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Advantages and Characteristics of a Machine-Sewn Seam | Up
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Appropriate Spacing of Machine-sewn Seams |
STITCH. A stitch is one unit of thread
formation resulting from passing a thread through
material at uniformly spaced intervals. The
class of stitch is indicated by a specifica-
tion number; for example, 301, which specifies
a United States Standard Lockstitch (one lock
knot for each stitch). The class 31 and 111
sewing machines sew a United States Standard
Lockstitch 301.
SEAM. A seam is a joint consisting of a
sequence of stitches uniting two or more pieces
of material.
STITCHING. A stitching consists of a
sequence of stitches for finishing an edge, for
ornamental purposes, or both in preparing parts
for assembling.
The seam or stitch formation is indicated by
a symbol consisting of three parts:
o f
NOTE: The three parts follow the three-
digit number showing the type stitch the
machine makes.
1. The frost part denotes the class and consists
two uppercase letters; for example, SS.
2. The second part denotes the type or the
class of the seam or stitch formation and consists
of one or more lowercase letters; for example, a.
3. The third part denotes the number of rows
of stitches used and consists of one or more
Arabic numerals preceded by a dash; for example,
– 1 .
The complete seam specification for the
examples given becomes 301-SSa-1. (Remember
that the “’301” is the machine class of stitch.
There are places where one seam will be better
than others. Experience has shown certain seams
are best to serve a certain purpose. These seams
have been standardized so that people who do
sewing can turn out the same type of work.
Standardization makes it possible to make
drawings and blueprints that can specify a desired
seam. This way, no matter who does the job, the
finished article turns out to be as strong and
durable as the designer wanted it.
Uses of Varying Classes of
Machine-sewn Seams and Stitchings
The uses of varying classes of machine-sewn
seams and stitchings are covered in the following
material.
Figure 10-33.—Superimposed seam.
CLASSES OF SEAMS.— The three classes of
seams are SS (superimposed seams), LS (lapped
seams), and BS (bound seams).
Class SS, Superimposed Seams.— These seams
are formed by placing one ply of material above
another with the edges together and the seam
along one side. Superimposed seams are usually
made with two plies of material, although more
than two plies can be used for special projects.
The edges may be folded under, but they are never
overlapped when the stitching is made. Types of
superimposed seams are SSa-1 and SSc-2, as
shown in figure 10-33.
1. The SSa-1 seam is the simplest method of
joining two or more pieces of material. It is also
used as the first step in the formation of other
seams, such as the LSak-2 seam.
2. The SSc-2 seam is used for making many
different types of covers. It is also used in making
channels for sash cord when making handles on
carrying bags and cases.
Class LS, Lapped Seams.— You form the class
LS seam by overlapping the material a sufficient
distance and stitching with one or more rows of
sewing, as shown in the cross-sectional views in
figure 10-34. Types of lapped seams are LSc-2,
LSc-4, LSd-1, and LSak-2.
1. The LSc-2 seam is used for the sectional
seams and the LSc-4 for the channel seams of
parachute canopy. The interlocking of the folds
makes the LSc seams the strongest of the seam
formations.
10-26
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