Opened ballnut...

OK, so I've opened the ballnut.
I'm actually rather glad I did.. it's really not as scary as I thought
(putting it back together may be though).

What I've found is that it does indeed consist of two halves. The front
half is a complete mini-ballscrew. This turns lovely when freed from the
main block, so I won't even bother removing the balls from this. In
fact, I've put tape on the end of the ballscrew to stop it twirling
itself off when it's placed vertically (it really goes!).

The rear-section seems to be screwed into the main block - I removed all
the balls from this. They all appear to be the same size of a tiniest
smidgen over 4.5mm. I checked them with a micrometer along different
axis as best you can with a sphere.. and they seem spherical to me.
Thanks for the advice of doing this on the floor Ballendo! That was a
lifesaver.. balls did indeed skitter and roll away.. all 100mm away.
Much better than if I'd done it on my hard wooden table....

Now my guess is that the rear nut is screwed into the main block (there
seems to be no other way in which they could be attached) and that this
takes up the backlash. Certainly it is this which is causing the
friction. If all comes to nought I'm quite tempted to just run with the
balls removed from this.

I can now see why my spraying loads of WD40 into the front ballnut made
no difference - it just wasn't getting into the balls of the rear one.
I'll now clean these up, and see what the result is. :)

Regards,
Abby