Easy Inner Grid Fab

For posts specifically relating to fusor design, construction, and operation.
Julian Kang
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Re: Easy Inner Grid Fab

Post by Julian Kang » Fri Jun 28, 2013 3:17 pm

Thanks Richard for the advice. I had forgot about the wooden sphere. David, are you planning on making a mold just for a plain sphere or with sort of a pattern involved. I was thinking that if you could attach a line of silicone in your mold where the wire would be, you could easily fold the wire around the wax sphere with lines engraved into it. Also, I think if you add vegetable oil or other liquids to your wax, it will melt quicker and at a lower temperature.

Julian

Richard Hester
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Re: Easy Inner Grid Fab

Post by Richard Hester » Sat Jun 29, 2013 12:15 am

I just checked Youtube, and the Meiro video is still up. Search using "Meiro fusion", and it's the first thing that pops up. It looks like he got his 15 minutes of fame...

David Swan
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Re: Easy Inner Grid Fab

Post by David Swan » Sat Jun 29, 2013 8:44 am

I'm still thinking about making a former.

Paraffin wax itself is a bit soft so I was thinking of adding one of the microcrystaline additives that candle makers use.

No hurry, this isn't a race. I'll take my time, do some experiments and get it right.

Those blender balls look very interesting but also look like they may have too much obstruction.

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Chris Bradley
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Re: Easy Inner Grid Fab

Post by Chris Bradley » Sat Jun 29, 2013 12:56 pm

The actual fabrication of a grid is going to be soooo much quicker than folks are investing in its discussion!

Wire [any!] ... pliers ... bend ... mount. Good start!

There will be bigger things to worry about than this, as there is scant evidence that accurate grid making makes too much difference.

Planning your work is good, but so is apportioning your attention towards the more significant details. You should already be planning on how you make adjustments to your set-up, including replacing/trying out different grids. I suggest you can worry about your perfect grid when you have, at least, an imperfect fusor to put it into!

David Swan
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Re: Easy Inner Grid Fab

Post by David Swan » Sat Jun 29, 2013 5:54 pm

In full sooth.

I'm going to use a fairly robust feedthough of brass rod (Easier to work than copper) with a 3mm tapped hole in the fusor end that I can screw in replaceable wire grids attached / built on a 3mm machine screw.

If I can get away with just running the rod through the PTFE stopper I'm using in my bell jar then I can use the 6mm stock that I've already got otherwise I'll use 10mm brass which will run through 10mm bore alumina tube.

A 10kV 37mA and a couple of microwave diodes are on the shopping list too, as is a reliable way of measuring the voltage (From the FAQs)

BUT.

I've had enough horrid expenses lately that I have no available funds for further work for a few months (My digital cine camera could fund a fusor from scratch), I'm just going to practice my wire-work since at the moment my efforts are fairly execrable.

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Chris Bradley
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Re: Easy Inner Grid Fab

Post by Chris Bradley » Sat Jun 29, 2013 6:22 pm

Zinc sublimates in a vacuum.

PTFE is not suitable in the vacuum envelope.

When exposed to a reducing plasma ptfe generates some toxic stuff too, so I am lead to believe. (I have teflon in my experiments and the chamber can stink badly after being opened up - I guess that's the toxic stuff I'm breathing in!)

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Jim Kovalchick
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Re: Easy Inner Grid Fab

Post by Jim Kovalchick » Sat Jun 29, 2013 6:39 pm

The U of Wisconsin folks have formed wire over foam spheres and then dissolved the foam in acetone.

David Swan
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Re: Easy Inner Grid Fab

Post by David Swan » Sat Jun 29, 2013 7:57 pm

That's a bother.

I guess in a hydrogen (Or deuterium) atmosphere under electrical discharge you'd get HF generated.

Chris, did the noxious substance smell acidic, a bit like HCl I suppose? I myself have never been brave (Or foolish) enough to get involved with HF.

What I'm planning ATM is a demo fusor just using air, so the overall plasma would be oxidising if anything.

My next option / plan is to re-organise the baseplate so instead of just the vacuum port and earth connection it will have the -ve feedthrough as well. when I was shopping this afternoon I was in a kitchen shop and saw some, nice nearly hemispherical, stainless steel mixing bowls that looked robust enough to stand up to vacuum. I may use one instead of the bell, then cut a view-port in the top and use either a mirror or a web-cam to look in.

No hurry.

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Chris Bradley
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Re: Easy Inner Grid Fab

Post by Chris Bradley » Sat Jun 29, 2013 8:49 pm

David Swan wrote:Chris, did the noxious substance smell acidic, a bit like HCl I suppose? I myself have never been brave (Or foolish) enough to get involved with HF.
Not sure how I would describe it. I suppose the best I could describe it is very slightly like the smell you get when you open up a plastic-wrapped book, but far more sickly sweet smelling with strong, almost overpowering, overtones of 'burnt plastic' pungent, slightly metallic type scent to it.

I don't know it that smell happens to be this dreaded stuff you get from PTFE;

http://en.wikipedia.org/wiki/Octafluoroisobutylene

.. toxic in 1 ppm, apparently ... maybe it was something else, or just very low concentrations, as I have reason to believe I am still very much alive.

David Swan
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Re: Easy Inner Grid Fab

Post by David Swan » Sun Jun 30, 2013 8:49 am

Thanks for that link Chris.

So it's due to pyrolysis in a reducing atmosphere. Presumably the viton gaskets I've been using would also be vulnerable to the same pyrolysis, though as I'm going to be running it in demo mode at sub-fusion input energy I may get away with it there.

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