Thanks for the feedback, Steve. I'm not sure that my electrodes are eroding
as much as they are simply discoloring. The stationary electrodes are
definitely eroding, but I have a stash of 3/8" tungsten rod to replace
those some day.
I do have a lathe and mill (which I didn't when I built this gap!), so
swapping to the bolt/nut combo for the electrode holders is doable. The
flying electrodes don't really get hot (or at least they're room
temperature after shutdown).
I have a 15kva pole transformer waiting in the wings unless I get my first
CM300 bridge going before I acquire the last big GE cap I need for the pole
transformer setup... For that I would likely add another electrode pair to
the other side of the gap and run the two in series to increase the
breaking velocity. I'd probably do that before switching to full electrode
holders.
And for anyone else following along, if you need to precision drill a round
part and you only have a drill press, the trick is to spin the part itself
and put the drill in the vise. The drill will tend to be self-centering if
you leave the vise floating on the table, and it won't break down to a
certain size.
On Thu, Oct 25, 2018 at 8:49 PM Steve White <steve.white1@xxxxxxxxx> wrote:
> Hello Andrew,
>
> Nice looking SRSG. I see that your 1/8" flying electrodes are showing some
> erosion. My rotor is 11" of 1/2" G10 spinning at 3600 RPM with a 1/2 HP
> synchronous motor. I also use 1/8" tungsten electrodes. I want to share
> something I did, quite by accident, that seems to reduce flying electrode
> erosion a lot. Instead of just pressing the electrodes into the disk and
> securing with a grub screw, I have each flying electrode mounted in a brass
> bolt (1/4-20 I think) secured by a brass nut. I drilled a 1/8" hole through
> each of the brass bolts for the tungsten electrodes to pass through. I then
> drilled and tapped 2 grub screw holes in the sides of the head of each
> bolt. The grub screws then secure the tungsten electrodes to the brass
> bolts. My motivation was to provide a more secure way to mount the flying
> electrodes to the disk, which I achieved, but there was an added benefit
> that I did not anticipate. The brass bolts serve as excellent heat sinks at
> the 3600 RPM rotor speed. After
> many hours of operation I can see no noticeable erosion on the flying
> electrodes even though my coil is powered by a pole pig and operates at 4.8
> KVA. The only disadvantage is that it adds more rotating weight to the
> rotor and thus is more difficult to balance, but I managed.
>
> Looking at your SRSG it would be pretty easy to change to this mounting
> method if you wanted. Just enlarge your mounting holes on the rotor. You
> need to have a precision method to drill the 1/8" holes through the brass
> bolts. Fortunately I have a lathe. You could probably do it with a drill
> press if you are careful.
>
> Steve White
> Cedar Rapids, Iowa
>
> ----- Original Message -----
> From: "Andrew Cobaugh" <andrew.cobaugh@xxxxxxxxx>
> To: "Tesla list" <tesla@xxxxxxxxxx>
> Sent: Thursday, October 25, 2018 1:01:48 PM
> Subject: Re: [TCML] SRSG strobe
>
> On the topic of balancing, when I built my ARSG, I ground the flying
> electrodes until they were within 1/100th of a gram of each other (used a
> reloading balance). That got it close enough to fine tune from there.
>
> For reference, the disc was 12"x1/2" G10, with 8 1/8" pure tungsten
> electrodes, spun by a 1/2HP 10krpm universal motor.
>
> I have a few pictures of the gap here:
> https://photos.app.goo.gl/VpwqXLNhbGJMVU4e8
>
> From there, I built a static balancing jig using hard drive motors and
> platters. The hard drive motors have high precision bearings, and the
> platters provide torque multiplication properties that made it very
> sensitive to changes in weight. A piece of drill rod was used as the arbor
> when balancing. I placed different amounts of putty on the disk until it
> stopped rotating on its own, and until it would stop at a random location
> each time it was spun. The putty was then replaced with an equal weight in
> screws and washers.
>
> Even after many minutes of runtime at 6KW+, I haven't noticed any
> significant amount of wear on the flying electrodes, and it doesn't seem to
> be vibrating any more than it did when new. I suppose I could pull a few
> electrodes and weigh them to quantify how much they've eroded (I kept very
> good notes during the build, so I know the starting weight).
>
> I can't seem to find pictures of the balancing jig at the moment. Picture
> something like this, but much smaller: https://tinyurl.com/yd7tm8hr
>
> I'm not sure if I like the idea of setting the electrodes parallel to each
> other. The alignment would be super critical to ensure they are eroding
> evenly. After they wear enough, the structural integrity, especially at
> those speeds, could be called into question if they are wearing more in the
> middle. It would also bring the arcs closer to the disk, which might mean
> exposing the disk material to higher temperatures. I think keeping the
> electrodes aligned with the ends facing each other is probably the safer
> way to go. If you need the extra surface area for power dissipation, I
> would lean towards increasing electrode diameter or running electrodes in
> parallel so you have multiple pairs aligning at the same time.
>
>
> On Thu, Oct 25, 2018 at 1:26 PM Daniel Kunkel <dankunkel@xxxxxxxxx> wrote:
>
> > Terry,
> > RC Plan Proper balancer! Genius! Thanks for pointing this out to me. If
> my
> > homemade balance wheel does not work this seems like a cheap and readily
> > available option. I just hope it is stout enough to handle the mass of
> the
> > rotor/disc/electrodes.
