IMPROVEMENTS IN SEWING MACHINES
Year: 1872

page_text: PROVISIONAL SPECIFICATION left by Alexander Cameron Dingwall
at the Office of the Commissioners of Patents, with his Petition,
on the 26th November 1872.
I, ALEXANDER CAMERON DINGWALL, of the City of Glasgow, in the
County of Lanark, North Britain, Machinist, do hereby declare the
nature of the said Invention for "IMPROVEMENTS IN SEWING MACHINES,"
to be as follows, that is to say :—
This said Invention has reference to special new or improved parts
of sewing machines (susceptible" of various modifications) for making
these produce the sewing so much required at the edges of cloth,
equivalent to the sewing known by the various terms of whipping,
overcasting, and over and over stitching, but by these improvements
with two threads and needles, one on the upper and one on the under
side of the fabric-and-sewing table of the machine.
And the nature of the Invention substantially consists all as follows:-
First. In the use of a nearly vertical revolving scroll or segmental
hook or loop needle for the under thread (of the shape of that used in
the "knotted," or "Grover," or "Baker" stitch, and machines, but not
revolving on a vertical axis as these do), which is led from its reel and
conducting and tension arms and eyes round a groove in the back, and

page_text: finally through an eye near the point of the hook (but it may also pass
through other eyes at the heel, or along the groove before reaching the
eye at the point to give more regular tension to and retain the thread in
the groove of the hook), which revolves on a nearly horizontal, or it
might be slightly angled shaft, so placed, nearly close to the ordinary
upper vertically reciprocating needle, feeding and carrying bed plate,
and parallel vertical plane with the edge of the cloth to be sewed, that
as the point of the hook needle revolves in the upward direction it enters
and carries the loop of the under thread with it through the loose loop
of the upper thread, as it is formed below the cloth and table in front
of and just as the needle begins to rise; and then up over the edge and
top of the cloth behind the needle, at nearly the same time as a new
nearly straight and pointed horizontal reciprocating loop holder passes
below the hook and through the said loose loop of the upper thread,
so as to hold it open and yet tight while the upper needle rises through
the cloth, which is then fed forward to the desired extent for the next
descent and stitch of the needle made through the loop of the under
thread, which was bent up over the edge of the cloth and behind the
needle for that purpose. When the upper reciprocating sewing needle
has thus caught the loop of the under thread on the top side of the
cloth, and is descending to tighten this stitch and the previous loose
loop on the under side, which after the reciprocating revolving hook has
been turned down and brought the under thread quite back out through
it, is set free by the backward action of the loop holder, so that it can
be so tightened and catch the last and first threads of each loop of the
under thread, as they are formed on the under and upper side of the
cloth, and hold the two threads of each under loop previously formed,
back over and up over or round the edge of the fabric or cloth being
sewed. The successive and sequential repetition of the said motions
or action of the parts and threads producing the said regular over and
over stitching along the cloth, fed in and guided as usual at the proper
distance from the edge below the ordinary upper needle, which as well
as all the other parts of sewing machines not herein specially referred
to, may be the same as in other sewing machines. The spindle of the
revolving hook needle may be reciprocated by a toothed pinion and
segmental or straight rack, or by a spiral screw spring formed on the
spindle and reciprocating nut or arm working therein, the motion in
either case being taken from a cam or crank action of the main shäft
through a lever and connecting rod, which by another connecting rod

page_text: and slide may be made to actuate the loop holder below which it
reciprocates at nearly the same time as the hook.
In the case in which the spindle of the hook is set horizontally or
at right angles to the upper stitching needle, the segmental part and
point of the hook is set at an angle or screw-like, so that the spindle
may be drawn on the end while bringing the loop of the under thread to
the upper side of the cloth, and to the back or rear side of the needle
without the heel or lower part of the hook touching the front side of the
upper needle, while it is down through the cloth and hook part of the
needle. This end motion may be given to the spindle and hook by its
own revolving motion, and a small cam fixed on it and a fixed stud or
friction roller working in it, or it might be by a curved or cam groove, or
feather on reciprocating rack working on a corresponding annular collar
or groove on the spindle or pinion near the toothed actuating rack. It
will be understood that when the spindle is set at an angle, this end
motion will not be required as the vertical needle will in this case be
able to pass down through the angled hook, which will thus be able to
pass the lower thread through the loop below on the front side of the
vertical needle, and carry it up to the back of the needle on the top of
the cloth; a small hole being formed through the bed plate near the
stitching needle and edge of the cloth, for the point of the hook needle
and lower thread to thus pass up through in either case.
To assist in slacking off sufficient of the under thread at the proper
time the hook needle requires it in turning the loop up to the top, it is
preferred to be passed from the real or bobbin, first forward through an
eye in the moving arm of the feeder, and then back through an eye in
a spring tension lever, and again forward through a third eye in a line
with the hook to which the thread is finally led directly, all so that the
backward motion of the first eye in the feeder slackens back on two
lengths of thread instead of one as usual, at the proper time to suit the
motion of the hook and taking it up again and off the bobbin on the
forward motion at the proper time also; but it will be understood that
other equivalent means of tightening and giving off the under thread
may be used for this as in other under revolving hook needle machines.