Abstract: A rotary compressor of the type having an outer metal cylinder casing, a metal cylinder with a vane slot and a vane and the method of assembling the compressor by forming the cylinder with a circular chamber, the center of which is in alignment with the central axis of the cylinder and having a circular outer wall slightly smaller than the inside diameter of the casing. A vane slot is cut in the cylinder which slot is open at one end into the chamber. A vane is placed in the slot to divide the chamber into a high pressure side and a low pressure side. The cylinder has formed therein three curved elongated ports spaced from each other in the cylinder between the chamber and outer wall. The length of each port and thickness of the metal between the port and outer wall of the cylinder cooperate to provide adequate strength for welding and sufficiently flexible to absorb any significant distortion forces caused by welding without transmitting the distortion forces to the vane slot.