Re: [CAD_CAM_EDM_DRO] PC ports, Encoder resolution and EDM PSU info

----- Original Message -----
From: Dennis Fielder <dennis.fielder@...>
>
> 2) Having 'sparked' an interest in EDM (and reading The EDM Handbook for
starters), does anyone have
> a source of info on the PSU designs used (seems it's mainly proprietary
black magic), and how fast
> does the wire move in wire EDM (the handbook above never mentions this).
>

Wire EDM is very complex - plunge EDM is bad enough, but wire EDM adds in
the complexities of cnc to maintaining a good spark. EDM machines, as far as
I can tell, use two separate PSUs, one for the electronics which is like an
ordinary computer PSU, and one for the spark which is a simple
transformer/rectifier/bank-of-capacitors type operating at a voltage of
between about 60 volts and 300 volts. The electronics of the machine mess
about with this to give a chopped supply to the electrode and to derive a
feedback signal from it. There is usually a big wire-wound resistor in
series with the supply which absorbes the excess power when the electrode
shorts out to the work.

I have seen two types of wire EDM machine which operated in different ways.
One fed brass? wire fairly slowly from a spool above the work, through feed
rollers and jewelled guides to a point below the work where it was chopped
into 3/4" lengths which then dropped into a bin for disposal. i.e. the wire
was only used for one slow pass. The other machine had spools above and
below the work about 8" diameter which had a length of tungsten wire fixed
between them. In use the wire unwound from the top spool onto the bottom one
in about 20 seconds and then reversed and wound back up onto the top one
again in the same time. This process went on continuously while the machine
was running and the wire was only changed when it got below a certain
diameter.

I am currently trying to locate a copy of the book Robert Langloise wrote on
making a simple EDM in the hope of being able to work up a design for a wire
EDM but the book seems to be out of print and so I'm having to be nice to my
brother in the hope that I can get him to spend some time searching second
hand bookshops when he goes over to MIT in a few weeks!

Ian
--
Ian W. Wright
Sheffield UK