Vacuum Chamber Construction

[Richard Hull]

Keep practicing, you will get there. Getting the current set right and your speed during the weld is critical. The puddling, if done well, will sort of set the speed of movement automatically as you get familiar with it.

Richard Hull

[John Futter]

Nic
You need some scraps of stainless about the same thickness as you are going to weld in anger
stainless is very much different from steel to weld --infact I find stainless much easier --but I was taught how to weld on Stainless

good Luck

[Nicolas Krause]

Thanks for the tip John, I found a metal supermarket up here in Edmonton and picked up some 304 SS offcuts of about the same thickness as my chamber. Last night I was able to get setup and make some passes, the photo below shows some of my handiwork. I started on the right just passing the electrode and controlling the puddle, then I added in the filler rod. Wasn't great to start but the welds started to improve. At that point I'd mucked up my electrode and had to regrind which accounts for the mess after a few decent lines. When I went to restart the welding mask I was using started to go on the fritz, it wasn't auto-darkening properly. I'd read some decent reviews online that I thought justified me saving a bit of money on some safety gear from China. Rather than try and fix it I think I'm just going to write off the cost since I bought the cheapest I could find and spend a bit of money on a half decent one.

[Rich Feldman]

I can attest that sunburn is a risk if you skip the gloves and long-sleeve shirt, buttoned up at least as far as the bottom of welder's mask.

Even TIG welding can occasionally pop & launch a shower of sparks,
actually incandescent droplets of steel which you don't want to fall into your shoe or pocket.

[Nicolas Krause]

I've continued to practice my welding, and its slowly improving. A lot of the work still looks pretty ugly, but I did my first joint last night and I can reliably put down an ok line on a flat piece of steel. I've got to monkey with a bunch of settings around my TIG torch, but the fabrication series on youtube has been a big help and has answered a lot of questions I've had. I've got to grab a bit more Argon gas as I've only got a small tank, but mostly I think I just need some more time in the saddle.

[Nicolas Krause]

Just a quick update with regards to the welding. As per the photo below, I've had a marked increase in the quality of my welds. A number of things have helped, I'll note the following. First I've changed the nozzle on my tip. I am now using a size 12 with a gas diffuser, and the shielding from the Argon is much improved. It was quite cheap, I think 30$ for a whole set of attachments off of Amazon. Secondly, cleaning and weld preparation makes a huge difference, I'd been lazy about setup to start, but cleaning the piece with acetone, making sure everything is stable and well aligned really does make the welding easier. Thirdly, I was putting too much filler rod into my welds, it's more a case of pushing the puddle forward with the arc, adding some filler, removing the filler rod and then pushing the puddle forward again. Finally, more power is better, I had been nervous about the amperage setting to begin with, but putting it on low makes it harder to weld. You've got to have enough power to move steadily and quickly, if not you mostly heat the metal rather then weld it. I do have a question about the colour of the welds, I understand that for steel the weld should be basically shiny and steel coloured, I've got a bit of a rainbow going on and I'm wondering if its something I can get away with, and if not, how do I reduce the coloration?

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[Richard Hull]

Some coloration is unavoidable. forget it. I do hope you are aggressively wire brushing the weld once cooled. You will be amazed at what a heavy steel brushing will do for the appearance of the weld. Do it by hand or with a round brush in a power hand drill.

Good weld!.....Needs a heavy steel brushing to beautify it

"Learning by Doing".....It's The Only way!

Richard Hull

[Nicolas Krause]

Another practice weld was successfully completed tonight, and after seeing the colour of the weld after brushing I decided I was ok to move on to the actual welding of the chamber.

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The fit between the two pieces was tight enough that I didn't need to use any filler rod. It's not perfect, but I'm quite happy with how it turned out. I do need to find a small wire brush though as I wasn't able to fit the current one in the chamber to properly clean the weld.

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[Richard Hull]

Smaller round wire brushes on a shaft will fit on a power drill and wire brush inside welds very well. Very tiny tightly confined welds can be brushed using a Dremel tool and its very small wire brush attachments.

Your interior weld is excellent looking. I deliberately machine all my fittings so that no form of wire feed is needed. Just simple fusion and a tiny bit of sacrificial lip or ledge supplies the filler metal by fusion to the joint. I hate wire filler feed and avoid it at all cost unless there is no work around.

Richard Hull

[Nicolas Krause]

I've ordered some small wire brushes for a few dollars, hopefully they'll fit, if not I'll look into finding a dremel. I do have a question about testing the soundness of the welds. I understand there are special dyes you can purchase to see if there are any cracks/leaks in the weld. Given the need for the welds to be airtight I was wondering if they were useful for checking for leaks or if it was better to troubleshoot once the whole system is hooked up to pumps.

