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Electrical Discharge Machine Version 2 (edmv2)

John Hasler

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#31
You won't get an event on a limit swtich unless you've hit a limit: that's something that needs immediate service. Interrupts will be disabled in the ISR. You can handle the debouncing there or disable interrupts globally and set a volatile variable to tell the main loop it has a limit switch event to deal with. Better, though, would be to use optical interrupters (or SR FFs and SPDT switches) and eliminate bounce.

Use a timer interrupt to poll the manual switch every 100ms. Only run the debounce code if it shows a change of state.
 

brino

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#32
@John Hasler ....ahhhh I see, your comment was meant for the limit switches. Yes they could be interrupts and not debounced.
and yes, optical sensors would be great, I had not thought of that...probably because I had already pictured mounts for some microswitches I have.
But I may rethink that now.......
One big plus for me using the arduino was to not need external flip-flops for switch debounce (......and the easy stepper interface, of course).
Thanks for your comments.

In my head I was thinking about the auto/manual switch and the up/down switch that only operates in manual mode. For those switches I originally had the code checking the auto/manual state every loop (with debounce) before entering the "Auto" state. I already proved that is a waste of time. I have plans to rewrite the state machine to stay in the "Auto" state until a single "Manual" switch event is seen, then go out of auto and debounce it. That way there is no switch debounce in the main "Auto" state, only on a change of state.

What I have found useful when debugging is pulling out the power plug for the high voltage supply -that causes the auto mode to lift the head, then I can squirt some water in to clean-out the debris and plug it back in to continue the "cut". This helps because I do not have to touch the switches mounted on the head and induce more motion in that wimpy (temporary!) column.

So many improvements are possible.....so little free time!

-brino
 
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brino

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#33
....anyone have ideas for a small pump and/or filter system for the water?

For the pump:
  • it could be 5VDC, 12VDC or even 120VAC
  • I would prefer to have an adjustable flow rate
  • unfortunately I do not have an idea of range for flow rates
I could seeing using those adjustable, segmented/articulated plastic coolant lines for aim-ability.

For the filter,
  • I suppose a small aquarium filter could work?!?
  • would automotive fuel or oil filters work okay with water?
  • I could also see using some magnets in the system to grab the conductive debris
Thanks for any ideas!

-brino
 

JimDawson

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#34
For the filter,
  • I suppose a small aquarium filter could work?!?
  • would automotive fuel or oil filters work okay with water?
  • I could also see using some magnets in the system to grab the conductive debris
Maybe an inline water filter from your local big box store?

I don't think a fuel or oil filter would well, I think they're designed to reject water.

Magnets are good, maybe in the filter canister?

Princess Auto has a number of small submersible pumps, some have adjustable flow.
http://www.princessauto.com/en/detail/300-gph-statuary-fountain-pump/A-p8317513e
 

rwm

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#36
I have a little giant pump and it has run for a long time. Amazon has some pumps for less than $15. I love the magnetic filtration idea.
R
 

brino

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#37
It has been bothering me for a couple days that the machine just did not have the ooomph that the previous one did.
Yeah there were some sparks and some metal removal, but not the aggressive rate as before....and no aggressive sound.
One of the books described it as a "bacon frying" sound with lotsa little pops.
Also when I had tried to get some still photos of the sparks I tried several times and didn't get any.

I am using the exact same high-voltage supply what's up? :(

Then I reread my post #27 above about one option being to play with the discharge(or spark) capacitor......hhhhmmmmm.
The spark capacitor.....I FORGOT THE SPARK CAPACITOR!!!! :confused 3::confusion::dejected::disgust::disillusion:

I show it in the version one thread here: http://www.hobby-machinist.com/threads/my-edm-project.41481/#post-356086
But I forgot to install it here and left it out of the drawing in post #21 above.
It should be "downstream" of the big series resistor.

Here is an updated version:
fixed_power_supply.jpg
(I will also go back and add a note in that post to refer to this one.)
(clickable, resizable thumbnail version below)

I am currently using a 680uF, 200V capacitor for the the discharge(or spark) capacitor.
Most of the versions I saw during my research had a bank of switches to select different caps and add them in parallel.

Now I cannot get pictures because there is so many black debris plumes being ejected from the hole!
Right now it looks like Coke.

-brino

fixed_power_supply.jpg
 
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brino

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#38
Based on the location of the anti-rotation pin in the slot, adding the missing capacitor has meant more progress in the last hour than the previous several hours of running!

It makes sense too. Without the spark cap right across the work/electrode gap it was the energy stored in the capacitor beside the diode bridge doing the work.......and it had to work thru that big 10-ohm 50-Watt series resistor.

