Wire EDM machine

[phill05]

Neale,

You have made some interesting reading so far, I cleared the workshop of an old friend when he passed on and was left with a lot of old drawings to good to throw out among them dated 1977 there are A1 size layout and construction drawings of a dry electric discharge machine, if they are of any interest to your group feel free to PM me.

Phill

[magicniner]

Neale,

You have made some interesting reading so far

All I've gleaned from this so far is that something wonderful has been achieved but it's all too complicated for it to be worth any of us seeing anything beyond a vague overview!

[Robin Hewitt]

I'd guess the clever bit must be in how much power you can feed down that tiny wire without over egging the pudding with Volts and lengthening the spark or over ramping the Amps and melting it. Lots of sparks per second seems to be better than a few fat ones, so you need low inductance and presumably power it from both ends of the wire which sounds tricky 'cause one end is under water and has to reach around the part being cut.

[magicniner]

power it from both ends of the wire which sounds tricky

Thanks Robin, I needed a laugh today! :D

[Neale]

I'd guess the clever bit must be in how much power you can feed down that tiny wire without over egging the pudding with Volts and lengthening the spark or over ramping the Amps and melting it. Lots of sparks per second seems to be better than a few fat ones, so you need low inductance and presumably power it from both ends of the wire which sounds tricky 'cause one end is under water and has to reach around the part being cut.

Not quite, Robin. The wire is earthed (it runs over various metal components in the frame that carries it). The workpiece, under water, is connected to the "live" side of the spark generator so that you get a spark between wire and workpiece. The water is non-conductive (there is a deioniser filter and a recirculating water pump to try to keep it clean) so that it does not short out the spark. The actual current during the spark we estimate to be an amp or so, which is not very much and certainly much less than the wire could carry. It's not really practical to try to measure the current so this is a "best guess" based on voltages, capacitor values, spark duration, and similar. The spark duration is also quite short - maybe 100microsec or so - so each individual spark does not have a lot of energy. The tricky bit is monitoring the spark voltage so that we know whether to advance the wire by a step (no spark so must be too far away), leave it where it is (spark happened) or move it away (shorted out - maybe wire touched workpiece or gap filled with debris from cut). On paper that's not too difficult, but actually implementing a system which reliably measures the relevant voltages in the presence of high levels of interference from the sparking isn't so easy.

If anyone is interested (and I get the feeling that this isn't very interesting to members of this forum but I'll say it anyway), then the machine should be on display and working at the Midlands Model Engineering Exhibition next month. One of the build team should be there with it to answer questions. Its next public outing will probably be at the Alexandra Palace model engineering exhibition in January.

[komatias]

Good to meet you again at the BSMEE Neale.

Saw it in action, really fun to watch. Cut out aluminium letters about the size of a 5p within a minute or so.

[Neale]

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...

[Neale]

For anyone who might be interested, the wire EDM machine will be at the Alexandra Palace model engineering exhibition this weekend (Fri to Sun). Assuming it survives the transport, it will be demonstrated running and I shall be happy to chat to anyone about it.

[rasta]

hi; the difference between cutting thick stuff and thin stuff mainly lays on water pressure , AND ,and this is a big AND , making sure that the wire contact are both top and bottom ath that the length of the wire between both contacts are kept to a minimun as possible...