I built the HSM's Build an EDM. It works as advertised, but I don't use it much. Most significant thing I did with it was a hole in the end of an arbor to engage a special shaped shaft. (imagine a circle or pie with one quarter removed) I duplicated the shaft in brass and plunged the brass electrode into the end of the arbor.
Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
~Practitioner of the Electromechanical Arts~
Theory & Practice-
Theory is when you know something but it doesn't work.
Practice is when something works but you don't know why.
It it dangerous to combine Theory & Practice;
nothing works and you don't know why.