Re: [CAD_CAM_EDM_DRO] Affordable ball screws

Jon Elson 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.
> >
> > Same thing can be done with the guides etc..
> >
> > One ebay I see a lot of 12V and 24V hydraulic pumps for tailgate lifts
> > etc. selling
> > for peanuts. They should work well for something like this.
> >
> > If you can get enough oil pressure inside the nut you don't have a metal
> > to metal situation
> > anymore, and the wear and friction drops to virtually nothing. The oil
> > can also take up
> > most or all of the backlash if done properly.
>
> There are hydrostatic bed machines that use the same principle to lube the
> ways. They have oil dams, collector galleys and scavenging pumps.
>
> Jon
>

Dear Sirs.
My little experience from having changed some 5 or 8 ball screws on
different machines is following:
Normal wear on the screw you get only when the nut wiper gets clogged up
with chips.
More likely you find these two reasons.
When the nut wiper gets worn chips may get in and get literally smooth
ironed, leaving a few holes in the screw, deforming the balls, wearing
the nut and tightening the nut by debrids.

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
only on bearing areas, not spots. So on each hit microscopic particles
get cold welded to the balls surface and torn of. After 2 or 4 years you
get holes on those spots. And we have to change the screws that are in
perfect condition on 99,8% of their surface. But they make horrible
jumps right within the ball bearing groove.

Those Fanuk lathe controls have ramp adjustment only on G01- not G00
movements. So after the clients started to use G01 on short fast
movements and G00 only on long movements things became much better.
That are only my 2 cents.
Best wishes
Sven Peter