alternating-pressure-foot sewing machine, we will
use the 31-15 sewing machine as a model for these
three sewing machines. The 31-15 sewing machine
is intended for sewing clothing such as flight suits
and is excellent for sewing lightweight canvas up
to 8 ounces.
The 31-15 sewing machine has a stitch range
of 7 to 32 SPI, a clearance of five-sixteenths of
an inch under the presser foot, and uses a drop-
feeding action. The major components of the
Singer Sewing Machine 31-15 are shown in figure
4-13.
PREVENTIVE MAINTENANCE
Preventive maintenance for the Singer Sewing
Machine 31-15 is the same as that for the 111 W
maintenance is the same, the oiling points differ
because of the design of the machine. Figures 4-13
through 4-15 show the different oiling points for
the 31-15 sewing machine. When you oil this
machine, remember 1 drop of a 10W mineral oil
at each oiling point is sufficient. Too much oil
may soil the project being sewn.
TIMING AND ADJUSTMENTS
The 31-15 sewing machine is the simplest
sewing machine in the parachute loft. As with all
oscillating-shuttle machines, the main timing point
is the needlebar. Once the needlebar is properly
set, only minor adjustments are necessary to have
a smooth-running sewing machine. Remember
you should always refer to the troubleshooting
155 sewing machine. Although the preventive
chart before making any adjustment.
Figure 4-13.—Front view of model 31-15 sewing machine.
4-17
