Upright Lap Seams.
Prepare the sheets as for flat lap seams, fastening the sheets securely to a board, as previously described. The burning should be begun at the lowest point of the seam. After regulating the flame, the point of the inner flame is applied to the edge of the outer sheet slightly above the point decided upon as the starting point, and at an angle of about 30 degrees, as shown at a in Fig. 29. As the drop begins to melt it will have a tendency to flow downward. By a quick turn of the wrist the flame must then be directed against the back sheet and slightly under the melting drop.
The under sheet should brighten at once, and the force of the flame, being partially directed against the melted drop, tends to force it against the bright spot on the back sheet, with which it instantly unites. The flame must then be withdrawn for an instant, to give the fused drop time to set. The operation must be repeated until the seam is finished. Using ordinary language, it may be said that the drop is cut from the upper sheet, carried slightly downward and then stuck against the back sheet by the force of the flame.
Fig. 29.—Burning an Upright Lap Seam.
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.