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Electrical Discharge Machine Version 2 (edmv2)

brino

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#1
Hi All!

My first attempt at a home-built Electrical-Discharge Machine was posted here:
http://www.hobby-machinist.com/threads/my-edm-project.41481/

It obviously did work, but was really just meant as a "proof of concept".

The short comings:
1) it had no vertical feed. Whenever the vibrating head had "cut" as deep as it could, I had to adjust the two pieces of angle iron that were clamped together to move the head down. Of course in doing so the entire thing also moved sideways and changed angles. So not only was it a two person job, it took multiple attempts to get the spindle realigned with the first hole.
2) the entire machine was energized to the discharge voltage
3) there was no control for angling the head to get into more awkward locations.

I considered just adding a lead-screw feed mechanism to the original design, but that would mean that I still need to "babysit" the machine and turn a feed handle when it stopped cutting. I would rather have one I could ignore for a while while it worked away.

I am currently working on EDMv2, it should overcome the problems above by:
1) using a stepper motor and lead screw arrangement for vertical feed.
2) having an insulator in the head so that only the chuck and tool are energized
3) using some extruded aluminum supports with t-slots to give better adjustment

All the stepper motor designs I found in my initial research (see part one linked above) used large single-purpose driver boards. I did not want to get into building a large circuit either on a bin-board or making my own PCB. Instead, I decided to use a small arduino board and pre-built motor driver board both from ebay. In the arduino code it is easy to instantiate a stepper motor and send up/down step commands.

link to arduino "pro-mini":
http://www.ebay.ca/itm/130977194597?_trksid=p2060353.m2749.l2649&ssPageName=STRK:MEBIDX:IT

a little USB programming dongle for it:
http://www.ebay.ca/itm/141150349286?_trksid=p2060353.m2749.l2649&ssPageName=STRK:MEBIDX:IT

link to stepper motor driver:
http://www.ebay.ca/itm/281551893660?_trksid=p2060353.m2749.l2649&ssPageName=STRK:MEBIDX:IT

The machine support arm will be built such that gross positioning is done manually with handles to lock parts in the t-slots.

When using the machine to remove a broken drill bit or tap only around 1 inch of total vertical feed is needed. Making a hex recess for an Allan key would need even less, maybe only 1/4 or 3/8 inch. Therefore an automatic feed range of only a few inches is required.

Using a stepper motor with 200 steps per revolution means I can have rotational steps as small as 1.8 deg.
Combine that with a lead-screw and we're talking about minuscule feed steps.
For a 1/2-13 lead screw one full rotation is 0.077 linear inch, so one motor step is 0.000382 inch!
For a 5/16-18 lead screw one full rotation is 0.056 linear inch, so one motor step is 0.000278 inch!

However, since the lead-screw mechanism is simply a piece of all-thread rod and a nut from the bin, I am under no delusions that the amount of slop would allow such tiny steps. In fact since the feed may be constantly switching direction(see below), backlash will likely be a major limit to minimum step size.

In the code for the arduino I will easily be able to control the minimum step size. It may turn out that I use say 10 stepper motor steps as the minimum step size for my vertical feed.

For controls I am planning to have one switch that chooses between automatic and manual mode.

In auto mode the processor will measure the discharge voltage and extend the head one step if the voltage is above a threshold. If the discharge voltage is below the threshold, then the head will be withdrawn one step from the work. The discharge voltage will be reduced thru a resistor divider, limited by some diode/zener circuit, and then finally capacitor filtered before being run into an arduino analog input for sensing.

In manual mode, another "centre-off" toggle switch will allow me to extend or retract the head for positioning the tool and work.

In either mode limit switches will set the end of travel in both directions. When these microswitches are operated, further movement in that direction will be disabled. If I have spare digital output pins of the arduino, I might hang an LED near each switch to indicate when it has been tripped.

All switches will be "debounced" in the arduino code to limit motor chatter due to mechanical contact bounce.

