Sinker EDM machine based on diy pulse generator

Hello,

there are already some threads about this, but most of them never continued the topic or vanished. So I wanted to start another (that hopefully not has the same fate). The topic would be homemade sinker edm machine with a pulse generator. Is it possible? I just had some thoughts:

- Using the pulse generator based on Ben Flemings book (Build a pulse edm machine), but replace all the knobs and pots (if possible have not checked yet) with software and/or relais and control them via a gui.

- For simple jobs use a G1 Z-??? F??? and then somehow measure the spark gap and use motion.adaptive-feed to adjust it. The feedrate could be trial & error. Add a timer that every x seconds sets motion.adaptive-feed to -1 (or more than 1, have not tested that function yet) to lift the ram up and flush. Then use the spark gap value again to move down.

- With a XYZ(C) machine maybe even orbiting the electrode?

- Has anyone here build the Ben Fleming pulse generator?

Just trying to gather information before jumping deeper into this topic.

Thank you.

I just worked through the Ben Fleming circuit (not 100 % yet). It seems that the voltage is ~ 100 V DC and the current can be limited by power resistors. A couple of mosfets get pulsed by a 555 timer, the pulse duration is set via pots. I replicated part of the circuit in LTSpice an ran a couple of different pot settings to get an idea of the pulse on and off duration. Also compared these values to commercial machines. The calculated frequency is ranging from 0,5 kHz to 60 kHz. Do I even need the 555 timer and the two pots or could I use PWM signal from linux to do that? A mesa card can go up to 386 kHz so should be plenty of room for that.

tommylight wrote:

All those can be easily done with any microcontroller, but might need better ADC converters.

That would be important for the voltage gap feedback. Would an off the shelf voltage to frequency converter work for that?

EDM pulsae generation _is_ simple. thats true.
Some of the support circuits are not (like ionization detector)

But NB: I said 'pulse' , as in ONE pulse.

The EDM process has no use for repetitive oscilator function
( PWM is right out) .
I you use a repeating time sequence,
 you will not cut as fast as you can, 
 you will not get a uniform crater ddpeth,
 you will get longer arcs after they begin
 you will get more arcs
 and you will have to accomodate 
  by waiting langer than needed before rnext pulse.

Yes, fiexed on off will cut, 
 jdut slower and with more nad discharges.



HOW TO MAKE ONE SPARKK:
The pulse generation sequence is:

 1) Detect when gap is ready for a pulse
 
  Tickler or Sensing Voltage:
  Apply a very weak yet high voltage difference across the gap.
   (say 100V with a 250mA supply)
   
  The potenttial will stay at 100V until...
   the tool gets close enough to the workpiece,
   so close that the dielectic breaks down and 
   a tiny weak spark occurs.
   
  When the gap is small ecough,
   the gap voltage willnose dive 
   markimg when the working pulse should begin.
   marking when the gap gfot IONIZED

 2) The genertor then makes ONE pulse: 
  NOTE the sprak is triggered by the porcess not a timer.
  The current is connected 
  and ontime is decremented till 0
  
 3) During OnTime current should be monitored.
  A scope will show the current rise to avalue and stay there till OffTime negins.
  The scope will ahow a very high frequency ringiing on the 'flat'
  If that ringing stops mid OnTime, you got and arc!
  ( we wre able to shut off a bad pulse within 4us, too slow!)
  
  Such a safety circuit is not discussed here,
  other than to say itrs a good idea.
  
  Turninf off the pulse is ghood,
  but you already arced! (ask Gemini how to predict arcs)
    
 4) Turn off the current:
  Turn it off as soonas you can.
  A sloping trailing edge is bad. 
  square is good and hard to achieve
  
  Remove all inductance thgat uou can,
  Use ultrafast diode across gap.
  
  Sharp turn off gets better removal,
    ( the implosion is more explosive)
    a slow turn off gets more re-cast
     (material coolimg back onto wkpc)
   
  5) Take a break: Off Time 
    Then a minimum delay time is waited out.
    ( The mfctrs say this value is usually enough
    time to let the gap recuperate. They say
    thius is a minumum, expect longer if you are not
    in a testing environment)

  6) Recuperation:    
    GAP restoration:
    The gap _was- clean, then got chrged and dirtied.
    
    Q: whats all thata black smoke in the oil?
    A: The oil is a hydrocarbon  
     that gets 'cracked' into hydrogen gas ( flammabvle)
     and carbon ( from oil, not from tool)
     
   When will the gap be ready again?
   
    The weak tickler voltage will rise to Uo
    ( say 100V) as soon as the gap is clear of debris.

    Waiting for a clear gap 
     makes the same environment for the next spark.
    
    Your circuit _could_ refire as soon as the gao clesars
     or ( sort of debouncing) you could recheck a few times first.
    
    Dont refire when Uo is not high.
     That would avoid the necessary dielectic 
     resistance and would cause pitting or arcing.
    
  8) repeat
    It's not on of on of on off
    It isd  Wait on of Wait on off Wait on rff
    
HTH TomP

some good reads on edm p/s
langfordw.pages.cba.mit.edu/desktopWEDM/electronics/
github.com/Bijoo/EDM-pulse-generator
oshwlab.com/ehdesignlabs/wire-edm
the G-EDM project looks good
there have been a few updates/chgs to design
Usimg an inductor is reminiscent of the Charmilles P25
github.com/G-EDM

tomp

Thank you tjtr33 for the good explanation of the spark process. In the last weeks (or months) i had done some experiments with a mosfet and a 60 V power supply, max 8 A. The mosfet was switched with a variable pwm signal from a esp32. A simple z axis was build from an old 3d printer. I used a hall sensor to measure the current in the gap and control the stepper motor based on a max current threshold. If a shot circuit occurs the electrode will lift up. The dielelectric fluid was distilled water. But because of the low voltage these weren't edm sparks and instead were short circuit sparks. Much more violent, loud and high wear on the electrode. See the test piece for the surface finish, it's bad. Next step would be to get a 100 V - 120 V DC power supply and close the loop with monitoring the spark gap, just as tjtr33 described it. The pwm doesn't care if a spark is good or not. But right now i don't have the time to continue this project (so another dead edm thread on the internet).

Part of the circuit i got from Peter Hofbauer, who has an excellent build log (in german) on his website:
www.hcp-hofbauer.de/indexerodierv2s4.htm