Linde BOC RAPTOR Operating Manual page 45

Convex Fillet Weld
A fillet weld in which the contour of the weld metal
lies outside a straight line joining the toes of the
weld. A convex fillet weld of specified leg length
has a throat thickness in excess of the effective
measurement.
Concave Fillet Weld
A fillet in which the contour of the weld is below a
straight line joining the toes of the weld. It should
be noted that a concave fillet weld of a specified
leg length has a throat thickness less than the
effective throat thickness for that size fillet. This
means that when a concave fillet weld is used, the
throat thickness must not be less than the effective
measurement. This entails an increase in leg length
beyond the specified measurement.
The size of a fillet weld is affected by the electrode
size, welding speed or run length, welding current
and electrode angle. Welding speed and run length
have an important effect on the size and shape of
the fillet, and on the tendency to undercut.
Insufficient speed causes the molten metal to
pile up behind the arc and eventually to collapse.
Conversely, excessive speed will produce a narrow
irregular run having poor penetration, and where
larger electrodes and high currents are used,
undercut is
likely to occur.
Fillet Weld Data
Nominal Minimum
Fillet Throat
Size Thickness
(mm) (mm)
5.0 3.5
6.3 4.5
8.0 5.5
10.0 7.0
Selection of welding current is important. If it
is too high the weld surface will be flattened,
and undercut accompanied by excessive spatter
is likely to occur. Alternatively, a current which
Plate
Thickness Electrode
(mm) Size (mm)
5.0–6.3 3.2
6.3–12 4.0
8.0–12 & over 4.0
10 & over 4.0
is too low will produce a rounded narrow bead
with poor penetration at the root. The first run
in the corner of a joint requires a suitably high
current to achieve maximum penetration at the
root. A short arc length is recommended for fillet
welding. The maximum size fillet which should be
attempted with one pass of a large electrode is
8.0 mm. Efforts to obtain larger leg lengths usually
result in collapse of the metal at the vertical plate
and serious undercutting. For large leg lengths
multiple run fillets are necessary. These are built
up as shown below. The angle of the electrode for
various runs in a downhand fillet weld is shown
below.
Recommended Electrode Angles for Fillet
Welds
1st Run
2nd Run
3rd Run
Multi-run Fillet
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