View Full Version : DIY Bell Jars / Vacuum Chambers


Jim Lafferty
February 7th, 2005, 11:33 AM
This might prove to be the right way to create a bubble-free microwax adapter:

First, there's a hand-pumped vacuum (http://scientificsonline.com/product.asp_Q_pn_E_3071338) for people who don't want to build their own from Edmund's at $90.

Then there's this article (http://www.sas.org/E-Bulletin/2001-12-07/features2/features.html).

This page (http://www.belljar.net/) looks to be a huge resource on the subject.

Another general site (http://www.ee.ualberta.ca/~schmaus/vacf/index.html).

This Canadian site of suppliers (http://www.ee.ualberta.ca/~schmaus/vacf/supps.html) might be promising for some with the green.

Some things to learn here (http://www.bnglifecasting.com/diy/chamber/) -- ideas for cheap components.

Lastly, there's this (http://www.berkut13.com/sucker.htm).

- jim

Frank Ladner
February 7th, 2005, 01:33 PM
Jim,

I'm about to check some of the links out, but I wanted to ask a question that I've been wondering since the vacuum devices were mentioned: Would this work with hot wax? Even if the device (what material?) could withstand the heat, what about when the wax cooled and hardened?

Keith Kline
February 7th, 2005, 02:26 PM
The vacuum chamber I'm borrowing is a diy one. We're in the process of putting together another one somewhat larger right now. I'll post some pics of the new one's progress. There's a few pieces I'm not sure the price of yet, but I think the whole thing can be put together for less than $50. Actually cheaper if you're a good scrounger. I'm on my way now to pick up a compressor so I can test it out. I still need to pick up some glass for mine tests, but I might just heat up the bit of wax I have to play around with a check to see if it'll pull enough of a vacuum. I'll post some picks this week hopefully when I get the glass and more wax.

Keith Kline
February 7th, 2005, 02:30 PM
Almost forgot. My friend that built this one has a tutorial online for it showing how he built it for anyone interested.

http://www.clevelandfx.com/crazylou/tutorials/vacuum.htm

Pretty simple stuff actually. The only thing I worry about with some of the ones posted is the plastic or rubber on the bottom where the container with hot wax would be. The ones like this are the opposite orietation of those so the bottom is stainless steel so the heat will have no effect.

Jim Lafferty
February 8th, 2005, 12:19 AM
I think in principle there are ways you can be smart about it and make sure the melted wax won't be a problem. For instance, many of the DIY designs sport a jar over a flat surface that has the vacuum port at the bottom. You could make this bottom plate out of something heat resistant, and the jar itself would have to be alreay very durable -- but that's somewhat beyond the point if you think about putting the melted wax inside a container that is then itself put inside the vacuum chamber.

The setup I aim to use will be melted wax in a borosilicate beaker, that is then transferred inside the bell jar. The jar would have to be sufficiently large to house the beaker, obviously.

For those who haven't use microwax yet -- once you get it fully melted, it doesn't beging to harden for quite some time, and for a long while it only hardens at the very top. So, in theory, transferring a beaker with melted wax and glass sandiwches into a vacuum chamber, then running the bubbles out of the wax shouldn't pose problems from a timing standpoint. Borosilicate beaker are naturally tempered and shouldn't crack -- you could (in theory) even use one for your vacuum chamber :)

- jim

Greg Boston
February 8th, 2005, 03:09 AM
Gentlemen,

I can supply you guys with whatever information you need about vacuum systems. I have a 25 year service record in the semiconductor industry as an equipment maintenance technician in the 'hivac' division. Meaning, I work on machines who's process pressures are in the 1x10-9 torr vacuum. We have to find leaks with a helium leak detector. The only other molecule small enough to get through such tiny leaks is hydrogen which is of course too dangerous. Photography, videography, and music are my side passions to serve my creative needs.

If you decide to start playing with cryogenic liquids such as liquid nitrogen, make DARN SURE you heed all safety advice. Especially in terms of not sealing the container and keeping it off of yourself. Many things behave differently when exposed to such temperatures. I have taken rubber gloves and poured liguid nitrogen in them as a demonstration to newer techs. Throwing the glove on the floor will make it shatter like glass.

Don't try some of these things without help unless you have a good fundamental knowledge of vacuum theory and physics in general. That's who those articles are aimed at.

Just be careful. We value our DV-INFO members and it's not worth getting hurt or killed trying to 'roll your own' adapters.

Best of luck,

=gb=

Jim Lafferty
February 8th, 2005, 10:04 AM
Greg,

Thanks for the heads-up, the emphasis on proceeding cautiously.

It was only after posting the initial links that I went back and read them through thoroughly. I, for one, will not be using liquid nitrogen. No thanks.

However, the dangers of an implosion should be pretty obvious to anyone attempting to build and operate one of these things using a hand or motorized pump. At my end, I plan on overkill with the density of the materials used.

