EDM - Electrical discharge machine

Discussion in 'The Projects Forum' started by shortbus, Jan 22, 2018.

  1. shortbus

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    To all of you helping an following this thread I have a question. I have my redrawn schematics done. Should they be posted in this thread or should I start a new one so they can be discussed and not get mixed up? It is basically the same schematic but with the changes that were suggested being made.

    Please let me know what you guys think is best, thank all of you for sticking with me and for all of the help. I can now see this thing being a working solution!
     
  2. cmartinez

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    I think you should post them in this thread, so as to leave a trace of the progress you've been making. In the end, I'd formalize everything in a clear and concise way, and I'd post the results in the finished projects section. ... just my 2¢ :)
     
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  3. LesJones

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    Hi SB,
    I agree with cmartinez's comments.

    Les.
     
  4. shortbus

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    Ok that's what I'll do, thanks for the feedback. I'll post them here as thumbnails, and after I figure out how to put them in a PDF will post them again. And again thanks for the help.

    edm pulse logic  2   145.jpg edm pulse power 2  144.jpg

    Don't know what I did wrong? Don't most thumbnails allow them to be enlarged when they open in a new window? I'm so dumb with computers, that's the reason for calling myself 'shortbus'.
     
  5. cmartinez

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    They open up at the right size when I click them... you have to click "show at original location" at the upper right corner of the enlarged image to have them open in a new window.
     
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  6. roong

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    Feb 11, 2017
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    My fuel pump stop working, I disamble it. It isnt centrifugal type. It is an axial flow . Not design to be repairable. I look at ebay link you gave me. Pritty cheap price, perhaps not made in USA otherwise the price should be tripple. Too bad they wont send to Bangkok or Vientiane.
    I try with water today. I didnt use any pump just submerge part in water. My electrode just stoped right before hitting the part because current just leaking into water and bubbles were form. The system loose more current than it can charge then nothing happen the electrode just freeze there.
    wonder how this is done.
     
  7. shortbus

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    @roong , Water from the tap won't work, it needs to be at the minimum distilled water. Deionized is even better, but still not ideal for sinker type EDM.

    Even using oil type dielectric just submersion won't work very good. There needs to be flowing liquid through the gap, to keep the debris moving through the gap. If debris collects in the gap it will short out the flow of electric, not allowing the spark.

    The Ebay link was just an illustration of what to look for. Can you get things in your country from Aliexpress? The unit I illustrated is made in China, so Aliexpress should have something similar.

    Do you have a link to the tap remover? Those type of things, while related to EDM aren't good at doing anything beyond removing broken taps or drills. Many of them are just DC power supply's and a solenoid that moves the electrode up and down. Kind of like old time DC door bells. But they use the work and the electrode to replace the points that the door bell circuit used.
     
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  8. shortbus

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    OK, worked through getting the schematics into a PDF.
     
  9. LesJones

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    Hi SB,
    When I looked at you original schematic (Post #16) I assumed that the set state of the flipflops (Q output high) would switch on the mosfets but now following the signals it looks to be the other way round. (The mosfets conduct when the flipflops are in the reset state) Although this will work it seems counter intuative. Like marking a light swtch off for the light to be on. Is my present understanding correct ?
    Is S2 a momentry push button that is pressed to start the procces ? (With no means yet of stopping the procces.) Or is it a toggle switch that starts the procces when it connects +12 volts to the left hand end of C1 and you hope will stop the procces when it is returned to the position it is shown in the scheamtic ? (It will start the process but it will not stop it.)
    Input "C" is in a floating state except when there is current though the gap. Without a resistor biasing it to ground it is likely to falsely trigger as it will be very sensitive to any electrical noise.

    Les.
     
  10. shortbus

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    Hi Les,
    It's not like you think. Both FF's when the switch is turned on will go to Q high due to the rising pluse. That will turn on the low side mosfets, this is needed to charge the bootstrap caps so when the high side mosfets are called to turn on they can. The high side won't work without charged bootstrap caps. In the first version I made a mistake when transferring from my crude paper drawings fixed it in this version.

    I just show SW2 as a SPDT switch to make things easier. In reality it will be a 3PDT relay, didn't want to complicate things showing the whole control circuit.

    With the relay one set of contacts will be to seal in the relay, like in a motor contactor circuit. Doing this will allow use of a push button for 'on', a push button for 'off' and a limit switch for a depth stop when burning a blind cavity.

    The second set of contacts are what SW2 represent, with "NO" being to turn on the reset part of the logic, and the "NC" putting a resistor in to drain the charge on C11.