The power supply for the discharge voltage will initially be the same one I used before. However, having automatic vertical feed will allow me to run better A/B comparisons to try different voltages, discharge capacitors and even reverse polarity.

For the dielectric fluid I see no reason to move away from the distilled water that worked well in the first installment. I may however, add a filter and recirculating pump as I get further down the road.

Some parts are already complete: the insulator, a plastic slider block for the spindle, motor mount and lead screw. I have basically just started writing code for the arduino, and have a bunch of assembly and debug ahead.

-brino
 

brino

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#2
The stepper motor I am using was from the junk bin, likely removed from a printer, scanner, or photocopier.

It is marked:
Step-Syn stepping motor
type 103-718-0340
DC 4.2V 1.5A
1.8 deg. per step
Sanyo Denki Co.
Made in Japan

The motor originally had the gold-coloured mount you see below.
That mount did not suit my purpose, so I sketched, cut and bent a new one and welded the corners.
motor_mount1.jpg motor_mount2.jpg

more to come......
-brino
 

brino

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#3
I decided to re-use the 1/4 inch spindle and drill chuck from my version 1 machine, but since I did not want the entire machine at the discharge voltage, I needed to put an insulator in the spindle.
I found some clear plastic rod kicking around and made this:

insulator1.jpg insulator_and_chuck.jpg insulator_and_chuck2.jpg

-brino
 

JimDawson

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#4
In auto mode the processor will measure the discharge voltage and extend the head one step if the voltage is above a threshold. If the discharge voltage is below the threshold, then the head will be withdrawn one step from the work. The discharge voltage will be reduced thru a resistor divider, limited by some diode/zener circuit, and then finally capacitor filtered before being run into an arduino analog input for sensing.
I love it! :encourage:
 

brino

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#5
The lead screw is a 4" piece of 5/16-18 all thread I found in my bolt bin.
The black tube was (I think) from one of those folding camp chairs.

I found some steel bar stock and made a shouldered bushing; the big end will go on the motor shaft with a set-screw, the small end is a tight fit into the tube.
From the same stock I also made a 5/16-18 nut with a plain cylindrical outside. It is also a tight fit into the other end of the tube.

The motor will spin the tube, the tube will drive the nut, extending or retracting the screw.

Both friction fits will get a spot of thread-lock on final assembly.
The hex nut will be used as a jam nut to lock the lead screw to the next part of the spindle.

20160818_222858.jpg 20160818_222937.jpg

-brino
 

RJSakowski

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#6
brino, it sounds like an interesting project. I am looking forward to seeing the completed project and a report on its use.:encourage:
 

brino

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#7
In the first version I made two brass bushings to hold the "spindle"*. Due to the welded frame of that version I ended up with some misalignment between the two bushings causing the spindle to bind if I tightly mounted both bushings. At that time, I simply let one bushing "float" to test the EDM concept. The spindle was guided by the one bushing and the solenoid. (two points enough to define a straight line!)

In V2 I decided that to avoid some misalignment issues I would do two things:
  1. make a single long bearing block with a drilled and reamed hole for the spindle, and
  2. make all the mounts as adjustable as I could.
The spindle was reused from the first version. It is just a 1/4-inch steel rod. It was cut to insert the clear insulator rod to isolate the rest of the machine from the discharge voltage at the head. The flat that was used for the solenoid on V1 is now used for a set screw to lock on a collar. This collar is threaded in the other end for the lead-screw.
spindle1.jpg spindle2.jpg

I used a block of white plastic for the bearing/slider block. Note that I do not need the insulating plastic here, it was just the material I found that looked suitable. The slider block is mounted on a aluminum angle with slots in two directions for adjustability.

Milling the mount slots:
slider_bracket.jpg

Here's how the plastic bearing/slider block mounts:
slider_block1.jpg slider_block2.jpg
slider_block3.jpg slider_block4.jpg

The long slot on the "front" of the bearing block will be used for a small (#4-40) pin to stop the spindle from rotating.
I have yet to drill and tap that hole in the spindle.

