Figure 7-11.Tapping method of starting the arc.
TAPPING method (fig. 7-11). In either method, the arc
is started by short circuiting the welding current between
the electrode and the work surface. The surge of high
current causes the end of the electrode and a small spot
on the base metal beneath the electrode to melt instantly.
In the STRIKING or BRUSHING method, the electrode
is brought down to the work with a lateral motion similar
to striking a match. As soon as the electrode touches the
work surface, it must be raised to establish the arc
(fig. 7-10). The arc length or gap between the end of the
electrode and the work should be equal to the diameter
of the electrode. When the proper arc length is obtained,
it produces a sharp, crackling sound.
In the TAPPING method, you hold the electrode in
a vertical position to the surface of the work. The arc is
started by tapping or bouncing it on the work surface
and then raising it to a distance equal to the diameter of
the electrode (fig. 7-11). When the proper length of arc
is established, a sharp, crackling sound is heard.
When the electrode is withdrawn too slowly with
either of the starting methods described above, it will
stick or freeze to the plate or base metal. If this occurs,
you can usually free the electrode by a quick sideways
wrist motion to snap the end of the electrode from the
plate. If this method fails, immediately release the elec-
trode from the holder or shutoff the welding machine.
Use alight blow with a chipping hammer or a chisel to
free the electrode from the base metal.
NEVER remove your helmet or the shield
from your eyes as long as there is any possibility
that the electrode could produce an arc.
After you strike the arc, the end of the electrode
melts and flows into the molten crater of the base metal.
To compensate for this loss of metal, you must adjust
the length of the arc. Unless you keep moving the
electrode closer to the base metal, the length of the arc
will increase. An arc that is too long will have a hum-
ming type of sound. One that is too short makes a
popping noise. When the electrode is fed down to the
plate and along the surface at a constant rate, a bead of
metal is deposited or welded onto the surface of the base
metal. After striking the arc, hold it for a short time at
the starting point to ensure good fusion and crater depo-
sition. Good arc welding depends upon the control of
the motion of the electrode along the surface of the base
Setting the Current
The amount of current used during a welding opera-
tion depends primarily upon the diameter of the elec-
trode. As a rule, higher currents and larger diameter
electrodes are better for welding in the flat position than
the vertical or overhead position. Manufacturers of elec-
trodes usually specify a current range for each type and
size of electrode; this information is normally found on
the face of the electrode container.
Since most recommended current settings are only
approximate, final current settings and adjustments
need to be made during the welding operation. For
example, when the recommended current range for an
electrode is 90-100 amperes, the usual practice is to set
the controls midway between the two limits, or at 95
amperes. After starting the weld, make your final adjust-
ments by either increasing or decreasing the current.
When the current is too high, the electrode melts
faster and the molten puddle will be excessively large
and irregular. High current also leaves a groove in the
base metal along both sides of the weld. This is called
undercutting, and an example is shown in figure 7-12,
With current that is too low, there is not enough heat
to melt the base metal and the molten pool will be too
small. The result is poor fusion and a irregular shaped
deposit that piles up, as shown in figure 7-12, view B.
This piling up of molten metal is called overlap. The
molten metal from the electrode lays on the work with-
out penetrating the base metal. Both undercutting and
overlapping result in poor welds, as shown in figure
When the electrode, current, and polarity are correct,
a good arc produces a sharp, crackling sound. When any
of these conditions are incorrect, the arc produces a
steady, hissing sound, such as steam escaping.