[Richard Hull]

I tested my hemispheres using a rubber gasket on an old bell jar plate. Check the construction FAQs for my fusor II images. You have so many ports on each hemisphere it would be tough. You would have to blank of all on each hemisphere.

viewtopic.php?f=24&t=13053

Richard Hull

[Nicolas Krause]

Welding continues steadily, I've nearly completed one hemisphere. The welds need to be cleaned and checked for leaks, and one its quite messy, I might use a dremel to smooth it out. Other than that, simply running out of Argon is what halted progress today.

[Richard Hull]

The good news is argon is extremely inexpensive. You must have a small tank. Mine is full sized and I have had it now for 20 years and used very little of it. I fear that when I need a refill, they will note the tank pressure inspection is out of date and charge me an inspection fee in addition to the argon. This is a penalty often impressed upon a small use welder. Big shops never suffer this as they exchange frequently.

Richard Hull

[Nicolas Krause]

I've nearly completed all the welding on my chamber. A single large weld remains, but having run out of time this evening it will have to wait.

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[Richard Hull]

Good golly miss Molly! Did you get a sunburn doing all of this welding?
If not, you did good....

Richard Hull

[Nicolas Krause]

Another quick update, I'm happy to report I've completed all the major welds on my chamber. They've been visually inspected and they all appear to be sound.

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I might in the future have to break out the welding equipment if I have some trouble pumping down, but for the moment all looks well. It's very nice to reached this point, I have a bit of official looking hardware on my desk.

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I've ordered some 8020 extrusion so that I can build a frame to hold the chamber and assorted components. It should arrive sometime next week. My focus now will move to the vacuum systems of the device!

[Richard Hull]

Now your are cookin'! You have to be proud of yourself! I know I am proud that you have proven to be a virtual unstoppable doer. "You have guts and guts is enough" ( R. Lee Ermey, Drill Instructor in the movie Full Metal Jacket)

Looking for continued forward movement and the reports of further successes.

Richard Hull

[Nicolas Krause]

Thanks for the encouragement Richard, it's been a long haul! I can't say enough about the community all the old timers have built here, its such a tremendous source of quality information, the only price for entry is some hard work. I've also been very much enjoying reading your postings about the history of the Farnsworth fusor effort. Fascinating stuff!

[John Futter]

Nicolas
For a first effort I give you a B+
Well done

[Nicolas Krause]

I'll take that John! Much better than an F, what would I have to do to take it to an A?

[Mark Rowley]

A+ in my book. Here’s why.
You are not a professional welder but your effort and extreme focus are far beyond 99.99999% of most people here who attempt this type of work on their own. ESPECIALLY at your age! Bravo to the extreme!

In the realm of amateur work (which is what this group is about) you get top scores.

Mark Rowley

Ps...yes, there’s always room for improvement. But that’s true for even the best cut diamond in the history of human existence. Doesn’t mean an A+ isn’t warranted.

[Nicolas Krause]

I am now working on the pumping system of the fusor. In addition to the previous vacuum sensor and uC board I've mentioned earlier I also have a surplus vacuum pump and turbopump without controller. I haven't turned on the vacuum pump since I bought it, nor have I monkeyed around with the turbopump. At this point I plan on working on the vacuum sensor circuit, and then building a controller for the turbopump. At that point I can start to troubleshoot the complete vacuum system.

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[Rich Feldman]

Nice looking sock there.

How 'bout starting with vacuum gauge, then characterizing the rotary vane (backing) pump?

Scratch-building a turbo controller would be a learning exercise much bigger than making and welding your chamber parts.
You can go a long way without it.

I would plumb up the chamber, with or without turbo pump, and learn the pumpdown behavior.
Then light a plasma using any old HV power source.
I don't remember whether NST-powered plasmas typically extinguish at pressures attainable with rotary pump (50 micron? 10 micron?)
They sure do in pencil-size glass tubes.

[Nicolas Krause]

Funnily enough I feel a lot more comfortable on the electronics side than the machining and welding side. I've got an electronics technologists diploma, I'm 3/4 of the way through an electrical engineering degree, and I've done some embedded programming for a small oil company up here in Canada. I think like a lot of people I initially joined up here hoping to be the one to crack the fusion puzzle, but reality sets in and instead this project has turned into a tremendous self-education tool. While I think building a motor controller would be tough, it's exactly the kind of thing I'd like to learn how to do.

All that being said, I think I'm going to take your advice Rich and test the backing pump with my vacuum gauge first, then I can move on to the turbopump controller.

I do have a couple options for high voltage supplies, I bought a high voltage transformer a few years back and I've got a busted spellmann supply I picked up off of eBay last year. Finally the quickest route might just be to grab one of those precipitator supplies off the internet.

[Mark Rowley]

Nicolas, the precip supplies work ok with the 2.75" system but will not put out the current needed for a large spherical arrangement like yours. Theyre cheap enough and it could be worth a try, just dont expect much from them with your arrangement. They may be ok for plasma / vacuum testing as long as you keep a sharp eye on the current draw.

Rich, it's been my experience to have NST driven air plasma extinguish well within the range of a decent roughing pump. Going below 35mTorr things quickly get flickery.

Mark Rowley