Easy Inner Grid Fab

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Julian Kang
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Re: Easy Inner Grid Fab

Post by Julian Kang »

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 »

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 »

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 »

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 »

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 »

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 »

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 »

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 »

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 »

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.
Silviu Tamasdan
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Re: Easy Inner Grid Fab

Post by Silviu Tamasdan »

Was searching for something else and came across this old thread. And an idea came to me. It would be useful only to those with big fusor chambers (I'm looking at a small grid, probably 2cm across only for my small chamber so I wouldn't be able to use this method).

Ping-pong balls.

They're AFAIK still made of celluloid. Which is nitrocellulose with a low degree of nitration. It doesn't explode, but it burns very very quickly, and leaves no residue. And it's rigid enough to withstand some pressure.

Wrap the grid wire over a ping-pong ball, then set it on fire. Done.
There _is_ madness to my method.
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Dennis P Brown
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Re: Easy Inner Grid Fab

Post by Dennis P Brown »

My grid, like most people's, is made from very thick steel wire that is more like a small diameter rod. Bending it into shape requires very large forces. I used an Al cylinder and wrapped it with the rod using four turns ( the cylinder held in a vice horizontally.) I removed the "coil" that was formed and placed one of the single turns in the vice. Then using vice grips, bent the other three loop's these (with a lot of force) into a 'spherical' set of loops. Took less than ten minutes and no welding.

The final product can be seen here in this recent post: viewtopic.php?f=6&t=12025
Silviu Tamasdan
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Re: Easy Inner Grid Fab

Post by Silviu Tamasdan »

Why SS and not tungsten? There is excellent tungsten wire available fairly cheaply. I personally am making my grid from "surplus" 0.0275" tungsten wire which I bought from the "orphan bin" at Midwest Tungsten https://www.tungsten.com/orphan-bin/

In particular I use the OB-18 on that page. It consists of 9 wires braided, 12 inches long. They can be very easily unraveled, and you get 9 lengths of 0.7mm tungsten wire for $1.80 (granted they have a $40 minimum order - used to be $25 when I bought it a number of years ago; but they have other interesting items there, such as molybdenum sheet, tungsten rods, thicker wire etc; the selection varies over time, but the OB-18 is present constantly and has been for 12 years) The OB-57 may be interesting too for making a cylindrical grid without too much trouble - I have a few of those too.

This wire is quite ductile and doesn't break easily. After unraveling it's wavy and needs to be straightened but that's easy to do. Last evening I wound one of these by hand (look ma, no tools) on a 2cm cylinder and there was no breakage at all. I then straightened it and wound it again on a 1cm cylinder, again no breakage. The ends of the wire are a bit fragile and can exhibit some minor chipping if you try to give them a sharp turn.
There _is_ madness to my method.
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