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  1. #1
    This thread is under the "Other Machines..." heading as it doesn't have its own category - yet?

    I know that some forum members will be aware of the Society of Model and Experimental Engineers (SMEE), a old-established society with mainly UK but also international membership. A small group of members of the SMEE Digital Group have been collaborating on a wire EDM(*) machine for the last couple of years. For those who haven't come across wire EDM, think of a hot-wire cutter as used for foam, but this time using a spark between the wire and the (metal) workpiece. Enough sparks for a long enough time, and the workpiece gets cut away, leaving a cut around 0.1mm wider than the wire used for "cutting" - and this machine uses 0.25mm wire, so that's a pretty fine cut. Move the wire under CNC control, and you can cut intricate and accurate shapes out of difficult-to-cut materials, including hardened metals that are next to impossible to cut otherwise. Wire EDM sits alongside laser and water-jet cutting as a go-to technology for tricky jobs. If the principle sounds easy (which it is), the practice is a bit more tricky. The wire has to keep moving as it gets eaten away as well, while maintaining tension; the spark voltage has to be accurately controlled by adjusting the position of the wire and thus the spark gap - too close and you need to back off, too far away and there's no spark; the whole thing is working in an incredibly noisy electrical environment as all the electronics is running a few centimetres from this spark transmitter.

    If you do a bit of googling on "wire EDM", you will find plenty of big - and I mean pretty big - commercial machines and companies offering wire EDM services. Look hard and you will find a few, a very few, "home-built" wire EDM machines. We now have a working wire EDM machine that is totally self-contained and small enough to go into the back of a car, and as a small demonstration of its capabilities, here are a couple of sample pieces I cut on it earlier this evening:
    Click image for larger version. 

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    The letter E is about 8mm high, the star about 4-5mm across. In fact, I had difficulty in finding the star in the tank (the cutting operation happens submerged in distilled water with a jet directed at the cutting area to flush away cutting debris).

    I know that there are people who have made claims to fabulous machines on this forum but have offered little proof of their existence. Well, you will be able to see this machine in the flesh at the Bristol Model Engineering Exhibition next week, where with a bit of luck and a following wind, I shall have it running on the SMEE stand for all three days of the show. Forum members are cordially invited to come along, and if you can't find me, just ask anyone on the stand. If you are also a wire EDM user, then you are even more welcome to come along and compare our efforts with your commercial machine!


    (*) Electrical Discharge Machining

  2. The Following User Says Thank You to Neale For This Useful Post:


  3. #2
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 3 Days Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 2,908. Received thanks 360 times, giving thanks to others 8 times.
    WEDM is on my desired toy list.

    Are you aware of the plasmaboog yahoo group, or http://www.mechatronicprojects.com/blog/ ?
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  4. #3
    Thanks - I had found EDM Yahoo group, but mostly seemed to be concerned with building from a kit of parts available in US. Hadn't seen that blog before - looks as if it started relatively recently.

    I'm currently custodian of our team's machine as I'm taking it to Bristol next week so I shall try to get some pictures, and if the technology isn't too much for me, a clip or two of it cutting.

  5. #4
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 3 Days Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 2,908. Received thanks 360 times, giving thanks to others 8 times.
    The mechatronics site is fairly new, but I think the author has been working on the machine for a couple years.

    Benny Croonen (IIRC) who started/runs the plasmaboog group has been working on one for a good few years, with the group being a spillover from the EDM group run by Ben Fleming (I've got his original EDM book/plans).

    I've liked reading the periodic posts regarding the problems faced. They're quite a complex machine that needs everything to work nicely together to get a good end result.

    Is there any more info about your machine published anywhere?
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  6. #5
    No, nothing published as yet. You are also right about the "complex machine that needs everything to work nicely together to get a good end result" - or even to work at all. The wire feed and tensioner (DC motor with PWM control for wire feed plus stepper for tensioning) is one sub-assembly and includes a solenoid-operated guillotine mechanism for chopping used wire into short lengths as it comes out the end. Then there's the water flow and filtration, the XY movement with ballscrews and profile rails (tank moves on one axis and wire guide assembly on the other) plus stepper motors, and then the electronics. This machine has three PIC embedded microcontrollers in it - one for the keypad and screen, one for wire control, and one for spark generation which also controls the XY motion as these are inter-related. If anything is below par, then nothing works. In testing, a few weeks were wasted chasing electronic faults when it turned out that the deionised water wasn't quite pure enough. It's that bad. Electrical noise has been a perennial problem which is why the main control board is now up to version 9b, there are three separate power supplies, and it's wall-to-wall opto-isolators and so on.

