A Better Vacuum Chamber




About: Professional work in various electrical and mechanical fields, obscure sense of humour and typically willing to help... Currently under contract designing environmental monitoring equipment.

If you look back upon my previous work you will find that I have been experimenting with vacuum metal deposition.

I have been attempting to vaporize metal and have it coat glass under a vacuum. There will be more on this once I get the process working flawlessly.

Ideally this is done under a very deep vacuum using a diffusion vacuum pump.

I am attempting to do this without the use of a diffusion pump.

The vacuum chamber that I have been using is showing signs of melting and burning which to say the least is less than ideal for the task at hand.

The first problem is the type of material used for the chamber base. The second is in dealing with the heat generated and the third is the vacuum seal.

I have come up with a solution to all three in the most unlikeliest of places...

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Step 1: SAFETY!

This experiment has some risks that you should be aware of!

The first is that it is not electrically grounded. It is best to not touch the chamber assembly while it is operating. This experiment uses a variable transformer connected to a step up transformer(240V 15A).( these are not shown here but will be discussed in another Instructable)

The second is that the glass jar shown is not safety rated for a vacuum. It is a very thick wall preserving jar. If you want to try these experiments it is best to have a vacuum shield while running under a vacuum. Mine was removed for the pictures.

The third is that the first time you see metal actually bonded to glass you may become addicted!

Step 2: Out With the Old

The original base was constructed from a thick piece of ABS plastic that was drilled and sealed with 2-ton epoxy resin.
The electrical components were brass rod and brass screws.

The element shown is a 3 wire tungsten pre-formed piece from Lithuania (eBay)

As you can see after several heating cycles the base is charred and melted. The epoxy shows signs of cracking.

Not to mention that the .190 Torr vacuum took over 30 minutes to achieve, despite using a 6CFM 2 stage vane type pump.

The electrical connections are clamps to the brass rods protruding from the side.

All that this base now produces is a pre-layer of soot thereby preventing the adhesion of metal to the glass.

Step 3: The IDEA!

I have to admit it took me quite a while to sort out how to achieve an electrically insulated vacuum seal through a metal plate.

Then it hit me!  A non resistive automotive spark plug!

The plug needed slight modification to be able to connect the electrics to both ends.

I chose to braze a 10-24 brass nut to the business end of the plug and use the plug wire connector end as a raised connection for the chamber element.

First carefully cut some if the threaded end off to expose the ceramic core jacket. This will allow for the space to braze a nut to the copper core.

place the nut and plug in a vise as shown the braze the nut to the core as shown.

It might be a good idea to make sure that the plug and nut combination still has 0 resistance with a multimeter.

Step 4: Get the Materials

I chose to rummage through the scrap bin the the local metal recyclers.

For a vacuum chamber, the ideal material is stainless steel.

I found various pre cut shapes and flanges.

The main plate is a 6 inch square plate the riser is an exhaust pipe reducer and the flange is a SCH 40 pipe flange. Total cost $1 per pound.

Step 5: Plan and Drill

I needed to make room for the electrical connections and possible future connection to a diffusion pump. (should I choose to).

The center hole needs to be large enough for rapid vacuum and small enough to provide a stable working surface. I chose a half inch drill for this.

The spark plug holes need to be 9/16 inch for a frictionless fit. make sure to leave enough room between the spark plugs and riser pipe for electrical insulation.

Use a small bit first and relatively slow speed. gradually increase bit size, this will greatly decrease drilling time. I used 3 different bits in this step. Once drilled the holes need to be de-burred and cleaned.

Any areas to be brazed may need to be cleaned with a wire brush.

Step 6: Assemble

First braze the flange to the riser pipe.
Set aside to cool.

Next braze the spark plugs to the top of the vacuum plate. Be sure to have the plugs aligned for ease of electrical connection.

Turn the plate over then braze the plugs to the bottom sise of the plate. This will ensure an air tight seal. Remove any glass left over from the brazing operation. This can be done with a wire wheel.

Next braze the riser pipe in place at the center of the vacuum plate on the underside of the plate.

Again remove any glass with a wire wheel.

Step 7: Enjoy

Make the electrical connections.

I placed the vacuum plate and riser assembly on my standard vacuum base which is connected to a 6CFM Ritchie 2 stage vacuum pump.

I am using the same tungsten element from eBay.

The metal being vaporized is copper from an old wire.

The transformer connections are 8GA wire with crimped eyelets. These are held in place with 10/24 brass screws.

Using the same jar as before, it took less than 4 minutes to achieve less than .100 TORR!

The glass shows minor copper deposits which are bonded!

More experiments to follow!

