IMPROVEMENTS IN SEWING-MACHINES WITH ROTARY HOOK
Year: 1883

page_text: PROVISIONAL SPECIFICATION left by Carl Pieper at the Office of the
Commissioners of Patents on the 13th April 1883. A communication to him
from Rudolf Gritzner of Durlach, Baden
CARL PIEPER, Civil Engineer and Patent Agent resident at 109-110 Gneisenau-
strasse, Berlin, S.W., Prussia, "IMPROVEMENTS IN SEWING-MACHINES WITH ROTARY
HOOK (a communication to me from Rudolph Gritzner of Durlach, Baden,)
This invention relates to improvements in sewing-machines with rotary hook
and has for its object constructing these machines in such a manner that the spool
for the under thread can be made of considerably larger dimensions than hitherto
and that the casing of the spool rests only upon a point, whereby the passage of
the loop of the upper thread is facilitated and rupture of the thread is obviated.
In machines constructed according to this invention the rotary hook is fixed
upon the main shaft and the needle-bar may have imparted to it the requisite up
and down motion by a simple circular eccentric. The casing with the spool is
loosely inserted in a suitable holder attached to the bed-plate of the machine.
It is provided at the top with a projection having a hole in it through which the
thread of the spool is passed, and at the bottom it has a projecting lip. Both the
projection and the lip enter into recesses in the holder, thereby maintaining the
casing in an upright position. The whole weight of the casing and the spool is
carried on the tip. The line of gravity passing through the tip does not coincide
with the vertical centre line of the spool and casing but lies before the same. The
loop, therefore, falling off the rotary hook before the central position is reached
will with certainty be drawn around the casing. To permit the loop to fall off
previous to reaching the vertical centre line, the end of the rotary hook is bent
slightly towards the centre of the disc on which it is formed.
In order to permit the loop of the upper thread to pass the tip of the casing, the
latter must be lifted. This is effected by determining the tension of the under
thread in such a manner that it overcomes the weight of the casing and the spool,
that is to say: during the time the thread necessary for completing the stitch is
drawn up, the casing will be lifted and held in a suspended position by the under
thread so that the loop may easily pass the said tip. Then the loop is drawn up
rapidly; but it is not allowed to pass the projection hereinbefore mentioned, which
bears against a surface adapted to limit the lift of the casing. It is, therefore,

page_text: necessary to bring the said casing down again into its normal position. To this
end the main shaft or preferably the feed bar of the machine is provided with
suitable means as, for instance, a lever which either operates upon the projection or
directly upon the thread, thereby pulling out the latter and causing the casing to
drop so that the loop is then free to pass the projection.
By arrangement of a loop guiding device it is prevented that both halves of the
loop pass on the same side of the casing and thus any failure of stitches is
obviated. Moreover, a part of the casing is cut away on one side in order to
permit the loop to be pulled up rapidly.
The projection which maintains the casing in, an upright position has also for its
object to hold out of the path of the rotary hook the under thread passing through
it and thus to prevent rupture or other accidents.
A flat spring or the like pivoted to the casing may be provided for in order to
hold the spool in its position.
The rotary hook is bent and shaped in such a manner that, when the loop has
been seized and is carried around, the part thereof next to the needle will move
out of the way while the other distant part will be retained at the bottom of a
guiding piece by which the loop is prevented from becoming entangled in the
rotating book. When the loop is fully opened, which in consequence of the
peculiar form of the rotary hook is effected with rapidity, and the guide piece in
its rotation arrives at a certain lower position, the loop falls off and is drawn
around the casing of the spool.