Re: EDM

some more info.
I suggest you use a step down transformer --120v to 60v
after you run the 60v ac threw a 20 amp full wave rectifer and a 2000uf cap.
you will end up with aprox. 80v dc----because of rms
98% of the edms use this voltage--why?---because a higher voltage=increased
electrode where.

My power supply can provide up to 9 or 10 amps.This is limited by ballast
resisters---200w
Most jobs use 5amps for rufing and 2-3 amps for finishing.

Caps---.1uf for fine finishes
a number of .3uf 5 i think
all caps can be connected in parallel by switches to change power
they are myler 400v
DO NOT USE ELECTROLYTIC TYPE CAPs
they cannot stand up to the high charge and discharge cycles --good for
the 4th. of july but not good for soft flesh.

on off times-- In order to obtain the lowest wear it is nessary to control
how long the discharge lasts in usec. and how long for the next discharge.
An example for low wear would be 100usec. on--25usec.off
In my machine this is controlled by mosfets.
we will get into this in more detail latter.

Details of op amp ckt.
It consists of 2comparators using a 1458 chip .
The voltage across the gap is compared to ref. voltages
set on the machine.
A high limit and a low limit
this in turn tells the stepper motor driver to advance or retract the electrode.
The gap between elec. and work being controlled and maintained at around
.001 to .002
Tim Goldstein wrote:

> From: "Tim Goldstein" <timg@...>
>
> Scott,
>
> Thanks for the quick reply and info.
>
> Here are the questions that come to mind.
>
> You suggest a 60 v power supply. What happens if you up the voltage?
>
> What type of amperage does your power supply provide?
>
> What type of caps are you using for the spark and how large a value?
>
> I am not following what you mean by adjustable on/off times.
>
> By adjustable power setting do you mean the capacitance or the voltage or
> both?
>
> Can you give details of the op amp circuit that controls the steppers? I am
> assuming it outputs a step and direction signal to the stepper controller
> board?
>
> Where do you get the graphite for the electrodes and the EDM oil from? Any
> suggestions for a source that sells small quantities?
>
> Thanks in advance for you help in this.
>
> Tim
> [Denver, CO]
>
> ----- Original Message -----
>
> > From: Scott Acorn <sacorn@...>
> >
> > Hi Tim
> > Well its a long story !
> > The machine i have is the result of about 5yr. of design and dev.
> > This machine will do some very fine work and i use it for making
> > plastic injection molds.
> > It has adj. on off times as well as adj. power settings.
> > The ram is powered by a small stepper with a small belt reduction set up,
> > so each step moves the ram down a very small amount.
> > A op amp ckt. looks at the voltage across the gap while the machine is
> cutting.
> > this in turn tells the ram stepper to go lower or to backup.
> > I can keep yoking but it may be boring if i do.
> > so if you would like any other info. just ask--- if the interest is their
> i can answer
> > just about any question on edm that you might have.
> >
> > Pit falls and dangers
> > use only edm oil in your mach. ------Fire
> > only edm in a sumerged tank of oil with a min. of 1" oil covering part
> > edm power supplies---use a step down transformer 60v is ideal.
> > best electrode mat. ---- graphite
> >
> > I guess the bottom line would be ----edm mach. can be very simple or very
> > complex---it all depends on the work you plan to do.
> >
> > Scott Acorn
>
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