Abstract: It is a difficult machining issue of world level for micro-hole of extra large aspect ratio, especially for those with aspect ratio over 1 000, and diameter less than 3 mm to be machined. On basis of analysis for the existing problems, when processed on generally purposed EDM machine tool or even specially purposed one existed for deep micro-hole, such as difficulty of evacuation for debris and disperse of heat generated in machining, unstable machining course, no proper way to guide the existing tube electrode and so on, a new kind of special three-jaw tube electrode is illustrated and discussed, which overcomes the above mentioned difficulties and ensures self guide and self stabilization in machining, and a practicable process strategy, which specializes in an up-side-down install- ation of work piece, with tested result, is demonstrated and analyzed in detail.

Key words: Electro discharge machining(EDM), Micro-hole of extra large aspect ratio, Self-guide tube electrode, Up-side-down installation