Re: EDM troubles

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
<davemucha@j...> wrote:

> Hi all,
>
> simple RC EDM unit. after test drilling some holes in steel with a
> copper electrode, I pulled the electrode out mid spark to inspect

the

> progress and now it does not start to spark easily.
>
> It went from full voltage to sparking voltage without a spark, then
> quickly went to a short.
>
> do the electrodes get dirty with carbon ?
>
> any suggestions ?
>
> Sparkless in New Jersey. (Dave)

Dave,

EDM electrodes take time to 'bed in' so that there is uniform
contact across a wide area, rather than just at one point. Even
rotating a circular electrode it takes time for the current to come
up to the calculated value on my commercial die sinker edm (Eurospark
H425).

I suspect that maybe you have raised your electrode, and lowered it
in a slightly different place (rotationally perhaps) so what was
bedded, no longer is.

Flushing the gap makes an enormous difference to the rate of cutting
by both carrying away the eroded material and ensuring correct
discharging conditions rather than arcing. I always pump fluid
through the electrode if the shape permits.

Interestingly, fresh edm fluid is less effective until it gets a
small build up of ionised debris in it, but too much debris and it
slows down again - my fluid is filtered though what look like two
large cylindrical lorry air filters as the machine runs.

(Of course it is always possible that your edm psu died as you raised
the electrode)

Andrew Mawson
Bromley, Kent, UK