Ballscrew or leave alone?

[Jonathan]

You can get 12mm (RM1204) ballscrews from linearmotionbearings2008 on eBay. The steel the ballnuts is made from is just about soft enough to mill, so if you need to make them a bit smaller that's a cheap option. It's probably easier to grind it and glean the nut thoroughly afterwards. Clearly the stiffness and critical speed of the screw are both reduced if it's smaller, however in this instance neither is significant since it's a small machine.