Re: Electrode holder material for a high-power RSG

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "BunnyKiller by way of Terry Fritz <twftesla-at-uswest-dot-net>" <bigfoo39-at-telocity-dot-com>

Tesla list wrote:

> Original poster: "Mark Broker by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <broker-at-uwplatt.edu>
>
> Hello, all
>
> I am making an RSG that I hope to one day (years away) use with a big TC
> (25kVA) at 3600RPM (thinking 5kRPM *MAX*), though I'll be starting with a
> 1200RPM motor (min speed).  Since I have the resources literally at my
> fingertips until this May, I thought I'd build this puppy now.
>

Snipperzzz...


Hi Mark...

looks like you do some very nice machining...   but...   consider using
electrodes that are long
enuf to be the total path of current ( dont use 2 smaller electrodes per
unit) it isnt that
difficult to grind tungsten electrodes to 2 thousandths accuracy.. make the
electrode holder as low
profile as possible with as much electrode extending above it. 1/2" is a
minimal extended length at
hi power.  ( at 15KV the arc isnt going to hit just the tips of the
electrodes, at hi power it will
jump up to 1/2" or more to make contact)

also consider using socket set screws ( cup point style) to secure the
electrode to the holder and
the holder in the disc. ( this will reduce air friction) If you make the
holes for the electrodes a
light slip fit, you will only need one set screw per electrode ( the 90
degree 2 set screw pattern
is needed when you have several thousandths clearance in the hole /shaft
assy. )

Since you have the intention to round off the heads of the electrodes, try
to make the heads
hemispherical instead of oblated ( bullet nosed).

Another item to consider is the amount of force that is going to be applied
to the disc -at- 5000 rpm
by the electrode assy. As the rpms increase, the mass of the electrodes
will want to shear out the
thinner area on the outside diameter of the disc, plus having a hole
tangent to the disc for
securing the electrode assy in the disc weakens the disc even more. ( you
can either make the disc
a bit larger in dia.((13")) and keep the 10" dia for the electrodes or you
can move the electrodes
in another 1/2" (( you want approximately the same thickness of edge
measure as the dia. of the
electrode holder... example if the electrode holder dia. is 3/4" you want
at least 3/4" of material
from the holder to the outside edge of the disc)).

What BPS are you looking for ?   12 electrodes at 5000 rpm will give you
1000 BPS ( good for
magnifiers but you will need a BIG pole pig and a small cap to make it
effective). Consider
reducing the number of electrode sets. 120BPS is a good starting point for
SRSG's.  ( 4 electode
sets at 1800 RPM , you can also drill holes for 8 electrode sets and add
the electrodes later for
240BPS -at- 1800 RPM).

In your cad drawing I noticed that your mounting holes ( shaft flange plate
to disc) are a bit
small in circumference. consider making the flang plate about 4" in
diameter. ( this will reduce
the opportunity of the disc to wobble ( develope run out).

hope this helped


Scot D