This seam is the one most used, and the beginner should practice it diligently. After mastering it in the position shown in the cut, the board should be fastened to the floor and the beginner should practice burning the upright seam from above the work. This position occurs many times in lining tanks, and the beginner who conquers the upright seam in that position can consider himself sufficiently proficient to attend to any job of lead burning that may arise. The beads of lead will appear more compact and regular than in the flat seam, and if properly done will upon cutting the sample show a very strong joint.
Inverted Lap Seam.
This seam should be attempted only after becoming very proficient with the blow pipe and flame, after which it becomes as easy to burn as in any other position. In order to get the range of the seam the sheets should be arranged in the position shown in Fig. 27. The burning is begun on the upright seam, and continued up and over the curved portion and on to the inverted seam. The graduation from the upright seam to the inverted seam is simple and gradual, and is hardly noticeable.
After accomplishing the inverted seam in this manner, strips of lead should be prepared and fastened to the board as described for upright seams. The board should be supported in an inverted position at a convenient hight over the operator's head. The flame should be shortened as much as possible. The burning may be started at any convenient point and continue in each direction. The point of the inner flame is applied to the seam at a slight angle, as a. The object is to obtain a fusion between the back sheet and the upper edge of the lap. When this is accomplished fusion proceeds easily.
Fig. 30.—Burning an Inverted Corner Seam.
The hardest part of this seam is in starting it, and when once started, with a little patience and care, the balance of the seam can be fused without any trouble. Fig. 30 shows an exercise which the beginner should practice after having conquered Fig. 27, as it teaches the making of an inverted corner seam. Of course, this position seldom occurs in small work, but if the burning of it is once accomplished it will give the operator considerable confidence in his own ability.
CHAPTER X.
PIPE SEAMS.
The Butt Seam on Round Pipe.
Pipes that are placed in a horizontal position are usually butt seamed, as a stronger seam can be made in that manner. This form of seam is also used in lengthening traps, bends, etc. To prepare a round pipe for butt seaming, the ends of the pipe should first be made perfectly round by inserting a drift plug and dressing the lead up close to it. The ends of the pipe should be rasped true and then shaved clean. Also shave the pipe for a distance of ⅛ inch each side of the edge. A piece of stiff writing paper should then be rolled up the size of the pipe and inserted in the ends. This paper will prevent any lead from running into the pipe and leaving rough edges, as these afterward form an obstruction.