Now there is nothing in the way of dumping a whack of energy when it sparks.

Leave it with me and I'll figure it out eventually!

-brino
 
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brino

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#39
It's been a little while since I updated this thread.
The project has been a little slow......but NOT stopped.

First I stiffened up the mount. The problem was this temporary mount was put together to be well, temporary. So I added a couple diagonal braces of 1" angle iron. Sorry no pictures. Now the head doesn't wiggle in an arc around the upright. (Long term I want to use a couple of aluminum extrusions I picked up. I just need to find ways to have them quickly adjustable ad lockable.)

With that done, I fired up the machine to finish the test hole in that scrap of 1/4" thick steel bar.

In post #27 above, I showed how it looked about 0.050 of the way thru.

Here it is a little deeper:
deeper1.jpg
deeper2.jpg

and finally a thru hole:
(the little nugget was the centre of the hole cut out by my hollow 1/4" copper tube electrode)
thru_1.jpg

thru_2.jpg

and from the back the hole looks cleaner since the head wasn't vibrating around (I fixed that before cutting all the way thru):
back.jpg

Once I figured out that spark capacitor blunder, it went much quicker.

-brino
 
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brino

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#40
Second I worked on a filter system.

During operation, the water in my tank changed from clear to this:
dirty_water.jpg

I have NOT figured out a great way to use magnets in the filter system.

As proof of concept I tried one rare-earth magnet in a zip-lock bag just thrown into the tank. I'm calling it a "bagnet".
Here's one bagnet in the bin:
bagnet1.jpg

Here's what it picked up:
bagnet2.jpg

and then I wiped the bagnet onto a tissue:
bagnet3.jpg

Sure it got some out, but how do I use it in a "continuous flow" manner. Still need some thought here.

I tried a simple coffee filter in a funnel and it did a great job.
Look at the muck it pulled out:
coffee_filter.jpg

and the water looked clear.

Next I bought a water filter with replaceable cartridges, like this:
filter.jpg

I had originally picked up one of the spare filters and a handful of ABS parts to make my own, but at the checkout realized that the parts cost as much as the filter off the shelf (about $31 CAD). Back I went. Plus this filter has a see-thru chamber for the filter.

I bought the one with a 5 micron filter cartridge and it pulled almost nothing out of the dirty water.
When I swapped it to the 1 micron cartridge the filtered water looked clear.

Oh, and I am using a pump like this:
https://www.amazon.com/500-Universa...402&sr=8-15&keywords=swimming+pool+cover+pump

That's it for tonight. I gotta get up early for car pool with my son.

-brino
 

brino

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#41
okay, it's waaaaay past time that I updated this thread.

The pump and filtration system is working great (even if I couldn't find a way to incorporate magnets!).
After a number of test cuts I could see the water flow slowing down, so I took the filter to the laundry sink and ran water thru backwards and it immediately restored the good flow.

What have I cut?

After adding a diagonal brace to stop the EDM head from swinging around I cut a new thru hole in that same 1/4" thick scrap steel bar using the same copper tube electrode.
I must not have dried it off after removal from the tank....it got kinda rusty.
However, it showed: i) the hole was much more round as the head did not bounce around, ii) the new nugget is cylindrical (the first one was a cone from the head swing).

bar1.jpg bar2.jpg

bar3.jpg nuggets.jpg

still more to come.......some spoilers........I tried a brass tube instead of a copper tube electrode, I have tried reverse polarity, and I tried a pencil "lead" electrode.......and more

-brino
 
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brino

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#42
......ohh and here is the copper tube electrode after the cut above......

1.jpg
2.jpg

-brino
 

brino

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#43
I also tested a 5/32" brass tube electrode.
I switched back to utility knife blades as my target metal, mine measure 0.025" thick.

The holes I cut are marked with red circles in the photos below.
(click for larger picture!)

With electrode negative it took 6 minutes to cut a thru hole:
brass_electrode_en.jpg brass_electrode_en_back.jpg


With electrode positive it 20 minutes to cut thru the blade:
brass_electrode_ep.jpg brass_electrode_ep_back.jpg

Interestingly, the electrode positive threw up a burr around the hole but on the top side!

Both left a slight ring visible around the hole, but it does not show up in the photos above.
(if I was cutting with oxy-acetylene I'd call it a "heat affected zone", here I dunno.......)

