Figure 3-9.Bevel angle, groove angle, groove radius, and root opening of joints for welding.
A butt joint is used to join two members aligned in
the same plane (fig. 3-6, view A). This joint is frequently
used in plate, sheet metal, and pipe work. A joint of this
type may be either square or grooved. Some of the
variations of this joint are discussed later in this chapter.
Corner and tee joints are used to join two members
located at right angles to each other (fig. 3-6, views B
and C). In cross section, the corner joint forms an
L-shape, and the tee joint has the shape of the letter T.
Various joint designs of both types have uses in many
types of metal structures.
A lap joint, as the name implies, is made by lapping
one piece of metal over another (fig. 3-6, view D). This
is one of the strongest types of joints available; however,
for maximum joint efficiency, you should overlap the
metals a minimum of three times the thickness of the
thinnest member you are joining. Lap joints are com-
monly used with torch brazing and spot welding appli-
An edge joint is used to join the edges of two or
more members lying in the same plane. Inmost cases,
one of the members is flanged, as shown in figure 3-6,
view E. While this type of joint has some applications
in platework, it is more fixquently used in sheet metal
work An edge joint should only be used for joining
metals 1/4 inch or less in thickness that are not subjected
to heavy loads.
The above paragraphs discussed only the five basic
types of joints; however, there are many possible vari-
ations. Later in this chapter, we discuss some of these
PARTS OF JOINTS
While there are many variations of joints, the parts
of the joint are described by standard terms. The root of
a joint is that portion of the joint where the metals are
closest to each other. As shown in figure 3-7, the root
may be a point, a line, or an area, when viewed in cross
section. A groove (fig. 3-8) is an opening or space
provided between the edges of the metal parts to be
welded. The groove face is that surface of a metal part
included in the groove, as shown in figure 3-8, view A.
A given joint may have a root face or a root edge. The
root face, also shown in view A, is the portion of the
prepared edge of a part to be joined by a groove weld
that has not been grooved. As you can see, the root face
has relatively small dimensions. The root edge is basi-
cally a root face of zero width, as shown in view B. As
you can see in views C and D of the illustration, the
groove face and the root face are the same metal surfaces
in some joints.
The specified requirements for a particular joint are
expressed in such terms as bevel angle, groove angle,
groove radius, and root opening. A brief description of
each term is shown in figure 3-9.
The bevel angle is the angle formed between the
prepared edge of a member and a plane perpendicular
to the surface of the member.
The groove angle is the total angle of the groove
between the parts to be joined. For example, if the edge
of each of two plates were beveled to an angle of 30
degrees, the groove angle would be 60 degrees. This is