Abstract: An electric discharge machine has an electrode and mechanism for driving the electrode on an orbital path. The electrode is mounted on an electrode holder having an upstanding post. The electrode is driven on its orbital path by a rotor about the post. There are two resiliently loaded drive arms mounted on the rotor and engaged with the post at circumferentially spaced points so that the post is subject to the compound driving force of both drive arms. Centering mechanism is provided to restore the electrode to a centered position with respect to its orbit in the event of a short circuit between the electrode and the workpiece, thus to break the short circuit.