Re: AW: [TCML] Coil pic w/ SRSG

[Joe Mastroianni <joe@xxxxxxxxxxxxxx>]

The tungsten carbide used as electrodes seems pretty impervious to the spark gap heat. So far there is zero pitting or erosion, though the longer ones are discoloring slightly. 

I am noticing some "sputtering" for lack of a better word on the srsg at higher voltages (higher than half max). The safety gap is not firing. I can only conclude this has something to do with either connection to the copper ring on the back side of the rotating disk or the idea that localized ionization of the air because the disk is so small is creating sneak paths. I have not noticed this ring of fire phenomenon some have suggested. The sparks in the gap do seem to be localized to the stationary electrodes. 

Sent from Joe's mobile phone.

On Jul 6, 2010, at 5:24 PM, Gary Lau <glau1024@xxxxxxxxx> wrote:

> You're right (obviously!) - yours IS tungsten carbide.  FWIW, gap electrodes
> are usually made out of welding rod - pure tungsten.  I'm not sure how
> tungsten carbide compares resistance-wise, but it will surely be more
> difficult to cut!  Performance-wise, it's not likely to matter
> significantly.
> 
> Terry Blake's original propeller gap just had the tungsten rod press-fit
> into a hole through the polyethylene arbor.  This was actually very snug and
> unlikely to move in operation, but I took it one step further and split the
> arbor and used two screws to clamp the rod (visible in my photos).  I have
> no worries of the rod moving.
> 
> On my propeller gap, the motor shaft has a flat, and I have a setscrew in
> the Delrin arbor (kinda visible in 3rd photo from top on
> http://www.laushaus.com/tesla/sync_gap.htm) that lands on the flat so it
> can't rotate.  So, it's important that the motor be able to rotate in its
> cradle for a rough phase setting.  Yes, the phase would be likely to get
> messed up quickly if friction was the only thing fastening the arbor to the
> shaft.
> 
> Regards, Gary Lau
> MA, USA
> 
> 
> 
> On Mon, Jul 5, 2010 at 10:52 PM, Joe Mastroianni <joe@xxxxxxxxxxxxxx> wrote:
> 
>> There's a copper disk on the back of the 4" garolite disk.  It's the stuff
>> they use for roof flashing.  Not so stiff.  Can be cut with snips, but makes
>> a messy circle.
>> I was able to cut it at one point with a fly cutter on my drill press.
>> For some reason I did it once, and it never worked again.  Tends to bind
>> with the bit.
>> 
>> I'm using collars on both sides of the tungsten rod.   I got the tungsten
>> from McMaster Carr.  It's sold as tungsten carbide rod.  # 8788A158.
>> 
>> I've actually got all the stuff for a propeller gap but I keep having this
>> nightmare vision of one of those 7" tungsten rods flying loose.  Also, I'm
>> wondering how to secure the white plastic to the motor.  Seems too "soft" a
>> connection if you don't machine it right.  I mean, you're not using a set
>> screw with that, right?  What keeps it from coming loose an screwing up your
>> dwell setting?
>> 
>> I will try the dremel on the tungsten.
>> 
>> Well, I disconnected the fan, lowered the strike ring - good results.   I
>> also tried stacking toroids - I still have my 12x3, and it put it below my
>> 18x4.5 just to see what would happen.  But just laying one on top of the
>> other didn't seem to do too much...
>> 
>> I was able to cut the garolite sheets I got, finally.   Got a Jasper circle
>> cutter, as was suggested here on TCML.  Got a spiral bit for my router and
>> used it in "plunge cut" mode.
>> 
>> Well, generally I hate spiral cutters.  I have a rotozip and I avoid using
>> it on home improvement projects - it just tends to spew wood/gypsum/paper
>> all over kingdom come.  The kerf from the blade is quite wide and all that
>> material gets flung outward toward the operator.
>> 
>> The Jasper + spiral cut is basically a rotozip on a jig.  Then making
>> another jig to hold down the garolite plate and setting the Jasper Pin in
>> the center - I was able to get it to work.  I'm covered in Garolite dust.
>> Used a mask - but mask or no mask, it gets all over and you're breathing it
>> no matter what.  And with the Jasper template you need to account for the
>> kerf from the bit.  I set mine to make a 7" circle and it came out 6 5/8
>> (you get the kerf on both sides of the circle - so the diameter is reduced
>> by the bit width x2)  Wish I had thought of that before I cut through a 12"
>> square sheet of G10.  Alas.
>> 
>> But I'm going to start on the "production" SRSG.  Thinking to do a design
>> like the ones on John's website, where each of the rotating tungsten
>> electrodes shorts out the HV supply on both sides - so there's no current
>> flowing through the rotating disk itself.
>> 
>> CHeers,
>> Joe
>> 
>> 
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