Re: EDM questions

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mark Stacey" <pav@x> wrote:

My two cents worth---I believe that the lightbulb /rectifier power
supply is similar to the one I suggested to Dave Mucha some time ago.
Dave mentions a resistor is required, the light bulb is the
resistance and the RC combination across the electrode/work gap(
which mimics a gas tube) supplies a sawtooth voltage (relaxation
oscillator) for the spark. It is my opinion that the capacitor size
(within limits) is not too important as the frequency changes
according to the RC constant and the cutting rate is controlled.A
large capacitor slows down the rate but blasts off a larger chunk of
the workpiece due to the higher current spark, a smaller C increases
the spark frequency but balsts off a smaller chunk of the workpiece
so that the time to cut a hole is pretty constant. My EDM is adjusted
so that the electrode never touches the work always maintaining a
gap,
and sparks instead of arcs! I use tap water containing a bit of
permanent antifreeze and it works well using a drip system right down
the electrode to flush away debris. Richard



> Thanks to all have replied this is all very helpfull.
> The circult shows two light bulbs. On the positive lead from the
> bridge rectifier the bulb is before the positive leads of the two
> capacitors. On the negative lead from the rectifier the second bulb
is
> placed between the two negative leads of the two capacitors. I'm
using
> 150watt incandescents.
> I've tried both water and kerosine as dielectrics. Not much
difference
> in results.
> My mill has a fairly fine resolution as it is retro fitted with a
> Centroid full servo system so that looks to be the next step after
> wiring a resistor and a double pole switch so when the mains is off
it
> discharges the capacitors.
> Thanks once again, lots to try!
> Cheers
> Mark Stacey
> www.cncprototyping.co.nz
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
> <dave_mucha@y...> wrote:
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mark Stacey" <pav@x>
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.
> >
> > <snip>
> > >
> > > 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?
> >
> >
> > There are a few solutions.
> >
> > #1) rotate the electrode. this will prevent the huge loss thru
> > electrolicys as the electrode goes deeper.
> >
> > #2) create a step generator and comparitor loop. Monitor the
current
> > and when it is under X amps, step. Between X and Y stop lower
than
> > Y it would reverse and also step.
> >
> > This would be in combination with a screw that would feed
something
> > like 20,000 steps per inch or some very fine feed.
> >
> > #3) lower the cap to under 20uF caps in series will reduce the
> > capacatance if you have a bunch of them. Switching them in and
out
> > will offer some selection.
> >
> > I don't recall the circuit, but as someone pointed out, you need
to
> > have a resistor between the power supply and the cap. This
limits
> > the cap charging time. A 100 watt lightbulb sould do.
Incandescent
> > please. Rated for the AC voltage.
> >
> > Dave