Re: X axis load cantilever?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "ghidera2000"
<ghidera2000@y...> wrote:

> I've just spent a few hours with pencil and paper, doodling out

some

> layouts for my (theoretical at this point) PCB mill/drill. I want
> to have roughly 18" x 18" usable area, for the Y and Z its not a
> problem (gantry style) but for the X axis I figure I'll have to get
> MUCH longer leadscrews and rails. But how much longer?
>
> If I fully support the 18x18 X-axis table with say, 6 linear
> bearings, one in each corner and one in the middle, I'll need a X-
> axis length of roughly 36" + bearingwidthsetc in order to access

the

> entire PCB. I can shorten that by pulling the corner bearings
> towards the center and letting the ends of the table hang in the
> air. If I used something like 1/2" aluminum for the table, how much
> overhang do you think I might be able to get away with? Keep in

mind

> I'll just be doing light work on this.
>
> I also considered a stationary table and moving the gantry - but
> that looks a bit scary... Have to use two matched screws and timing
> belts etc.

I think the term 'overkill' might be applied ?

If you move two bearings in a few inches, you can still get your
table movement with 4 bearings, no problem.

and, if you support under the X axis with some rollers/bearings, all
the Z force will be on the rollers, not on the rails. That makes the
load requirement for the Y axis much less.

Dave