> > Thanks,
> > ~Dan
> >
> > On Wed, Oct 24, 2018 at 7:27 PM Terry Oxandale <Toxandale@xxxxxxx>
> wrote:
> >
> > > Yeah, I had to use a prop balancer (from my old RC airplane days) to
> get
> > > mine close enough were I felt comfortable with the very small
> vibrations
> > > that still exist.
> > >
> > > -----Original Message-----
> > > From: Tesla [mailto:tesla-bounces@xxxxxxxxxx] On Behalf Of Steve White
> > > Sent: Monday, October 22, 2018 10:12 PM
> > > To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> > > Subject: **External Email** Re: [TCML] SRSG strobe
> > >
> > > Dan,
> > >
> > > Since I read that you are using a 3600 RPM rotor, balance will be
> > crucial,
> > > otherwise it could fly apart or shake your coil to pieces. I had a very
> > > hard time balancing just 4 tungsten flying electrodes on an 11" rotor
> > > turning 3600 RPM. I can't imagine how I would balance 16. I hope you
> have
> > > special balancing equipment. Even if you get the rotor perfectly
> > balanced,
> > > as the the flying electrodes wear, the rotor will begin to unbalance.
> It
> > > all depends on how even the erosion is. What I am saying is that the
> more
> > > flying electrodes that you have, the more difficult things become.
> > >
> > > Steve White
> > > Cedar Rapids, Iowa
> > >
> > > ----- Original Message -----
> > > From: "Daniel Kunkel" <dankunkel@xxxxxxxxx>
> > > To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> > > Sent: Monday, October 22, 2018 8:37:46 PM
> > > Subject: Re: [TCML] SRSG strobe
> > >
> > > Steve,
> > > I'll definitely experiment with the bps. 16 holes will allow for quite
> a
> > > lot of possibilities....
> > > 120
> > > 240
> > > 480
> > > 960
> > > I can't wait to see the final results!
> > > ~Dan
> > >
> > >
> > > On Mon, Oct 22, 2018, 8:30 PM Steve White <steve.white1@xxxxxxxxx>
> > wrote:
> > >
> > > > I know that using an optical sensor with an oscilloscope provides a
> > > > very precise way to insure that the flying electrodes line up with
> the
> > > > stationary electrodes at whatever phase angle on the 60 Hz power line
> > > > that you pick on the oscilloscope. Now, whether or not that is the
> > > > optimum firing point may be a different matter. On my pole-pig
> powered
> > > > coil which runs at 240 BPS, the firing angles of 0, 90, 180, and 270
> > > > degrees which I set with my oscilloscope did indeed seem to be the
> > > > optimum. I built a very nice John Freau style phase adjuster to make
> > > > fine adjustments. When I used it to vary the phase angle from the one
> > > > that I set with the oscilloscope, I saw no difference in streamer
> > > > performance or quality. Maybe the effect is much greater with a 120
> > > > BPS NST-powered system. Some posters have suggested that a 240 BPS
> > > > system is closer in performance to a ARSG because it fires 4 times
> per
> > > cycle where firing points may not be as critical.
> > > >
> > > > Steve White
> > > > Cedar Rapids, Iowa
> > > >
> > > > ----- Original Message -----
> > > > From: "Gary Lau" <glau1024@xxxxxxxxx>
> > > > To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> > > > Sent: Monday, October 22, 2018 5:09:07 PM
> > > > Subject: Re: [TCML] SRSG strobe
> > > >
> > > > What exactly is the goal here? Assuming that you're successful in
> > > > getting the timing light to sync and fire 120PPS, that still gives no
> > > > useful information as to whether the RSG is set to fire at the
> optimum
> > > > phase angle. The best you can hope for is confirmation that the
> motor
> > > > is in fact synchronous and that the phase can be varied. I'm unaware
> > > > of any means to set the phase other than varying the phase and
> > > > monitoring spark performance. The optimum phase of the RSG relative
> > > > to the mains phase will vary with primary cap size and Variac
> setting,
> > > there's no fixed "best"
> > > > setting relative to mains peak. That's why the variable Freau SRSG
> > > > controller* is such a godsend - it's always something that you'll
> want
> > > > to tweak. In my experience, the SRSG phase is super-critical at
> > > > 120BPS, there's a clear increase in spark performance as I retard the
> > > > firing, up until a critical point, and then it becomes unstable, so I
> > > > back it off a tad.
> > > >
> > > > As far as protecting the NST, a safety gap in parallel is mandatory
> in
> > > > parallel with the RSG.
> > > >
> > > > For a simpler means of viewing the phase of your SRSG relative to
> > > > mains phase, attach a small magnet to the shaft, and mount a small,
> > > > high turns count inductor so that the magnet sweeps past it. Scope
> > > > the voltage across the inductor and sync the scope to the line. You
> > > > should see induced voltage blips with each sweep of the magnet, and
> > > > you should see that waveform shift as you vary the phase of the SRSG.
> > > >
> > > > *See my RSG web page - http://www.laushaus.com/tesla/sync_gap.htm
> > > >
> > > > Regards,
> > > > Gary Lau
> > > > MA, USA
> > > >
> > > >
> > > > On Sun, Oct 21, 2018 at 11:55 PM Daniel Kunkel <dankunkel@xxxxxxxxx>
> > > > wrote:
> > > >
> > > > > I'm getting ready to build my phase controller to control my new
> > > > > SRSG. I thought I've heard of others use an automotive ignition
> > > > > timing light to strobe and watch the phasing, but I can't get mine
> > > > > to trigger off a 60Hz source. Can anyone offer some advice here?
> > > > > ~Dan
> > > > > Kansas City area
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> --
> andy
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