As is said on the one site (http://www.bnglifecasting.com/diy/chamber/):

More acrylic sandwiched together makes the lift-off top for the chamber. This is a bit under an inch thick; probably more like 2cm. As before, I have no idea if this is overkill, gross overkill, or riding the ragged edge of disaster. On the other hand, it hasn't failed in well over a hundred cycles, and it doesn't show any signs of cracking or strain...

I intend on going to Canal Plastics here in NYC to have a lot of my components custom cut and drilled -- the top at the very least, but depending on what they've got, possibly the jar itself. When things come together, I'll let everyone know what I'm using -- they even have numbers for a given type/density/color of plastic.

If I can't get a good plastic or glass jar, I'll use a metal one like shown on the other site -- whatever the case, I'll err to the side of overkill.

edit: A question for you, Greg:

When looking over these tutorials, I notice the mercury valve component -- is this something really needed for our purposes? What we're trying to do is relatively innexact, and doesn't need to be a fancy vacuum setup -- shouldn't it be possible to just create a good seal in a chamber, and run a vacuum pump to a certain level of pressure, or is this mercury component needed to complete the loop somehow?

- jim

Greg Boston
February 8th, 2005, 11:38 PM
<<<-- Originally posted by Jim Lafferty :


edit: A question for you, Greg:

When looking over these tutorials, I notice the mercury valve component -- is this something really needed for our purposes? What we're trying to do is relatively innexact, and doesn't need to be a fancy vacuum setup -- shouldn't it be possible to just create a good seal in a chamber, and run a vacuum pump to a certain level of pressure, or is this mercury component needed to complete the loop somehow?

- jim -->>>

Jim,

It probably isn't that critical for what you are trying to accomplish. However, it's a good thing to know what your vacuum level is, so that you'll know if you have a leak. A good way to find vacuum leaks at rough vacuum pressures is with good old rubbing alcohol. When it penetrates a leak, the pressure will rise for a bit until the alcohol is pumped away. Being a solvent, this won't take long.

By the way, sandwiching three or four layers of plexiglass together with epoxy is good enough for high vacuum applications. I know cause I had to do this as an emergency when we broke a site glass (viewport) in the middle of the night. My plexiglass replacement was still working years later when they finally took that tool out of production.

I just looked at the Edmunds $79 hand vacuum pump. Do yourself a favor and go to your local auto parts store. They sell the same pump for a lot less money. It's for testing and actuating vacuum operated components on your car engine. I've got one out in the garage in my toolbox.

-gb-

Jim Lafferty
February 9th, 2005, 12:12 AM
Wow -- great! Thanks for the response :D

Rob Lohman
February 9th, 2005, 06:54 AM
One thing I have been wondering is why you/we/they would need
such a system and how exactly would you accomplish that thing
you need to (with this system)?

Jim Lafferty
February 9th, 2005, 07:37 AM
To make a very thin, bubble-free layer of microcrystalline wax sandwiched between two pieces of glass. The thinner the layer of wax, the more difficult (near impossible) it is to get the bubbles to leave.

My method will be -- in a beaker, heat the wax to melting with the glass sandwich already in place, submerged in the wax vertically; put the entire beaker in a bell jar, apply a vacuum; wait for the bubbles to stop appearing on the wax's surface; let the wax cool to a semi-solid and bring the glass sandwich out; clean it.

Bob Hart
February 11th, 2005, 10:08 AM
You could always use the vacuum port on your car for a vacuum source.

You may not need anywhere near a total vacuum to pull wax up between two sheets of glass. What it will do is make any entrained air bubbles become larger and hopefully move through and out of the panels as more wax is pulled through.

You won't want to pull too much vacuum. It may distort your glass disks and vary the wax thickness.

Jim Lafferty
February 11th, 2005, 11:53 AM
Well, next week I'm working one less job, with some freelance work behind me (finally). With that I should have some time freed up to finally try this out. I'll let everyone know the results, naturally.

Thank for the advice, Bob.

- jim

Bob Hart
February 11th, 2005, 10:36 PM
An added thought or two.

Any dissolved gases or gases created by the heating of the wax are going to keep on being generated as the wax moves thorugh the glass sandwich unless the molten wax is kept molten under vacuum for awhile before you pull it through the glass. Any moisture or vapors are going to come off during this process as their boiling points are going to be significantly lowered.

I would suggest reducing the wax temp before the draw-through so that during the draw-through, remaining potential gas pockets in the wax do not vaporise on the way through the glass sandwich.

I would also be inclined to provide for submerging the glass sandwich afer draw-through and restoring atmospheric pressure before the wax sets. By this means, hopefully any pinpoint entrained gas bubbles will compress to almost invisibility. This hopefully will also take care of mechanical distortion of the glass disks.

Under vacuum some of the volatiles in the wax are probably going to continue to come off during the entire operation. If the process is prolonged, maybe the physical character of the wax itself will be changed detrimentally, however it is up to the chemists among the dvinfo population to correctly predict that one.