    The third set of contacts will be to power only the 4013 FF's. By turning them off/cutting the power to only them and leaving the rest of the logic on will shut the sequence of the circuit down. The rest of the logic needs to be 'live' to allow a "manual" mode of operation, another part of the control circuit not shown. Other than the 4013, the rest of the circuit will come on with the main switch.

    Didn't think the "floating" applied to non logic IC's. Thought comparators were made to avoid a problem like that. And are they really floating at all? They are connected to something even when not in actual use aren't they? Was under the assumption that the high input impedance eliminated any problem.
     
  11. LesJones

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    I can see that you force the flipflops from their initial unknown state to switch on the lower mosfet when 12 volts is switched to the left hand end of the capacitor. What I can't undersatnd is why you won't hold the flipflops in the state that switches on the lower mosfet when it is in the idle. (Not burning state.) that way the bootstrap capacitors will be charged ready for the top mosfets to be switched on.

    I think switching off the power to the 4013s is a very bad way of terminating the burn. As I said above holding the 4013s in the state that switches on the lower mosfets is a better solution.

    The only think they are connected to is the two diodes in series to ground. These will not prevent a negative excursion until the breakdown vltage of the diodes. They will only limit a positive excursion above about 1.2 volts. As the imput impedance is very high any slight leakage or small amount of electrical noise will influence the voltage. When there is no current through the gap you need a defined state of the output of the comparator. The inverting input of that comparator is held at + 0.6 volts so if the non inverting input drifts even a few microvolts either side +0.6 volts the output wil be changing state from high to low. If you did not care what the state of the comparator output is the there is no point in having that comparator.

    Les.
     
  12. shortbus

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    Hi Les.
    If I understand you correctly, you're saying put an OR gate on the 4013set pins, and when the relay is off use one of the NC contacts to put 12V into the OR. Didn't see that way of doing it, just might work.

    After you said that about the comparator I had to do some research on them. Holding only one input high or low is all that is needed to keep a 339/393 off. Where would the electrical noise be coming from in this particular instance? When the gap is conducting, the comparator would be off. If it isn't conducting there shouldn't be any source of 'noise' to worry about. Since the only real noise in the circuit should be from the spark gap. Even though I don't show them there will be caps on each IC power connection.

    You said something about a resistor in post #109 -
    Where would this resistor go? If it is at point "C", parallel to those diodes it would need to be pretty high wattage wouldn't it? Or could it be put at the comparator input?

    It think this is what we talked about before, where RonV suggested putting in a reverse biased diode to the inputs of the comparator.
     
  13. shortbus

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    Like the first version here is the schematics broken into blocks to make it easier to discuss.

    pulse edm 2 block147.jpg pulse edm 2 block power148.jpg
     
  14. LesJones

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    Hi Sb,

    I would have the switch when it was in the NC position apply 12 volts to the Set pin. You do not need to apply a pulse to the set pin when the normally open contacy closes as it is already in the set state. (So no OR gate would be required.) As it has been held in the set state the bootstrap capacitor will be charged. So all you need to do is to pulse the reset pin high after a short delay to start the charge phase. (There will probably be s delay between the NC contact opening and the NO contact closing so you would not need the first RC pulse circuit to produce a delay.)

    I don't know where you found that infotmation on comparartors as it is wrong. The state of the output depends on the RELATIVE voltage between the two inputs. If the + input is more positive than the - input (Even if it is only a millivolt ) then the output is high. If the difference is the other way round the output is low. With one input floating it is like saying which is the highest "Unknown voltage " or 2 volts. In you circuit the - input of the comparitor is at about +0.6 volts (The forward voltage of D1) During the discharge the + input (Signal C) will be about + 2 volts. (This is my estimate of the voltage across D6 and D7 with the high discharge current though them) so the comparator output will be high. When the discharge ends there is no current through these diodes so the + input is at an unknown voltage. You need it to be at a volage less than 0.6 volts so the comparator output goes low. If you want to build it without a resistor to ground you could see how it behaves. It would be easy to add it later. The resistor does not need to carry much current as there will only be about 2 volts across it. It would probably work with quite a high value resistor (Say 100K) but I would choose about 100 ohms. (That value resitor would dissipate about 40 mW)

    Putting the resistor in parallel with the diodes and between input C and ground is exactly the same thing. Ron's suggestion of adding reverse biased diodes to the C input of that comparator would be to protect it from any high voltage spikes. For this to be effective you would also need to add a resitor between the top of D6 and the comparator input. (I would choose about a 10K ohm resistor. The two reverse biased diodes would only need to be low current rating such as 1N4148 type.

