Re: [CAD_CAM_EDM_DRO] Commercial EDM capacitance ranges

Hi Larry:
The open circuit voltage is irrelevant to the spark gap voltage as far
as I can tell, and can't be manipulated on my machine, but the voltage range
in which a spark can be provoked across the gap can be manipulated, as can
the characteristics of the pulse.
Frequency, amplitude, rise time, duration can all be doodled to suit the
job...all of this capability attempts to permit the achievement of
acceptable finish in the face of spark gap contamination while preserving
the electrode as much as possible.

This ability to manipulate the pulse characteristics far exceeds that of
home brew rigs which appear to depend on the discharge of capacitor banks in
response to a reference voltage, to generate a pulse train.
The discharge characteristics of the capacitors therefore govern most of the
characteristics of the resultant pulses, and can't be easily manipulated.
(correct me, anyone, if I'm wrong here...I don't know diddly about
electronics!!!)

Moving on to the dielectric; there are lots more reasons to use deionized
water in wire cutting than just the basic stuff I described.
Water works so well, at least in part because it is so fluid, and the bulk
of what the dielectric has to do in a purely mechanical sense, is to
penetrate the slot and flush out the crud.
This is at least 50% of what makes a wire EDM go, and to this end, high
pressure flushing up to 300 odd PSI is used routinely.
The position of the flush cups is critical to success and the dielectric
"constant" of the deionized water is critical too (of course, it's not
really constant because it's continuously being contaminated by metallic
ions).
Stagnant zones and worse yet, starved zones kill the process dead!!
So the fluidity of the medium is crucial in many senses.

When we consider wire consumption, a lot is at play here too.
Wire speed, the current across the gap, the thickness of the block, and to
some relatively small extent, the characteristics of the dielectric, will
influence the rate of wire erosion.
So will the polarity of the job vs the electrode and the stuff the wire is
made of.

In wire EDM operations, consistency of the process parameters is King...you
aim to get everything cooking just so, and the speed of the cut will depend
on your ability to get there in the first place, and then to maintain it
that way for the duration.
This is possible because the geometry of the slot never changes. (from the
point of view of what the wire sees)
With a sinker, the geometry of the spark gap is constantly changing as the
electrode penetrates into the job, and starts to wear.
From the perspective of the dielectric fluid trying to crawl into the gap
and flush all the crap out, it's a constantly varying task.

So the problems are quite different from a process point of view between
wire and sinker.
Since the sinker electrode is a labour intensive part of the job, any gains
in your ability to preserve it are valuable, and the ability of the
dielectric to remain reasonably constant in dielectric properties, for long
periods of gross contamination is far more important simply because you
can't hope to circulate it as efficiently.
Sinker oils aim to get there, but precisely how they achieve that is beyond
my current understanding.

Regarding price.....oh how right you are!
I think of these words every time I need to buy copper, fill my dielectric
tank, fart about getting the cut to stay stable etc etc etc.
EDM is not for the faint of heart if you intend to make money at it.
But it's a fascinating process, and mastery of it enables you to make things
that nobody else can even get close to.
It's one of the coolest (but smelliest) processes around for metalworking.
Hope all this helps.
Cheers

Marcus

----- Original Message -----
From: "Larry Edington" <ledington@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Monday, February 10, 2003 7:11 PM
Subject: Re: [CAD_CAM_EDM_DRO] Commercial EDM capacitance ranges


> Very good information thanks.
>
> Can you adjust the voltage level your machine puts out when it's open
> circuit?
>
> I assume you can adjust the on and off time of the spark?
>
> The water versus oil in the wire makes sense now. The wire is 'wasted' so
> you don't
> care if the water causes more electrode errosion.
>
> Seems to me though for the home shop or hobbiest, using oil instead of
water
> to make that wire
> go further would be a good thing to do. I've priced EDM wire and it's not
> cheap. But neither is
> anything else that has EDM stuck on it. Kind of like Mercedes and
airplanes
> <grin>.
>
> thanks,
> Larry Edington
> ( so I won't be confused with the other Larry E. here )
>
>
> ----- Original Message -----
> From: "Marcus & Eva" <implmex@...>
> To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> Sent: Monday, February 10, 2003 10:48 AM
> Subject: Re: [CAD_CAM_EDM_DRO] Commercial EDM capacitance ranges
>
>
> > Hi Larry:
> > My Hansvedt EDM (sinker) runs typically at about 30 to 40 volts
while
> > sparking and 80 volts open circuit.(depends on what gap I need to flush
> > well)
> > The lowest power setting runs at about 0.1 amp, and max on my machine is
> 20
> > amps.
>
> > I can set the capacitance from zero to about 20 microfarads (I think
it's
> > microfarads!!) in 0.05 microfarad steps.