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 danger of overheating iron or steel is not very great but when heating copper or brass care must be taken not to melt the metal. If solder of a high silver content is used the work need not be hotter than cherry red which would be a safe heat for brass or copper. The craftsman's best guide in judging the temperature of the work is color. He should therefore work with his back to the light rather than facing it. An improvised shield can be used to shut out light and drafts. Figure 19 gives information and drawings for small brazing.
A convenient form of solder for brazing is silver wire which can be bought from supply houses which stock materials for brazing. This wire comes in gauges from about No. 24 to No. 19 on the Brown and Sharpe gauge. These numbers on the gauge are about the thickness of an ordinary dressmaker's pin to half the thickness. If there is no silver solder at hand an ordinary silver coin can be used. A ten cent piece can be hammered down very thin and used as solder. This silver solder can be used for joining brass, copper, steel, iron, Gun metal and gold.
Silver solder comes in various compositions ranging in melting temperatures from 1200 to 1600 degrees Fahrenheit. The higher the Silver content the lower the melting point. Silver solders with a higher melting temperature contain more copper and zinc and are comparatively less costly. The color is also governed by the amount of silver in the composition. Those with a high silver content are almost silver white while those containing less silver are more the color of brass. The larger concerns who manufacture material for brazing and welding will gladly inform the craftsman as to the different compositions they have. The beginner will do well to start with solder which melts at the lowest temperature.
The procedure for the cleft is the same as for the butt joint with the exception of making the cleft and wedge. In setting up the butt or cleft joint on the yoke the joint should be left slightly open to admit the flux and solder. After the joint has been heated to a cherry red apply the flux and follow up with the solder. When the solder can be seen to fill the joint one end is tapped lightly with a hammer to bring the ends together and force out the excess solder. If the solder should roll up into a ball instead of flowing into the joint it is usually caused by insufficient heat or lack of flux. In preparing joints the surfaces should be made to fit closely. Only a small amount of solder is required for a strong joint. Filling a large space with solder does not make a stronger joint and is a waste of solder.