Electrical Discharge Machine Version 2 (edmv2)

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.
 
@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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....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
 
brino said:
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
Click to expand...

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
 
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
 
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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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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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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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
 
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