question about ball screws

[senor J.]

When speaking of ballscrews does preloaded mean it will have no backlash?

[ESjaavik]

Yes.
The message was too short, so this is added to make it longer.

[Bubba]

Only if all the other parts are also zero backlash (for instance all the bearings to hold the screw from moving axialy (sp?) )
Don't ask how I Know

[samualt]

A regular ball screw will have some backlash. This is usually brought about when you change direction and the ball bearings move from one edge of the screw threads to the other. No matter how tight that gap is there is always some movement.
A preloaded ball screw usually has (I guess) two actual ball units on it. One has bearings on one side of the screw threads and the other ball unit has bearings on the other side of the screw threads. This also means there is slightly more tension and thus torque needed to turn the ball screw. They can be adjustable and/or factory set as to the tension between the two ball units. They are also more expensive because you have a second ball unit.
Of course, you are just eliminating the backlash of the ball screw. You can still have lots of backlash in the bearings and other places.

I hope some of that makes sense. I'm still figuring it all out myself!

[ESjaavik]

Preloaded ballnuts can also have only one nut.
Then the preload is made by the separate ball paths in the nut being offset. Just like 2 nuts insde one. Another approach is to use slightly oversize balls. This is more compact, as the same balls take the load regardless of direction.