Question on "Driving the Nut"

[Dman65]

I have been reading and there are some older posts that talk about driving the nut on the leadscrew instead of turning the actual leadscrew.

This involves using a timing pulley and belt on the stepper and then putting the other end of the belt around the nut. I am wondering if anyone knows what particular type of pulleys and nuts you would use for this. All of the acme nuts I have are hexagonal, so I am not entirely certain how to get the nut inside a timing pulley.

Thanks for the help.

[ger21]

It's even more complicated than that. The nut/pulley system also has to be supported by bearings. Not nearly as simple as just buying a nut and pulley. Custom fabrication is required.

Here's the simplest one I've seen.

http://www.cnczone.com/forums/showpo...2&postcount=14

[Dman65]

Thanks for the link Gerry. I guess I will have to try and mock one of these up and see if it will work for me.

[svenakela]

I've made a "cylinder" with the nut pressed into the inside and the supporting bearings on the outside. It's a ballnut, but the principle goes the same way.
I made a sturdy housing for the bearing as well when I mounted it on the machine (you can use two bearings instead of one preloaded double as I did, easier to install but a little bit more expensive)

In this thread are some video examples:
http://www.cnczone.com/forums/showthread.php?p=651909

[Dman65]

Thanks for the picture svenakela.

I will have to see if I can figure out how it works.

Did you machine the cylinder yourself?

[svenakela]

Yes, I did it in my lathe.
The idea is very simple, look at the videop clips. The outer shell of the bearing is fixed in a housing. The cylinder is fixed with the nuts that you can see in the picture around the inner ring of the bearing. The ballnut itself is locked in the cylinder. The nut is rotated by a belt wheel clamped on the outside of the cylinder. Runs really smooth.