SINGER 404K - Manual (Page 18)

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.
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