Re: [CAD_CAM_EDM_DRO] Affordable ball screws

Sven Peter wrote:

> >
> > Nic van der Walt wrote:
> > .... If you can somehow drill a couple
> > > of small
> > > oil feeds around the centre line of the nut and then pump high pressure
> > > oil through
> > > it you form a pretty good imitation of a hydrostatic bearing.
>
> Dear Sirs.
> My little experience from having changed some 5 or 8 ball screws on
> different machines is following:
> In a bearing factory I see the case that the screws get pitch damages.
> The contact area of the balls to nut and screw are only spots. Each time
> there is a G00 movement acceleration is incredibly high and the
> carriages inertia gives a hit to the ball contact points. In batch
> production that are always the same points. Pressure oil feed is good

I'm pretty sure the original poster was thinking of a hydrostatic nut
retrofit to an Acme screw machine. I think it is a pretty crazy idea, and
would require hundreds of micro-sized holes drilled in the faces
of the thread to work. Just squiring oil into an Acme nut will not turn it
into a hydrostatic bearing. You have to establish a fluid film under high
shear in the space between the two surfaces, and a nut's threads
are a complicated geometry to do this in. If the whole nut was a very
tight fit against the screw, both at minor and major diameter as well as
at the flank of the thread, then it might be possible to just squirt oil in
the middle. This might work with a cast (a la Moglice) nut. Oil collection
would still be a complicated problem, as the screw would likely be
dripping along its length.

Jon