Sounds like you're a glutton for punishment, so here goes. Modern edm’s have provisions for both suction and pressure flushing. They also cut submerged, i.e.; the tank fills to a level above the work piece. This serves several purposes, to thermally stabilize the machine, fixturing, and work piece, to prevent fire by denying oxygen to the sparks, and to allow for “no flush” burning. The no flush aspect means the gap is flushed by high speed jumps, movements in the z axis that create a hydraulic pumping action that removes the debris. Think of it like a peck cycle on deep hole drilling. I doubt you’ll be using that approach, so you are correct that suction can be preferable to pressure. This depends on your part or electrode configuration allowing for drilling the appropriate holes. If you drill a very small hole thru the electrode, you will likely have to use pressure, as you can not draw enough volume at negative one bar. The edm drills use copper tungsten tubes with thru holes, and as much as ten bar of pressure. (One bar = one atmosphere = approximately 14 psi. One of the reasons the edm drills use water is the lower viscosity flows better thru small passages. Another point for edm drills is they rotate the electrode for more efficient burning. The graphite used for electrode material is hot isostatically pressed isotropic material of a particular grain size. The smaller grain size gives you greater density, less wear, the ability to machine delicate details, and a smoother surface finish. The biggest name in edm graphite is Poco, you can check out their web site. You are correct in your follow-up that pencil leads and other superficially similar materials are not good candidates for edming. This is the predominate material used in the US. In Europe they use a lot of copper electrodes. This eliminates the hassle of machining dusty, abrasive graphite. It burns slower, and with less wear, but adds the potential problem of de-burring what you machined on the electrode. I use a synthetic oil called Ionoplus that I think is excellent. It runs about $16.00 US per gallon. Rustlick also has an entire line of oils. The natural oils are about half the price. I’ll stop here, not to overload you. You might want to check out
http://www.mmsonline.com/edm/index.html ,
Lots of good technical articles, and an edm specific chat forum. Still want more? Let me know.
Regards,
Roy