Abstract: Arrangement for working internal rotational surfaces of metal parts in a cylindrical cavity in a blind bore or in a throughgoing opening having a high slenderness ratio. For working, the arrangement uses an electrode connected to the negative pole of a source of burning electrical impulses, the positive pole of such source being conductively connected with the worked metal part. The electrode is fixed conductively on a supporting tube which is arranged rotatably and eccentrically in a cylindrical hollow space from which it is insulated. In the course of the working operation the electrode or the workpiece rotates, and the electrode performs an axial advance relative to the workpiece.

Abstract: Arrangement for the electrospark working of internal conical surfaces of metal parts having a hollow space with a high slenderness ratio, terminating in a conical surface. The working electrode is guided in the hollow space of the workpiece and is provided with a simple and effective system of advance of the electrode, with the possibility of stoppage of the operation of the apparatus if due to some non-conductive dirt between the electrode and the worked surface correct operation is impossible, and with the provision of effective rinsing of the burning products.