Preparing the iron.

essential for good soldering. The tinning operation is applied to a new iron or to

one that has been heated to a temperature so high that the coating of solder has

been burned.

(1) Filing.

(a) The tip of the soldering iron is filed to shape the point and to

remove old solder, pits, and tarnished spots from the working surface of the iron

so that it may be properly tinned.

(b) Before it is filed, the soldering iron should be heated hot enough to

melt old solder left on the surface. With externally heated soldering irons, this

heating process may be accomplished by several methods. If a hot gas flame such as

a bunsen burner is used, the iron should be placed over the burner with the point

outside the flame. A gasoline blowtorch may also be used. Using this method, the

flame of the torch should be concentrated on the thick end of the iron. Because of

the high heat conductivity of copper, the point will be heated to practically the

same temperature as its thick end.

(c) If the tip of the soldering iron is badly pitted or uneven, it may be

necessary to repoint it. This is accomplished by heating the tip to a dull red

and hammering it on an anvil until the point tapers back about one-fourth the total

length of the copper portion. The hammer blows should be distributed evenly on the

faces. The iron may then be annealed (softened) by being reheated and plunged red

hot into cold water to permit filing the point to a finish. The tip of an electric

iron should not be hammered, filed, or plunged into water until the heating element

has been removed.

(d) A vise or holding clamp should be used to secure the iron while

filing. The working surface of the tip should be parallel with the top of the vise

or holding clamp. The tip should be filed on all sides until bare metal can be

seen, using a fine flat file to prevent cutting away too much metal.

(2) Tinning.

(a) The iron should be heated to the minimum temperature required to

make solder flow readily; an overheated iron will not tin properly. An externally

heated iron is ready for tinning when the surface appears to be covered with

various colors; a green flame coming from the heated tip indicates that it is too

hot. Electric iron overheating can be recognized by the sudden tarnishing of the

bright metal on a newly filed tip.

(b) After the tip of the iron has been properly heated, it should be

rubbed on a block of sal ammoniac flux and solder applied (omit the sal ammoniac

flux if core solder is used). All sides of the tip should be tinned for general

soldering practices. However, if the job surface requires that the iron be used in

an overhead position, only one side of the tip should be tinned. When attempting

to solder with the iron in an over-head position, a completely tinned tip will

result in the solder flowing away from the joint as shown in figure 24. Excess

solder may be wiped off with a clean dry cloth.

(c) The tinned point should be cleaned with a soft wire brush or clean

dry cloth each time it is removed from the heat; otherwise it will become coated

with the flux residue and oxidation of the solder.

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