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CNC Vacuum table

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Unread postAuthor: evilvet » Wed Mar 20, 2013 5:55 pm

Thanks anyway, appreciate the effort
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Unread postAuthor: Zeus » Thu Mar 21, 2013 4:30 am

Yeah, all the HPLCs I've seen are pretty anemic, I reckon an air con compressor is the way to go.
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/sarcasm, /hyperbole
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Unread postAuthor: jimmy101 » Mon Mar 25, 2013 3:39 pm

Have you thought about how much vacuum you actually need?

To hold something in place there is a point of diminishing return. The difference between an OK hard vacuum pump and a spectacularly expensive one is zero (in this application), except for cost.

You might not need more than a couple inches of vacuum, which a shop vac will do. One inch of vacuum (low pressure side at ~13.7 PSIA) will apply 144 pounds of force to a 12"x12" object. The shop vac has the advantage that it is designed to move a lot of air.
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Unread postAuthor: evilvet » Mon Mar 25, 2013 4:49 pm

Indeed a fair point.
It's frightening when you work out the air pressure on something as familiar as your dining table, in my case about 20 tonnes.

What I am going to start with is this
extracting against a length of 100mm PVC pipe. I ordered this to go with it

I got the pump of reduced price and free freight as I was ordering other bits.

100mm I/D PVC pipe @ 1000mm long = 7.85 litres of vacuum chamber as a reservoir against leaks, the volume under the work piece is probably somewhere around 50ml

All the bits should be in the shed by the end of this week.

The pump can pull 16" of vacuum, 0.535 ATM and do it at 12 litres per minute so evacuating the chamber won't take long.
Ball valve leads to the vacuum clamp itself, another ball valve vents to the atmosphere to dump the tank and release the clamp.

Assumed work-piece is 300mm x 300mm = 0.09 sqm

Assuming 100% efficiencies then that gives me:

0.535 ATM = 0.55Kg / cm2 = 5,500Kg /sqm

0.09sqm work area = 495kg force.

That's half a tonne to hold down a plate while I engrave it. I reckon it might just do the job.

Photos and video as soon as the kit arrives.
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Unread postAuthor: RBurke83 » Mon Mar 25, 2013 5:13 pm

I dunno about shipping, but Harbor Freight is advertising a cheapo vacuum pump for 15.00$. Pulls 28"Hg, 4.5CFM@90 psi. Their other pumps are 90.00$ and 140.00$
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Unread postAuthor: evilvet » Mon Mar 25, 2013 5:28 pm

And only $77.95 USPS international shipping, sounds like a bargain :D
Not all of us on the forum have the luxury of CONUS purchasing :P
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Unread postAuthor: jimmy101 » Wed Mar 27, 2013 6:06 pm

Sounds like that pump will work. A shopvac or household vac would probably work as well even if they only pull down to 13~14 PSIA but they are probably a lot noisier. Those vac's probably don't need any kind of a reservoir since they move so much air.

What are you gong to use as a gasket and how many holes on the platen?
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