Method and apparatus for machining cylindrical tubes

Apparatus for machining an elongated cylindrical tube having eccentric inner and outer cylindrical surfaces to reduce the eccentricity thereof, said apparatus comprising means for rotating the tube about the axis of its outer cylindrical surface, ultrasonic measuring means for measuring the wall thickness in a radial direction from the tube center of a relatively small spot on said tube prior to machining while it is rotating and said means producing an output signal whose magnitude is proportional to said tube wall thickness, said measuring means including a sensor, means for mounting said sensor adjacent to said tube, and externally of said tube at a fixed distance from the axis of rotation of said tube to measure the wall thickness of the tube as it rotates, machining means for removing material from said tube wall at a spot adjacent to said sensor, and subsequent to measuring the thickness of the wall at the spot, means for simultaneously moving said sensor and said machining means longitudinally along the length of said rotating tube to measure and machine the wall thereof along a helical path, and drive means coupled between the output of said measuring means and said machining means to move the machining means toward and away from the tube in a direction transverse to movement of the sensor to cause a depth of cut on the tube if required equal to the measured wall thickness minus a pre-selected final machined wall thickness thereby reducing the eccentricity of the inner and outer surfaces to the tube.