    Cutting area is something like 100mm square (although I need to check this). It uses a variable spark voltage of something like 35-60V although it generally seems happy at about 50V. Sparks are generated from a bank of capacitors switchable from 10uF to 100uF or so (again, need to check but it's something like that). It uses MOSFETs for switching - turn on one to charge capacitor bank, when charged that MOSFET turns off and another turns on to cause the spark. When the capacitor voltage has dropped below some threshold, the spark is turned off and the cycle restarts. The motion control is linked to this; if no spark occurs the wire is advanced and if the voltage drops too low the wire is stopped or even backed up a little. It's a very simple idea but has taken a lot of work to make it function. Wire speed is separately controllable. All the motion control software was custom-written; no use of modified Mach3, LCNC, Kmotion, grbl, or anything else. This does mean that the software has complete control of wire motion so it is possible to backtrack the entire cutting path if needed, for example if a cut ends in the middle of a workpiece rather than cutting its way out again.

    We do not use any fancy commercial EDM components apart from the reel of EDM wire. So, no commercial wire guides, wire contacts, or things like that. Keeps the price down but whether this is going to hang together in the long term remains to be seen. It certainly works at the moment. There is already a long list of "wouldn't it be great if we could..." ideas!

  7. #6
    Quick video showing the main features of the wire EDM machine. Video clip of operation currently in the editing suite!

  8. #7
    hi; i also making my own wire edm, can you please tell me if the schematics of this machine are available?
    Also what control hardware/software are you using?
    regards
    Mariano

  9. #8
    Quote Originally Posted by rasta View Post
    hi; i also making my own wire edm, can you please tell me if the schematics of this machine are available?
    Also what control hardware/software are you using?
    regards
    Mariano
    Mariano,

    This was a group project and I do not have current circuit diagrams, but I have asked the guy who designed this part if he can let me have copies and I shall be happy to make them available here. However, this comes with a warning! The actual electronic design is not particularly difficult or exotic, and it uses fairly standard switching techniques. A lot of the cleverness is actually in the firmware that runs on the embedded PIC microcontrollers. Again, I'm happy to describe our algorithms but I'm not sure that there is much point in actually publishing the code. It might take me a week or two to get hold of a copy of the circuit diagrams, so please do not expect them immediately.

    There are a couple of main reasons why we have not published this kind of information before. One is that the whole project is experimental and things keep changing. In particular, we recognise that the current electronics design is lacking a few significant features/capabilities, so if we built another machine, we would base it on the current design but definitely not copy it as it is today. Secondly, as I said, the design is not particularly difficult if you have a good background in modern electronics. If you do not have a good understanding of this, and the very significant problems of getting high-power switching, digital electronics, and a massive spark/electrical noise transmitter in close proximity, you are not going to get it to work. Understanding the circuit diagrams is not the problem here; it is to do with board layouts, cable runs, isolation between different parts of the circuitry, good earthing practice, etc. It is not an easy system to build and to make work. In fact, I would even go so far as to say that if you do not have the skills and experience to design the electronics, you probably do not have the capability to recreate our design and make it work. And we do not have all the diagrams, etc, to show how our machine was put together at this level of detail. It was a one-off and a lot of this was developed and modified during building. Our electronics guru has a large cardboard box full of discarded PC boards, gathered over a couple of years of development.

    As for control hardware - we have avoided use of any of the usual motion control systems (Mach3, LCNC, grbl, etc) and written our own. Gcode-to-step translation is done offline by separate software rather than using real-time translation as these other systems do, and we download a "step file" which is a step-by-step instruction list to the PIC memory. The PIC drives conventional stepper drivers and stepper motors moving the axes via ballscrews and profile Hiwin-style rails. All the firmware running in the PIC microcontrollers, which includes a very simple user interface, was written by members of the team. This does mean that our spark generator and motion control PICs communicate in a way that is probably a little bit different to most of the published techniques, which often need modification to standard software to allow pausing and reversing to take place. Again, this is an area which we know needs to be improved, another reason why we have not published our design. Why publish something which we know is deficient and which we would never do again if we built a Mark 2? We would build on the existing system, but not copy it.

