Re: Question fro Jon Elson

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
> thscarince@h... 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