PURPOSE: To machine the external surface of a tube without causing unbalanced wall thickness over the entire length thereof by making trailing rollers in rolling contact with the external surface of the tube, and the position of a cutting tool follow a tube bend after initial machining on the basis of data of wall thickness distribution and runout before tube machining.
CONSTITUTION: In order to measure preliminarily the outer diameter, the wall thickness distribution and the axial bend of a tube 5 at several lengthwise positions, the external surface of the tube 5 is cut or machined and mounted between a face plate 4 and a tail stock 3. Then, a wall thickness sensor, an outer diameter sensor and a mill scale sensor built into a sensor box 8 are made in contact or in rolling contact with the tube 5 for measuring the wall thickness, the outer diameter and the bend thereof. And calculation is made on the basis of said measurement and the position of a cutting tool 7 is corrected, thereby machining the external surface of the tube 5. Thereafter, trailing rollers 65 and 68 are made in rolling contact with the external surface of the tube 5 and the cutting tool 7 is made to follow the tube end. According to the aforesaid constitution, the entire length of the tube 5 becomes free from unbalanced wall thickness and this thickness and the outer diameter of the tube 5 can be kept within a tolerance.
HYODO SHIGETOSHI
FUKUTOME TETSUO
SATO KENJI