Here's how the electrode looked when finished:

brass_electrode1.jpg brass_electrode2.jpg

-brino
 

brino

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#44
....after seeing that last post again I thought I could do better (brighter) pictures

Here's the electrode negative:
brass_en_front.jpg brass_en_back.jpg

and the electrode positive:
brass_ep_front.jpg brass_ep_back.jpg

-brino
 

brino

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#45
I had read in one of the references about using graphite electrodes.

Well I do NOT have any of those, but I did find some cheap pencil "lead" refills.
Made of 100% unknownium!
What have I got to lose by trying it?

The green circle shows an attempt with electrode negative.
The red circle shows the electrode positive attempt.

pencil_lead1.jpg

I gave each attempt over 7 minutes, and basically used up the entire electrode in that time.
It did almost nothing except leave a bunch of grey floating crap in the water and make a smell like some brushes on an old motor I remember.

Here's the pencil lead refills I tried:
pencil_lead2.jpg

Full images attached below.

-brino

pencil_lead1.jpg
pencil_lead2.jpg
 
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dieselshadow

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#46
This is a pretty cool science experiment. I'm enjoying this thread. Thanks Brino.
 

brino

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#47
A little info on dielectric fluids..... @mephits asked some questions here:
http://www.hobby-machinist.com/threads/goofs-blunders-you-should-avoid.49036/page-11#post-443219

In order to keep that thread on topic, I'll tell what I know here.......

Interesting. So the EDM doesn't push enough wattage to crack the water into free hydrogen and oxygen? That would create a whole new set of flammability issues!
I suspect there is some electrolysis going on, I do see bubble formation when the high voltage supply is turned on.
However, I believe there is so little H2 and O2 produced that is is rapidly diluted in the shop air.
I suppose I could try catching some in an inverted test tube and running a few tests.

So as a question to all and sundry who actually have EDMs. What about standard cutting fluids like emulsified synthetics makes them less desirable here? Conductivity issues? Cost?
Dielectric strength is the biggest concern, ideally you want the electrode close to the work before the break-down and the spark occurs.
Other considerations are flammability, performance, health affects of the fluid (both vapour and liquid), and of course cost.

In my research into home shop EDM, kerosene is used most of the time.

In "Build an EDM" by Robert Langlois, he says he started with varsol, then kerosene but was concerned with flammability of both. He also relates a story of hand wounds taking longer to heal after exposure to a commercial dielectric oil. He tried water, but suggests it should only be distilled water and that it should not be recycled (like I'm doing!). He also suggest plain water is not "wet" enough due to the surface tension. He ends the chapter with "I now use an ethylene glycol, soluble oil and water mix of 5:5:90. This works but my research on this continues...."

In the EDM How-To book by Ben Fleming he also mentions kerosene and a commercial fluid: Rustlick EDM-30.

-brino
 
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brino

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#48
I had promised some pictures of ball bearings that I attacked with EDM.
Here's the first installment.

I tried to hold this ball in the recess of the vise jaws where the bolt head is for mounting the jaws.
I thought it was tight enough, but the ball spun leaving some strange craters.

crater1.jpg crater2.jpg

-brino
 
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Subwayrocket

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#49
Someone else mentioned little giant , i've used a Little Giant 500203 pump for a few things. It's a good little pump , won't do higher pressure thru long thin lines but it works well. If u need something a little beefier, I've got over a hundred hours on a Shurflo 8000-912-288 on demand pump in a 50psi application thru long thin hose , my TIG cooler . I've also got the same pump (12V version) running about 10 years as the "on demand" water supply for my off grid cabin . It's a pretty cool project you've got there Brino , you should shoot some video of it in action !
 

brino

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#50
I tried another ball bearing.
This is an old 1/2" bearing from the bin.

Just as before it was held in the old drill press vise. The fluid used is distilled water.
The electrode was a bare 14 AWG copper wire, it had to be replaced a couple times due to wear.
That's why the entrance hole is larger than the exit hole, either the work moved, the head still has some jiggle, or one of the electrodes was bent.
This burn took 3-1/2 hours.
I really need to get limit switches mounted so I do not have to babysit it.

Here's a shot of the bearing and used electrodes:
hole1.jpg

The entrance hole:
entrance_hole.jpg entrance_hole2.jpg

and the exit hole:
exit_hole.jpg exit_hole2.jpg

I am a little disappointed at the (lack of) speed.

But I am not done I want to try:
-copper-clad, carbon-core welding electrodes,
-different spark power supplies,
-different spark capacitors,
-different arduino software with different motor step sizes,
-whatever else I can tweak

-brino
 

brino

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#54
Hi All,

I got some time to try some other electrode types.

