[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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

Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

An easy method to add a radius to the pure tungsten edge is to insert the electrode into a drill and simple spin the electrode edge against a file. I've actually put very large radius's on my electrodes using this method. It's quite easy and no special machinery is required. After the radius is achieved, spin the electrode into a mass of steel wool to give it a nice polish.

Take care,

Tesla list wrote:

Original poster: "Scott Hanson" <huil888@xxxxxxxxxxxx>

Kevin -

Putting a chamfer on the mouth of the hole is NOT the same as putting a chamfer on the leading edge of the electrode. You must put the chamfer on the electrode to prevent broaching material from the hole and losing the critical interference fit. Remember that one end of the electrode gets pushed completely through the disk, so you need to prevent broaching during the entire pressing operation.

Pure tungsten is quite hard, but a chamfer can be created on a lathe with a sharp tungsten carbide cutting tool, a bench grinder with a diamond or "green" wheel ( as used for sharpening tungsten carbide cutting tools), or even on a belt sander with a 220-320 grit belt. I used a belt sander last week to chamfer some pieces of 3/8" tungsten rod from the recent "group buy" here on the TCML. All you really need to do us break the edge so it won't scrape material from the RSG disk as it is being pressed in.

Scott Hanson

----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Saturday, May 27, 2006 3:15 PM
Subject: RE: FEA analysis of 12" rotary spark gap disk, any tapering on the electrodes?

Original poster: "MakingLightning" <MakingLightning@xxxxxxxxxxx>


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?


-----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

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:

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:


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.