10 Thread tension (general hints)
1 0.1. Bobbin thread tension:
The lower tension should be as weak as possible, yet clearly noticeable. Make sure
that the bobbin thread can be pulled from the bobbin evenly, regardless whether the
bobbin case is in the machine or has been taken out. Tension trouble may occur as a
result
of
spring breakage, loss or slackness
of
the regulating screw, accumulations
of
dirt on the underside
of
the tension spring, damage
of
the bobbin or the bobbin case
and knotty thread.
10.2 Needle thread tension:
The needle thread tension should be adjusted so that the needle and bobbin threads
interlock in the center
of
the material, i.e. the concatenation
of
threads should lock
the same top and bottom. This ensures maximum elasticity
of
the seam. The degree
of
needle thread tension is dependent on the bobbin thread tension, the fabric
weight, the thread size, the setting
of
the thread check spring and feeding
mechanism. As a rule, the needle thread tension should be as weak as possible in
order to prevent puckering
of
the material and ensure maximum elasticity
of
the
seam.
10.3 Tension release:
When the sewing foot is raised, the needle thread should pass through the upper
tension lightly when pulled. When the sewing foot is lowered so that it rests on the
material or the needle plate, the upper tension should be fully operative.
10.4 Thread check spring:
1
0.4.1 The thread check spring should be tensioned so that it will return to its stop
smoothly and swiftly, yet with a certain power reserve.
If
the needle thread tension
is weak, the thread check spring should likewise be set for a weak tension. And,
conversely, when the needle thread tension is strong, the tension
of
the thread check
spring should be increased or a more powerful spring be inserted.
1
0.4.2 The thread check spring stop should be set so that the spring is through acting when
the needle point has reached the surface
of
a piece
of
material
of
normal thickness.
A slight modification
of
this setting may become necessary either way.
6
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