Theory says to use graphite electrodes. Not having any of those on hand, and continuing in the experimental ways of this project I tried carbon-cored, copper-clad electrodes. I have these on hand as my first welder was a home-made unit using an old electric space heater I got at a yard sale. That unit was based on one my Dad made, and I believe his was roughly modeled after an old popular mechanics article where they removed the carbon rods from alkaline D-cells. My 120V welder basically has a high-current heater element in series with an insulating handle that allows you to bring two of these electrodes together (the heater element would glow) then separate them and a beautiful purple arc would form between them. It was mostly used to braze, but could get hot enough to weld thin steel parts.

Here's the package from the last set of these electrodes I bought along with some random electrodes:
carbon_core1.jpg

Here are four holes and the electrode used:
carbon_core2.jpg

It took only 6 minutes to puncture the utility knife blade.
It took about 8 minutes to produce a clean thru-hole............This surprised me!

The previous tests with hollow copper and brass tube electrodes removed (burned, disintegrated, eroded?) only a thin ring of material.
This solid electrode had to "process" a much larger volume of material so I expected it to take longer.
Maybe that's why it is preferred.

Full sized pictures below.

-brino

carbon_core1.jpg carbon_core2.jpg
 

brino

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#55
....also, as Greg (@f350ca) suggested I tried a tungsten TIG electrode.

It made a clean hole thru the utility knife blade in 6 minutes (see the orange circle):
tig1.jpg

I need to measure the consumption rate of the electrodes to make this a more scientific dissertation, but I want to keep this fun, not work.....;)

Once again full sized images are below.

Be well!
-brino

tig1.jpg
 

brino

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#56
It has been a while since my last update, but recently I had to fire the machine up for more than just testing.
I snapped off a 6-32 tap in a workpiece!

The project is a custom drill extension for a friend. He's making wooden salt shakers and pepper mills. For deep drilling of the bodies he needs to run his current forstner bits deeper than the shanks allow. Some off the shelf drill bit extenders are available, but all the ones we saw had heads bigger than the 1" minimum size hole he wanted.

I came up with this:
project.jpg

The idea behind the double-ended split clamp is to allow use of various shank lengths, or even to allow stepping the length up but retain minimum tool stick out at each step.

It's a 4-1/2" long piece of 7/8" dia. steel bar drill 2" deep at each end for a 3/8" shank. (The hole does not go thru.) The side is slit along the entire length, but I still need to slit half way thru the bar 1-1/2" from each end to provide a split clamp. I was going to do the last slits after tapping the holes for four 6-32 socket-head cap screws.

Of course I broke a tap.......Bugger!

the tap:
broken_tap1.jpg broken_tap2.jpg

the plugged hole:
plugged_hole1.jpg plugged_hole2.jpg


My EDM machine is not exactly finished.....I still need to incorporate an arduino power supply and a stepper motor power supply (still using a bench supply for both), I want to try different spark power supplies, I need to package it all up, I'd like to make a more adjustable head, etc.

I tried to just pick and punch the broken tap tip out, but it would have none of it......so EDM it is.

I used a piece of 14AWG house wire as the electrode and lined it up in the plugged hole:
line_it_up.jpg

After only a few minutes I could tell by the rhythm of the machine that it was thru!

thru_hole.jpg

Then just a small punch got out the rest of the debris from the broken tap. I followed that with the tap drill to be sure it was all out.
punch_and_debris.jpg


debris1.jpg debris2.jpg

debris3.jpg debris4.jpg

It worked!
I had to buy a new tap and have not had a chance to try again. Hopefully the hole wall is still "soft" and normal.

I'll try to post back with a video of it working too.

-brino
 
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ch2co

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#57
Come on, you broke that tap on purpose because you were tired of burning holed in knife blades.;)

Seriously folks, this is really cool, congrats! The beast is alive.
 

brino

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#58
Come on, you broke that tap on purpose
Ha, nope! I would never break a tool intentionally.
....but I have had enough accidents that I knew an EDM would be worth it!

-brino
 
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Turnaround

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#59
Back in the day, our automobile oriented machine shop used hex shaped carbon rods, submerged in a jury rigged puddle of kerosene to erode hex shaped holes through whatever was broken off inside some threaded holes of very expensive parts. Once the hex hole was developed, an Allen wrench would unwind the stub. Problem was, someone "borrowed" our EDM for an emergency job, and that was the last we saw of that beloved EDM.


Sent from my iPhone using Tapatalk
 

rwm

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#60
Nice work! I bought some nitric acid for this purpose but it would not have worked given the steel workpiece.
Robert
 
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