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3.4 Thread tensioners and limiter
3.4.1 Description
The main tensioner (1) serves for creating the tension of the threads
when tightening the stitch. The auxiliary tensioner (2) reduces the
risk of pulling out of the thread after the thread trimming when
removing the sewn material, when the thread is passed through
this material and when the main tensioner is relieved. The main
tensioner is relieved by the mechanism controlled by the shaft of
the presser foot lifting (3), on which the lever (4), is mounted
which shifts the prop (5), which pushes the metal sheet lever (6).
This lever shifts the pin (7) and this pin pushes onto the washer
(8) and relieves the spring (9).
With the machines provided with a thread trimming device,
the main tensioner (1) is relieved as well when switching on the
electromagnet (10), when its armature (11) pushes against the
lever (6). The mechanism of the adapting spring (12) maintains
the thread in its tensioned state when passing through the
hook. The thread limiter (13) limits the length of the thread
fed by the take-up lever when moving from the upper to the
bottom dead centre to get a controlled passing of the thread
through the hook.
3.4.2 Setting the tension of the main and auxiliary
tensioners
The tension of the main thread tensioner is regulated by means
of the nut (1). The force of tensioning the thread is measured
by the dynamometer (2) as it is shown on the illustration. The
size of this force differs according to the category of sewing
and is indicated in the par. 11.2.
The tension of the auxiliary tensioner is regulated using the
nut (3). It should be the least possible, but sufficient for
unthreading the thread from the sewn material when removing
the sewn material from the pressing element without leaving
the tensioner.
3.4.3 Setting the tensioning mechanism of the main
tensioner
The nut (1) must be screwed off in such a way that the metal sheet
lever (2) bears on the plate (3) and, at the same time, the lever (4)
is not limited by the prop (5) in its rotation. The lever (4) must be
fixed against the shaft (6) in such a way that, when the presser
foot is in its lowest position, the nut (1) bears on the metal sheet
lever (2) with its minimum clearance.
Caution ! Danger of injury!
Switch off the main switch! Before starting the setting
operation, wait until the motor stops!
- Unscrew thoroughly the nut (7) and loosen the screw (8).
- Put in one line the axis of the shaft (6), the axis (9) and the axis
of the spherical surface of the nut (1).
- Unscrew the nut (1), until the metal sheet lever (2) strikes
against the plate (3). However, the lever (4) must rotate freely
in the sense of the arrows in both senses.
- Screw in the nut (7) almost to the stop.
- Remove the sewn material and lower the presser foot.
- Turn the lever (4) in the sense of the arrow up to the stop.
- Return the lever (4) a bit back and tighten the screw (8).
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