Spanish newbie (with a couple of CNC projects for photography)

[Jonathan]

I see there are machined and not machined ballscrews, what's the difference ?

'Machined' means the ends of the ballscrew have been turned on a lathe. This is to create a smooth and accurate cylindrical surface to attach the bearings and coupling. The ballscrew will not be accurate if the bearings are just placed on the threaded portion of the screw, if indeed they fit there at all. So in short, yes you do need end machining.

If you get the ballscrew from linearmotionbearings2008 on eBay the end machining is extremely cheap - just a few £.