A quick update, as I got some time to work on the machine tonight, but no pics (will post some tomorrow):

I have my first ballscrew mounted, as I figured before I attach the Z-mounting plate the Y Axis needed to be finished. Used a Bosch 17mm bi-metal hole cutter to bore the holes in the gantry sides for the ballscrew and I find these tend to cut ~1mm over size (possibly due to my bench drill being a little wobbly). This is fine however as I need a little clearance to allow for alignment adjustment and have ~1mm rather than the intended 0.5mm.

The floating end is attached using an FK bearing block and circlip and the fixed is also a larger FK type which goes in the stepper motor mount and that is bolted to the gantry side also.

I have come across one of those annoying gotchas where the supplied ballnut mount protrudes ~1mm too far outside the gantry, so I need to work out whether I can "pocket" the ali plate for the z axis by 1mm using the tools I have. I'm thinking of very gently/slowly milling the pocket using my bench drill and an 8mm TC End Mill with the z axis plate clamped to my small cross slide table (normally only used for drilling holes in a straight line) - not sure I should mention a foolish move like this here, but it's a problem that needs solving (I have also toyed with using a low speed on my hand wood router, but I don't trust myself with that method.....).

Hopefully tomorrow I will also get try out the new circular saw on the ali plate (didn't finish work till late and the neighbours would probably not appreciate the tortured machining noises;-) ).

I must also try to resist connecting up the Y Axis just to get something moving under its own steam.....