Re: Rotary gaps
Subject: Re: Rotary gaps
From: mark.graalman-at-mediccom.norden1-dot-com (Mark Graalman)
Date: Thu, 20 Apr 1995 20:55:00 -0500
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Te> Date: Thu, 20 Apr 1995 15:11:30 -0400
Te> From: Esondrmn-at-aol-dot-com
Te> To: tesla-at-grendel.objinc-dot-com
Te> Subject: Rotary gaps
Te> I am planning to build a rotary gap and would appreciate any
Te> suggestions or comments from those who have already done this.
Te> I am planning to use a 12.0" diameter nylon disc probably 3/8" or 1/2"
Te> thick. If I remember what I've read, my first choice for electrodes
Te> should be tungsten, then brass then copper. Is this correct? I can
Te> only find tungsten in 5/16" dia. I think it is available in up to 3/8"
Te> but I haven't found any yet. I was thinking that I wanted about 1/2"
Te> dia. electrodes. Any comment? I will use set screws in from the
Te> outside to hold the electrodes in place. I know I want to make the two
Te> stationary electrodes adjustable so I can vary the gap. If using this
Te> in series with a quenched gap what do you set the gaps for? Something
Te> like .050"?
Te> This gap will be asynchronous. I want to be able to control the speed
Te> so it will fire 4 or 5 times during each half cycle (I have a
Te> transformer that will supply plenty of current so I might as well take
Te> advantage of it) - does this make sense? If I use 8 electrodes, I need
Te> to run at up to 3600 to 4000 RPM. I would like to use a universal DC
Te> motor so I can control the speed with a variac and a full wave bridge.
Te> Can a small sewing machine motor handle this? The bearings in the
Te> motor may not support it. How about mounting the disc on a separate
Te> shaft with bearings on each side and driving it with a belt?
Te> I would think it needs to be a sturdy construction (so the gaps aren't
Te> moving in relation to the disc) so I probably want to build it on a
Te> steel frame.
Te> Any comments would be appreciated.
Te> Thanks, Ed Sonderman
MG> Ed, First I would recommend building the disk out of Lexan, it will
MG> not shatter under any circumstances, in my rotary I used 3/8 thick
MG> clear Lexan 8" in diameter with 8 electrodes and I spin it at 5000 rpm.
MG> I use 1/4-20 theaded rod on the disk with a stainless steel acorn (cap)
MG> nuts on each end for each electrode. It has been my experience that
MG> "rounded" electrodes quench much better than flat ones. The stationary
MG> electrodes are 3/8" diameter Tungsten mig welding contacts that are
MG> mounted on heat sinks, each gap is set at about .020".
MG> My disk is mounted right on the motor shaft (1/4") with a hub I had
MG> specially machined to insure it was true. The entire gap system is
MG> mounted in a box made out of 3/4" plywood for safety and the box is
MG> pressurized with a blower.
MG> I run an input of 5KW with a primary capacitor of .09 ufd and these
MG> electrodes have no problem standing up at this power level.
MG> Mark Graalman
... Alias, Mark the spark
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