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UNDERCUT GASPOCKET
F_gure
!2
Figure
13
TRAPPED SLAG
PENETRATION
Figure
T!
Run the first pass on beveled plates with a 5/32-inch
rod
and use as high a current as you can handle to obtain a
small bead on the underside. If this is not done, insufficient
penetration
wit] result, as shown in figure 11. Be sure to
clean each pass before laying on the next. Aft beads are
laid by moving the rod in a straight line with no weaving
or side-to-side movement. On the last or reinforcing
pass,
a weaving motion must be used to obtain a wide weld that
witl completely
cover preceding beads. For the beginner,
the side-to-side movement (with a slight hesitation at each
end) will produce a smooth top without undercut or overlap.
Select severat practice
welds of different
thicknesses and
cut them into 1-1/2-inch
strips. Clamp each strip in a vise
and bend it at the weld (fig. t2). If it breaks through the
weld, study it to find the cause of failure.
Corner
welds are made on light sheet metal by running
a single bead along the top, after tack-welding
at three-
inch intervals to prevent warping (fig. 13). If numerous gaps
are present, a back-up
strip may be used. On heavier
:metal two passes may be necessary and, if the design
permits,
a smaller pass can be laid
on the underside.
Beveling may be used to advantage on the thicker metals.
FJLLEET
WELDS
FRONT
Figure
6
Fillet welds are used to join two pieces of metal with sides or
edges at right angles to each other. The size of such a
weld is based on the leg length of the largest isosceles right
triangle
that can be inscribed within
the cross sectional
area,
as shown by the dotted-line
triangle
(fig.
1). The
size of a fillet weld may also be measured with a square
and ruler, subtracting
1/32-inch from all dimensions under
3/16-inch
and 1/16-inch
from all over 1!4-inch
(fig. 2).
For example, a 1/4-inch fillet weld should measure 5/16-
inch. This will offset any inaccuracy due to the slight radius
at the toe of the weld and allow for concavity of the bead.
When a fillet weld is stressed to its maximum capacity,
failure wiff usually occur through the throat section (fig. 3).
Therefore, the strength is determined
by the throat dimen-
sion multiplied by the length of the weld. Finished welds of
this type should always be at least four times their size in
Length; that is, a 1/4-inch
fillet weld should never be tess
than one inch long. The direction in which the load is applied
to a weld greatly
affects its strength, which can be clearly
demonstrated by breaking
the weld (fig. 4). A joint so
loaded should always be welded on both sides with fillets
equal to the plate thickness (fig. 5). if this cannot be done,
bevel the plate to assure complete penetration and position
the work at a 45_degree angle if possible.
For practice,
tack-weld
three
pieces
of scrap iron together
to form a cross (fig. 6). Use a 5/32-inch
rod with high current
and hold it as indicated
in the front and side views.
Move
the rod at a steady even pace
atong
the seam without any
side-to-side
movement
and
deposit
one inch of weld
for
each inch of rod melted.
The surface
contour
of a good weld
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