Re: [CAD_CAM_EDM_DRO] Another EDM Approach

Hi,

I wouldn't really want to get an EDM anywhere near a PC I was bothered
about. Don't forget that the power line to the electrode which you're using
to sense the current has pretty high power RF spikes flying about on it. An
early circuit I was playing with tried to sense the current by feeding it
directly onto a transistor - the transistors lasted milliseconds!!!
Its a problem I have been musing about for some time and, whilst it would be
appropriate to use a PC for the motion part of a wire EDM, I would want to
be very sure that there was very effective isolation between it and the
power parts of the circuit.
I had wondered whether it would be possible to pick up enough current for
sensing by wrapping a few turns of wire around the power wire to the
electrode and limiting the voltage on this by using a fast zener diode or
something.

Ian
--
Ian W. Wright
Sheffield UK
www.iw63.freeserve.co.uk

----- Original Message -----
From: <vrsculptor@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: 30 July 2001 03:31
Subject: [CAD_CAM_EDM_DRO] Another EDM Approach


> Just musing, I'm out of my depth here....
>
> I'm also interested in EDM. I had concluded, before the recent posts,
> that useable home EDM was not feasible. Seeing the recent posts I'm
> not so sure. How about simplifying the proposed circuitry by
> offloading most of the control to a PC. The parallel port already
> controls my Z axis using a step and direction pin. Could the third
> pin be tied to a one shot circuit to fire the pulse? A trim pot with
> knob on the one shot circuit could manually control the pulse length.
> Determining optimal operation (no spark, just right, short) seems
> like a much harder task. It could be done if the EDM interface board
> could post the operational status using some of the remaining
> parallel port pins. The software to drive such an arrangement would
> be trivial.
>
> Roger
>
>
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