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Re: [TCML] G-10 blistering

Using 1/2 inch brass rod for the feedthru eliminates this problem
completely.  I have never had one come loose and never use setscrews to
eliminate the cracking problem you described.  I run all mine at .75" in to
edge of brass rod.  This calls for larger rotors but it's safer.

I ream for .0005 differtial and use a large press (as you mentioned).  I
also always use a milling machine turntable to get the centerpoints .001"

This is another reason (safety) why builders should use proper materials and
step up and always have a competent machine shop do this work especially if
the coil is going to be run in any type of public event.

The $50 you save by not using brass is quickly lost when you begin paying
attorneys.  Sure, your home insurance, or the public events insurance,  may,
under some circumstances cover it, but then their attorneys come after you!

Dr. Resonance

On Sun, Jun 15, 2008 at 6:27 AM, <FIFTYGUY@xxxxxxx> wrote:

> 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
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