Re: [CAD_CAM_EDM_DRO] EDM questions

Mark Stacey wrote:

>I've built an EDM from the article in Machinists Workshop Oct/Nov 2002
>pg 24 to 26.
>I've been testing it out using my drill press and get either violent
>pops every second or so or I end up with the wire I'm using spot
>welded to the work piece. I've modified the design slightly to use
>what is avalable. It's fed by 230V 50cycle single phase (standard
>houehold current in New Zealand) The capacitors are 680uf 250v. Bridge
>rectifier is rated at 250V 20amps.
>
>

I think that is WAY too large a capacitance. I built a simple RC EDM.
I have
some switches in there so I can connect up 1.5 to 12 uF capacitors. I
usually
end up using 1.5 ot 3 uF combinations. This is at about 30 V, using a
hydrocarbon-
based dielectric fluid.

>Will most of the problems disappear if I use the slow feed on my CNC
>mill rather than a nervious hand on a drill press?
>
>

I did it with a slow feed by CNC, but it was a feed rate of about
.00015"/second.
Unless you have very high resolution on your CNC, the steps will likely
be too
big.

>Can anyone sugest what I can switch across the output leads to drain
>the capacitors after I've turned the EDM off? I don't want to
>accidently discharge the capacitors through the CNC or for that matter
>myself.
>
>

Yes, use a 1000 Ohm 2 Watt resistor.

Jon