Thread Clamp (Thread Pulling Device); Possible Faults, Cause And Remedy For The Short Thread Trimmer - DURKOPP ADLER 767 Service Instructions Manual

15.4 Thread clamp (thread pulling device)

2

15.5 Possible faults, cause and remedy for the short thread trimmer

70
With the thread clamp 2 and the corresponding electronics the needle
thread is drawn downwards and a loop is formed at the sewing start. In
order that the thread does not break (it may be clamped between foot
and fabric) the sewing foot is released for a short time.
The degree of release is coupled with the position of the setting wheel 1
(stroke adjustment).
High stroke
Low stroke
The correct function of the thread clamp 2 depends on the setting of the
potentiometer (normally this is set correctly).
Main setting rules
1. The thread pulling knife slightly rests on top of the centerpiece
support.
1
Correction: setting 1.
2. The cutting pressure should be as low as possible.
Correction: Setting 2.
3. The overlap should amount to 0.5 mm.
Correction: Setting 5.
4. The thread pulling knife must have no clearance to the rear when in
cutting position.
Correction: Setting 6.
Fault
Thread is not cut
Needle thread too
short
Thread clamp does not
clamp
Needle thread is not
drawn downwards or
thread breaks at the
seam beginning
Thread pulling knife
does not catch the
thread
Thread pulling knife is
not brought to the
catching position
Notes!
Attention!
It has to be checked whether the hook casing is pressed against the
guide of the base plate by the eccentric of the upper fastening screw.
(Service instructions item 4.3; description of correction).
Attention! The needle thread is not caught and forms a loop
around the thread pulling knife
Check the adjustment of the cutting curve and adjust according to the
top dead centre of the thread lever.
= high degree of release (thick material)
= low degree of release (thin material)
Cause and remedy
- Check parameter;
- Blunt or faulty knife;
- Cutting pressure drawknife - counter-knife;
- Position drawknife;
- Cutting cam
- Pretension too strong;
- Cutting cam too early
- Foreign matter in the thread guidance;
- Check parameter;
- Check connection at the printed circuit board
- Check parameter;
- Check stroke adjustment;
- Foot lift too slow;
- Check throttle;
- Thread clamp does not clamp;
- Check connection at the printed circuit board
- Check the position of the cutting cam;
- Thread pulling knife does not run smoothly;
- Thread pulling knife not in initial position;
- Magnet not adjusted correctly;
- Pressure of the counter-knife too strong