[hive8]

I had a question, when i use 2005 ballscews, instead of a 1605, do I need a lot more torque to move it. My thought train was this, since there are more balls packed it would offer a larger resistance, also to go one more, if i use double nuts does it add a lot?

I am going with 283oz-in closed loop stepper system from leadshine for a fix gantry version mill.

[Fastest1]

The numbers just refer to the diameter of the screw. With 283oz steppers, you wont be taxing a 1605. Unless you just like bulk I would save my money. Most of use are running the 1605 on X & Y of our 0704's, the 2005 for the Z. IIRC the 5 at the end refers to 5 revolutions per inch but I could be wrong there (the more I think about it, being a metric screw. It could be 5mm per revolution?).
The quantity of balls really just effects the load carrying ability, more balls , more load. Regarding effort to turn the screw, there shouldnt be much difference. Not enough to make a stepper lose steps or anything.
In regards to double nutting and the extra effort that may require. It would depend on how much preload you put between the 2 ballnuts.

[691175002]

Both screws have 5mm pitch so the torque required will be similar.

Double nuts does make the screw slightly harder to turn, but it is really nothing compared to the friction of dovetail ways, or the weight of the Z axis.

[hive8]

Thank you for the answer, yes the 2005 ball screw means 20mm diameter and 5mm pitch (lead) so at one revolution the ball nut moves 5mm. I will not be using dove tails, on all axis I will be using linear guide rails from HiWin, the heavy duty rails with blocks. For the Z axis weight it will be the carriage and the 80mm High speed spindle with ATC.