Fig. 66.—Shaft Broken at End of Square Shank, its Weakest Point.
Fig. 67.—Broken Part of Shaft Removed and New Piece Added, thereby Moving the Weld away from the Weak Part.
(99) When working on shafts the welder will encounter such articles as automobile propeller shafts and rear axles, which generally break adjoining the square ends. He will no doubt wonder whether it is advisable to weld this square end back on, or whether to try and build up the shaft the desired length. Undoubtedly the point of fracture is the weakest portion of the entire shaft, else it would not break there. The execution of a weld at this point where no additional metal can be added or any means of reinforcing used is not to be recommended. [Fig. 66] will show the problem which confronts the welder, and [Fig. 67] the suggested means of overcoming the difficulty. By removing about four inches from the broken end of the shaft and adding a new piece, about ten inches long, of the same diameter, the weld will be removed from the weak point; a heavier weld can be made, and the end can be machined off to the desired size. This procedure is recommended on all jobs of like nature.
(100) Occasionally case-hardened ring gears are brought to the welder to have teeth built up or new ones added, and although the welder must realize that the hardening is destroyed by the action of the flame, yet he does not understand why it is necessary to reharden the gear. A little thought on this subject will make him appreciate the fact that if he destroys certain properties in metal which have been introduced for a reason, these must be replaced if he would bring the job back to normal. It would be like heating up a tempered lathe tool, or cold chisel for that matter, and trying to use it before it had been retempered. Therefore if hardening or temper is destroyed by the flame it must be restored.
Fig. 68.—When Welding a Small Section to a Larger One, the Flame of the Torch is Directed toward the Heavier of the Two.
(101) If a weld were to break, it would be necessary for the welder to remove all metal added in the first weld before attempting to reweld. This is true of his own work as well as that of others which he may be called upon to do. For no matter how good the surface may appear, without a solid foundation no weld is of any value, and unless he clears out all of the old metal he cannot be sure of the work. This will apply not only to steel work, but to all metals, and it is a point which should be borne in mind.
(102) At times there are jobs come up in which one piece of work is to be fused to another which is much larger, and will absorb much more heat during the weld. When handling such work, it will be necessary to play the torch upon the larger piece most of the time, as shown in [Fig. 68], in order to bring both pieces to a fusion point at the same time and keep them in that condition.
(103) Once in a while it will be necessary for a welder to fuse cast iron to steel or vice versa, and the question will arise as to which filler-rod he will use. It has been found that a cast-iron filler-rod can be used with success and of course when using a cast-iron filler-rod, a cast-iron flux will be necessary. Work of this nature is not very frequent.