Re: Propeller gap destruction test

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

Original poster: "Gerry Reynolds" <gerryreynolds-at-earthlink-dot-net> 

Hi John,

What part of the propeller gap broke?

Gerry R

 > Original poster: "John Richardson" <jprich-at-up-dot-net>
 >
 > Hello,
 >
 > I've been intrigued by the simplicity of Terry Blake's gap idea for some
 > time, mainly because of the simplicity of the design, and recently had
some
 > correspondence concerning any problems he may have had.  My biggest fear
 > was tungsten hitting tungsten, and possibly making an interesting hobby
 > into a deadly one.  I constructed a bullet proof box around this gap, and
 > proceeded to do things that you wouldn't normally do to see what the
 > results might be, and to determine what kind of minimal safety
measurements
 > one should pursue in order to avoid injury.  The first couple of tests
were
 > done by setting the stationary electrodes close enough to just clip when
 > the rotor was turned by hand.  I enclosed all four sides, got a long
 > extension cord, and plugged it in from a distance.  After doing this
 > several times, I checked it out, and could see where it was hitting, but
 > still no shrapnel.  I set the electrodes a bit closer, so that there was a
 > more pronounced clipping, and plugged it in again.  Certainly could hear
 > it, but upon inspection, there was no damage.  I am assuming that the
 > plastic for the rotor arbor has enough elasticity to allow it to give as
 > the tungstens hit each other.  So far so good.  The next phase of my coil
 > project involved setting up the control panel, and setting various
trannies
 > on the platform to determine what power source I wanted to use and what
the
 > best layout would be.  FYI, the platform is a 2 by 2 foot piece of plywood
 > with a perimeter of 2 by 4s.  Pretty stout.  I finally decided on a 12/120
 > and set it in it's place.  Prior to this, satisfied with my safety runs, I
 > had set the gap distance nice and close, figuring that this phase of the
 > project was out of the way.  Moving to the workbench to proceed with
 > something else, I plugged the gap in to let it run for a while, planning
to
 > check to see if it would get hot running completely enclosed.  No sooner
 > had I done it than I heard shrapnel flying.  Turns out the extreme weight
 > of the 12/120 caused enough flex in the plywood base to cause the gap
 > spacing to get to a point of severe interference, and a nice big shard
flew
 > off.  I think this gap style has lots of potential, but play it safe.
Even
 > after testing this design, it was the unknown factor of the tranny flexing
 > the base to cause a mishap.  Could have been disasterous if everything
 > wasn't enclosed.  Also, for those building such things with a minimal of
 > tools, take lots of time to make sure that holes are centered and true,
 > etc.  There is potential here for a decent gap on the cheap, but enclose
it
 > all the way around, use good craftsmanship, and you'll have a decent
 > RSG.  Judging from what I have learned, I would suggest to keep the gap
 > space a little wider than usual, and to place the stationary electrodes
 > behind the flying electrode, so that even on the one in a million chance
 > that the rotor tungsten started to creep, it can't hit the
 > stationaries.   And don't forget that good ole Murphy likes to help with
 > your projects too!
 >
 > John Richardson
 >
 >