Re: Ballscrew balls ?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, figNoggle <david@...> wrote:

>interesting, what kind of ballnuts have different sized balls and why?

Hello,

Higher grade (ground) ballnuts use two sizes so that the balls rolling
the "wrong" direction are not load bearing.

Think about it, in the loaded state, a given ball is rolling against
both its neighbor balls AND the housing. Causing sliding when all
balls are the same size. Now sliding is a VERY bad thing where
efficient motion is concerned...

If every other ball is smaller, then the ones going the "wrong way" do
not slide against the housing, only their neighbor balls. Sliding is
reduced.

With the cheap load-bearing-grade ballscrews and nuts we often find
being used in DIY-CNC, the balls and housings themselves are so
inaccurate as to make this two-size ball loading all but useless.

But you CAN improve things greatly by using oversize balls and running
them in, and then re-loading with fresh--oversize--balls. It's a very
good way to maximise the effectiveness of your inexpensively purchased
components...

Hope this helps,

Ballendo

P.S. The ball nut housings--and linear bearings--use a "gothic arch"
form rather than a semi-circular one for the same reason; it
prevents/minimises sliding and promotes rolling. Golfers understand
this from putting!<G> (Masters week, why not<G>)

And keep in mind that the round balls themselves become ovoid under
load...