Matt, you are teetering on the brink of a slippery slope!

I think (can't quite recall as it's years since mine was removed) the problem is that the standard screw doesn't reach the back of the slide casting so would need an extension which is a bit fiddly. Easier to drive from the front end.

If you were replacing the screw with something longer you might fit a ball screw to get rid of most of the backlash as well as being easier to drive. A non-PXF S7 can only accomodate (I think) an 8mm ballscrew, mainly because of the diameter of the nut which won't fit the "tunnel". Those are available but expensive compared to larger sizes like 12 or 16mm, and need a bearing at the back as well. This is the approach taken by cncyourmyford.

I use a 12mm screw but in a PXF machine which has a much larger tunnel, and I have the nut "turned round" so the parallel section that normally locates in a bored hole projects out. I drive it direct from a NEMA stepper with an Oldham coupling.

As you see I've fabricated a new bracket.

Once you have a stepper on the cross slide you'll need to be careful not to slide down the full CNC rabbit hole, though I can tell you that it's very nice once you're in!

If a stepper motor has power applied it acts as a brake. With power disconnected is turns freely but…it then acts as a generator so it can backfeed any electronics attached to it. Turn it slowly and there is no problem, spin it fast and it can provide too much voltage for the electronics and burn them out.

Here are some better photo's ,the rear bracket is just fixed with 2 screws ,originally
it was just the location for the BW electronics wire DRO ,when i converted to the
cnc setup i had to alter the bracket to this "Y" shape to be able to fit
the stepper motor and and also the encoder .Fitting at the back of the machine
allows the cabling to be out of the way and you don't have the motor hanging out
half way across the workshop.
I made a new leadscrew to fit the existing nut and it has a top hat oilfilled nylon
nut piggy backed on the original nut ,the small peg hanging down in the photo 3
allows the second nut to rotate to adjust the backlash ,the retaining housing uses the
existing screw fixings and clamps up the second nut to retain it .You can see
here in photo 4 the plain part of the new leadscrew and the solid coupling.
It is not really necessary to use a ball screw if you are intending to keep the machine
as part manual use it would be better off to retain the existing setup ,its 17 years
since i changed this screw there is very little wear present ,in any case it is only £7
of material and few hours work to make a new one .
I have 7 machines that have been made or converted to cnc none of them
have ballscrews all except 2 are part manual use ,they all use the same cnc
system "Compucut" an old system now but still very reliable, on the Myford
i unplug the crosslide axis when it is used manually and use the Compucut
system to drive the leadscrew for power feed.

John

Mine is driven directly by a NEMA 23 motor probably running at about 1.5 amps 40v. It is a ballscrew so a conventional screw may need more – originally I used an ordinary screw in a bronze nut and had a 2:1 pulley reduction.

You could do it this way and used an eccentric to engage or disengage the stepper motor from the feedscrew. It will also enable about a 10:1 reduction gear ratio. My one is geared down 10:1

Alan

I have been reading this post with interest, due to the problem I have with my hand and getting worse and eyes not as good as they used to be , I have bitten the bullet and ordered the full kit from Rocketronics, I ordered some pulley’s from makers hut and what a load of rubbish they are serves me right for cutting costs so they are going back, I have now ordered some from gear & sprockets, although the kit hasn’t arrived yet ( but cleared customs ) I can’t do to much but I have worked out where to fit the Z stepper and pre made the bracket and yes I did make a mistake and drilled the holes in wrong place but it’s only a mounting plate and the plate is fixed using the 2 bolts that bolt the motor mount so no hole drilling , I am also fairly sure I can mount the encoder where the change wheels were ( fingers crossed) I will start a new post when I get going properly.

Dell