some replacements.