Thread Trimmer; Function Sequence; Activation Timing Of The Bobbin Brake; Braking Effect Of The Bobbin Brake - Duerkopp Adler N291 Service Manual

3. Thread trimmer

Turn off main switch!
Otherwise there is danger of injury!

3.1 Function sequence

When the pedal is heeled completely to actuate
the trimming action:
– When the 1st position has been reached
(handwheel position F) a solenoid valve is
activated that momentarily pressurizes the
cylinder 6 with air. Its piston rod then presses
the roller bolt of the element 8 against the face
of the cam 9.
– The thread tension is released momentarily.
– The sewing machine runs at the trimming
speed 150 rpm.
– The piston rod of the cylinder 6 presses the
roller bolt of the element 8 into the recess of
the cam. At the same time, the thread catcher
is swung away from the counter knife.
When the thread catcher is swung towards the
counter knife:
The function sequence is as follows:
– The thread catcher catches both threads.
– The bobbin brake is activated momentarily.
– The threads are trimmed. At the same time the
bobbin thread is clamped.
When the take-up lever is nearing the top of its
travel and thus the 2nd position has been
reached:
When "positioning the needle at the top of its
stroke" is activated:
– Turn back the arm shaft until the needle has
reached the top of its stroke.
When "positioning the needle at the top of its
stroke" is not activated:
– The motor stops.
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3.2 Activation timing of the bobbin
brake 1
Explanation:
When the thread catcher draws bobbin thread,
the bobbin should be braked to prevent it from
"over-running".
Rule:
The distance between the latch 11 and the
shackle 10 should be 2.5 mm, when the screw
3 of the lever 4 rests against the housing.
Correction:
Turn the screw 3 at the lever accordingly.

3.3 Braking effect of the bobbin brake

Rule:
When the bobbin brake 1 is activated, a slight
braking effect should be perceptible when
thread is drawn from the bobbin.
Check:
– Turn the handwheel into position B.
– Initially, swing the thread catcher away from the
counter knife, and then swing it back until the
latch 11 is located below the shackle 10.
– Draw thread from the bobbin by hand.
Correction:
Change the position of the shackle 10
accordingly.