lever
has almost reached
its
top
position.
The
thread nipper
should
release
the thread again after the needle has entered the goods.
To adjust, move the thread nipper tripping segment to or fro on the rim of
the feed cam, as appropriate. Thread nipper tripping
segments
are avail
able in different
lengths
to
suit
machines
having
different gear ratios (see
Spore Parts Catalogue). The order numbers
are
as follows:
No.
22504
No.
22504
j
No.
22454
]
No.
22858
If severol thread nipper tripping segments should be arranged on the rim
of the feed cam, repeat this adjustment for each segment.
The above setting applies to normal operating conditions. If materials and
threads of different weights ore used on this machine, minor deviations from
this basic setting may become necessary.
Make sure the thread nipper lever does not jam and the thread nipper
spring releases the thread completely when the former is at its inoperative
position. The thread nipper spring should extend parallel to the flat spot
on the needle bar so that the thread
tension
will
not change
while
sewing
(Fig. 43).
The small prong of the thread nipper spring must project into the recess in
the needle bar so that the thread cannot slip out of the thread nipper
during
sewing.
(2)
Needle
Thread Tensions
The Pfaff
3334
has two needle thread tensions
(Fig.53).
The upper tension holds the needle thread taut while the threads are being
cut. Set this tension device so that it exerts just a light tension on the thread,
and the thread can be cut easily. If the tension is too light, the knives will
pull an excessive
amount
of
thread
through the tension
and
the
thread
will not be caught properly. If the tension is too tight, the thread will be cut too
early, leaving too short a
thread
end.
The
lower, or main, tension holds the thread tout while the
stitch
is being set
in the material. Begin by setting the
upper
tension. Then set the main ten
sion so that the stitchwill be pulled into the fabric properly.
55
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