-brino

*-Really the word "spindle" is wrong here as it will not "spin". Instead it will have an oscillatory motion.
 

brino

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#8
For the sake of maximum adjustability, I decided to use some aluminum t-slot extrusions that I found at my local used tool store.

These will be used for the EDM motor and head mounting:
20160818_214929.jpg


So here is everything except the lead-screw test fit on the extrusion:
top_half.jpg bottom_half.jpg
entire.jpg

The lead-screw will go in the gap between the motor and the spindle. It's a good thing that gap is adjustable!

I will try to get some shots with the lead screw installed uploaded soon.....and perhaps some video of the head moving in manual mode.

-brino
 

brino

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#9
Sorry for the delay, I got distracted by a couple auto repairs; exhaust on my wife's vehicle and coolant leak on mine. Now after a replacement coupler & clamps and a new radiator I had time to get back to this.
Also, up 'til now the programming was being done at the computer desk in the basement office space. Now with getting ready for higher voltage and a bucket of water I had to make room in the shop.
Currently it's on my welding bench, but I need to move it over to the bench where the shop PC is for program debug. So I need to move my sons project over to the welding bench. I need a bigger shop!

Progress since last update:
-I got the spindle drilled and tapped for the anti-rotation pin that rides in the slot of the white plastic slider block
(it is tapped #4-40 and of course I broke a tap on the first hole....if only I had some kinda machine to deal with that.........)
-I threw together a temporary stand, welded out of an old bed frame (the final frame will be manually adjustable)
-I used another piece of aluminum angle for a temporary switch mount (the top switch is auto/manual, the bottom switch is manual up/down)


So here's the latest:
top.jpg
middle.jpg
bottom.jpg

more to come....

-brino
 

brino

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#10
I am currently using a two-output power supply. Each half running at 5V, but I wanted to separate any electrical noise of the motor pulses from the arduino supply.
power_supply.jpg

okay...it is still a bit of a rats nest......the arduino pro mini is plugged into a bin board for testing. That is mounted to a piece of mechano from an earlier robot project. I made up a couple supports that are repositionable within the t-track slots to mount the mechano and the motor driver:

arduino.jpg


full1.jpg

full2.jpg

full3.jpg

-brino
 

brino

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#11
So far my arduino code only supports manual mode, the auto mode is like an "off" setting.
I think the manual mode speed is waaaaay too slow, it might be nice for fine adjustment, but it's way too slow for rough set-up.
Perhaps I need both a slow and fast manual traverse, like a "jog" position for rough setting.
In the code I have control over both the speed and the number of steps to take, so I just need to play with the values some.

Below is a short video clip of manual mode, it is very hard to see any vertical movement, but it should be great for "auto" mode......

It does make some noise, but was nearly drowned out in the video by a plane overhead, the shop door was open.

-brino
 

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brino

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#12
Hi All!

This post is just to show how I approached this project. It is sorta a "inside my brain" view.
I am sure everyone has their own approach to both the design and build phases, but I don't see "the process" discussed much.

Feel free to skip ahead to more interesting posts(coming soon!)
Also, feel free to chip in about how you approach a new design.

I had meant to upload along the way some of the design sketches I made of the various parts.
No deep design, no math (until I got to the electronics).
I did not use any CAD, CAM, g-code, or cnc.
I used paper and pencil first, then manual mill and lathe later.

Much of my research about EDM was done earlier with my first version of the machine (see post #1).
This design was mainly about the new vertical feed mechanism and learning about arduino.

I tend to do sketches of the various ways it _COULD_ go together, kinda a "brainstorm" of random ideas. In this step I may think about particular tricky bits for days, and then have it come to me when I'm driving to work. I might also present a small problem part of it to my wife or my sons to get me out of an idea rut and to see new perspectives.

