Re: EDM home brew units ?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Graham Stabler" <eexgs@n...>
wrote:

You are talking about setting the gap voltage but you

> can't do that like you do with a free running RC circuit because the
> cap will always be charged (to some level) when applied to the gap.
> You could change the level you charge it to but then you would need

to

> control the gap by looking at how long it took to discharge or
> something. Shorter discharge suggests lower gap resistance and

hence

> closer to arcing. Long discharge times or no discharge suggests

O/C.


You are so right! In the Langlois system the the voltage levels on
the
capacitor tell the electrode to move towards the work or away from
the
work via the comparators and stepper motor and mechanical linkage and
the gap width determines when the spark starts. When the discharge
starts the current will be C dv/dt and will discharge very fast and
the
cycle will repeat. The electrode will try to retract during the
charging time which is controlled by the power supply and the RC
network. The gap/maybe electrolyte acts like a gas tube hence the
sawtooth waveform on the charging cycle. Your control of the gap
width needs to be fast as well for a
nice system.

Richard