edm machines

Mark, From my original request for info in April 2019 I decided to go the Ben Fleming route but have to admit that I have not achieved very much, just collected a few components and done a little on the hardware so perhaps I’d better join that club!

,

I was looking at this for my EDM head:

You do not need to rotate or oscillate the electrode for successful EDM. In fact doing so will reduce accuracy of cut, because the motion will need clearance to work, and that clearance will be multiplied by the distance from electrode tip to rotate / oscillate mechanism , cutting the hole much larger than the electrode.

An accurate linear slide to hold the electrode, and a DC gearhead motor or servo to operate a leadscrew to drive the slide up and down are all that is needed, if you use the Ben Fleming design. If you are going to spend some cash, get a decent linear slide and forget about rotating the electrode with the apparatus in your picture.

I built a Ben Fleming Mk.1 conventional EDM (sink) machine in 2009-2011 with such a slide (from Deltron in the USA) and some other variations and it has worked great since. If I make copper electrodes .003" smaller than the desired finished hole dimension the holes (whatever shape) come out VERY close to dead nuts on size.

I to have a mostly finished Ben Fleming EDM.

What are people using for the dielectric fluid?

Dave

RIGHT ! Guildford was Maurice Fagg. Dilectric fluid parafin ! I bought the only 2 books on the subject available at the time and took the bits I liked from both to build a powerful EDM. Drilling holes in tungsten carbide with copper wire was a party piece ! Most of what was used was what was found lying about, apart from a few £s for electronic components. The 2 transformers gave me 66v at 6A and came from old 1arm bandits, before the days of LED ! Jeff is spot on ! The over cut is about .004" and brass makes good electrodes. If you can file the shape you can EDM it. I used a draw slide with 12v DC motor/gearbox and leadscrew. Speed is goverened by volume of metal to be removed. As the oft talked of removal of broken taps goes, small ie under 1/4" use thick copper wire or brass to take out the middle. For BIG ones use copper tube and just cut off the "legs" and it all falls in the middle.

I'd better get out the books and draw up my circuit diagram, for those who may find it interesting.

More later. Noel

I use a Valvoline dielectric oil specifically made for EDM, sold by a large oil dealer in my area (Ontario Canada).

I suggest calling a local oil dealer to you and ask what they recommend. Or call a mouldmaking shop for injection moulds, they use it out of 45 gallon drums.

Rustlick is another USA brand I have tried but I find it smells unpleasant, where the Valvoline one does not. Virtually no smell and almost clear transparent in colour with the Valvoline product. Great stuff.

I would not recommend any paraffin / kerosene unless it is specifically formulated for EDM. Lighter kerosenes can catch fire under some EDM conditions, ie work submerged less than an inch deep. Kerosene also smells strong, and EDM smoke is oily and sticks to curtains, clothes etc. so if it smells bad it can be a big issue in the household.

Edited By Jeff Dayman on 06/05/2021 20:29:18

The second book I bought was HOW TO EDM by Robert P. Langrois. One design used a dc motor/leadscrew, the other a stepper motor/leadscrew.. I found the dc motor easier and less complicated to make. Noel

Liquid paraffin may be a suitable dielectric fluid. Chemists don't seem to sell it any more due to limited practical use an some abuse (not going into detil as this is a searchable forum). It is howeve used for horses so equine suppliers sell it in useful quantities. Called "mineral oil" in the USA. It has good dielectric and thermal properties and not highly flammable. It has low volatility and high purity. It's used in temperature controlled baths in standards labs.
EDIT: If liquid paraffin is too viscous you could try odourless white spirit. This is of course a lot more flammable

Robert G8RPI.

Edited By Robert Atkinson 2 on 06/05/2021 22:00:44

I can buy parafin from a local motor factor in 20 or 25L drums, though it's dearer than petrol. I have heard it said that de ionised water will work, though I've not tried it. Noel

When did that happen? Used to trip down to the local Esso Blee Dooler for a gallon for the room heater.

Regards Ian.

When the above posting is modded due to the "Overlap", this seems to occur when you add the " and then insert a cut and paste quotation instead of the "Norm" of adding the whole posting and wasting space.

Didn't get this with the old system, DOH!

Regards Ian.

P.S. Spline chunk still don't work.

.

I find the best compromise is to quote and then edit the quotation ... as demonstrated ^^^

... that way you properly reference whomever you are quoting.

MichaelG.

