Wire EDM machine

For testing purposes (and because I wanted one) I tried cutting a tiny screw-cutting tool for my lathe on this machine. It cut a 3/16" high-speed steel toolbit with a 1mm long 47.5deg tip (which some people might recognise as the thread angle of a BA thread) basically by cutting straight across with a deviation to form the "point" of the tool. Took around 5-10mins to cut - wish I'd timed it but I wasn't really expecting it to work at all! I can see a use for this machine for myself, cutting form tools for lathe work directly into HSS. According to one guy I spoke to, EDM works well with tungsten carbide as well.

That cuts far quicker than I thought it would.

For video purposes, would slowing the pump flow make the work area more visible?

Cuts a lot faster than we expected! Faster than a blunt junior hacksaw blade...

Pump flow is something we might look at. If you start without it running (which is what I normally do for demonstrations) you hear the spark quality go down after a few seconds and pick up once the pump is started. So, some flow is needed. At the moment, we probably have too much flow for this thin material, but I'm not sure that there is enough for the thicker cut like the HSS toolbit. The debris can build up in the cut behind the wire and almost weld the waste material back to the bulk. A nozzle to direct the flow would help. Commercial machines tend to blast liquid at to and bottom, I believe, but that's for much thicker cuts than we anticipate.

Double post...

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Originally Posted by Neale

I may have misunderstood, but I'm not quite sure what you mean by this.

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

https://2.imimg.com/data2/AA/AF/MY-2...es-250x250.jpg

?

Quote:

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Originally Posted by Neale

Cuts a lot faster than we expected! Faster than a blunt junior hacksaw blade...

Pump flow is something we might look at. If you start without it running (which is what I normally do for demonstrations) you hear the spark quality go down after a few seconds and pick up once the pump is started. So, some flow is needed. At the moment, we probably have too much flow for this thin material, but I'm not sure that there is enough for the thicker cut like the HSS toolbit. The debris can build up in the cut behind the wire and almost weld the waste material back to the bulk. A nozzle to direct the flow would help. Commercial machines tend to blast liquid at to and bottom, I believe, but that's for much thicker cuts than we anticipate.

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If you're just using a basic impeller pump, can you add a flow control valve? A pair of mole grips/small g-clamp/pipe clamping pliers would also work for testing purposes.
Or would increasing the depth of water work, so there's not quite as much disturbance from the flow?

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Originally Posted by m_c

If you're just using a basic impeller pump, can you add a flow control valve? A pair of mole grips/small g-clamp/pipe clamping pliers would also work for testing purposes.
Or would increasing the depth of water work, so there's not quite as much disturbance from the flow?

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It's actually a diaphragm pump intended for use in caravans with a pressurised accumulator to damp out pressure pulses. We do have a control valve - a little clamp with an adjustable screw! The pump output splits; part goes through a deionising filter to keep the conductivity of the water down and the rest goes through the jet playing on the cutting area. It's possible to juggle the relative flows but it's an adjustment that I have not played with. Depth of water is a bit critical - too low and it doesn't flood the work (sparking is much more effective under water or the right kind of oil, believe it or not), too high and the splashing ends up in the electronics. Bad news - the machine's first outing came to an end during the first cut when spillage on to the control panel shorted out something critical which meant a new PC board was needed. A good question to which I do not have the answer is, "but why did non-conductive water short something out?" It just did!

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Originally Posted by magicniner

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

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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:smile:

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.

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

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.