The EDM machine uses two wire spools. One for new wire and one for spent wire. Re-reeling spent wire has some advantages. Empty spool bodies are free (at least if you purchase a new spool) so an empty spool body can be used to collect spent wire in a neat way. If you machine a work piece with a very long uninterrupted cut, the wire can be re-used for a second cut.
The wire spool setup for this machine uses a belt brake to create an adjustable drag for the new wire spool. The spool for the spent wire is driven by a geared DC motor. A servo and custom control solution realises a back and forth re-reeling motion such that the wire reels evenly.