Figure 7-18.Butt welds with multipass beads.
Figure 7-19.Weave motions used in manual shielded arc
Tack welds should be used to keep the plates aligned for
welding. The electrode motion is the same as that used
in making a bead weld.
In welding 1/4-inch plate or heavier, you should
prepare the edges of the plates by beveling or by J-, U-,
or V-grooving, whichever is the most applicable. You
should use single or double bevels or grooves when the
specifications and/or the plate thickness requires it. The
first bead is deposited to seal the space between the two
plates and to weld the root of the joint. This bead or layer
of weld metal must be thoroughly cleaned to remove all
slag and dirt before the second layer of metal is depos-
Figure 7-20.Undercutting in butt joint welds.
In making multipass welds, as shown in figure 7-18,
the second, third, and fourth layers of weld metal are
made with a weaving motion of the electrode. Clean
each layer of metal before laying additional beads. You
may use one of the weaving motions shown in figure
7-19, depending upon the type of joint and size of
In the weaving motion, oscillate or move the elec-
trode uniformly from side to side, with a slight hesitation
at the end of each oscillation. Incline the electrode 5 to
15 degrees in the direction of welding as in bead weld-
ing. When the weaving motion is not done properly,
undercutting could occur at the joint, as shown in figure
7-20. Excessive welding speed also can cause undercut-
ting and poor fusion at the edges of the weld bead.
BUTT JOINTS WITH BACKING STRIPS.
Welding 3/16-inch plate or thicker requires backing
strips to ensure complete fusion in the weld root pass
and to provide better control of the arc and the weld
metal. Prepare the edges of the plates in the same
manner as required for welding without backing strips.