RE: Rotary SG Safety

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

Original poster: "Lau, Gary" <gary.lau-at-hp-dot-com> 

Are you saying that a #8 acorn nut or remnants thereof were able to
penetrate 1/4" thick Lexan?  Or did it just find a gap in the shield to
slip through?  Lexan is VERY tough stuff, and I find it hard to imagine
electrode remnants having enough energy following a crash to actually
penetrate such a barrier. Photos of the breached shield would be
interesting, as I just finished building a propeller gap with a 1/16"
Lexan shield:  http://www.laushaus-dot-com/tesla/sync_gap.htm

Gary Lau
MA, USA
============================================================

Original poster: Zimtesla-at-aol-dot-com

Tesla List readers,
Recently a friend of mine who has been building Tesla coil projects for
over 20 yrs, built a small asychronous rotary gap. He wanted it for use
on
small coils so it has only a 6" rotor disk. He used a small universal
motor
from a vacuum cleaner. The rotor is 6" by 1/8" Lexan and the rotating
hardware was #8 brass acorns and all thread.

The rotor and motor were fully enclosed in plastic. The rotor case was
1/4"
Lexan. The motor case was acrylic. The overall appearance is like an
office
fan but made of plastic. The finished project was a work of art with
everything carefully balanced so that it ran with no noticable
vibration.

When I was over to see the progress on the rotary,  he had not installed

the stationary electrodes which were to be tungsten. We spun up the unit

and made speed measurements with a strobe tach. At 60 VAC the little
motor
was turning over 6000 rpm and the unit had somewhat of a siren quality
to
it. We stopped at 70 VAC as this speed was more than would be needed. I
am
always a little wary when near rotating equipment that is in the whine
to
siren mode.

A few days later, my friend was not in a great mood. He had installed
the
stationary electrodes and gapped them at around 0.040". He decided to
run
more safety checks and cranked it up to 80 VAC. At this point there was
a
loud bang and shrapnel proceeded to eject through the 1/4" Lexan and
some
small threaded parts left an indent in the shelves across the room. He
stated there were parts 30 ft from ground zero. Fortunately nothing hit
him. The probable cause was that the 1/8" rotor flexed enough due to air

pressure being ported through special holes for that purpose so that it
caused the flying electrodes to be sheared off. The Lexan disk did not
break.

Fast forward. Due to his experience, I decided to rework my tungsten rod

propeller gap as used by some folks on this bulletin board. I had a 4"
tall
fiberglass shield around it but it was fairly flimsy. So I replaced it
with
a "firewall" of 1/4" masonite I had around. The masonite has bricks
embossed on one side - thus the term firewall.  The shield was much
deeper
(rotary is horizontal) so that flying parts have to bounce around a
while  before leaving the area. Today when I was running this rotary, I
heard a moderate "bang". The system shutdown on its own so I figured on
a
blown cap. Instead, the tungsten propeller rod had turned into three
pieces
and hit the firewall without too much ado. I was glad for the added
safety
of the masonite.

I will forward photos of the Lexan rotary to Terry  for possible
inclusion
in his hotstreamer site.

Keep your coiling safe. Assume your rotary will fail so provide
shielding.
Jim