Re: tungsten alloys for SG electrodes?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Edward Wingate" <ewing7@xxxxxxxxxxxxxxxx>

Tesla list wrote:
>
> Original poster: "David Rieben" <drieben@xxxxxxxxxxxxxxx>
>
> Hi all,
<snip>
> Also, how suitable would tungsten carbide be for rotary elec-
> trodes, as far as heat & electrical conductivity is concerned?
> I remember reading some of the late Marc Metlica's posts re-
> garding use of tungsten carbide for SG electrodes. He had
> easy access to tungsten carbide because of some of his tool-
> ing supplies and he really liked using the carbide for this pur-
> pose. I know that tungsten carbide is extremely hard though
> and almost impossible to machine without special diamond
> tipped cutting tools, so I would prefer to use the high density
> tungsten alloy (90/6/4 - tungsten/nickel/copper percentage)
> if possible, since it's much easier to machine and is available
> in the 3/8" to 1/2" range that I'm looking for. Any comments
> from the more metallurgicaly inclined would be welcome :^)))
>
> David Rieben

Dave,

Forget about the tungsten/nickel/copper alloy. This alloy is made for
conventional EDM use. It is highly machineable, but next to worthless
for spark gap electrodes. I've tried it. It pits, burns and blackens
quickly, leaving a black glassy deposit on the face of the electrode.
You would be better off with plain brass. Tungsten carbide will work,
but you pretty much have to find shapes that will work for you without
modification, unless you have access to a wire EDM machine or grinder
equipped with a diamond impregnated rubber wheel and have lots of spare
time. There is nothing better than pure tungsten rod stock for rotary
spark gaps or even fixed gaps for that matter.

Ed Wingate RATCB