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    24 Discussions


    6 years ago on Introduction

    Great Instructable and quite ambitious! "Mrkin0" mentioned a great reference: "How to make a telescope" by Jean Texereau. Thanks! I would like to mention another invaluable classic reference by John Strong written in 1938 entitled "Procedures in Environmental Physics." Chapter IV covers the topic of Coating of Surfaces: Evaporation and Sputtering." There are many printings of this book that cover hands on experimental science.


    6 years ago on Step 7

    where do you set the copper or sacrificial metal to be deposited?
    and for how long of time.

    1 reply

    I use bits of copper and aluminum wire that have been mechanically cleaned then the system is plasma cleaned under deep vacuum. more on this later.


    6 years ago on Step 3

    Just speculation... I haven't tried it.
    For those without access to brazing/welding equipment, it might be possible to thread a metal spacer onto the electrode of the sparkplug. Then a screw in the other end of the spacer would be the mounting point for the heating elements.

    1 reply

    6 years ago on Introduction

    Really cool project, I'd love to get one of these going at home so I could get a thin coat of metal on simple flowers or seed pods and then electroplate them. I don't mean for this to sound too negative, but I wanted to add a few notes on the glass:

    1. If you are using tempered glass be sure to use new, completely unscratched glass. Scratches in tempered glass cause really significant weaknesses, and the vacuum will exacerbate this problem.

    2. In our lab we use borosilicate glass for this because of all of the heat you are putting into the system. Keep in mind Pyrex kitchenware isn't actually borosilicate anymore, it's tempered. Tempered glass will work, with the added benefit that when it implodes it will form tiny little squares of glass that may be slightly less dangerous than long sharp blades.

    3. If you can, it would be good to find a bell jar that is parabolic in shape. It's much stronger than the shape of canning jars.

    4. I realize how expensive actual vacuum rated glass is (I just had to order a new one for our lab, and it was over $1000!). If you're going use less expensive glass, it would be easy to build a little wooden box with a thick, 2" diameter plastic porthole to monitor if everything is working properly. This way if/when it implodes you and your workspace are protected.

    Great 'ible, keep it up!

    1 reply

    Reply 6 years ago on Introduction

    true. Like I said I use a vacuum shield constructed from poly carbonate when drawing a deep vacuum on standard glass. I hate pain more than anything else.


    6 years ago on Introduction

    Hi, What a lot of work! It made me think of a unit in a book for depositing vaporized aluminum onto glass mirrors! You can download the book "How to make a telescope" by Jean Texereau here :http://archive.org/details/HowToMakeATelescope
    and on page 292 there are details of how to make a small scale aluminizer.
    It might give you some help with what you are trying to do. please note that you need a high voltage 5Kv transformer but you could probably use a microwave transformer.

    1 reply

    Reply 6 years ago on Introduction

    Thanks for the link. Good info. I have managed to acquire 6 HV transformers and will be experimenting with these shortly.

    Nice work! Once copper has been deposited onto the glass slide, the slide could be used as a substrate for a printed circuit. I would have to assume the possibilities of depositing silver or even gold onto glass as well. I'm filing this one away for future reference.

    1 reply

    6 years ago on Introduction

    Pretty dang cool! I used to do vac-dep for a living. really cool process.
    What materials you depositing?

    1 reply
    Mig Welder

    6 years ago on Step 7

    That's pretty awesome now that I see how it works!


    6 years ago on Introduction

    Very nice bit of work! I would like to make 2 friendly suggestions that might help with your ultimate vacuum.
    - Don't weld both sides of the connections. For deep vacuum work you only want a single weld so that there is no possibility of trapped air that can migrate out through very small cracks. These virtual leaks can prevent a system from ever reaching low vacuum. If you have a 1 liter chamber at 0.01 T then a 10 microliter trapped volume (at 760 torr) has about the same amount of gas in it. Since it is leaking through a small crack your pressure won't get below .01 T for weeks. It's better to avoid the trapped volume and make sure that the single weld doesn't leak.
    - If you have a pretty good vacuum gauge you may find you can find leaks by using rubbing alcohol. Be very careful that you don't have any sources of ignition near by while you are doing this, of course! Wait for your pressure reading to be pretty stable before starting. Use an eyedropper to put alcohol near junctions where leaks may be occurring. The alcohol has low enough viscosity to be sucked through small leaks. Once on the low pressure side it vaporizes and the pressure gauge will show a noticeable bump. This technique works best below about 0.05 T so you might not see much at 0.1. I'm assuming also, that your pump is capable of deeper vacuum when it is connected only to the gauge.
    Keep up the good work. I'm really excited to see your next results.