Photo
15
Photo
16
amount given above since this would necessitate increasing the needle
thread
tension
and
m.ight
result
in
thread breaking.
10.
Regulating
the
Needle
Thread
Tension
The
PFAFF
3114
has
two
needle
thread
tensions which
are
both
released
when the machine is inoperative.
When
starting the
machine,
the top
tension
Sp 1
(Photo
17)
is engaged
first.
It is set for a
normal
amount
of
tension
and causes the
knotting
stitches,-
to
be
locked
inside
of
the
material.
After some stitches, the lateral tension Sp 2 is engaged and increases the
needle thread tension so that the bobbin thread
will
be
pulled
up and both
threads
will
interlace on the top surface of the
fabric
and
form
a straight
purl-line
along
either
parallel
of
the buttonhole.
To
prevent breaking of the needle threaa, the tension Sp 2
should
not be
set tighter than is absolutely necessary for obtaining a raised seam coti-
struction without risking thread breaking.
16
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