Wire EDM machine

[Neale]

How would you cut any of the more complex of these shapes, the four largest generally round ones for instance -

Assuming the question is a serious one and not "if your CNC router can't handle 8x4 25mm ply, why are you bothering to talk about it at all - it's a toy", then there are a number of answers.

First is that we don't know if it can cut this kind of depth. Unexplored territory. There are issues of wire tension that become more significant the deeper the workpiece, which affect surface finish as well as accuracy. The current control panel does not give the kind of accuracy, rehoming, etc, that the usual motion control software provides and as a result it is more difficult for us to do what some of the big boys do which is to take a roughing cut somewhat oversize - say, 0.05mm - which is aimed more at speed of cut than anything. The narrow kerf means poor debris clearance which combined with a more intense spark leads to more surface pitting leading to poor surface finish. However, you then take a second, sizing, cut with a lower-power spark which is now moving along an open face. Better surface finish and accuracy. Again, the big boys talk of micron accuracy with this kind of technology. If and when we upgrade our controls, this is an area to explore.

Second answer relates to work-holding. Something else we haven't figured out. The workpiece clamp we have at the moment is, again, a quick and simple solution for testing purposes. I would not trust it to hold the kind of blank (presumably by the edge to allow uninterrupted cutting) of the depth used for some of those examples.

Your picture shows some workpieces with a feature that we can only dream about (along with auto-wire threading, wire break detection, etc). That is the ability to separately move top and bottom of the wire. This allows sloping cuts, bevelled edges, and all sorts of features. It's a kind of wire EDM version of a 5-axis VMC. In principle the hardware is do-able, but the software sounds like fun. For someone else...

On the other hand, coming back to the bit of the real world that the team inhabits, we have already had a request to cut out custom brass letters to make nameplates for model locomotives and similar. Rolls Royce use EDM to cut 2mm curved holes through the length of nimonic alloy turbine blades (something to do with running fuel through for cooling, I understand). We could cut out little brass letters. Horses for courses

A final point is that anything our machine could do, a laser could probably do as well, maybe better. At the high end, lasers are sometimes unacceptable due to metallurgical changes at the cut surface that can lead to micro-cracking which is a reason that EDM is used instead. I doubt somehow that we are likely to be working with materials where this is going to be a problem. However, I suspect that despite the work that has gone into it, wire EDM is probably a better cutting technology for the home workshop than high-power laser; I know already that we can cut materials that are just not possible with any laser that is reasonably available to the amateur. If you are a commercial workshop, justify the cost of a commercial machine based on your own workload, or outsource/subcontract to a service company. As a bunch of amateurs, we need no cost justifications to show to shareholders, we do it for the fun of it. I would argue that our machine is a little more useful than a steam model locomotive or a matchstick model of Salisbury Cathedral, but I would not deny the right of anyone to build those if it takes their fancy.

[magicniner]

Sorry,
I thought you might be developing a useful, functional machine with wider applications, Kudos for making it work at all but it's so disappointing that it's been intentionally developed down a remarkably limiting dead-end :-(

- Nick

[Neale]

Nope, if you're looking for a commercial scale, production-quality machine, you're right out of luck in this thread.

Life's a bitch sometimes...

Let's be realistic here. A bunch of amateurs wanted a challenging technical cross-discipline project that was feasible in a home workshop (or three). The team has built a prototype that met and actually exceeds its modest ambitions and design goals. It would scale fairly easily - the mechanical bits are straightforward application of ballscrews and profile rails, cutting and inertia loads are low, and a bigger, heavier machine would be easy. The wire support arm needs beefing up anyway, but that's not rocket science at this level of sophistication. The control electronics and software are not a problem - probably need to move away from the PIC to an Arduino or something like that. SMOP, as I said earlier. The really difficult bits, the spark and motion control electronics, don't really need to scale at all within reason. Could up the spark energy a bit with some bigger capacitors, but my guess is that we could do a reasonable size (for some definition of "reasonable") job with what we have.

My bet is that we could cut things like die blocks for model steam loco valve gears, ratchet wheels and pawls directly into hardened carbon steel rather than cutting first and risking shape change on heat treatment; one suggestion received was cutting combs for musical boxes. So, our toy machine could do a useful job making bits for other toys. Not really in the business of cutting keyways in bevel gears for wind generators or any of the jobs the wire EDM service companies provide. I'm quite interested in the idea of being able to cut profile tools for use in a lathe; although my lathe would take something like 16mm shank tooling, for many purposes something much smaller is perfectly OK and within the scope of this machine. Quick search on AliExpress, wave a credit card, and you could have your own machine delivered with much more capacity and sophistication with a lot less effort.

Happy to discuss what we did and how we did it, if there's any interest, but I'm not putting this forward as "the only way to do it" or even "the best way to do it." Whether our original aims were challenging enough is a separate question but even George Stephenson didn't start out by building Mallard!

