The necessity for proper tensions, To regulate the tensions, Upper – SINGER 404K User Manual
Page 18: Under
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The Necessity for Proper Tensions.
The tensions on the sewing machine must be adjusted to suit various
materials.
There
are
two
tensions,
the
upper
and
the
lower.
The
upper
tension controls the thread from the needle, while the lower tension controls
the thread from the shuttle or bobbin case.
The definition of the word tension as given in the dictionary is : “stress
by pulling.” It is the pulling of the threads together that completes a stitch
made
by
the
sewing machine.
After the
needle thread passes
around the
shuttle, the upper thread is pulled by the take-up lever to take up the slack
and complete the stitch by locking both threads together. If both threads
are under proper tension, the lock occurs in the centre of the material and a
perfect stitch is formed, as in Fig. 34.
To Regulate the Tensions.
For
ordinary
stitching,
the
tension
on
the
upper
and
under
threads
should
be
equal
and
just
sufficiently
strong
to
lock both threads in the centre of the
work as shown in Fig. 34.
If either tension is stronger than the
other,
imperfect
stitching
will
be
the
result. (See Figs. 35 and 36).
F
ig
. 34. C
orrect
S
titch
.
F
ig
. 35. N
eedle
T
hread
T
ension
.
TOO S
trong
.
~V "• V~
F
ig
. 36. N
eedle
T
hread
T
ension
TOO W
eak
.
A correct stitch can usually be obtained by
varying
the
tensions
on
the
upper
or
needle
thread
(see Fig.
37)
—To
increase
the
tension
on
the
upper
thread, turn the thumb nut to the right ;
to lessen the tension turn the nut to the left.
The
tension
on
the
under
thread
is
regulated
by the small screw holding the spring under which
the thread passes on the long shuttle or the round
bobbin case, but as all machines are correctly adjusted
before leaving the factory, it is seldom necessary to
alter this
under
tension. Should it become necessary,
however, to do so, tighten the tension spring screw to
increase the tension and loosen the screw slightly to
lessen the tension, using the small screwdriver provided
for the purpose.
The tension on the upper thread should be adjusted only when
the presser foot is down, and the amount of tension should be so that
the pull on both the upper and the under threads is as nearly as
possible equal.
T
hum b
N
ut
F
ig
. 37.
18