Tungsten-carbide results

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "sundog by way of Terry Fritz <twftesla-at-uswest-dot-net>" <sundog-at-timeship-dot-net>


 Hi all,

 It's been a fun holidays, work work and more work.  And somewhere in there,
a day off to tinker.

 I got my polepig ballasted, (running ~2.5kva for the moment), and some
tungsten-carbide rods from McMasterCarr.

 The tun/carb Marc sent me worked beautiful in static gaps.  It dissapates
heat really fast, conducts as well as anything, is *tough!*, and boasts
nearly zero wear. But the bits were odd-shaped, and proved difficult to
silver-solder to brass or copper.  So, I ordered some tun/carb rods, and
modified my stationary electrodes to accept the 1/8" rods.  I use ~2" in
each electrode, with 1" exposed.  A 4x40 set screw holds the tun/carb in
place.

 For testing, I used a 30kv 33nf cap and 240bps sync gap, running ay 2.5kva.
I made 1 set of electrodes to destroy, and later 1 set to use.
 *EYE PROTECTION IS A MUST!!!!!!*  Tungsten carbide is *very* brittle, and
likes to explode into razor-like shrapnel!  Get goggles.  wear them while
you're working with the stuff, even just to handle the stationarys.  You
drop it, it'll break.

The tun/carb is very tough, but brittle. Don't waste your time with a
hacksaw or dremel tool, nor the $25 cutoff wheel.  I clamped mine in a vice,
with about 1/8" more than I wanted sticking out, wrapped it with a rag and
gave it a sharp whack with a small hammer.  *snap!*  Good clean break.
Every single piece seemed to break with a chunk out of the front, but that's
easy to fix.  Next, chock up tho tun/carb in your trusty drill, and fire up
the grinder.  Hold the drill wide open, and keep the tun/carb 90 deg to the
grinding wheel.  Move it around, or you'll just cut a hard-to-get-rid-of
groove in your grinder wheel. Not pretty. You should end up with a nice flat
surface. Don't bother rounding it off into a little ball, it won't matter.
   I then clamped my stationary in a vice on the drillpress table (you can
use a hand-drill, but it's more difficult to get a straight hole drilled). I
drilled ~1.25" into the 1/2" brass rod.  I drilled and tapped the holes for
the 10x32 brass rod (electrical connection) and 4x40 set screw.  Slipped in
the tun/carb, and tightened the setscrew.  Add some washers and nuts, a
quick trip over the wire wheel to shine it up, and it's done!


   The testing,   I had no secondary in place for testing.  I ran a gap
spacing of about 1/8" (to allow for rotor wiggle and vibration), and fired
it off.  After maybe 30-40 seconds, I could see small sparks flit up from
the gap.  When I cut power, the tun/carb was glowing.  But even while red
hot, it quenched very well and did not powerarc.  I ran the gap for about 10
minutes total, then pulled the electrodes for inspection.  There was a crust
of what I presume to be oxidation and carbon-crud.  It flaked off pretty
easily.  The electrodes had virtually *NO* wear.  The sharp 90 deg edge was
rounded a bit on the side the arc starts on,  but not enough to even merit
bothering with.  I made another set to run on a coil.  Same setup, just
added the secondary and tuned a bit.  With the secondary in place, the
electrodes never got anywhere near red hot.  Even after a 40-50 sec run,
they were hot to the touch, but not scalding.  At the end or about 10
minutes total runtime, there was a bit of whitish oxidation, but no crud or
crusting.  The ground edge was still razor sharp.  I shorted the toroid to
ground and re-ran the coil for 5 runs, each run around 1 minute.  Even under
that heavy of a load, the sparkgap didn't overheat, and the electrodes
didn't change much in appearance.  There was very little new oxidation that
formed, and the ground edge was still razor sharp.

 My consensus is that the tun/carb is just as good, if not better than the
pure tungsten or 2% stuff, at a lot less cost to the average joe.  I have
yet to run it at a high power level (5-10kva), but new years is coming up
soon.  I'll continue to abuse it a lot, and keep the list posted of the
results.  But me, I'm hooked.  a 12" rod is around $10, and can easily do 4
stationary gaps.  Another rod can take care of your flying electrodes. Easy
to machine (leave yourself extra and grind it off), cheap, and works
beautiful!  I'm sold on it!
												Shad