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3.4 Thread tensioners and limiter
3.4.1 Description
The main tensioners (1) serves for creating the tension of the thread
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 mechanism controlled by the shaft of the presser bar lifting (3)
holding the lever (4) with a pulley. The motion is then transmitted by
the lever (5) and the tie rod (6) on the thread tensioner plate (7) whose
displacement (motion) relieves the thread tensioner springs (8). In
machines provided with a thread trimming device, the main tensioners
(1) are relieved as well upon the switching on of the electromagnet
(10) whose electromagnetic field will attract the thread tensioner plate
(7).
The mechanism of the adapting spring (12) maintains the upper
thread in its tensioned state when passing through the hook
entering the needle into the sewn
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.
The auxiliary guide (14) maintains the
upper thread in front of the needle in a tensioned condition and helps
against pulling the thread from the needle after thread trimming.
3.4.2 Setting the tension of the main and auxiliary
tensioners
The tension of the main thread tensioners is regulated by means of the
nuts (1).
The force of tensioning the thread is measured by the
dynamometer (2) as it is shown on the illustration.
force differs according to the category, and its orientation value 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 mechanisms
of the main tensioners
In the rest position of the tensioners, when pushing the plate of the
tensioners on the spot “A” 3.4.1, this plate must have the socalled dead
travel of about 0,5 mm. At this lifting, the tension discs of the tensioners
must not be relieved. This can be attained by a suitable shaping of the
relieving disc of the tensioners-this has been set up in the manufacturing
factory. In the maximum opened position of the tensioners, the plate of
the tensioners, when pushing it at the spot “A” 3.4.1, must still have
the minimum lifting. This can be attained when axially shifting the lever
(3) with the roller (5) on the shaft (4).
The disengagement of the main tensioners must be coordinated with
the top roller lift. To achieve this, turn the lever (3) with the roller (5) on
the shaft (4). The movement of the roller (5) on the slanting surface (6)
of the lever (7) disengages the tensioners. In this way, also a lag of the
upper thread tension disengagement after the top roller lift can be
obtained.
Caution ! Danger of injury!
Switch off the main switch! Before starting the setting
operation, wait until the motor stops!
-
Remove the rear cover with the top roller lift magnet.
- Loosen the screws (1) and (2) of the lever (3).
- In the rest state of the machine (with not relieved tensioner discs) set
the lever (3) in turning it slightly on the shaft (4) to a position in
which the roller (5) of the lever (3) is in contact with the slanting
surface (6) of the lever (7) and is about 0.1 mm distant from the flat
surface (8) of the lever.
- At the maximum lift of the top roller, the roller (5) moves on the flat
surface (9) of the lever (7); in this condition, there must be a minimal
play at the tensioner plate lift (when pushing qat the spot “A” (3.4.1),
the plate must still have a minimum lifting - between the roller (5)
and the surface (9) there is a minimum clearance). Retighten the
screws (1) and (2), check the play, and correct it in case of need.
8
The main tensioner is relieved by
and when
material. The thread limiter (13)
The size of this
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