the material. This shrinkage is shown in Figure 6-26. In
areas where these dimensions must be maintained, a
shrinkage test must be done to establish the amount of
shrinkage. Figure 6-27 shows how such a test is made.
Heavier materials will shrink more than thinner
materials. Double-groove welds will shrink less than
single-groove welds. This is because less welding is
involved and less filler material is used.
T-Joints and Welds
Various T-joint designs are used to join parts at an
angle to each other. Depending on the intended use of the
weldment, the joint may be made with a single fillet,
double fillet, or a groove and fillet weld combination.
Figure 6-28 shows these designs.
Fillet welds are made to specific sizes that are deter-
mined by the allowable design load. They are measured
as shown in Figure 6-29. Where design loads are not
known, a “rule of thumb” may be used for determining
the fillet size. In these cases, the fillet weld leg lengths
must equal the thickness of the thinner material.
The main problem in making fillet welds is lack of
penetration at the joint intersection. To prevent this
condition, always make stringer beads at the intersection.
Weave beads do not provide the desired penetration on
fillet welds.
Lap Joints and Welds
Lap joints may be either single fillet, double fillet,
plug slot, or spot-welded. They require very little joint
preparation. They are generally used in static load appli-
cations or in the repair of unibody automobiles. Where
corrosive liquids are involved, both edges of the joint
must be welded. See Figure 6-30. One of the major prob-
lems with lap joint design is shown in Figure 6-31. Where
the component parts are not in close contact, a bridging
fillet weld must then be made. This leads to incomplete
fusion at the root of the weld and oversize fillet weld
dimensions. When using this type of design in sheet or
plate material, clamps or tooling must be used to main-
tain adequate contact of the material at the weld joint.
An interference fit eliminates this problem in
assembly of cylindrical parts, Figure 6-32. The inside
diameter of the outer part is made several thousandths of
an inch smaller than the outside diameter of the inner
Chapter 6 Weld Joints and Weld Types 65
Figure 6-23. Welds made on mismatched joints often will fail
below the rated load when placed in stress conditions.
Figure 6-24. Mating the joint at the bottom equalizes the load
during stress when the weld is made from the top and pene-
trates completely through the joint.
Figure 6-25. Joints of unequal thickness absorb different
amounts of heat and expand at different ratios. Equalize the
heat flow by tapering the heavier material to the thickness of
the thinner material.
Figure 6-26 Butt welds shrink during welding in both transverse
and circumferential directions.
Figure 6-27. Weld joint shrinkage can be determined in four
steps. 1. Tack weld the test joint together. 2. Scribe parallel
lines, as shown, on approximately 2” centers. Record this
dimension. 3. Weld joint with test weld procedure. 4. Measure
linear distance and compare with original dimension.