There are two kinds of seams proper, viz.: The butt seam and the lap seam. The butt seam is used principally for joining horizontal waste pipes and in lengthening traps, or for any purpose where it is desired not to have the point of junction show. This form of seam can be burned clear through—that is, the lead can be heated until fusion takes place nearly through the entire sheet. It is generally necessary to add lead to the seam if it is desired to make the seam as strong as the sheet it joins, unless the article to be burned is of such a size as to be possible to allow of its being burned on both sides, which makes the strongest of seams. The lead for the butt seams is prepared by rasping the edges of the lead sheet to be joined straight and true, Fig. 22, so that when the edges of the lead are brought together they will fit close its entire length. The edges are then shaved for a distance of ? inch each side of the edge, making a seam ¼ inch wide. On stock heavier than 12-pound sheets the edge should be shaved off, making a deep V-shaped groove, and the seams must be made by adding lead. This allows the fusion to take place nearly through the sheet. The butt seam is the simplest form to burn, no matter in what position it is placed.

The lap seam is the seam commonly used, and as between the butt seam and the lap seam the latter is generally to be preferred. As it is not necessary to cut and trim the edges true, it dispenses with any additions of lead, except at rare intervals; it leaves the left hand free to handle the shave hook, and the lap can be dressed to fit any uneven spots. It also makes the next best seam to through fusing. By lap seaming a tank can be lined in about half the time required to butt seam the same article, which is an important item to the customer.

The lead for this form of seam is prepared, as its name indicates, by lapping one sheet ½ to ¾ inch over the other sheet. The under edges are to be shaved clean, as also the upper edge. The lead required to make the seam is melted from the upper lap and is fused on the lower sheet. There is no reason why the lead at the point of juncture cannot be made as thick as the original lead. This is the point aimed at in practicing, and the only accurate way to determine the relative strength of the seams is to cut squarely across a finished seam, then bend the beam slightly. The thickness can then be noted. A cross section of a perfect lap seam is shown at a in Fig. 23. The beginner should practice the different seams until the thickness of the joint can be told by the looks of the lead. A few days' diligent practice at the bench will soon train the eye to note any imperfection that may arise.

The different seams will be taken up serially. A description of how the seams are prepared and the several positions of the blow pipe, as well as the little difficulties that may arise, is the extent of the instruction that can be given. The rest must come with practice and the application of a little common sense. There is no royal road to this business; but practice, and practice hard, is the only way to satisfactorily master the blow pipe and flame, and in practicing remember that all this work has been done before, and can be easily done again, and by you. Do not get discouraged by failure to make a perfect seam at the first application, but stick to it for a short time and it will be found to be a most fascinating pastime, for which the persistent student will eventually be well repaid.

Flat Butt Seam.

For practicing I would recommend the beginner to use pieces of sheet lead about 12 inches long, as strips of that length are much easier to prepare. The edges are straightened with a fine rasp which is held lengthwise of and parallel to the edge to be trued, in the manner shown in Fig. 22. The rasp must be used lightly, or it will be apt to tear the lead and so leave it in worse condition than before using it. The edge should then be gone over with the shave hook and cleaned. Then shave the top surface a distance of ? inch each way from the edge, which will make a seam ¼ inch wide when finished. Then butt the edges together and secure the sheets firmly to a board with a few tacks. The extra lead that is necessary to add to make a butt joint full must be obtained from a strip of lead, which should be about ? inch square and shaved clean.

After regulating the flame to the proper size and shape the burning should be begun at the end of the seam nearest the operator. With the point of the inner flame melt off a drop from the lead strip and have it fall squarely on the seam just slightly in advance of the point of fusion. Follow it up with the flame, placing the point of the inner flame directly over the edges of the seam, which is almost under the lead drop. As soon as fusion commences on the lead seam the melted drop will flow to the bright spot and immediately unite with it. The flame must then be quickly removed and the drop be allowed to set.

In order to avoid any misunderstanding regarding the time required for the lead drop to set I would say that the drop will cool immediately upon the flame being removed from contact with it. It is not necessary to wait for any specified time, but if the flame is allowed to play constantly on the sheet it is apt to get overheated, and when in that condition it takes very little heat to set the lead running like water. To avoid this the flame should be lifted clear of the seam for an instant after each drop has been fused into place.

These remarks apply to all seams that are made by the blow pipe process and should be noted, as this particular point will not be referred to again. Now melt off another drop and let it fall as before, only it should lap on the previous drop about one-half its diameter. Secure it to the seam as before. This operation should be repeated until the seam is completed, and if the seam is correctly done a section will appear as a in Fig. 24. This form of flat seam should be practiced until perfectly familiar with the blow pipe flame and until the beginner can approach the lead with the flame without burning holes through it, which will probably be the first thing to happen.

Upright Butt Seam.

The upright butt seam is seldom used on large work, as it is a difficult matter to make an upright butt seam that will stand the test, as, if a finished seam is cut into short pieces, an examination of the severed ends will show many weak places that were previously thought to be very strong. The reason of this is that the heat necessary to fuse through the lead will cause the lead to run from the seam and leave a hole.

The sheets for practice are prepared as described for flat butt seams, and must be securely tacked to a board which can be supported in an upright position. The burning is begun at the bottom of the seam. The flame must be shortened considerably, as the fusing must take place somewhat slower than in flat seams, as in upright or inverted seams the attraction of gravity remains to be overcome, and the operator must have plenty of time between the commencement of brightening and the actual fusing to drive the melting drop to the exact position desired.