Often I change the design between the drawings and the making. Once I have it in my head, I can bring the raw materials to the bench and try fitting things to see how they go. Look for interferences, different/better ways, and look for problems (will all adjustment screws be accessible?, will the chosen parts take the forces involved, etc.). Sometimes this spurs new sketches and finding new stock for parts. Sometimes it also means new tools, if I can justify a different way of doing something.

Enough "talk" below are a few of my early sketches. Some will look like the parts above, some were changed along the way with no new sketches made.....

Stay tuned for some real project related updates.

-brino

sketch1.jpg
sketch2.jpg
sketch3.jpg
sketch4.jpg
 

brino

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#14
Check out this use of EDM:
That is very impressive, thanks for sharing the link!!
In a discussion with a friend this week he suggested mine needs an X-Y table for making it into an engraving machine. I told him basically "baby steps!"

-brino
 
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brino

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#15
okay, progress continues.

I changed the manual feed to be 200 motor steps, that's 1 revolution per "step" of the lead-screw.
Now you can see it move!
This looks good for the manual positioning of the head.

-brino
 

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brino

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#16
Now some electrical design......

As mentioned I wanted the arduino processor to monitor the discharge voltage and drive the head accordingly; drive down when the voltage was high and retract the head when the voltage was low.

I am reusing my original power supply that looks like this:
power_supply.jpg

Out of the transformer I see ~84 V AC.
After the diode bridge and filter capacitor I see ~114 VDC.

The switches and LED above are still TBD. I want them in the completed unit, but so far have not implemented them.

The LED is meant to be a warning of high voltage present at the head.
The second part of the switch and the resistor marked "Rdisc" would be for discharging the capacitors when the power is turned off. This should reduce the number of shocks I get when fiddling with it.

-brino
 

brino

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#17
In order to protect the arduino processor from the high voltage I needed to reduce it for sensing.
My 5V arduino cannot accept a voltage above ~5VDC.

This is what I came up with:
input_protection.jpg

Resistors R1, R2 and R3 provide a voltage divider to scale the voltage down. R1 and R2 are in series and so the values simply add together. They could be one resistor, but since I am dropping significant voltage I thought two discrete parts would give more options for part selection.

D1 is a 5.1V zener diode for protection. Typically, zener diodes are used in voltage regulator/reference circuits. If the
voltage across it goes above 5.1V it "turns on" and conducts. R4 adds some series resistance to limit the current thru the zener. I am using R4=1k-ohm.

The capacitor shown above is meant to stabilize the sense voltage to the processor. I chose 100nF (based on past experience).

D2 and D3 provide more "safety".
D2 conducts if the input voltage gets once Vfwd higher than Vcc.
D3 conducts if the input voltage gets one Vfwd less than GND.
I choose 1n4148 fast switching diodes because I had a drawer full of them. ;)

-brino
 
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brino

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#18
Details of the voltage divider resistor selection are below.....

resistor_divider1.jpg

resistor_divider2.jpg

Although today's power supply generates around 114VDC, I decided to design the resistor divider able to handle a higher voltage. I decided on 200VDC as the maximum, that should give me plenty of headroom to play with discharge voltage sources.

I chose R1=R2=100k-ohm as a standard value and worked out R3 to be 5.128k-ohm.
I had a 5.1k-ohm resistor so "good enough".

Based on those values the current thru the resistors is low so 1/4 watt thru-hole resistors were used.

-brino
 

brino

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#19
I wrote the arduino code to support these electrical design decisions.

I found that the arduino already supported a great way to debug programs.
The serial port used to program the arduino pro mini could also be used for status updates from the running program. Much like the venerable "printf" statements in other high-level languages.

