An indexer for drilling fusor grid holes

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Re: An indexer for drilling fusor grid holes

Postby Doug Coulter » Mon Sep 29, 2014 5:01 pm

Funny, but I wonder what happens if you bend over and the hat falls off? It's already a problem with stuff in my shirt pockets. I'm not real fond of hats anyway...I probably just need a bracket on the bench or something.

I did put in a McMaster order today, including a set of pointy countersink drills down to 0000 from 0 - we'll try starting holes with that. I don't really need as large as .020" except for the main hole, a smaller start should center the "big" .020 drill just fine. I'll probably get it tomorrow, and if the sun shines, we'll try the stuff and see how it goes. These holes are 5-6 calibers deep - it's almost like making a gun barrel, except if a gun barrel isn't just right, you can adjust the sights. Here it's gotta be perfect in the feedforward sense. It's not going to be perfect, and at some point, I think space charge might rear its head and bloom out our focus anyway. But...we measure an actual negative net plasma, so space charge in the classic sense might not apply as directly as it did in say, vacuum tubes with only one species present. It would in fact seem to me that there could be a higher probability of an electron being closer to a nucleus than normal when it's not bound, and thus in some sense helping us bring them closer together. I still have my doubts about this "virtual cathode" made of electrons stuff I hear around. Seems to me the lighter thing(s) would do the moving towards the heavier thing(s), all else being equal, just plain Newtonian mechanics there.

But that's why we test things. There's no practical way to simulate all this - but the universe is a good model of itself and has the advantage of running in real time. It's just that those "edits" take time (eg, changing the experimental setup).
One oddball thing that makes this work is going to be "up next". Turns out the tungsten rods we get aren't quite round, and that's what actually keeps this all together - they kind of grind their way into the hole, being perhaps 22 mils by 18 mils diameter, elliptically. And there are some serious gram-level forces trying to take the grid apart, which go up a lot of there's an arc - this needs to be really tight.

It would therefore seem that once I hit a certain hole spacing accuracy, I'll have to also align the rods such that they themselves aren't the main source of errors. As it is, I cut around 12 of them to get 8 that will roll down a sheet of glass (no warp on top of the rest of the error). You can bend them a little - but they probably just spring back again when heated to incandescence, which happens sometimes, at least at a point along the length at full power. Trying to bend them straight is probably as (in) effective as trying to do that with match rifle ammo in a runout fixture - it doesn't stay straight very long.

I'm even wondering if I shouldn't make a fixture to light these guys up in vacuum before I even cut them to find out which will still be straight after heating. We'll just have to see what happens as we approach the effective limit - we'll never get there even in theory as regards the deBroglie wavelength of a D+ (it's a lot smaller than the width of a single tungsten atom), but I suspect other effects will kick in pretty soon that negate that "perfect in theory" stuff. It's just that we've not yet seen the other side of this peak yet, or even a leveling off - so far, every halving of error has 4x'd the fusion and Q - square functions are nice when they're on your side. The trend is, so far, our friend (till it ends, then we have to figure out the next critical path). Just another piece of the puzzle, I believe. Even now, when a grid is so good you can't just see the errors, the errors in the visible focus are much larger, blobs on a wavy string (which is one reason I insist on being able to look at it). There's a lot of complexity going on. Yet making the grid better makes this look better, and has great results.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Doug Coulter
 
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Re: An indexer for drilling fusor grid holes

Postby Doug Coulter » Tue Sep 30, 2014 10:39 am

Don't you wish all your vendors were this fast and this good? I ordered this yesterday about this time, and here it is:
GraphitenDrills.JPG
Stubby drills and graphite rod - 23 hours after clicking "submit".


The graphite rod is even 5 mils oversize, so I can turn it to the precise dimension. Win! I'm working on something else right now - the MCA project with Phillipp - but I'll get to this real soon.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
User avatar
Doug Coulter
 
Posts: 3515
Joined: Wed Jul 14, 2010 7:05 pm
Location: Floyd county, VA, USA

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