The blow pipe is held so that the flame strikes the seam squarely and at about a right angle with the sheet, as shown in Fig. 25. When fusion starts the flame should be drawn quickly to one side, and if the lead is at the proper temperature the melted drop will follow the point of flame, and as it comes in contact with the adjoining edge it will properly unite. It is not necessary to add lead to these seams oftener than at intervals of 5 or 6 inches, or as often as the lead shows signs of weakening, when it may be added by holding the lead strip against the lead sheet and slightly above the flame. The melted drop will unite with the sheet and can then be driven to any desired position. This seam will show the characteristic beads, but they will lie nearly level with the lead sheets, and if a scratch cloth be rubbed over the seam all traces of the position of the seam will be removed.

To make a really strong seam it must be gone over with the flame at least twice, as after fusion of the edges takes place the flame can be used quite strong without fear of the lead running from the seam. Do not leave this seam until you are satisfied that it is nearly perfect. It is good practice, and every hour spent only makes the mastery of the next seam come so much more quickly.

Horizontal Butt Seam.

This form of seam cannot be used to any advantage on general work, but, like seams in other positions, it cannot always be avoided. The practice sheets are prepared and tacked securely to the board, as previously described, and are then placed in the position shown in Fig. 26. The position of the blow pipe is as shown at a. The flame should strike the sheet nearly square. The edge of the upper sheet should be heated first, and as it brightens the flame should be directed onto the edge of the lower sheet. If properly done, fusion will at once take place.

The object sought is to get a light fusion between the two sheets before attempting to burn the lead clear through the seam. If this is not done, the lead will run from the upper sheet and cause holes, or at least will seriously weaken the upper sheet, as shown in cross section at b. After fusion is once obtained it is a simple matter to go over the seam a second time, which can then be fused clear through without much danger of burning holes through the sheet. Lead can be added in the same manner as in upright seams if necessary.

Inverted Butt Seam.

This seam is used extensively in joining waste pipes which conduct the acid from tanks to the drain. These pipes are usually in a horizontal position and the seams must be burned in place. The most difficult part of the seam is in starting it. When fusion has once taken place the balance of the seam is easy. The seam is prepared the same as described for other butt seams. Care must be taken to have the edges butt close. The board can then be supported in the required position by any convenient device.

The blow pipe flame must be made as short as possible and still melt the lead. The point of the inner flame is then placed squarely on the seam. Both edges must be heated at once. If the edges begin to brighten and do not show an inclination to fuse, the flame should be drawn quickly to one side, and the melted drop will follow the point of flame and unite with the adjoining edge. This seam, in common with the other butt seams, should be gone over the second time to assure a perfect seam. It is difficult work to add lead to the flat inverted seam. When necessary to do so, however, it can be added by burning the end of the lead strip to the seam. The strip is then melted off, leaving a drop of lead affixed to the seam, which can then be drawn to the required spot with the flame.

The characteristic inverted seam shows pits upon examination of the reverse side of the sheets. These are caused by overheating. The operator will often be surprised at the inverted butt seam showing a remarkable fullness. This is accounted for upon the examination above referred to. The lead, upon the application of the heat, runs from the upper or back side of the sheet and forms a very full seam. For that reason the inverted butt seams always appear stronger than they really are. See inverted lap seam, Fig. 27.

Lap Seams.

The lap seams are the seams commonly used on all classes of work. When the beginner becomes proficient with the blow pipe no trouble will be experienced in making lap seams that will show when cut a joint equal in thickness to the sheets that are joined. The lead sheets for the flat lap seam are prepared by shaving clean the exposed edge; also, shave the sheets where they touch each other. The upper edges can then be shaved for a distance of ? inch each side of the lap, which will make the finished seam ¾ inch wide, as shown at a in Fig. 23. The sheets should be lapped ½ to ¾ inch, according to the weight of the stock. It is very evident that light weights would not require as large a lap as would heavier sheets, as the object of lapping the sheets is to leave the sheets practically as one piece, and the lead, to accomplish this object, is to be melted from the upper sheet.

From the foregoing it will be seen why a 12-pound sheet requires a ½-inch lap, while a 24-pound sheet would require a ¾-inch lap. The flame, when regulated to the work, is brought to bear squarely on the edge of the upper sheet, slanting slightly in the direction of the lower sheet, as shown. When the edge has brightened almost to the fusing point the blow pipe should be drawn quickly to one side and from the upper sheet to the lower sheet. If the metal is sufficiently hot the melted drop will follow the point of the flame and instantly fuse with the lower sheet, and if properly done the seam will resemble b in Fig. 23. This process is repeated, advancing about ? to ¼ inch each time. Do not attempt to fuse a large surface at a time. Experts cannot do such a thing satisfactorily, so why should a beginner try to? Rather, try to fuse small surfaces quickly and strongly, as better work and more of it can be accomplished in that manner.

Horizontal Lap Seams.

This seam is prepared precisely as described for flat lap seams. The strips can be fastened to a board with a few tacks. The strips can then be supported in the position shown in Fig. 28. The burning is commenced, as before, at the side nearest the operator. The flame must be made as short as is consistent with the weight of the stock. It will be found to the beginner's advantage to have fusion take place slowly. The point of the inner flame is brought to bear on the outer edge of the lapped sheet and at an angle of 45 degrees. Both sheets should begin to brighten at about the same time. The melted drop must be driven against the back sheet by the force of the jet of flame, and if the sheets are clean fusion will take place quickly.

The drops or beads of lead will appear very small on this form of seam, owing to that great obstacle, gravity, which causes the drop when melted to flow downward and so swell the seam. The drops, in common with other forms of lap seams, should be made short, letting each drop overlap the previous drop as much as possible. Great care must be taken not to weaken the seam, as shown at a. The beginner should strive to get the seams so that when cut into small sections each section will resemble the result shown at b.

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.

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.

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.