Clambered about in the spare bedroom this evening and Got out the EDM ! So long since I last saw it, I had even forgotten how I'd built it. Due to the transformers I had used I had 2 voltages, 66v at 8A and 100v at 3A It also gave me 12V at ample current for the cutting head positioning and 5V for the control circuits. The 2 bridge rectifiers + other handy bits, like the transformers came from gaming machines, when all the flashing lights were proper bulbs and needed quite some power. I had added a bank of capacitors in increasing values to 2200uf, all switchable so almost any value could be used. The heavy resistor that was going to be expensive, I used a NOS electric fire element cut down to give the required ohmic value. I used VERO(strip) board to build the circuit, no fancy PCB. An old metal box was adapted to make a good solid case to contain all the bits, and a cooling fan from something kept everything from breaking into a sweat as the resistor could get quite hot. The cutting head is a readily available small 12v motor/ gearbox unit, the accurate verticle movement is achieved using an ordinary ball draw slide and the tool holder is an old 3/8" drill chuck. An old fridge drawer served as a tank and a small machine vice was the work holder. To remove some of the debris an old speaker magnet laid in the bottom of the tank. It was built as 2 parts, the power supply and controls and the cutting unit. I will try to post some pictures in the near future. Noel

Today weather has stopped me cutting the grass, so I have used the time to look at the issue of an EDM. ME carried an article by C.R. Amsbury in july 1976 and an update in October 1981. There appear to be several errors, one being the switching transistor in Fig 3 of the update which should read 2N3055. The dearest part of making an EDM is going to be the power transformer. Anything above 40V at 4A on the secondary will be good up to about 100v and 6 or 8A., if it also has 12v and 5v you are laughing. Capacitors of 400v rating will be good. For simplisity the capacitor discharge system and a DC motor is best - and cheapest. What you build and what circuit you use will largely depend on what you have or can get cheap or for free, making friends with the maintanence man at an amusment arcade may pay dividends. Noel.

I have dismantled the EDM today,it was built in 5 parts, The case, front panel with all the controls, the power supply, capacitor bank and control board. I have included some pictures of the parts.to give an idea of how it was built. The control circuit board is based on Ben Flemings circuit but built on strip board. The 2 ic s that were used were mounted in holders to avoid the risk of damage due to static or heat and make testing or repair simple. The front panel starting top left, mains fuze 5A, mains switch, to the right 5 switchable capacitors, & the 66V or 100V switch. Bottom left,cutting head motor switch on/off, centre off, up or down. A bicolour LED to indicate up or down movement, this is a failure & will be changed for 2 separate LEDs. Set voltage pot and voltage spread pot. Red and Black power output sockets. Lower left is the cutting head indexable socket. Whilst the ampmeter was fitted, I have not got round to fitting the Voltmeter - yet ! I Suppose you want me to draw up the strip board layout and cutouts ?

The cutting head I have yet to find, it's in one of the sheds, there is as much work in making this as the power supply and is the real key to good operation and results. One thing I found vital was to be able to obsereve the rotation of the leadscrew, this was achieved by sticking a strip of barcode round the shaft. Steady fore and back movement, but more fore indicated cutting, constant fore indicated you were through, hold motor up, job done !   Noel.

Edited By noel shelley on 09/05/2021 14:26:47

Actually a commercial grade EDM machine can be easy and cheap to build, the problem is there is a misconception that there’s some sort of manufacturer’s design secret to these machines which makes people overcomplicate their home build designs usually by using some sort of code to control the actual burn. There's no need to buy a book or anything like that, the electronics are simple and mainly use "off the shelf" parts and the resulting machine performs, in my opinion, better than any DIY build I've ever seen online.

It might be worth you having a look at the video that I posted on YouTube a few days ago in response to other people having design problems, showing a simple machine that I built a few years ago, which I think you will agree proves my point

https://youtu.be/I6EgTPVLrwU.

That looks pretty usable, promising and "doable" .

Thanks for sharing

Whilst I will agree that many on line machines are complicated and there is no need for them to be so, that your machine was cheap, that term is relative ! Neither of the 2 books I'm aware of on the subject use code and many who build will use parts they have to hand and adapt things to achieve the desired result, rather than buy ready made parts and just wire them up. It really depends on why your building an EDM, what you want it to do and how much you want to spend.

Your machine looks good and seems to work well, that it was easy to make - may be ! That it was cheap, is less clearly proved. Noel.

The gentleman is a Guru, I'm sure we will find out shortly.