Donice.. while I have ya for a moment.. Check this out with regards to the cryogenics I spoke of with Nitrogen cooling the electrodes and this link better explains and has a 4 pics showing the effect with an out roundness issue with the electrode tip. Fascinating.. 

"The topography of electrode used in conventional EDM process and EDM with cryogenically cooled electrode at magnification of 60X for various processing conditions is shown in Fig. 7. The fig. 7 shows that the electrode surface profile is less distorted in case of EDM with cryogenically cooled electrode. The shape of electrode tip changes in case of conventional EDM process. The better shape of electrode tip with the use of cryogenic cooling can be attributed to the fact that use of cryogenic fluid leads to less melting of the electrode tip as the temperature reduces because of liquid nitrogen. Since, the volume of electrode melted is less; it leads to better retention of the initial profile of the electrode tip"

https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.310.9445&rep=rep1&type=pdf