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.
The tinning explained in the lessons up to this time has been done on metals that have a much higher melting temperature than that which can be obtained with a soldering copper. Lead is a metal that will melt at quite a low temperature (about 615 degrees Fahrenheit) and if the soldering copper is too hot it will be melted. When soldering on lead if the copper is very hot it must not be allowed to rest on one spot but should be moved along to prevent melting the lead. A good way for the beginner to avoid this is to try the copper on a piece of junk lead first. If the copper melts the lead as soon as it is touched it is too hot and should be allowed to cool a little before it is placed on the work. After a little practice the beginner will know how hot the copper should be. The time spent in practice on a piece of lead will repay the craftsman many times if he has occasion to solder a split in a lead pipe due to freezing or if there is any other soldering to be done on lead. If a pipe should be split on the side or bottom it would require an expert to make the repair. If the split is on the top of the pipe or if the pipe is connected by unions of some kind which can be disconnected it will not be hard for the man with some knowledge of soldering to repair it. The best seam to put on a lead pipe is a V-bead seam. If there is a piece of junk lead pipe at hand the following will be very good practice.
A piece 4" to 6" long will do nicely. If it should be dented or flattened place it over a piece of iron pipe, or a broom handle will do, and with a small piece of board beat it to its original round shape. With a wood saw or a hack saw cut a straight line to split the pipe. Open the pipe up for about an inch and with a wood rasp or scraper bevel the two edges as shown in Figure 7. After the edges have been beveled close the pipe up again to its round shape. Have the two edges as close together as possible. This will leave a recess the shape of a V which is the reason it is called a V-bead seam.
This method for beveling the edges cannot be used very well on a pipe that is in service. The V would have to be made by scraping. After the pipe has been closed up apply a little tallow to the very ends of the seam. With the copper put a drop of solder at each end of the seam to keep the pipe tightly closed. The seam has now been closed up as much as possible but by drawing a blunt point such as is found on a wire nail the lead can be drawn or smeared so it will close the split up completely. This will prevent the solder from running through the split into the pipe.
Figure 7 shows the position of a large nail when drawing it along in the seam. The seam is now cleaned by scraping and the pasters are put in place. It need not be more than 3/8" wide but it can be made narrower if preferred. The idea of this V is to have a body of solder to strengthen the seam. A small piece of paster should be put across the seam at each end. The seam can now be run in the same way the practice seam was run in Lesson 4. The only difference being the precaution that will have to be taken not to melt the lead.
In this lesson soldering on zinc will be practiced. A soldering job on zinc is not done very often in the average workshop because the use of zinc is not as common as it was some years ago. It is a very easy metal to tin but like lead its melting temperature is quite low (about 775 degrees Fahrenheit) and there is danger of melting the zinc if the copper is too hot. It will be a good idea to take a piece of sheet copper and a piece of sheet zinc and seam them up for some practice.
It has been mentioned under "Fluxes" that the casing on dry cells is made of zinc. While this is not very heavy sheet zinc it will be good enough to use for this purpose. Clean the metal and fold the seam. Be sure the soldering copper is not too hot. Touch the copper to a piece of zinc to make sure it will not melt it, but it must be hot enough to do the tinning properly. The experienced tinsmith carries his copper very lightly when soldering on zinc allowing very little of the weight to rest on the metal. The beginner should not be discouraged if he should melt the metal. He will soon know how hot to have the copper after a few attempts.