edm machines

would like to build a EDM machine but finding information hard to come by. any assistance would be appreciated .

Hello Bernard

This is good: **LINK**

https://www.camdenmin.co.uk/products/the-edm-how-to-book

... That said; I bought a copy years ago, and still haven't built one

MichaelG.

Construction of an EDM was a four part series in MEW. Issues 168 to 172. I have only read it in passing, and never constructed one.... yet! Just have to finish a couple of other projects first!

Hi Bernard, would recommend the book "how to build an EDM" by Ben Fleming in the USA. Great reference book. I built an EDM in 2011 using his circuit in the book as a general guide. You do not need to purchase a PCB from him to make it, I did have some issues with the comaparator IC he specified not being able to withstand the current draw of some of the components I used. A friend helped design an equivalent-function circuit using very cheap but high current discrete components. It has worked just fine since. If you do end up using this circuit please contact me before buying parts and I'll give you full details of what I did and some pics and video of the EDM I built.

I would not recommend the sink EDM design published in MEW a few years ago, the one using a vibrating electrode and hand-operated capacitor terminal connections at line voltage. This design had serious electrical safety issues and vibrating electrodes is not at all necessary and ruins accuracy. It can be useful for blasting out broken taps but for precision work it is not recommended.

Plus one for not using the vibrating electrodes. I made my living in a toolroom for many years operating EDM machines. Some had the vibration setting but was a gimmick that upset the stability. Getting an EDM machine working well is all about balance of servo/flushing of debri and the correct pulse on pulse off times. I suspect a home built machine will just work on relaxation principle and not pulse?

I have built an EDM machine based on the bits of information I could find on the web about Ben Fleming's design. It is the capacitor discharge version as I could not fined enough information on his pulse version. (I was too mean to buy his books.) It works quite well.

Les.

I am building Ben Fleming's second EDM machine. It is described in his book "Build a Pulse EDM machine". The book is not cheap and the electronics is even more expensive. I choose the pulse design because sensible capacitors for the resistor-capacitor set up used in his first book are hard to find.

Ben's second machine uses a voltage of around 100vdc which is switched by a MOSFET (a bank of 6 in his case) at frequencies up to about 20kHz. There is also provision to lift the electrode every ten or so seconds to flush out the debris. Everything is adjustable in the design, the front panel of the electronics box is very intimidating.

I can provide photographs etc if anyone is interested.

.

Yes please

MichaelG.

As requested, 3 photographs of the electronics box. The names of the controls are not stickers but an annotated photograph as a reminder to me (dither is the period of withdrawal of the electrode to allow escape of the debris).

Ben suggested using an old PC box. I had one but found its construction so complex that it became easier to build my own. The box is possibly too small but the use of 12" long metal stock allowed a quick and easy construction.

The circuitry is not complex. The power is provided by 80vAC through a full bridge rectifier. The maximum power is 650VA and is controlled by a bank of forced air cooled resistors. The switching of the power is by a MOSFET controlled by a 555 timer. Another 555 timer is used for the dither period. The electrode position is determined by comparing the discharge voltage with a required operating voltage and a minimum voltage required to prevent the electrode hitting the work. The electrode position is driven by a simple servo motor. I know there are other ways of controlling the discharge and position of the electrode but as an electronics simpleton I am happy with most of Ben's circuitry.

I have to say that the project is very much "work in progress". I have just started on the electrode head.

Thanks for those, JA

... much appreciated.

MichaelG.

Yes, very good JA. Nicely done, thanks for sharing.

Dave

Thanks for all the info I will get the book from Camden and see what that looks like but after looking at the pics it looks a little bit daunting to a mechanical man with only simple electronic knowledge. Again thanks for all the info.

There is also some information on Ron's Model Engineering web site:

**LINK**

If you choose 'Resources' on the left hand side followed by 'How to?' You will see a list of topics. 'Remove a Broken Tap' takes you to the pages on 'Making and Using a Basic EDM'

Best regards

Roger

An EDM design and build article appeared in the Strictly IC magazine many years ago, so if you have a friend with that mag collection you have another choice.

Emgee

Much as I'd like to build something as sophisticated (and impressive) as the EDM machine JA has built - I'm afraid it's never going to happen at this stage in life. However - whatever their limitations - there are much simpler designs around that I might consider building - especially for the removal of broken taps and making small 'oles-in-ard' things...

I saw this simple EDM set-up at Guildford MES in 2016 - and had a chat to the builder (sorry I did take his details but cannot find them att). As I understand it, an electromagnet pulls the anvil up until a capacitor fully charges, where upon it falls back and touches the work, thereby discharging the capacitor - and causing the required spark - the cycle then repeating ad-infinitum. A very simple concept and no complex electronics required.

I'm not sure if this is the same as one of the other EDM systems already mentioned and there may well be all sorts of limitations associated with this simplicity - but it would certainly cover most of my (admittedly) limited needs...and the work samples shown were quite impressive...

Regards,

IanT

PS Sorry - image started off right way up but seems to have done a 90 degree rotation on up-load...

Hi, Bernard - sent you a PM.

I met Maurice's machine and loved its capacity to make blind square holes but haven't the electronic nous to make one.
Instead I bought a Watton Electronics Ltd "Arc-out" Model 1B (from 1965 or so).
It lacks electrodes, and herein lies my question - how are they attached?
The fitting is a brass thread 1/4" x 26 BSF, with an axial hole of variable diameter through which water is supplied, the bottom of this fixing ("a" is rough.
This is capped by a nut, closed at the bottom with hole .165" ~ 4,19mm in diameter.
A "lollipop" with a cylindrical head could be retained by the cap but - "a" is rough ; this would leave a tube, od 4mm, id circa 1mm., which would be rather fragile if threaded.
I suppose larger diameter tubes could be added and secured with a side locking screw, or did Watton have another way?

Kind regards, Rob.

There was(?) a very simple version that used 2 light bulbs & a bridge rectifier published in an old Popular Science book (Google on the web), March 1968. Intended, mainly, I believe, as a proof of concept although it could do real work. That said, this thing was *dangerous* with line voltages (110-120 volts or dc equivalents) "all over the place." I guess if I were desperate to remove a broken tap - where all else failed - I might give it a go. I have not reached that point - yet (not to say that I have had my share of broken taps). Reprints float around the web but I have no direct links.

The US magazines - Home Shop Machinist/Machinist's Workshop - (uncertain which one) had some updates to the original Popular Science article.

There must be an unspoken of club for unfinished EDM machines, similar to the Quorn cutter grinder. My electric box is done and untested.I need to make the burning head and it's ready to go, going on 7 or 8 years so far.