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Re: Thorated vs Pure Tungsten

I doubt that a cobalt drill will cut into a ball bearing!

I've just completed an "air blast" spark gap. I used 1/4" solid carbide
(sintered) end
mills for the spark gap electrodes. These were broken on the cutting side
but flat and
smooth on the shaft end. They seemed to work good for the short time  used
them (blew
my cap). There is absolutely no wear in the surface. The ends were not
rounded and you
can see some black marks all around the edge suggesting all the arcs came
from these
there. I'll bet rounding the ends will help localize the arc and reduce the
dwell
time. It would also keep the arc in the air stream.  There are mounted into
1.25"
aluminum bar stock with 1/2" deep concentric grooves cut into it to keep it
cool.

Any comments on using carbide??

Tesla List wrote:

> Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
>
>         Today I replaced the 2% thorium electrodes with pure tungsten.
The gaps
> actually fired much sooner with pure tungsten??  However the firing voltage
> was more stable.
>
>         I think the firing voltage depends mostly on the rather sharp
edges I left
> on the rods.  I will try to really round them out and see if that helps the
> stability.  In retrospect, the sharp edges only make high field stress
> points.  However, the thorium electrodes do seem to suffer much more from
> ionization caused by the radioactivity and thus like to sporadically fire
> far too early.  I may end up using ball bearing electrodes to get a much
> more stable firing voltage for the safety gaps.  I assume cobalt drill bits
> will cut through ball bearings to mount the shafts that hold them?...
>
>         I definitely would stay away from thorium and other radioactive
> electrodes.  Pure tungsten is supposed to wear faster but the worry of
> radioactive dust getting in one's lungs during the difficult cutting and
> grinding of this gnarly material out weighs that.  "Playing" with the pure
> tungsten is far better than worrying about dust particles from the thorium,
> or cesium, or lanthanum...  Some claim good wear from non radioactive
> alloys of tungsten too, but this is getting to be too complex as it is...
>
> http://www.arcsmith-dot-com/wni/products/tungsten/tungsten.htm
>
> explains much about these rods...
>
> I still find myself strangely drawn to the 3/8 inch diameter rods :-))
>
> Cheers,
>
>         Terry
>
> BTW - If all elsa fails, I still have 100+ Victoreen gaps :-)...