10
3.5 Thread tensioners and limiter
3.5.1 Description
The main tensioners (1) serve for producing the thread tension
when tightening stitches. The auxiliary tensioners (2) prevent
the pulling out of the thread after having ended the thread
trimming when removing the sewn material, when the threads
are being passed through this material and when the main
tensioners are relieved. The main tensioners are relieved by
means of a mechanism which is controlled by the presser foot
lifting shaft (3), on which the lever (4) with a pulley is attached.
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 electro-
magnet (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
and when entering the needle into
the sewn material
. 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.
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.
3.5.2 Setting the tension of the main and auxiliary
tensioners
The tension of the main tensioners of both threads is regulated
by the nuts (1) and by the nut (2) of the common tensioner.
The force of tensioning the thread is measured by the
dynamometer (3) as it is shown on the illustration.
The size of
this force differs according to the category, and its orientation
value is indicated in the par. 10.2.
The tension of the auxiliary tensioners is regulated by the
nuts (4). It must be the least possible, but sufficient for getting
out the threads from the sewn material under the pressing
element after having ended the trimming operation, without
leaving the tensioners.
3.5.3 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 3.5.1, 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 3.5.1, 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).
3
4
5
6
10
A
7
2
1
13
12
14
8
3
4
1
4
1
7
3 2 5
8
0,1
6
9
2
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