For Film of this working see Sparking splines in cone
Sparking slots in the core of the base gave an interesting problem- the core is much higher than the depth of our sparker’s tank.
We solved this using some mouldings- fortunately ABS glues well, and is resistant to the dielectric in the sparker.
We glued parts of 2 cones together to give a submerged sparking operation. It isn’t normally this easy to do this on a tall job!
These are spaeked on one of AAVPD’s Sodick AM35 CNC Spark eroders.