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spark gap design



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From:  terryf-at-verinet-dot-com [SMTP:terryf-at-verinet-dot-com]
Sent:  Saturday, August 22, 1998 2:06 PM
To:  tesla-at-pupman-dot-com
Subject:  Re: spark gap design

Hi Jim,

        Cleaning the gaps in my 60 x 4 mil gap is easy.  I get a 4 mil
ribbon of metal and just force it down through the gap sections.  The epoxy
is strong enough to take the stress.  The metal ribbon pushes out the
"stuff" that builds up.  I have been able to force out some pretty nasty
melted blobs and stuff with little trouble.  If you really want to clean it
well, a fine 400 grit wet dry sand paper ribbon will just barely slide into
to gaps and you can pull it back and forth the clean the sections.  You
will need some air in a can or something to blow the dust out.  It is very
important to use lots of strong epoxy on the sections to be able to clean
the sections in this rough way.  Of course, gluing a section bake in place
is no great challenge.
        I have noticed that the black oxide that builds up does hurt
quenching some but after a point really doesn't seem to do much harm.  The
real killer is to push very high currents through the sections and allow
the sections to over heat.  This allows the copper to melt and then you get
melted copper bits shorting the sections.  Fan cooling does a lot to
prevent this.  If the sections could be plated with a high melting point
material it would help much.  Perhaps someone knows of a simple way to do
this.  Perhaps having the sections chrome plated would be worthwhile??
        I have been trying to think of a way to have the sections rotating
during operation.  This can be done, but I was trying to find a way that
wouldn't require any high tolerance machining and such.  The part I am
stuck on is how to center a 1/4 rod in the pipe sections.  It would have to
be very accurately centered.  Other than precision machining, I can't think
of a way to do it.  Mounting and rotating the shafts would not be difficult
once I had the sections on steel shafts.  I can get bronze bearings that
would work but that is expensive and not everyone would be able to find
them.  I definitely want to keep it cheap and simple. A small low-speed
motor turning a axle with rubber band drive belts to each section could
provide a simple, cheap, and low tolerance drive system.  Preferably, the
sections would be insulated from the shafts.  The best I have come up with
so far is to wrap shipping tape around the shafts until it reaches the
inner diameter of the pipe.  A long difficult process at best.  Fans and
such blowing on the assembly should provide very good cooling.  I will
probably go the 3/4 in copper pipe with somewhat wider sspacing for such a
design.

Any thoughts, hints, or ideas are welcome.

        Terry Fritz
        terryf-at-verinet-dot-com




At 11:16 PM 8/20/98 -0500, you wrote:
>
>----------
>From:  Dsurfr-at-aol-dot-com [SMTP:Dsurfr-at-aol-dot-com]
>Sent:  Thursday, August 20, 1998 4:50 PM
>To:  tesla-at-pupman-dot-com
>Subject:  spark gap design
>
>Hi All: I finished cutting the copper pipe for an RQ sparkgap I plan to
>assemble this weekend. In my impatience to see the improvement I placed the
>segments in a row (ala Terry F's gap) on a piece of plexi, holding them in
>place with double faced tape. Gap was .03, ten gaps total. Even without re-
>tuning the improvement was obvious & I recommend anyone still using bolts for
>a static gap should switch immediately. My question is as follows: I noticed
>that there was some "carbonization"? building up on the pipe segments after
>only a few short runs. How often do you have to clean the gaps, how hard is
>this to do & does sanding or whatever widen your gap each time causing you to
>regap? If so it would seem that Bert Pool's gap design (where the pipes are
>laid on fiberglass rods allowing them to be rotated or easily removed for
>cleaning) would be far superior. Thanks,  Jim
>
>
>