Re: [CAD_CAM_EDM_DRO] Machine base question

David G. LeVine wrote:

> Has anyone used or considered air bearings running against a surface
> plate as a support for a gantry?
>
> I assume with small clearances they should be pretty stiff when two
> opposed bearings (on opposite sides of the plate) work against each other.
>
> Comments, thoughts, etc ate all welcomed.

Surface plates generally have only one precision surface. The
sides are usually ground fairly square to the top, but not
parallel to each other. This is how the axis beams on an
Excellon PCB drill work, but those beams are ground parallel to
insane tolerances. If you can get a plate with parallel sides,
and they need to be REALLY parallel, like .0001" deviation
across the length of the sides, then it should work. You can
also set it up so that the slider pads set down and lock the
axis when motion is not wanted, and lift up and float when the
air is turned back on. You need to be able to machine, lap or
scrape some very flat slider plates. Using the surface plate as
a reference, you can just lap the sliders on diamond-coated
plastic polishing sheets, or embed diamond in brass shim stock
and lap on that. The sliders should have a 1" diameter recess
in the middle to distribute the air. This can be .005" deep or
so. They need to be truly flat, so the lapping has to be done
very carefully, or you end up with convex sliders that rock and
let the air escape.

Jon