Electrical Discharge Machine Version 2 (edmv2)

[brino]

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).





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

 

[brino]

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




-brino

 

[brino]

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:



With electrode positive it 20 minutes to cut thru the blade:


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:



-brino

 

[brino]

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

Here's the electrode negative:


and the electrode positive:


-brino

 

[brino]

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.



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:


Full images attached below.

-brino

 

[dieselshadow]

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

 

[brino]

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

 

[brino]

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.



-brino

 

[Subwayrocket]

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]

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:


The entrance hole:


and the exit hole:


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