Fig. 17.
If a vise is not available, the copper may be held against the edge of the bench with one hand and the point filed clean and bright with the file held in the other, or a coarse sheet of emery cloth may be placed flat on the table and each face of the point rubbed bright on it. A file is by far the best for this purpose, however, and if it is chalked before using, the copper filed away will not clog it.
When the copper is clean and bright at the point each face should be thoroughly covered with a thin film of soldering paste or dipped into the soldering acid.
The copper should then be placed in the fire and heated to the melting point of the solder.
Heating.—While the copper is heating get ready a piece of tin about 2 by 4 inches—any clean flat scrap or part of a can will do. Spread a little soldering paste into the center of the tin and lay it on the bench near the heating apparatus. A few drops of killed acid may be placed on the tin instead of the paste, if the acid is to be used.
After a few minutes heating the copper should be removed from the fire and the end of a strip of solder touched to the point. If the solder melts quickly and easily against the point the copper is ready to tin; if it melts very slowly, “slushy”, the copper should be returned to the fire and heated a bit more. The copper should never be heated red hot under any circumstances; this must be borne in mind. If the copper is heated to a red heat, the soldering paste will be burned off and its action destroyed, for a red hot copper will not pick up solder, nor may it be tinned again until the copper is cool and refiled bright and clean, recoated with flux and reheated. If the copper is heated red hot after the point is tinned, the tinning is burned from the point and solder will not stick to it until it has been cooled, refiled and retinned.
This is the most important point to remember about soldering and is the cause of many failures. Remember that soldering is impossible without a flux to keep the metal clean when it is hot; too much heat will burn soldering paste or killed acid away; the tinning and the solder adhering to the point will be burned or oxidized and rendered brittle and useless.
A heat that will melt the solder almost instantly and cause it to flow with a brilliant glistening color should be maintained at all times when the copper is employed for soldering. This is never a red heat.
When the copper is first heated to be tinned, it should be removed from the fire when it melts the solder easily, and several large drops of solder should then be melted from the bar or strip of solder onto the piece of tin placed by the fire and on which some soldering paste or acid has been spread. Rub each face of the point of the copper into the solder on the tin until each face is thoroughly covered with a bright coating of solder. Hold each face flatly down against the solder on the tin during the rubbing process. The copper may have to be heated once or twice by the beginner, as it may get too cool to melt the solder easily. As soon as the solder begins to work stiffly, “slushy,” and looks gray instead of glistening, it is time to reheat the copper.