Re: [CAD_CAM_EDM_DRO] Affordable ball screws

bjammin@... wrote:

> So the idea that oil fims would not form in a plain nut/screw combo because
> it may reverse is 180 deg out. Also way out is the idea that these combos
> will not serve hydrostaticaly under a steady oil supply, when in fact they
> serve hydrostatically under just being dosed with an oilcan now and then.
> In short, if you have oil and two parts moving relatively in it, a
> hydrostatic film always and inevitably forms and there's nothing you can do
> about it at least up to pressures on order of 2-3000 PSI.
>
> >Hydrostatic bearings require very thin layers of the lubricant fluid and some
> >other tricks to make them stable.
>
> Really, once you're above boundary layer thickness, there are no
> hydrostatic bearings.
>

Just trying to put this in context of a precision positioning system, the problem
with excessive clearance in the nut/screw interface is it will allow the position
to drift under load, without movement of the screw. The lube fluid here is not
specifically for wear tolerance, but for predictable positioning and zero backlash.
(Now, of course, ballscrews have been providing this service for years, are
well understood, and can be bought off the shelf.) It would take a low viscosity
fluid operating in very thin layers to meet this goal - ie, minimal change in film
thickness whether the screw is turning or stationary, and whether the axial
load is small or large. This whole thing is theoretical, I suspect, because the
difficulty in making the nut work properly sounds like a great master's thesis
topic, if not a doctoral dissertation.

Jon