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RE: [TCML] G-10 blistering

I made aluminum collars for my electrodes with 1/2" aluminum bolts (then
drilled a 1/4" hole down the axis of the bolt. Then I tapped an 8-32 thread
for a set screw to hold the electrode in place)

One thing I did notice was that the extra material poking out from the 12"
disc (the collars) did create enough air drag that my SRSG (with two flats
machined into the rotor for 3600 RPM) would jump out of phase regularly. I
finally machined the collars so no extra material was exposed, and then
removed two of the contacts that would be passing through zero volts (it now
has 6 electrodes instead of 8). This reduced the drag to a point that the
SRSG maintained synchronization.



-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of David Rieben
Sent: Monday, June 16, 2008 8:47 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] G-10 blistering

Hi Phil,

I like the clamp-on shaft collar idea and went ahead and ordered 16
of those aluminum ones from McM-C today. As long as I place one on
each end of each of the 8 flying electrodes, I don't see why the rotary
disc would need to be (re)balanced, so long as it was decently ba-
lanced in the first place and the motor is suffciently strong enough to
spin the additional mass of the added collars. This should definitely in-
crease the thermal mass and the aluminum would also conduct heat
away from the tungsten "core" electrodes better.

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
> collars:
>    From McMaster-Carr (_www.mcmaster.com_ (http://www.mcmaster.com) ):
> 6157K13
> 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:
> 6435K13
> One-Piece Clamp-on Shaft Collar Black-Oxide  Steel, 3/8" Bore, 7/8" OD, 
> 3/8"
> Width
> 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
> conductivity.
>    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
> **************Vote for your city's best dining and nightlife. City's Best
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