Ball screw without bearings?

[Halfnutz]

I saw a mill/drill retrofit package, a pretty nice looking one, and it looks as though the ballscrew is attached directly to the stepper shaft with no bearing in between, just an anti backlash coupling. The other end just floats in a simple bearing. Is this something anyone has any experiance with? It seems like Ive seen this done with some routers also. Any clues? Is this a bad/good idea?

[ViperTX]

and what is a "anti-backlash coupling"......I suspect they are counting on the stepper to take the backlash....not a good idea in most cases......

[Halfnutz]

Anti backlash couplers are those expensive helical one piece units that dont introduce any backlash, as opposed to the two piece design that has tons of axial slop in them. They will literally pull completely apart from each other unless the screw is secured by the bearing. Some of the helical couplers cost as much as 80.00 each. If the bearings in the stepper are OK then there shouldnt be any backlash in the system, unless the nut is bad. So nobody has a system like this, or knows of one? If it works, it would sure be nice, to save all the work and expense of angular contact bearings.

[sbrpollock]

In a situation like this, you are transmitting the cutting load to the bearings in the stepper. The bearings in stepper motors are not designed to carry that load.

[Halfnutz]

Yes that is what I thought, or well, its obvious, but I didnt know if there was a load carried through the screw. I geusse there would be, if your pushing alot of weight. So what type of bearing should there be, an angular contact?

[ViperTX]

Normally angular contact bearings are used in that application. There are several people who have used 6xxx bearings.

It's not just the weight of what you're moving, it's also the torque produced by the cutting action that is transmitted to the screw.

[Halfnutz]

OK, thanks, so it sounds like a cheap shortcut, or thier bearings are hidden where they cant be seen. Ive been using anglar contacts from VXB Bearings, they have 10 mm for 9.95 a pair and 12 mm for 14.95 a pair. I dont know how well theyl hold up, just have to wait & see. They have 17 mm for 1.00 a piece, theyre just a little big for the 5/8" screw.