EDM and CNC

[davestea]

Sorry if this shows my ignorance but is there any reason one could not put an EDM tank on the table of a CNC mill such as a Taig, put an electrode on the top of the milling spindle (or in its place) and use that for EDM?

What I am wondering about is the down feed and timing. Is there some kind of feedback path via the spark current that tells the z axis to feed downward?

I don't want to do a lot of or any specialized EDM - just want the ability for when (get that - not if) I break a tap off in some project.

[gmac]

No reason you cant do it, just that it is not particularly easy. it is very important to make sure you have the electrical setup correct so that noise generated by the EDM arc and power supply will not disrupt or damage the CNC electronics. to do this you need to keep the EDM power circuit completely isolated from the mill and CNC parts. use an insulated toolholder so that your sinking die is not electrically connected to the mill spindle, select clamps and materials so that the pan is either non-conductive or isolated from the mill table. if you want to get a little fancier you could set up an alarm so that if the edm current gets too high, the program will stop or at least stop feeding the tool. this will happen when the sinking die breaks off or if you feed too fast and which will cause the die to run into the workpiece, probably damaging both of them. if you are really ambitious, you can probably set up a low-current detector that would be input to the program to incrementally step up the feed speed.

you could probably do electro-engraving if you had the interest, with this setup.

[Andre]

You mean something like this one.
web page
There are others available also.

[AndrewMawson]

Dave,

I have a commercial die sinker type EDM, and that has a servo that controls the spark gap. Changing the servo settings markedly alter the finish and rate of removal. I suppose it you could set your cnc to drive downwards VERY slowly it could work, but you need to allow for the shorted gap situation.

When tap removing it is usual to use a suitably sized piece of copper tube, and pass the fluid through it to keep the gap flushed. As the cut progresses you produce a cylindrical spigot (of old tap) inside the tube. Towards the end of the job, this spigot tends to sag sideways and cause difficult spark conditions. If you had no servo it would just be a dead short at times.

A 'buzzer type' edm is a very simple type to use for removing taps. The servo consists of a solenoid, the armature of which has the electrode on the lower end. EDM current passes through the solenoid raising the electrode. This opens the circuit, and the armature descends under gravity and starts the cycle over again. Still needs a copious fluid flush to work well.

[davestea]

OK - a short question -

what does die sink EDM mean?

as opposed to some other kind ?

[AndrewMawson]

A die sinker EDM is a ram type machine where the action (usually) is to sink an electrode into the work - typically a shaped chunk of copper or graphite that is the male profile of the female shape that you require. Used in the die making industry for producing coplex moulds for plastic injection moulding and the like.

The other form of EDM is the wire machine, which can be thought of rather like a bandsaw. Very thin brass wire is the electrode, which runs between spools via the work piece. Either the workpiece or the wire is moved to form the shape. Most often the wire is single pass - ie discarded after one pass.

[AndrewMawson]

If you want a basic introduction to edm, I have an article that I wrote for the SM&EE journal that covers the introduction - it runs to 743K if you want a copy give me your email address or point to somewhere I can upload it for you.

[JimGlass]

Dave;

Have you seen this? This is a sinking EDM that I built. I used a programmable controller to monitor the spark voltage. The plc then controls a DC gear motor to raise or lower the electrode. Works very well and has been handy to have. It is all set up with limit switches to contol depth and make it totaly automated. Often, I run it unattended and return to find a finished job.
Jim

[Herm Williams]

Hello
You are talking about a metal disintegrator. Electro Arc Manufacturing Co.
Ann Arbor,Mi.(go to google, type "electro arc" sells a whole line for different maint functions. From simple (use your drill press to hold electrode holder) to computer controlled type. In it's simplest form you ues a copper or brass tube and burn out the tap web then use a scrib to remove the outside flutes, or use a tube to burn out the center of a stud and remove the threads like removing a spring from a hole. A die sinker or cnc mill is like using a Lincoln where a Datsun should be used. my .02 worth.
Herm Williams

[davestea]

Thanks for all the info -

[none]

Please send me a copy of the edm thingybob!
hdecambre@netzero.net [img]/ubb/images/graemlins/blush.gif"%20alt="[/img]

[AndrewMawson]

Please send me a copy of the edm thingybob!
hdecambre@netzero.net [img]/ubb/images/graemlins/blush.gif"%20alt="[/img]

I did, and your email bounces !