Vacuum press idea

[Rounder]

I asked a buddy of mine to help me build a vacuum press. As we were discussing it, he suggested using one of those storage bags you see on TV. The one that you put clothes in and attach a vacuum cleaner to.

Would that work as a vacuum press for woodworking?

[gmack5]

The Bag might work, but IMHO, you'd be hard pressed to get a vacuum (cleaner) to pull enough of a vacuum to do the job properly. YMMV

[Rounder]

That is what I thought also. I have an extra vaccum motor in my shop that I use as a leaf blower.

[Pappy]

How well do those bags hold a seal? For a press, you are talking about holding a couple of atmospheres.

[LCHIEN]

quote:Originally posted by Pappy

How well do those bags hold a seal? For a press, you are talking about holding a couple of atmospheres.

Its real hard (at least on this planet) to get a vacuum of more than 1 atmosphere.

[LCHIEN]

quote:Originally posted by gmack5

The Bag might work, but IMHO, you'd be hard pressed to get a vacuum (cleaner) to pull enough of a vacuum to do the job properly. YMMV

A vacuum cleaner does a fair job at pulling a vacuum. You've
seen those ads where the hose is used with a funnel to pick up a bowling ball.
The problem is that most of them depend on the air being moved to cool the motor. Pulling against a dead end load for a long time could burn up the motor. There's a few vacuums that have fan cooled motors, I think the Feins have it.

[rbfunk]

We use those bags (Space Saver) for storing clothes. They will hold a vacumm for 6 months atleast. I don't know if you'll get enough pressure but they're not that expensive that you couldn't try a small one. I think you might have more problems with the bag wrinkling then any thing else. IF you can get it smooth and only pull half an atmosphere, you'll still have about 7 PSI. I think you can pull a little bit more then 1/2 but you won't get a complete vacumm. The bags have a one way valve so you don't have to run the vacumm continuosly.
Bob

[WEG]

"Its real hard (at least on this planet) to get a vacuum of more than 1 atmosphere." -Loring

Hey,Loring; It's real hard to get a vacuum of more than 1 atmosphere on any planet!

WEG

[rbfunk]

Got some hard numbers. I am watching a tivo'd Wood Works episode and good ole' Dave Marks just mentioned that he gets 1500 pounds per square foot on his vacumm press. That works out to 10.4 PSI or 70% of a total theoretical vacumm. Now all we need is some specs on vacumm cleaners.
Bob
P.S. If anyone wants to check my math or correct my spelling, please do. They where my 2 worst subjects.

[boblon]

I've often wondered about those bags also. I've never held one though. To those out there that might have one..

How tear resistant does the material it is made out of seem?

Vacuum pressing would involve shaping tightly around corners and edges, will it hold up?

Thanks,
BobL.

BTW..I'm going (slowly) along these lines

http://www.joewoodworker.com/veneering/welcome.htm

I'm going to start with a venturi I already have. Haven't been able to get a good deal on a pump yet.

[LCHIEN]

quote:Originally posted by WEG

"Its real hard (at least on this planet) to get a vacuum of more than 1 atmosphere." -Loring

Hey,Loring; It's real hard to get a vacuum of more than 1 atmosphere on any planet!

WEG

I was thinking that the atmosphere of large planets was much denser than therefore PSI than earth's.

But reading the planetary info on the web it appears that a planet like Jupiter or Saturn is pretty much gas all the way down, there's no sold boundary you can call the surface. Somehwere at the core is liquid hydrogen apprently.
So when you read the diameter of a planet like Jupiter they conside the diameter to be the point where the atmospheric pressure is
equal to 1 earth atmosphere.

So I think you're right.

I also read that at one time the earth atmosphere was 20 psi
but some of it has boiled off into space.

[Jim Boyd]

1 bar = 14.7 psi or 1 atmosphere
A really good a/c vacuum pump will only get around -29 inches of mercury.
At sea level atmosphereic pressure is 29.92 inches of mercury. So it can't be that hard can it?
Standard Atmosphere Tables

[Thom2]

While I haven't done any vacuum press work yet, I have been using vacuum quite a bit for a clamping jig I made and have done quite a bit of research on various things, one of the best sources for info that I've found is this site www.qualityvak.com

from their faq section ... https://www.qualityvak.com/faq.html

How is vacuum measured? Vacuum level is usually measured in terms of inches of mercury (“Hg). This is the same term used when the weatherman reports the barometer reading “the barometer is 29.21”Hg and falling”. The maximum vacuum that can be achieved on a standard day is 29.91999.

Inches of water is another term used to measure vacuum where 1"Hg = 13.6"H20. Inches of water is normally used when measuring low vacuum or air pressure. Vacuum can also be measured in torr, microns, mbar, atmospheres, however, these terms are not usually used in the woodworking area.

Your elevation from sea level affects the amount of vacuum that can be achieved. A rule of thumb is to subtract 1"Hg for each 1000' above sea level. Thus if a pump normally reaches 27"Hg at sea level, then in Denver (5000' above sea level) it will only get 22 - 23"Hg.

Now with that in mind, I've been using a HF $9.99 air powered vacuum pump that I gutted and removed the venturi assembly. Then I plumbed that for my specific application. I'm achieving about 24" or so of vacuum which roughly equates to 12psi (2" of vacuum roughly equals 1psi) That equates to 1728 lbs. applied EVENLY across a sq. ft. With a shop-vac, I was hard pressed to pull even 6" of vacuum, but that STILL equates to 432 lbs. per sq. ft. (which IMO still isn't too shabby)

Now in answer to George's question, I do have a feeling those bags will indeed work, it's actually been discussed in the chat room already, although I'm not sure what kind of life span you can expect from them. They may leak down a little, but that only requires keeping an eye on them and reapplying vacuum from time to time. One of the things that I would do is buy this fitting from JoeWoodworker's site ... valve stem assembly... and use that to connect your vacuum hose to the bag assembly, another thing to be SURE to buy is a check valve for the vacuum line. With a check valve, you'll only need to run the vacuum pump long enough to achieve full vacuum, then occasionally to reapply vacuum as it leaks down.

Well I hope something out of this long winded ramble proves to be of some help, give a yell if you have any questions or if I can clarify anything further. I will say tho', between qualityvak's website and JoeWoodworker's website, there's a lot of good reading there that pretty much covers just about anything you need to know.


Thom
just a ramblin' man in PA

[WEG]

Loring; C'mon, it's a joke! The atmosphere on a planet is the atmosphere on a planet. Can't get more than you got! Atmosphere's aren't measured by Earth Atmosphere. They might be compared to Earth's atmosphere, but you can't get more than you got!
Have a good week...and keep the Funk and Wagnall's handy.
WEG

[rbfunk]

quote: and keep the Funk and Wagnall's handy

Hey! I resemble that remark!
Bob (who never meet a Wagnall)