Re: [CAD_CAM_EDM_DRO] Vacuum Table

>From: Jon Elson <elson@...>
>To: CAD_CAM_EDM_DRO@yahoogroups.com
>Subject: Re: [CAD_CAM_EDM_DRO] Vacuum Table
>Date: Sat, Jun 23, 2001, 5:23 PM
>

> 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
>
>
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