Re: [CAD_CAM_EDM_DRO] Re: Question fro Jon Elson

thscarince@... wrote:

> Ah Ha!
>
> Out of curiosity I searched McMaster-Carr to see if they might have
> copper hex stock (electrode by the foot!). They don't, but they do
> carry *beryllium* copper hex wrenches for non-sparking applications.
>
> No idea if the beryllium would be a problem...

I wouldn't use it! The EDM fluid would be serious HAZ-MAT after
use, and you wouldn't want to touch it. The polarity of the EDM
circuit puts most of the erosion into the workpiece, but the electrode
does wear away, too. And, so, you would have finely atomized beryllium
floating around in the fluid.

>
> BTW, I was captivated by Jon's junkbox EDM setup! Is that really all
> there is to it?

Well, it works! but, it isn't fast.

> Does EDM require short pulses or a continuous arc
> like a welder?

It is short pulses. If a continuous arc develops, it will burn a big hole
in both
the work and electrode at that spot. What you want is lots of little sparks

all over the tiny space between work and electrode.

> Does polarity matter?

Yes, it is the only thing that determines which is electrode and which
is workpiece!

> How about AC?

No, then the electrode and workpiece would be eroded equally.

> What properties
> are make a good electrode material?

Something that resists burning away. Copper-loaded materials (brazing rod,
brass, copper, bronze, etc.) and graphite are favorites.

Anyway, my (and many others') RC EDM circuits are slow and a bit
temperamental.
For the best results, an electronic switch that cuts off current some time
interval after the discharge starts, and then restores the power after a
set 'deionizing' time will give much faster cutting. You can probably get
10,000 discharges a second with a pulser, and rarely more than 100 with
the RC. But, it is simple, and it does work.

Jon