Re: [CAD_CAM_EDM_DRO] Affordable ball screws

"Scott M. Thomas" wrote:

> I agree that oil collection would be an interesting problem.
>
> How would this compare to the crankshaft, connecting rod and camshaft
> bearings in an automobile engine? They exhibit relatively loose tolerances
> and still maintain the hydrostatic effect.

These bearings are hydrodynamic, not hydrostatic. They work due to the
rotation of the journal in the bearing. This is like the lathe spindle bearings
that have an oil drip cup that supplies maybe one drop per minute of oil.

That is very different from a bearing that may stop and reverse direction,
or just move very slowly, and still needs lube protection. the closest thing
in an IC engine is the wrist pin and connecting rod top end, which don't
have anything close to continuous rotation. I know that there are some
tricks related to microfinishing of the pin that help in this area.

Hydrostatic bearings require very thin layers of the lubricant fluid and some
other tricks to make them stable. A standard car crankshaft bearing would
probably just jump to one side, or maybe rattle, if you tried to make it work
as a hydrostatic bearing, and keep the bearing flying over the journal at
zero speed. This is the condition that the bearings of a machine tool axis
works under, however, slow or no movement, but it has to be stable and
resist cutting forces.

These are used in some high-end machines for the way slides. I've never
heard of anyone actually making a hydrostatic screw and nut, but it is at
least feasible.

Jon