RE: FEA analysis of 12" rotary spark gap disk, any tapering on the electrodes?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Rich" <rdjmgmt@xxxxxxxxxx>

I am not making a gap myself but I have pressed many steel bushings into
alum holes when I was working in the aircraft industry. If a small
radius, chamfer or starting undercut is not included on the male part
you stand a good chance of the electrode acting like a broach. May I
suggest that you put the electrode in the freezer over night, and the
disk be warmed up to its maximum suggested operating temp. We used LN2
and it worked fine for .0005 to .0015 interference.

Rich , from the middle of Missouri

-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Saturday, May 27, 2006 5:15 PM
To: tesla@xxxxxxxxxx
Subject: RE: FEA analysis of 12" rotary spark gap disk, any tapering on
the electrodes?

Original poster: "MakingLightning" <MakingLightning@xxxxxxxxxxx>

Jim,

I was thinking it would be too hard to put a taper on the electrode,
maybe
this could be done on the hole when I am getting it machined?

Kevin

-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Friday, May 26, 2006 7:42 PM
To: tesla@xxxxxxxxxx
Subject: RE: FEA analysis of 12" rotary spark gap disk, any tapering on
the
electrodes?

Original poster: "Jim Mora" <jmora@xxxxxxxxxxx>



Hi Kevin, et al,

Nice analysis! I hope you don't mind I sent a copy to my machinist. I'm
wondering if any taper is put on the ends of the electrodes (.5") or are
they just pressed in (.0005") with a square edge?

Jim Mora

-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Tuesday, May 23, 2006 8:41 PM
To: tesla@xxxxxxxxxx
Subject: FEA analysis of 12" rotary spark gap disk

Original poster: "MakingLightning" <MakingLightning@xxxxxxxxxxx>

I am designing a 12" rotary spark gap.
I really wanted some hard numbers so I knew where I stood on the
safety margins. I also wondered how good a press fit electrode was
held in. I had it 3D modeled in SDRC IDEAS and then analyzed it with
their FEA package called Visualizer. It was calculated and the
numbers matched what the FEA came up with.
It was really nice to see how the press fit stress reacted with the
spinning disk.

Chip posted graphic representations of the results for me at:
<http://www.pupman.com/kevin>http://www.pupman.com/kevin

The disk I will be using is:

12" diameter 1/2" thick G-10 fiberglass laminate.
8 - 1/2" diameter x 1.5" long pure tungsten electrodes Top speed 4000
rpm which equals 533 BPS, way more than I anticipate using.

G10 Fiberglass:
<http://matweb.com/search/SpecificMaterial.asp?bassnum=PGLAM04>http://ma
tweb
.com/search/SpecificMaterial.asp?bassnum=PGLAM04

Tungsten:
<http://matweb.com/search/SpecificMaterial.asp?bassnum=AMEW000>http://ma
tweb
.com/search/SpecificMaterial.asp?bassnum=AMEW000

In my presentation that chip posted for me you will see that the top
shot is the disk with the hole in it, at rest.
The one next to it is spinning 4000rpm.

The next set starts with the 0.5" electrode press fit into a hole
0.0005" undersize hole, as Dr Resonance recommends. On the left is
the disc at rest and the right is spinning at speed.