So in the automatic mode I had it sense the analog input voltage, "math" it into real values, and print it out. The code was:

case Auto:

Asamp = analogRead(PIN_VDISC_SENSE);
Vsamp = (float) Asamp*5/1023;
Vdisc = Vsamp/0.0249;

Serial.begin(9600); // open the serial port at 9600 bps:
Serial.print("A0 reads:"); Serial.print(Asamp); Serial.print("\t");
Serial.print("Pin Voltage="); Serial.print(Vsamp,2); Serial.print("\t");
Serial.print("Discharge Voltage="); Serial.print(Vdisc); Serial.print("\r\n");

Serial.end();

Next_State = Start;
break;

the screen shot showed:
ScreenShot001.jpg

okay so a little more coding and I can make some sparks.....

-brino
 

rwm

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#20
Very interesting. What is the typical voltage/current of a commercial machine and what do you expect from yours? I assume you could get a resistance of 0 at the work head so how do you limit the current? Should you consider having your discharge resistor permanently in the circuit rather than switched? That seems safer. You could use a high resistance value and still discharge the cap pretty quickly.
Robert
 

brino

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#21
@rwm

Thanks for pointing out something I left out of my recent posts.

Here I had not mentioned the series resistor I used.
In the "version one" thread I mentioned the 10-ohm 50 watt resistor that is in series.
Like this:
upload_2016-9-3_19-25-24.png


This is also a great opportunity to point out:
  1. Do this only at your own risk!
  2. I am (and this site! are) not responsible if you hurt yourself, someone else or any property by doing this.
  3. Electricity and fluids can be a bad combination.
  4. This is from the internet -do your own research, understand what your doing, etc. etc.
Note: Since my workshop is a two-car garage attached to my house, I chose to use a non-flammable dielectric fluid. Distilled water is my dielectric rather than the typical kerosene, varsol, etc.
This build should also allow me to experiment with various fluids for wetting, cooling, etc

With all that said, I should actually be able to try this machine in auto mode this weekend.

-brino

!!!!EDIT!!!!!
Please see post #37 of this thread for an updated drawing!
Above I forgot the discharge or spark capacitor!
 
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rwm

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#22
OK. That makes sense. So at max it pulls about 14 Amps? Must be a big transformer. Can't wait to see it run! I have some questions:
I see you have a constant power supply. Does the EDM power need to cycle on and off to work? Does it make a spark when operating? Is this process kind of like super-electrolysis? Or is there some other destructive mechanism as work?
Robert
 
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brino

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#23
Today was full of software frustration!!

After having the USB-serial port work okay up 'til know I ran into a blue screen of death (BSOD) whenever I let the arduino monitor window run for very long. This put a big wrinkle into my debug plans.

The USB-to-serial converter I was using (link above somewhere) uses a "Prolific" device so I had installed version 1.12 of the prolific driver, initially it worked okay....but that was only for short periods. When I started seeing the repeated BSODs I went searching for a solution and found people recommending an older version 1.10 driver:
http://superuser.com/questions/680737/bluescreen-when-putty-reads-from-serial-port

I could not find the older driver, so I tried a newer one version 1.14. That one showed BSODs as well. CRAP!

I never did find an old version of the Prolific driver online, but luckily stumbled across a copy I used years ago.
I found version 1.1.0 from 2009 (the one I expect they meant in the link above).
I installed it and I no longer see the BSODs. I have attached it here.

However, now after a short time of using the monitor window, Win7 sees the string of data on the serial port and assumes it's some kind of mouse and installs a driver for a "Microsoft Serial Ballpoint Mouse". This seems to disable my real mouse and really screw with the system. Sigh.

After searching, I tried a number of things fr0m here:
http://answers.microsoft.com/en-us/...e/e0e03b9b-e9ae-4645-8b3c-5754f06ec3b5?auth=1

So far the only work-around is to let it start the "Ballpoint" install and then in Win7 Device Manager disable that device.

What a pain!

However, I did eventually have some progress. I will try to post it later.....

-brino
 

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#24
EDM_V2 is alive!

I had picked up a cheap, used drill-press vise for this project. I drilled and tapped a hole for a stainless bolt to connect the positive lead to the vise.
So far I am just re-using the original electrode from version 1, it is just a piece of 1/4" copper tube.
I had a 1/4" thick, by 1" wide by 3" long piece of mild steel as my first test piece.
I started with clean distilled water as the dielectric fluid.

