New tiny rod cutoff jig

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New tiny rod cutoff jig

Postby Doug Coulter » Sat Dec 13, 2014 4:56 pm

Well, Bill had to go and find out you can get straight .009" rods made of tungsten carbide. Should be good for fusor grids? We're going to find out, as I've upgraded my lathe toolpost "dremel tool with guts" to tool steel shaft, grade 7 bearings, and well under 3 tenths runout (.0003" peak to peak). And earlier I built a stepper motor/arduino jig to hold grid ends and rotate them "precisely" 45 degrees (have no way to measure the error, but if the books I read are right, and this motor is typical, that error should be pretty tiny too...3% of one step, ..054 degrees or so. At any rate, the star of today's show is the jig I just built to cut these tiny rods off all the same length, using the toolpost dremel with a diamond wheel and the lathe axis to move the wheel into the cut - and make them the same all the time and not bend or break them (WC is on the brittle side...). I could sort of do without this with pure W, and .020" rods sort of by hand with a spacer jig, but this should be a lot better for those too - I didn't always get those right, and bent a couple, had a couple short/long ones, etc and usually had to cut 12 to get 8 reasonably good ones. Well those were fairly cheap - WC rods .009" are not cheap. So this time I'm improving my odds of getting things right on the first go. I won't bother to describe the build process in detail here - anyone who has run a mill, a drill press, and the usual suspect hand tools will know how I did this. I got lucky (for me) and only had to mouse out one of the screw holes...so it locates very tightly. I used a 20 mil W rod clamped in there "just so" to put a tiny dent on both the milled Al, and suprisingly, the milled steel as well - it now auto-centers the .009" rod perfectly for me. If I ever make the barely-visible dent too deep, I can just mill off some extra and go again, no sweat - unlike the slim, lithe one I drew, I made a monster, since I had the stock laying around...you know how that is.

Here she is:
NewRodJig.JPG
All ready to get to work...cutoff wheel will just barely not touch the end of the jig, and the screw that holds the diamond wheel won't have to get close enough to be an issue here.


I assume this will work a charm. I'll report once I've tried it. When you're off the grid, wintertime kind of stinks for working late in a power hungry shop. I'l already down to zero power input from the panels at 5 pm. I'll be much happier after the solstice.
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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Re: New tiny rod cutoff jig

Postby Doug Coulter » Tue Dec 16, 2014 6:31 pm

Well, this doesn't quite work as expected. The rods simply break off flush as soon as they are touched by the diamond wheel, and if they're not in there perfectly straight (eg in the dent) they break inside the jig too. I can modify this for different lengths, but that kinda sucks - these are much more brittle than I thought, I thought with a slow enough feed, I could just grind through them at various short lengths past the end, but nope, they just break instantly at the first contact. Life! At least they break off straight and flat...But if I want variable length, I'll have to drill through the jig from behind and put in a setscrew to adjust that - or something similar.
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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Re: New tiny rod cutoff jig

Postby Jerry » Sat Dec 20, 2014 3:55 am

I dont think carbide is going to work worth a damn. Tungsten carbide like this is not pure carbide. It is Tungsten Carbide powder in a cobalt binder. Cobalt melts around 2700f and will probably evaporate out at fusor temps.

The amount of cobalt to TC is what makes the difference in the grades of TC from C1 which has the most cobalt and it toughest to C-6 which has the least cobalt and holds the sharpest edge while being the most brittle.
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Re: New tiny rod cutoff jig

Postby Doug Coulter » Sat Dec 20, 2014 4:28 pm

This is what we got, it's C2: http://www.amazon.com/dp/B005GQ6O8A/ref_=biss_dp_tp_det
It's awful brittle for having a lot of cobalt in it. We just thought it worth a try, we'll have to see. We don't appear to actually need the higher grid transparency that this would provide (most of the loss appears to be at the back end of the grid, and of course on the tank walls when electrons hit them), but it seems like a neat idea to have half the rod area anyway if it was do-able, and there appears to be no easy source of *straight* pure W this size. The other issue is that WC should have a much lower secondary emission of electrons, and thus higher Q, other things being equal. Dunno the ratio of cobalt to the rest for C2, but some of the carbon should migrate and become CoC as well, under heat, reducing secondary emission from the Co as well. Or for all we know, make hydrocarbons with the D and reduce the WC, stranger things have happened, and in fact when the mass spec was up, we saw hydrocarbons (simple ones) after running D and graphite grid ends together - the assumption is that some of the D got with some of the C and made some simple HC compounds...not a sure thing, but they didn't show up till we had the graphite in there. At that, it's a real small percentage of what shows up after a run (it's less than things with mass <=4 and water and CO - basically just enough to see at all).

Since I have all the other tools to do this (had to make some of them) might as well give it a spin and see how it works out. Most things in there don't get that hot, red at most. We'll see if this sags under that heat and load - and I'll make the end loading as light as possible with the materials at hand (in this case, graphite, but I can reduce the cross section somewhat for the end supported by the rods).

Kind of stinks I can't cut it off with a diamond wheel, it just breaks at the fulcrum, even with a finger behind the wheel to hold it stable, but I can drill a hole through the jig and put in a set screw to allow for any length if I want to. Assuming it works at all - I can try with this length (1.084") to find that out. I'll do that next time I break vacuum. Most of the work here is still on remoting this so I can go to high Q oscillator mode again without dieing from rad exposure. That was a huge leap forward (factor thousands)...but I dare not run like that with me in the room again. Once of that rad sickness was more then enough warning. For now the thing is setup in "safe mode" at a couple million neuts/second so I can test the remoting gear, the oscillating stuff is out of the picture till I can do this from 50 yards away. I have a few new observations to chase down in the meanwhile, like anomalous high neutron output from the ion generator grid when it has a series inductance along with the regular ballast. Could be it's cycling a bit and inductive kickback makes for momentary very high voltage at a time when the ions are all aligned right instead of a mostly-plasma situation I think is what we have when we run "stable" mode. Or it could be (unlikely but possible, since I take a lot of care and precaution) just EMI. Have to check and verify all that, so I've got plenty on my plate.
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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