Quote Originally Posted by charlieuk View Post
Whats the advantage/disadvantage of rotating the ball nut rather than the screw? why did you choose to do it this way? Are there any more pictures of how you did it
The advantages are that only the ballnut is rotating so you don't get screw whip that can be common on long screws. Also the rotating mass is much less so smaller motors/drives can be used, alsoon a lesser note there's some speed advantage.

Problem or should say disadvantage with them is the cost if you try to buy the real thing.? They are silly money. This design is Jonathans and they where made by him just search the forum for rotating ballnut and you'll see he's posted the design.

While DIY you still need to be pretty well tooled up and know your way around a lathe and able to work to good tolerences and still there is a cost involved compared to normal setup that IMO negates the cost saving of being able to use smaller motors/drives.
So the real advantage IMO is that you take away the risk of whip/resonance etc that comes with long screws. I'd certainly use it over other means like R&P for long machines but you do need to be proficeint with a lathe and engineering. Farming the work out to a engineering company would not cost effective as well IMO as there is a fair amount of time involved to make these.