    Les.
     
  15. shortbus

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    Hi Les
    I copied just the first part of the logic schematic, and made changes before seeing your reply. Kept the first half mono and used it to give a pulse on U3.1 (4071) as the start signal. And like you said above put the NC contact of one of the relay poles at 12V. So you are teaching and I'm learning. :) Again thank you.

    And also put a resistor at the + pin on U6.1

    May have misunderstood, but read it at a TI forum. https://e2e.ti.com/support/amplifiers/etc_amplifiers__other_linear/f/18/t/484791 Quote, "For LM393, inverting is ground so ouput will go high or more accurately open (off). The non-inverting input (and output) will be a little above zero."

    Here's the partial schematic with the changes. pulse edm change 2 150.jpg
     
  16. shortbus

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    Hi again Les. After thinking more about the schematic I posted above, I don't think it would work like I thought it would, so back to the drawing board. Above I did away with the falling edge detector, doing it that way would keep U3.1 on all the time, not a good thing. So I added that part back in, so that will only give a short 'high' pulse to start the circuit sequencing, then go low so the circuit will keep running to shut down.

    pulse edm change 3   151.jpg
     
  17. roong

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    Feb 11, 2017
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    Hello, Mr Short Bus , Remember my system has a 70vac big transformer and a much smaller 110 vac transformer in parallel. So this translate to 102vdc 152vdc and I set first threshold value to around 130v second threshold around 60v. I don't use two differential amps like you do but two zeners diode. Last time I tested with water the current had leaked too much for small transformer to handle and my electrode just stopped before hitting target and hizz sound occurred like you are electro-plating something. This time, I lower value of the upper threshold voltage hoping that large transformer could cope with leaking current. I put my drinking water in a small food box and test.
    It work like magic. My test only last for one minute because water start getting dark. I can tell you this, It cut faster than diesel. Surface is rough but clean. The link about tap remover I show to you...mine working half as close to that so I don't think that tap remover uses pecking method like you said. Form now on I think I will go away from oil. I am so thrill, so I let you know as you are only person I have ever discussed with.
     
    Last edited: Feb 25, 2018
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  18. LesJones

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    Hi SB,
    I don't think it is quite a case of going back to the drawing board. Remove U3.1 Connect the signal that went to the lower input pin of U3.1 to the lower input pin of U4.1 (I can't read all of the pin numbers on your PDF file clearly) Keep the falling edge detector and use the output of U1.3 to reset the charge flip flop by connecting it straight to the reset pin. (Which with your circuit switches on the charge mosfet.) When the relay contact was in the NC position (Stop) it would hold the set inputs of both flipflops high. (So both the charge and discharge mosfets would be off. And the bootstrap capacitors held in the charge state ready to switch these mosfets on.)
    Which schematic drawing software do you use and and is it free ? It would make life easier if we could both edit the schematic and update the version number each time.

    Les.
     
  19. shortbus

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    Didn't mean completely just that partial schematic. Did you see the second one in post #116? I'll have to think about what you were saying and try to understand what you mean in this last post.

    What I've been trying to do with the comparator for output"C" is detect when the gap is 2 diode drops above ground and then shut down the 'charge' mosfet. doing this allows the full open circuit voltage to ionize the dielectric. I found this in a paper online about EDM.

    The software I'm using is called DipTrace, and is free for non profit use. I have tried to learn or understand how to use every one of the free software out there with little effect. But DipTrace was the easiest for me.

    Trying to learn all of this stuff starting around age 58 is not easy. Now 70 and slowly getting the hang of things. Knew what I wanted and needed to do, but not having the knowledge on how to get there has been a struggle. Your the only one that has stayed with me this long, and I thank you more than I can ever explain! Most people have tried to send me down other paths because I'm not able to speak the 'language' or it doesn't match their idea of how electronics work, and it's not there fault. Mainly because what I'm doing isn't how most people use logic/digital. But then again EDM isn't like any thing most electrical engineering people ever come across. Other than the Tesla coil people or electronic ignition people who would intentionally want to make sparks, and controlled sparks at that?
     
  20. shortbus

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    I don't understand what your saying about what your doing. Maybe post your schematic? Would be welcome here, since this is my thread.

    Using drinking water,you almost need to do it as a total loss system. That means just let it go over the work and down the drain. Water unlike oil absorbs to much of the gap by products, unlike oil based fluid.

    You just showed a picture of the tap blaster not a link. The answer I gave was based on the ones I had used 40 years ago, and the ones I've seen plans for on the internet.
     
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