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Figure 4-9.—Bobbin case area | Up
Aircrew Survival Equipmentman 1 & C - Aviation theories and other practices | Next
ADJUSTMENTS |
If the presser-lifting eccentric is not, prop-
throat plate height and travel aft together; if they
erly timed, it can cause the machine to feed
do not, continue to step b.
backward or prevent the machine from making
b. Turn the balance wheel and loosen the
the full stitch length.
two set screws (figure 4-10B [C] and figure 4-10
[A]) on the presser-lifting eccentric.
The maximum stitch length of 3 1/2 SPI
c. Hold the eccentric to prevent it from
should beset while you are making the following
turning; then turn the balance wheel a small
adjustments:
amount toward the operator and tighten one of
the setscrews.
a. Turn the balance wheel toward the
d. Repeat steps b and c until the front foot
operator and observe the action of the feed dogs
meets the feed dog at the throat plate height as
and the front presser. They should meet at the
the balance wheel is turned toward the operator.
e. Ensure both setscrews are tight.
ADJUSTMENTS
For the sewing machine to operate smoothly
and to make a proper locking stitch, you must
make some minor adjustments. Even though the
machine is in time, a single part that is out of
adjustment can cause the sewing machine to skip
stitches, break thread, fail to feed the material,
or make loose stitches.
1. Adjusting the bobbin-case opener
As the hook rotates clockwise, friction on
Figure 4-10A.—Presser-lifting eccentric connection link.
the bobbin-case opener causes the position lug
Figure 4-10B.—Presser-lifting eccentric.
4-8
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