Re: Brand new to the group

Jon, In message #14380 I was referring to the 'Langlois' EDM machine
which I am using. And it works like a gem.
The spark is moving all the time. The stepper motor moves the
electrode away from the work when the 'gap' voltage falls below a
preset value,and toward the work when the voltage rises to another
preset value. This is controlled by the use of a window comparator
plus the other necessary logic circuitry needed to drive the stepper.

The problem in this case is the relatively slow response time of the
stepper and the screw setup which moves the electrode. It is not in
the order of microseconds.

There is one other feature in the Langlois machine which gives a
rough control of the rep rate of the charge/discharge system in that
you can choose several capacitor values (time constant).

Yes, you are right in what you said regarding pulse width means of
spark control but I don't think it would be an easy change for me to
make on my unit. Thanks for the response. Richard

--- In CAD_CAM_EDM_DRO@egroups.com, Jon Elson <jmelson@a...> wrote:
>
>
> Richard wrote:
>
> > Ian,I fooled with some timers and then quit. I looked at the spark
> > waveforms using an oscilloscope and hidden in all the noise
seemed to
> > be a sawtooth waveform, a dead give away that what we have is a
> > relaxation oscillator. The frequency of the arcing waveform is
> > dependent on the capacitance, resistance and I'm sure the spark
gap
> > and the fluid used for the dielectric.Thus it seems to me that the
> > frequencies will be dictated by the circuit and mechanics. Please
> > don't get rough if you think I'm wrong.
>
> Precisely. The EDM discharge is going to control the whole process,
> for sure. But, you can control the nature of the spark by turning
current
> off after the discharge has been going for some desired time, and
allow
> ions to recombine for some desired time before making voltage
> available to the electrode, again. I think this is how the
electronically
> controlled EDM systems work. I think the whole idea is to keep the
> spark 'moving', ie. don't let the discharge keep burning in one spot
> for more than a few microseconds, before you interrupt it and let a
> new discharge develop at another point.
>
> I'm going to have to try this, it doesn't sound too difficult.
>
> Jon