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Discussion Starter · #1 ·
A co-worker of mine had the fortune of buying this vacuum pump at auction for, I believe $35. Since people at MLS have suggested that I need a vacuum pump in order to properly cast windows, figures etc. I asked him if he would want to sell it. He asked if $100 would be too much. I have no idea what I'm even looking at, not to mention what features to look for. He said everything seems to work except the center valve, which he believes changes the pressure from negative to positive. Does this make sense?
I realize that this is probably severe overkill for my purposes, but I doubt (in my ignorance) that I could get much of anything for that price. I do believe he would probably take $75.
Anyway, I would very much like your opinion / input on what you would do in my situation.

Thanks,
Matt
 

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Matt

Here are a couple of ideas.
[*]Get yourself an old refrigerator compressor that still works, if one doesn't pull enough vaccum put two in tandem. [*]Or if you already have a fairly large air compressor already you might try the following. [*]Air vacuum pump from Harbor Freight
Stock# 3952-0VGA [*]McMaster-Carr / Through-Wall Cplg, 6mm Tube OD X 1/4" BSPT Female (if using a vaccum bag)
Part #51115K364
McMaster Carr [/list] [/list]
 

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Posted By SteveC on 02/20/2008 2:09 AM


Matt

Here are a couple of ideas.
[*]Get yourself an old refrigerator compressor that still works, if one doesn't pull enough vaccum put two in tandem. [*]Or if you already have a fairly large air compressor already you might try the following. [*]Air vacuum pump from Harbor Freight
Stock# 3952-0VGA [*]McMaster-Carr / Through-Wall Cplg, 6mm Tube OD X 1/4" BSPT Female (if using a vaccum bag)
Part #51115K364
McMaster Carr [/list] [/list]


The Harbor Fright site says the product is not available online or has been discontinued.  But I am still curious... what it the device?
 

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Charles

It was a venturi type vacuum adapter that attachés to an air compressor line and it has a ball valve that you can secure the vacuum line after pumping it down. It's been a long time that I've used it and I gave it to one of my friends who started doing automotive AC work, which is where I ran across the device.
 

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Discussion Starter · #5 ·
Hey Steve,
By your response, should I assume  that you are suggesting $75 is too much, or that this table is just not something you would suggest?

I should have mentioned, he said it will hold @ 18 lbs.

Never thought about the refrigerator idea. Of course, I'd have to research to even have the slightest idea on how to build one.

Thanks for your response and ideas.

Matt
 

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Matt

No not really, I wasn't suggesting that the price was out of line really. I'm just a natural born tinkerer and cheap thrifty. /DesktopModules/NTForums/themes/mls/emoticons/hehe.gif

Additionally, I'm not an expert on much of anything, but I see so much raw material being thrown away and it seems that no one is willing to expend the time and effort to take advantage of the opportunities that present themselves. Try doing a google search using the value 'cheap vacuum pump' and see what pops up.
 

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Matt,
It depends on the condition and the brand of the vacuum pump. I have 2 and both can pull at least 27 HG which is what you need if you are going to pump the air out of silcon mold ruber.
I would be careful using it for casting.
I use mine for a couple of seconds and don't let it go over 24 HG. The reason for that is that resin reacts quicker to the catalyst and that action appears to create gases. If you go for it and try to remove all the air, you will end up with a ruptured mold and a blob of harden bubbles like insallation foam.
What you really want to do with resin is to pressureize it.
I use a 3 gal pressure paint pot and place the mold filled with resin inside it and apply 60 psi of pressure to it.
Since a liquid cannot be compressed, and a gas can, the airbubbles are compressed to microscopic proportions. The pre vacuuming before the compression gets the big bubbles out, but not the tiny ones.
 

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Discussion Starter · #8 ·
Steve,
I understand, I like to tinker, and my wife will vouch for my being a tightwad thrifty person.;)

Richard,
I was hoping you would respond.:D So, if you were in my shoes, would you just get a paint pot, even though they are about the same price ( for a cheap one )?
Also, do you know why a pot would be warranted for painting, but not casting? Maybe it's just a liability thing, since it is designed for painting.

Thanks,
Matt
 

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Matt,
You still need a vacuum chamber to make the mold. Without it, you can't compress the casting resin. If you try, the tiny airbubbles that are left in the silicon rubber will colapse and you will end up with a ghoulish looking mutation (for a figure) or a funny set of windows.
Get yourself a good HG guage. You can get some good ones for about 6 bucks (if you are lucky on ebay) You still have to pay shipping on them. Take that guage to your friends house. Attach it to the vacuum pump with a valve to close the open end of the intake.
Start the pump up and then close the valve.
If it is a good one, then you should get at least 27 HG in a second after closing the valve.
If you get 25 HG make sure that there are no leaks in your plumbing and stop any that you find and restart.
Of course, that doesn't tell you how many cubic ft of air space it removes in what time.
Both mine go to HG 27 and remove 3 cubic ft of air in a minute. Slow, but fast enough for me since a 3 gal pot is about half that.
I have a couple of Thomas vacuum pumps. One double action and the other single.
Here is a link to the double.
http://cgi.ebay.com/3-5cfm-THOMAS-V...ryZ46548QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
The single doesn't evacuate air as quickly as the double, but works great as a vacuum clamp and a back up if the other goes out.
Sears carrys a good economic pressure pot for about 99 bucks. You can go online and have it sent to your local sears instead of paying for shipping.
You will have to convert the pot top by taking out the siphon tube and stopping the air output line up. Cost is about 12 bucks.
To use the same pot as a vacuum chamber you will need a 12x12 3/4 inch thick piece of acrylic (new, not used). Carfully drill a hole an inch and a half from 1 edge. I forget the diameter of the hole, but it will need to be the size required to tap the plastic to recieve the threaded pipe you will need to fit the coupler for your vacuum line. I use an regular M type tip and coupler. Use the coupler on the vacuum side, so that air can escape when you remove the line. Other wise it will take you a good hour to get your piece out, maybe much longer if you get a good seal on your threads and all.
 
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