This section is from the book "Soldering For Workshop, Farm And Home", by John Bonert. Also available from Amazon: Soldering For Workshop, Farm And Home - Information On Soft And Hard Soldering - Projects For The Workshop Explained And Illustrated.
Figure 16 shows how a new bottom can be put in a pail. The body of the pail will not extend below the bottom as the pail was originally constructed. The new bottom will be flush with the bottom of the body but it will give just as good service. The metal will have to be cleaned before any seaming is done.
In Figure 16 the work is laid out in steps which can be followed as the work progresses. The first step shows the pail after the bottom has been cut away. This cut is made as straight as possible and when the bottom has been removed the cut can be straightened. It would be good to scribe a line about 1/2" from the bottom before making the rough cut. The final straight cut could then be made on this line. Next, a line is scribed around the body 1/4" from the bottom. The edge is turned out at this line by using a pair of flat pliers. This should be done gradually as the pail is revolved. It will be necessary to work around several times to make this flange. The pail will now be as in step Number 2.
A piece of galvanized iron will now have to be cut for the bottom. This will be a circular piece 1/2 "larger in diameter than the edge of the flange. Scribe a line all around 1/4" from the edge. Bend the edge at this mark with a pair of flat pliers going around several times until the edge is upright. This flange can be straightened up nicely if there is a circular object at hand which will lie flat inside the flange while it is hammered all around. If there is no such piece at hand the flange will have to be straightened with the pliers. The body is set inside this flange and it will be as in step Number 5. The outer edge is now hammered gently to bend it over the flange of the body as shown in step Number 6. A heavy steel bar or a large diameter pipe is now placed in the vise to bend the two flanges against the body. The bar or pipe will have to extend far enough from the vise so it will reach the bottom of the pail. This bar or pipe will have to be directly under the spot which is receiving the blows and the end will always have to be held against the bottom. If this is not done the metal will bend and kink elsewhere. The bending of the two flanges toward the body can be started with the pliers. After that it will be necessary to go around once more with the pliers and squeeze the flanges together before the hammering is done. It is best to beat the flanges with a rawhide or wooden mallet as a steel hammer will make the bends too sharp and may cause the iron to crack where it is folded.
If the craftsman wishes a demonstration of why the mallet should be used on any job done with sheet metal he might try the following: Take an ordinary piece of sheet iron and place it on a hard surface. Strike four or five hard blows at a point in the center of the metal with a steel hammer. When the iron is turned over it will be found that a bulge has appeared on the under side. This bulge was made because the metal has become thinner by the blows of the hammer and naturally stretched. The metal being stretched had to go somewhere so it bulged. It can be seen that this bulge can never be corrected again. If the metal is placed on the bench with the bulge upward and again hammered down the bulge will appear on the other side. That is why the mallet should be used on sheet metal work in preference to the steel hammer.
After going around the flanges with the pliers they may be hammered down against the body. The pail will now be as in step Number 7 and the seam is ready to be soldered.