Method of manufacturing a reservoir tube

Reformation of a round tube to a tube with a selected polygonal segment is achieved by supporting the round tube on a mandrel having rounded corners that mate with the tube's inside diameter. The mandrel is otherwise provided in the resultant polygonal shape. The supported tube is subjected to the compressive force of a die having upper and lower die sections that define an elongated polygonal cavity. The planar sides of the cavity are offset relative to the parting line. Preferably, the corners of the cavity adjacent the parting line are wrapped by a leg of the die section. Upon closure of the die sections, the tube material is allocated to a particular quadrant by contact with the die section and the tube is reformed. Excess material that may result from tolerance permitted variations is delivered to the corners of the polygonal tube section maintaining uniform wall thickness across the flat sides of the reformed tube.