Here are a few short video clips showing the machine in action.
You can hear the stepper motor, it is sort of a tapping noise.

movies1-3 are just different views of it running.
movie4 is a close-up
movie 5 is a view of the "spindle", I added some red and black sharpie lines so you can tell which way it's moving.

Here the machine is running in auto mode. One step in my code is equal to 10 stepper motor steps. I am using a threshold voltage of 50V.....if the discharge voltage is above 50V the arduino drives the head down, if it is below 50V the head is driven up.

-brino
 

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brino

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#25
Here's the dimple left after a few hours of running

Just out of the tank:
dimple1.jpg


and after wire brushing:
dimple2.jpg

I measured it at about 50 thou. deep.

-brino

I have added thumbnail views below.
dimple1.jpg dimple2.jpg
 

brino

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#26
It occurred to me that this machine was not working very fast.

I have a finite-state machine running on the arduino that samples the three switch, debounces them to eliminate mechanical noise, eventually gets to the "Auto" state, measures the discharge voltage, outputs some debug info on the serial port (state transitions and voltage readings) and then finally drives the head accordingly.

I decided to make a new arduino sketch with just the bare minimum code.
It simply measures the voltage and drives the head; no switch reads, no debug info, no other state changes.
I also made the step size equal to one motor step.

That sure changed things......see movie6 below.

-brino
 

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brino

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#27
I still have a number of system improvements to make:
  1. I need to make my temporary machine stand much more sturdy. When the motor is moving fast it sets up a little wobble in the machine. I expected this, I have seen twisting in the upright spine. Currently I believe the cut is wide and removing more metal than necessary. Perhaps I need to bite the bullet and start construction of the final, adjustable stand.
  2. I need some kind of filter and pump system. I am amazed at the amount of reddish, magnetic debris left in the water. I believe it would also help the cutting progress to wash this debris from the cutting area. Currently I am flushing it using a syringe every once in a while.

In the code I already have ideas about:
  1. re-writing the state machine such that the "auto" state is a single tight loop.
  2. the switch debounce time could likely be shortened significantly
  3. I still want to add limit switches to disable the motor at end of stroke.

I still have many variables to look at:
  1. I can adjust the number of motor steps per machine step taken in auto mode
  2. I can adjust the motor speed (separately)
  3. I can adjust the voltage threshold
  4. I can play with various high-voltage power supply options, including adding more discharge capacitance.

That's all for tonight.

-brino
 
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brino

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#29
@rwm , sorry Robert I missed your questions......'til now......

Does the EDM power need to cycle on and off to work?
The EDM high-voltage supply does not need to cycle on/off. Basically when the electrode gets close enough to the work that the arc jumps the discharge capacitor dumps it's entire load and erodes a little bit off the work piece. There is a high-wattage series that drops the entire voltage if the electrode contacts the work piece. Either way, the power supply will need some time to recover the output voltage for the next spark.

Does it make a spark when operating?
Yes! These things are also called "spark erosion machines". All the action takes place under a dielectric fluid....basically an insulating fluid but with a polar molecule. Many systems use parafin. I am using distilled water, since parafin is flammable. (and my workshop is attached to my house!)

Is this process kind of like super-electrolysis? Or is there some other destructive mechanism as work?
It is really just the jump of electrons from the negatively charged electrode to the positively charged work piece that erodes off the "high-spot", then the next high-spot, etc.

-brino
 
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brino

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#30
Use interrupts to handle the switches.
Hi John,
I believe from other posts that you have done many microcontroller projects.
But your comment confuses me.

An interrupt is for something that needs immediate service.
I WANT to debounce the switches as mechanical contacts are notoriously "noisy", there could be dozens of contact bounce events per switch operation.....that would drive an interrupt handler crazy!

-brino
 
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