FIELD: combination working of ducts of different cross sections and perimeters. SUBSTANCE: method comprises steps of moving tool-electrode in lengthwise direction by action of constant effort; controlling lengthwise feed effort due to changing pressure inside working portion of tool-electrode inversely proportionally relative to change of perimeter of cross section of worked duct. Tool-electrode has working portion with cathode plates and insulators of wear resistant material. Cathode plates are in the form of chain links mutually joined by means of axles and having grooves allowing to change length of perimeter. Axles are rigidly mounted in adjacent links. Insulators are arranged on outer surface of links with possibility of mutual overlapping at their motion. Position pickups connected with regulator of pressure inside working portion of tool-electrode are placed in grooves of links. EFFECT: enhanced efficiency of method, improved design of apparatus. 2 cl, 3 dwg
