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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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