Re: [CAD_CAM_EDM_DRO] Another EDM Approach

----- Original Message -----
From: "Jon Elson" <elson@...>
>
> The second way is to use a current transformer. Find a toroid core with
> several
> hundred turns of wire already wound on it. pass one of the EDM wires
through
> the center of the core. This is a 1:several hundred current transformer.
This
>
> signal could be prepared to trigger digital circuits rather easily. It
could
> trigger
> a 555 timer by just using a low resistance across the secondary winding as
> a 'burden', and a series resistor to limit current into the 555. You'd
need to
>
> make the polarity correct. if the pulses came out negative, then reverse
the
> way the power wire passes through the core.
>

Hi Jon,

The 555 would work for a simple plunge EDM but for a wire EDM I think it
would be necessary to sense the actual current pretty closely. I assume
that, in a wire machine, the electronics measure the current flowing through
the electrode/workpiece and use that as some form of feedback to control the
speed of the CNC part moving the work against the wire. Someone did mention
the idea of using a simpler form of current measurement which simply stopped
the CNC feeding if the current is within certain limits but I think this
would probably give a questionable surface finish - I may well be wrong and
would value the views of the group.

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