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gobler
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jegner
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 Posted: Mon Apr 23, 2007 8:28 pm Post subject: |
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Cool!
I don't know much about vac-pumps, but that one looks the business!
Jim |
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gobler
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| Posted: Mon Apr 23, 2007 9:04 pm Post subject: |
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Well it's a 7CFM 2 stage and pulls 15 micros  And Stomper mentioned it's one of the better brands so I'm quite stoked.
Cheers,
Jeff
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Stomper
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Location: Woodburn, Oregon USA
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| Posted: Mon Apr 23, 2007 10:47 pm Post subject: |
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HOLY SMOKES!!!! You got a DEAL on that!! That is the same one I use out of my service van.... you won't regret getting that pump! 
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Tony Krewson
FEAR... is not my god!! |
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gobler
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| Posted: Tue Apr 24, 2007 12:59 am Post subject: pressure valve?? |
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OK here is a question. I will be using this pump (for the time being) as both Vac table pump and for my degassing chamber. Is there a flow (pressure) valve to control the micron level? I only need 28-29 for degassing and I don't want to collapse my chamber. Also, should I get a filter unit?
Cheers,
Jeff
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Stomper
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Location: Woodburn, Oregon USA
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| Posted: Tue Apr 24, 2007 7:29 am Post subject: |
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I have never seen any such controlling device for a vac-pump like we're using. You won't be getting down to 29-25 microns in the blink of an eye, so I wouldn't worry about it collapsing your chamber.
one micron is one MILLIONTH of a millimeter, and you are talking 29 MILLIONTHS of a millimeter of the mercury column.... that's just about as close to an absolute vacuum you are going to get on this planet w/o a vac-pump the size of a truck! 
What are you using for a vac-chamber? Can you post pics of it? I'm wanting to build a 2' x 2' x 4' chamber out of 3/4' or 1" thick acryilic slabs epoxied together in a box.
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Tony Krewson
FEAR... is not my god!! |
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gobler
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| Posted: Tue Apr 24, 2007 12:15 pm Post subject: |
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No pics yet, just picked up my chamber yesterday. It's a piece of schedule 40 PVC pipe 16' Diameter by 18" high. The wall is a good 1/2 inch thick and I will (depending on the cost) use a 2" thick 18' x 18" piece of PVC board for the base and a sheet of Polycarbonate 1/2" thick for the top (lid). It's big enough to put a 5 gallon bucket into with room to spare. I will be taking photos of the build to share and help out any one who may have questions.
Cheers,
Jeff
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drcrash
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| Posted: Tue Apr 24, 2007 1:12 pm Post subject: Re: pressure valve?? |
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| gobler wrote: | OK here is a question. I will be using this pump (for the time being) as both Vac table pump and for my degassing chamber.
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The difference between 28 in. Hg and a perfect vacuum isn't much in terms of the stress on a vacuum vessel---there's already so little pressure on the inside that the inward pressure is almost a whole atmosphere. If your vessel can take 15 psi pressure, you're good, no matter how hard the vacuum is.
For vacuum forming, the difference between taking 90 percent of the air out and 99 percent isn't a big deal---the differential pressure on the plastic is only about 10 percent higher. For degassing it's a bigger deal, because it makes the bubbles 10 times bigger, so that even very tiny bubbles inflate enough to float up out of whatever goo you're degassing.
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Paul (a.k.a. Dr. Crash)
Tired of buying cheap plastic crap? Now you can make your own! www.VacuumFormerPlans.com |
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gobler
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| Posted: Tue Apr 24, 2007 2:00 pm Post subject: |
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That's good to know. Does anyone know what the tolerance of .5 x 18"x18" Lexan (Polycarbonate)? Is it strong enough to withstand the vacuum with a surface exposure of 16"x16". Or should I use 1" acrylic? I know this is the VacForm section but...it does involve vacuum
Cheers,
Jeff
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drcrash
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| Posted: Mon Jun 18, 2007 7:14 pm Post subject: |
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| gobler wrote: | That's good to know. Does anyone know what the tolerance of .5 x 18"x18" Lexan (Polycarbonate)? Is it strong enough to withstand the vacuum with a surface exposure of 16"x16". Or should I use 1" acrylic? I know this is the VacForm section but...it does involve vacuum
Cheers,
Jeff |
Did you ever find an answer to this question?
Given those choices (1/2" polycarbonate vs. 1" acyrilic) I think I'd go with the 1" acrylic. Unless polycarbonate is way, way stiffer than acrylic, it will flex less. (And be less likely to get to the point where it breaks.)
For a given material, stiffness is generally proportional to the cube of the thickness, so 1/2" plastic will flex 8 times as much as 1" plastic. So the polycarbonate material would have to be 8 times stiffer than the acrylic material to give the same effective rigidity.
I noticed that the vacuum chamber on the BJB web site uses 1" acrylic for the lid, across the chamber's inside diameter of 13.5". I don't know if 1" is enough for a 16 inch span. (Especially if your chamber is square, not round.)
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Paul (a.k.a. Dr. Crash)
Tired of buying cheap plastic crap? Now you can make your own! www.VacuumFormerPlans.com |
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