I use the EDM-1 for roughing and EDM-3 for finishing. I also stay away from magnetic work holding as I found that my flushing cannot flush out the burned off scrap and get more wear on the electrode, and burrs. This is due to the burned off scrap being magnetized to the work piece. What radius is needed at the bottom of the part? Maybe a roughing electrode and a finish electrode is what you need. I would still rough machine as close as you possibly can before moving to the edm. Berrilium copper is a PITA to work with and would probably be easier to just machine multiple graphite electrodes rather than the berillium copper. Poco also has a graphite they use to edm copper with. But I believe that is highly dependent on flushing of the work area. Maybe use a higher pressure on your flushing and see if that makes a difference. for more info you can go to
www.poco.com.