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Re: [TCML] G-10 blistering

David, takes pics at some point. I would like to see the mounting. Even though my electrodes are nice and tight, I obviously have not run enough power through them to get them hot enough to adversely affect the G10. Still, since this problem "can" occur, I might as well take care of it now rather than find out the hard way.

Take care,

David Rieben wrote:
Hi Phil,

The shaft collars arrived from McMaster-Carr today and I removed
the rotary disc of my ARSG of my Green Monster Tesla coil to install
these collars on the flying tungsten electrodes. Just as you noted, one
or two of the flying electrodes was actually loose enough to slide up and
down in the mounting hole with the set screw still in place! The heat
(and probably the vibration too) can definitely cause the flying elec-
trodes to "loosen up"! Not too good ;^0 I have not had a chance to
try firing it off with these collars in place but at least hey should make
for a more secure placement to the disc. They did not seem to adverse-
ly affect the balance of the disc, though. The flying electrodes are still
sticking out about 1/4" or so beyond the surface of the aluminum shaft
collars so hopefully, the stationary electrodes won't spark to the collars,

David Rieben

----- Original Message ----- From: <FIFTYGUY@xxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Sunday, June 15, 2008 7:27 AM
Subject: Re: [TCML] G-10 blistering

In a message dated 6/14/08 2:00:43 P.M. Eastern Daylight Time,
bartb@xxxxxxxxxxxxxxxx writes:

I have 8 flying electrodes on my disc. Each of these  flying
electrodes is a 3/8" x 1.5" long solid tungsten rod.

Some notes with bare tungsten press-fit to  G-10:

   When I assembled the 3/8" tungsten rods into my  12" G10 disk (sound
familiar?) I did some testing in a scrap piece of G10 (the corners of the squares
I cut off to make a circle from the square piece of  3/4" thick G10). I
drilled a hole with the same distance-to-edge as the actual rotor holes and reamed it out to .373" to begin with. The rods were .375" dead-nuts, to the best of my measuring ability. I had a .374" reamer in case they ended up too tight. It took about two tons of force to get the rods into the holes, or to adjust
them once they were in. So I reamed  all 8 rotor holes to .373".
   Another thing I wanted to check was the retaining  ability of G10 at
elevated temperatures. So with a torch and a non-contact thermometer I carefully warmed a rod up to 300 deg F (past the 284 deg F max service temp of G10!). Guess what? That press-fit rod now freely slid back and forth in its hole!
After it had cooled, it was nowhere near a tight fit as it  had been.
There has been discussion here that adding a retaining setscrew thru the rotor edge actually weakens the G10. Maybe the best bet is clamping shaft

   From McMaster-Carr (_www.mcmaster.com_ (http://www.mcmaster.com) ):

One-Piece Aluminum Clamp-on Shaft Collar 3/8" Bore, 7/8" Outside Diameter,
3/8" Width
In stock at $2.25 Each

   or if you prefer thermal mass over  conductivity:

One-Piece Clamp-on Shaft Collar Black-Oxide Steel, 3/8" Bore, 7/8" OD, 3/8"
In stock at $1.99 Each

   The plain steel would probably suffer in  that environment. They also
offer stainless steel for substantially more  cost and lower thermal

I've seen some folks use shaft collars as the sole means of retention on their RSG's. Of course you'd have to re-balance after adding the collars to
both sides of the rods. Would add about $40 for my  8-electrode RSG, but
certainly seems worth it if it keeps the tungsten slugs from escaping! Might have
to watch out that the collars don't arc to the  stationary electrodes.
   Some folks use rings on the faces of the disk,  but I dunno how they
secure the rods. I also dunno how you would get heatsinking from it unless you
tack-welded the collars to the disk after  everything was assembled.
Maybe the best would be to use a solid aluminum rotor with an insulated hub or belt drive. I've got all the parts for a timing belt drive, but I
figured I'd start simple.

-Phil LaBudde
Center for the Advanced Study of Ballistic  Improbabilities

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