Re: [CAD_CAM_EDM_DRO] Re: Vacuum Table

On Monday 12 February 2007 20:28, turbulatordude wrote:

> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "cncnovice" <crcitser@...> wrote:
> > Group,
> > I have a 5ft x 5ft cnc router I built a couple of years ago. It has an
> > aluminum table, and I now want to add as a accessory a vacuum hold down
> > table of about 2ft(X) by 4 ft.(Y).
> >
> > Does anyone have any advice or plans that they would care to share?
> >
> > TIA,
> > John Champlain
>
> It is really simple to make such a table. the underlying table needs
> to be flat, and if you check think and tinker, I think they carry a
> foam that can be used for sealing the part.
>
> A shop vac should be all you need for larger parts, as the total
> surface area will potentially have tons of force.
>
> Even at 10 inches of water (1/3 psi) per sq inch, a 3 sq inch area
> would have one pound of force. That is about 50 pounds per sq foot,
> or for a 4x8 sheet, about 1,500 pounds.

--snip--


In a larger CNC router, you might want to have sections with valves, to only
apply vacuum to one section of the table.

As Mucha pointed out, you're going to have a ~1500 lb force due to atmospheric
pressure (1 atm = 14.696 pounds / square inch) pressing down the top of your
vacuum hold down table. You'll need to design internal bracing in the hold
down table to resist this, or it will implode (or more likely, sag a bit).

Regards,
-Sebastien Bailard