    I'm sorry if I sound rather unhelpful, but suggesting that you could take our design, copy it, and have a working system is so far from true that I can only say that you could use it get help your own design, but I would almost guarantee that even if you copied our design to the last detail, I would be surprised if it worked. And I can't even give you those details because many of the subtle changes to wiring, board layout, etc, have never been documented.

    However, I do wish you luck with your project - getting a machine like this to work at all is a major achievement, and not many people (outside the commercial space) have managed it.

  10. #9
    thank you Neale;
    I know how difficult is going to be, altougth I have some experience with cnc wire edm , and been building my own for a few years (on and off) , you are right on what you say how difficult is to get the right spark and getting the control to backup automatically when there is a problem.. that is why all the information that I can get is never enough, and that any information that you can share will be very much appreciated..
    regards
    Mariano


    Quote Originally Posted by Neale View Post
    Mariano,

    This was a group project and I do not have current circuit diagrams, but I have asked the guy who designed this part if he can let me have copies and I shall be happy to make them available here. However, this comes with a warning! The actual electronic design is not particularly difficult or exotic, and it uses fairly standard switching techniques. A lot of the cleverness is actually in the firmware that runs on the embedded PIC microcontrollers. Again, I'm happy to describe our algorithms but I'm not sure that there is much point in actually publishing the code. It might take me a week or two to get hold of a copy of the circuit diagrams, so please do not expect them immediately.

    There are a couple of main reasons why we have not published this kind of information before. One is that the whole project is experimental and things keep changing. In particular, we recognise that the current electronics design is lacking a few significant features/capabilities, so if we built another machine, we would base it on the current design but definitely not copy it as it is today. Secondly, as I said, the design is not particularly difficult if you have a good background in modern electronics. If you do not have a good understanding of this, and the very significant problems of getting high-power switching, digital electronics, and a massive spark/electrical noise transmitter in close proximity, you are not going to get it to work. Understanding the circuit diagrams is not the problem here; it is to do with board layouts, cable runs, isolation between different parts of the circuitry, good earthing practice, etc. It is not an easy system to build and to make work. In fact, I would even go so far as to say that if you do not have the skills and experience to design the electronics, you probably do not have the capability to recreate our design and make it work. And we do not have all the diagrams, etc, to show how our machine was put together at this level of detail. It was a one-off and a lot of this was developed and modified during building. Our electronics guru has a large cardboard box full of discarded PC boards, gathered over a couple of years of development.

    As for control hardware - we have avoided use of any of the usual motion control systems (Mach3, LCNC, grbl, etc) and written our own. Gcode-to-step translation is done offline by separate software rather than using real-time translation as these other systems do, and we download a "step file" which is a step-by-step instruction list to the PIC memory. The PIC drives conventional stepper drivers and stepper motors moving the axes via ballscrews and profile Hiwin-style rails. All the firmware running in the PIC microcontrollers, which includes a very simple user interface, was written by members of the team. This does mean that our spark generator and motion control PICs communicate in a way that is probably a little bit different to most of the published techniques, which often need modification to standard software to allow pausing and reversing to take place. Again, this is an area which we know needs to be improved, another reason why we have not published our design. Why publish something which we know is deficient and which we would never do again if we built a Mark 2? We would build on the existing system, but not copy it.

    I'm sorry if I sound rather unhelpful, but suggesting that you could take our design, copy it, and have a working system is so far from true that I can only say that you could use it get help your own design, but I would almost guarantee that even if you copied our design to the last detail, I would be surprised if it worked. And I can't even give you those details because many of the subtle changes to wiring, board layout, etc, have never been documented.

    However, I do wish you luck with your project - getting a machine like this to work at all is a major achievement, and not many people (outside the commercial space) have managed it.

  11. #10
    Quote Originally Posted by Neale View Post
    Thanks, George - good to have corroboration that it was there and working! I'm not suggesting that this might be your next commercial offering, though After all, where's the market for a machine that cuts out small aluminium letters?

    Anyway, good luck with the CNC conversion kits - hope there are folk out there that recognise that C5 costs just a bit more than Chinese C7...

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