the collet 612 chucks both of the electrode tube 7 and its leak proof seal 71 female threads 6111 inside the nut 611 and male threads 62 provided at the lower end of the spindle 6 are tightened or loosened to load or unload the spindle nut 61 the seal 71 and the electrode tube 7 as a whole unit fig4 shows the cutaway view of chucking the electrode tube 7 wherein the spindle 6 descends until it holds against both of the nut 611 of the spindle nut 61 and the holder 413 the nut 611 contains the collet 612 the electrode tube 7 and the seal 71 to press against the holder 413 so the holder 413 descends and compresses the elastic member 412 to a proper position but not all way down to the end at this time the spindle 6 turns clockwise to engage both of the spindle nut 61 and the spindle 6 while chucking tightly the collet 612 the seal 71 is pressed and the electrode tube 7 properly chucked meanwhile the elastic member 412 pushes back the holder 413 for the holder 413 to maintain restricting the nut 611 from rotating until it is screwed into the spindle 6 as illustrated in fig5 while unloading the electrode tube 7 both the spindle 6 and the spindle nut 61 are descending to where the nut 611 merely presses against and descends the holder 413 until the nut 611 clears away.