Re: Pointseries gaps 'vs' other types

To: ccurran-at-execpc-dot-com
Subject: Re: Pointseries gaps 'vs' other types
From: Esondrmn-at-aol-dot-com
Date: Wed, 14 Feb 1996 12:11:02 -0500
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In a message dated 96-02-13 21:22:09 EST, ccurran-at-execpc-dot-com (Chuck Curran)
writes:

>
>Hello Ed:
>
>>Then I built a rotary gap using a lexan disc---
>
>I am curious about material selection for a rotary spark gap.  I too 
>am interested in being careful with the rotor in the rotary gap.  Do 
>you know, or anyone else what a good material choice might be?? or 
>phrased in another way did you select the lexan because of 
>appropriate features or was it handy in the parts box?  I was 
>planning on ordering the plastic for the gap but need to resolve 
>this point first.  Do the metal parts get very hot--is temperature a 
>concern for the selected material? 
>    I would also be interested in the material thicknesses that  
>have been used for rotary/series gap rotors.  I sure would 
>appreciate your comments Ed and anyone else that's worked with this. 
>   I've purchased flange blocks with bearings rated at 7500 RPM, 
>(with reduced life above this) for my gap.  The Carter motor will 
>drive through a Lovejoy flexible coupling into a 5/8" diameter 
>centerless ground shaft.  I've made an adapter to mate the "plastic 
>rotor" to the shaft, next step is to order the plastic.  There will 
>be a minimum of 5 1/2" from the motor(motor case will be grounded) 
>to any high voltage area on the gap--good or bad? Comments 
>appreciated.  Thanks in Advance!
>
>Chuck Curran
>
>

Chuck,

I used Lexan (polycarbonate) for the disc because it is a very durable
plastic.  You can hit this stuff with a hammer as hard as you can and it will
only damage the immediate area where the hammer struck.  It will not shatter.
 I suppose nylon would also be a good choice.  Mine is 3/8" thick.  I had a
plastics shop make it so it would be well balanced.  I am using a 1/2
horsepower 10,000 rpm motor.  I would rather have had a 5,000 or 7,500 rpm
motor.  I use two variacs in series to control it.  I leave the first one set
at about 60% to control the maximum rpm and then bring the other one up
slowly to get it up to speed.  
I use 1/4" stainless steel acorn nuts for the contacts.  They are bolted
together through the disc using cut off 1/4" bolts approx. 7/8" long.  I also
use external tooth star washers on each side to keep them tight.  I used lock
tite the first time but it causes a chemical reaction with the lexan and
produced cracks radiating out from each hole.  I am actually on the third
discl.  I haven't seen any problems from heat damaging the wheel.  The acorn
nuts do get burned pretty good.  You should go to a fastener shop and buy a
box of these so you can have spares to change them after several hours of
running.  If you buy them one at a time they are expensive.

Ed Sonderman