17
the lower thread
can
be noticed at
the
underside of the work.
This
is caused
by the transport of the
material
around
the
sewn
corner,
while
the one
raised
needle
bar
is
at
rest.
The
rotary
hooks
of
models
LTW-27BK
and
LSW-27BLK
are
equipped
with
devices
which
prevent the
looping
of the
lower
thread by withdrawing
by means of springs any
excess
of thread.
Fig.
27A
shows
the
method
of
threading
of the
bobbin
case
of
model
LSW-27BLK.
Fig.
27B
shows
the
position
of thread take-up
spring
(1)
ready
to
pick
up any
excess
of
thread
for
the
prevention
of
loops.
Also
note
that
the dotted outline of the thread take-up spring
(lA)
which shows same in a
rest
position
prior to
pulling
back
excess
thread.
As can be seen
froni
this
figure,
spring
(1)
travels
a
distance
to
where
its eye
coincides
with
the
thread
guide hole in retainer (2).
When
in this position,
further
demand
for bobbin
thread
is
then
pulled
out
from
under
bobbin case tension spring (3).
The
function
and
effectiveness
of spring (1) is such
that
slack
thread
loop containing as
much
as 20 mm
(25/32'')
of
thread
can
be absorbed.
THREAD
CONTROLLER
SPRINGS
There
are
two separate
and
individual
thread
controller springs—one for
each of the two upper (needle) threads—installed in the machines.
Rg.
28
When sewing angular seams with either one of the two needle bars
stopped, upper thread is not drawn out at an equal rate for both needle bars.
Consequently,
two
thread
controller
springs
are
required
to
cope
with
this
condition.
These springs can be adjusted individually.
A)
Adjusting
the rear thread controller
spring
Loosen
set
screw
(2),
turn
thread
controller
spring
stop
(3)
to the
right
for
more
action
;
for
less
action
turn
stop
(3)
to the
left
and
tighten
set
screw
(2).
From the library of: Superior Sewing Machine & Supply LLC
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