[lazy_mosquito]

Hi all

I am designing a kind of cnc mill and have a question regarding the mounting of the ball screws. I read already a lot of it on this forum and some other, but couldn't find an answer for my question. In general you have four mounting options for a ball screw: fixed-loose / simple-simple / fixed -simple / fixed-fixed.
The problem with the simple mounting is that it gives you less axial rigidity. The problem with the fixed-fixed mounting is that it is very difficult to assemble yourself.
What would happen if you would use the fixed type bearings but without fixing them? More specific: Assemble them like you would with the simple bearings. The fixed type bearings would give you a better axial rigidity, but the fact that they still can move along the axis (like the simple bearings) would make them a lot easier to assemble.

English isn't my mothertongue, so excuse me in advance for the abuse of your language...

Pieter

[ger21]

IMO, simple/simple is an option that shouldn't be used.
Not sure how you would mount a "fixed" bearing so it could move? The purpose of the fixed bearing is to NOT move.
Just use one fixed and one simple. That's what most people do, and it works fine.

[lazy_mosquito]

Hi Gerry,

The idea is not to use a simple - simple mounting but a fixed - semi-fixed. I try to explain what i mean with semi-fixed.
You would have at the end of your ball screw also the two bearings you normally would have at the fixed side. The bearings are also fixed, the only difference is that you would fix the bearings to the supports in the same way the simple bearings are fixed. So they can move only along the axis.
With the normal simple bearing there is a certain play possible which makes that the ball screws have a lower critical speed. When you have the semi fixed bearings there will be less play and the critical speed will be higher.

Hope this makes everything a little clearer.

PS: Even more easy to accomplish, would be to replace one simple bearing by two simple bearings, which would at least give more stiffness albeit less then two angled bearings.

[RICHARD ZASTROW]

Why re-invent the wheel????????

Dick Z

[Dylwad]

I think it's going to be impossible to get performance like a fixed bearing when you have to have clearance between the ballscrew and inner bearing races to allow axial movement.

If it was viable, it would be an option on the calcs and documentation

Sent from tapatalk