Why do we spin the screws?

[Jcadwell]

Why do we spin the screws with the stepper motors? Why don't we spin the nuts. In some cases it looks easier to mount the motor in a position to spin the nuts rather than the screws. The screw would then become an additional scructural member. Any thoughts?

[Zagroseckt]

Yes easy ancer.
Torq on the nut....
to get a Zero backlash on the nut using berings would be such a headach
Were talking Serious headach.
Altho there are some systems that do, do this

[bunalmis]

If the machine axis lenght too long, screew weight (inertia) increase and there for your said methode using at the fast and long machine.

I see this type machine at the industry. Motor turn the nut and motor and nut move together.

[ToyMaker]

I think the reason you don't see more driven nuts is in the mechanics. Driving the screw usually is two end supports and a coupler between shafts. To drive the nut requires the end supports plus thrust bearings on either side of the nut plus gear, belt or chain linkage. It's just more complicated.
But even with that some DIYs have done. There is a thread here in the Zone discussing it: "alternative drive" might be the title.

robotic regards,

Tom
= = = = =
If you focus on results, you will never change. If you focus on change, you will get results.
- - Jack Dixon

[doug6949]

The new Flow waterjets use a rotating nut. There are a few advantages that can be significant. First, it allows you to use lighter screws because there is no problem with critical velocity and the attendant shaft whip. Second, it reduces load inertia. Both can result in better performance.

Disadvantages: It's a pita to build the carriage for the rotating nut. And cheap ballnuts don't like to be spun - they won't last long. Ballnuts designed for rotating cost quite a lot. For example, the one inch by .2 pitch preloaded nut that Rockford sells is about $175. The rotating version is around $450.

For hobby purposes the cheap ballnuts will probably hold up fine when rotated.

Doug

[turmite]

How are the spinner nuts different tht fixed? Are there major differences in tolerence, size of balls...? I have two 1.125"/.200 pitch, anti-backlash double nut screw setups that could save me some serious money when I get to buil my machine if I can get the spped I need by spinning the nuts and fixing the screw. Whit that said I need 300 ipm as a max using the .200 nut and I need to push something in the 200-275 lb range. The machine itself will be a heavy frame and will be using linear ways such as Thk etc.

Mike