12.
Regulating
the
Thread
Tensions
Regulating
the
needle
thread
tension
i"urning tension nut M (Figs. 7 and 13) clockwise
increases
the tension, turning it
counter-
:iockwise
decreases
it.
t
the
upper
tension
is
too
loose,
the
bobbin
thread
draws
the
needle
thread
down
so
lat
it forms small kinks on
the
underside
of
the
material,
as
shown
in Fig. 8.
: the
upper
tension
is too tight,
the
bobbin
thread
is
drawn
up to
the
upper
surface
of
">e
material
or
the
needle
thread
breaks
(Fig. 9).
-oth
tensions
are
correctly
balanced
if
both
threads
Interlock
in
the
center
of
the
material,
as
illustrated in Fig. 10. /
oper
tension
too
loose
or
lower
tension
too
tight.
jper
tension
too
tight
or
lower
tension
too
loose.
Fig. 10
ith
tensions
correctly
balanced.
-len
the
presser
foot
is
raised,
the
upper
tension
is
automatically
released
so
tha^
-3
work
can
be
easily
removed
from
the
machine.
To
remove
the
work, pull it
toward
?
back
(in
forward
feeding
direction),
never
toward
you.
as
this
might
cause
bending
the
needle,
skipping
of
stitches
or
thread
breaking.
egulating
tlie
bobbin
thread
tension
<e
the
bobbin
case
out
of
the
machine
and,
using
the
hook
screwdriver,
turn
screw
Z
g. 6)
clockwise
to
increase
the
tension,
or
counter-clockwise
to
decrease
It.
e tension is
correct
if a
noticeable
resistance
of
spring
Y (Fig. 6)
has
to be
overcome
en
pulling
the
thread
out
of
the
bobbin
case.
Duckering
occurs
on
delicate
fabrics
although
the
tension
has
been
set
correctly,
56
both
tensions
slightly.
13.
Regulating
the
Stitch
Length
On all cylinder-bed machines with right-hand balance wheel, the stitch lenght is regu
lated by turning
screw
S (Fig. 11). Turn this
screw
clockwise for
shorter
stitches, or
counter-clockwise
for
longer
stitches.
The
numbers
on
the
scale
indicate
the
stitch
length
in
millimeters.
All machines, with the exception of the Pfaff 343
U-12
and 353,
are
regularly fitted with a
spring-return feed regulator. A tension spring incorporated in this mechanism
perma
nently holds the feed regulator lever down in forward feeding position. To backtack
the
end
of a
seam,
simply
push
this iever up as far as it will go. When the lever is
released,
forward
sewing
is
resumed
instantly.
C'f
desired,
all
machines
featuring
this
type
of
feed
regulator
can
be
equipped
with
a
;edal which makes it
possible
to reverse the direction of feed by foot action.
R
7000
:0m
Fig.
11