Re: [CAD_CAM_EDM_DRO] Vacuum Table

William Scalione wrote:

> Anyone out there ever built a vacuum table for a cnc router? I am
> in the process of building a new larger router and would like to add
> a vacuum part hold down to it. I picked up a couple of vacuum pumps
> at the NC State University surplus today although I am not sure if they
> will work for it yet. They are nice units direct drive high vacuum lab
> units.

Don't ruin these pumps with vacuum table operation. These are 2-stage,
low volume, very high vacuum pumps. they also have extremely fine
tolarance parts inside, and will quickly be ruined by even a small amount
of dust. The inside of these pumps are totally coated with expensive pump
oil, and are run under an oil bath. This will trap dust particles in the
pump.
The pump oil needs to be changed frequently even under normal service, and
it is really expensive, like $150 / gallon! Also, they really don't move
much
air, just a few liters a minute.
What you need is a high volume, low pressure differential pump with no
close tolerances inside.

> What I need to know is what size and number of holes would
> I drill in a 4' X 4' table? I will probably add some valves to section
> the table off, possibly go back and get another pump and section it
> into thirds, one pump for each section. Use only the sections I need
> to, depending on the size fo the work. I was thinking of using an acrylic
> sheet maybe 3/4" thick for the table. Will it require a large O-Ring
> around the edge or will just the holes be sufficent? Any tips would be
> appreciated.

IF you are thinking of having the 3/4" acrylic support the full air
pressure,
it won't work. You would need something behind the acrylic to resist the
air pressure. Remember, only a 1 PSI difference exerts 144 Lbs / sq Ft,
so there wouls be 144 * 16 = 2304 Lbs over the 4 x 4' sheet! You will have
to build a substantial structure to resist the effort of the air to collapse

it. You will probably get somewhere around 5 PSI differential, giving over
5 tons of force on that sheet.

Jon