Apologies to anyone who thought that this thread was advertising machines for sale, or even a proven design and source of PC boards and components to build one. Mike Bax in the Netherlands is, I believe, working towards doing something like that; the plasmaboog Yahoo group would give more information on that although Mike seems a little reticent to say too much about how his development works for commercial reasons.

[m_c]

Getting water on electronics is rarely good. Perhaps an additional cover, or maybe some tank extensions that slope inwards to try and help contain splashes?

What I suspect Nick is getting at, is how are you going to generate the code to machine complex parts, if you can't use some kind of standard/common code that most CAM packages can produce?

While I remember, a KFlop running KMotionCNC can be run in reverse. Simply command a negative FRO, and it'll run as fast in reverse at it will forward. If it only it could also put the material back while running in reverse... :-)

[Neale]

Ah, design in retrospect - always the easiest approach! You are quite right, though, and one simple change has been to put a clear waterproof cover over the front panel, which should help. There are also covers over the rest of the electronics, partly to keep out fingers as well as water. No-one but an idiot would put a large open container of water directly over a heap of sensitive electronics... I remember once visiting a hotel that had just been closed - the swimming pool had developed a leak into the electrical plant room below, so we aren't the only ones. The real point, though, is that this was built as a proof of concept, something that would, if it worked, be able to do something demonstrably useful albeit on a small scale. If I admitted that the current controller can only accept designs that are something like 16K steps long, which equates to about 200mm cutting length, am I going to be nailed to the wall again? Extending that part is, again, just a matter of upgrading the front-end software and hardware. SMOP.

As for "standard gcode", I possibly did not explain myself very well. Normally, for example, you would design in, say, Vectric vCarve and use its CAM module to produce gcode aimed at specific motion control software - Mach3, say. Mach3 translates that gcode on the fly into steps which are sent to the stepper drivers. We design in Vectric vCarve and use its CAM to produce gcode. We use the grbl post-processor. To simplify the software running in the EDM machine micro-controller, we do the gcode to step translation in a separate application which runs on a PC. The step file is then downloaded to the machine. The work flow is very little different from, and the design stage is identical to, that used with the kind of machine that most people on this forum use. There is one extra step that we make explicit that most people do not see as it happens in the motion control software.

Use of Kflop or similar is a valid point, but we took a simpler approach. Our approach means tight coupling between spark generator and motion control at a spark-by-spark level. I suspect that this is one reason for the surprising rate of cut but this is a guess.

[Robin Hewitt]

So if someone wanted to rip off all your good work and build one of these things to play with, what do they have to do? I am a long way from Bristol.

[Neale]

So if someone wanted to rip off all your good work and build one of these things to play with, what do they have to do? I am a long way from Bristol.

Interesting question, but probably not a relevant one. As has already been suggested and discussed, what we have is by way of a working prototype. Yes, it does work. However, if any of the team felt motivated enough to build another, it would use some of the same principles and key bits of technology, but probably wouldn't look that much like the one we have. By the same token, no-one in their right mind would want to make an exact copy of what we have built. That's exactly the same reason that I, or many other members of this forum, wouldn't bother to publish plans of their CNC router or whatever because the majority of people don't want to build a copy, they have their own ideas that they want to contribute. There are common basic principles but the application of them can and probably will differ for each machine builder. Despite many pleas for "publish a design that anyone can build!", it ain't happened yet and probably won't. Same for our wire EDM machine. No point in publishing details as someone skilled and experienced enough to build one of these would want to change a lot of it. Look at the number of threads on this forum that deal in some way or other with noise and grounding problems with a router. That is dealing with a bit of EMI from a spindle or motor drive pulses, probably an order of magnitude or two below the kinds of EMI when you have digital electronics a few inches away from a spark transmitter and trying to reproduce someone else's design won't necessarily help much with that.

However, there is nothing secret about the working principles here, it's just that there is little point in detailed circuit diagrams designed around what was to hand as much as the ideal components, and the electronics is also tightly coupled to code running in the PIC microcontrollers. Again, nothing secret about the code, it's just that it would be difficult to reproduce in a different environment.

Distance is not an issue as the original design was put together by a team based variously in Aberdeen, South Devon, and various locations in the home counties, often via video-conferencing. I'm happy to discuss any technical points here on the forum or by PM, although the topic is really not mainstream for this forum (the difficult and interesting bits of the project are not directly the CNC stuff, the mechanics of which are trivial) and the wire EDM Yahoo group (plasmaboog) is the place to go for more technical and specialist discussion. That has a number of contributors with strong backgrounds in building and developing wire EDM technology on this kind of small scale. I'm not ducking the issue; I'm just feeling that this isn't the appropriate place to have brought up the topic. But it's here now, it is what it is, warts and all.