US3783813A

US3783813A - Underbed thread trimming device for sewing machines

Info

Publication number: US3783813A
Application number: US00280701A
Authority: US
Inventors: G Kroll
Original assignee: Singer Co
Current assignee: SSMC Inc
Priority date: 1972-08-14
Filing date: 1972-08-14
Publication date: 1974-01-08
Anticipated expiration: 1991-01-08

Abstract

A device for severing both the bobbin and needle threads of a lockstitch sewing machine in which a movable cutting blade is carried beneath the sewing machine throat plate for cooperation with a ledger blade formed on the bottom surface of a throat plate insert having a needle aperture formed therein.

Description

United- States Patent [191 Kroll '[111 3,783,813 1 Jan. 8, 11974 UNDERBED THREAD TRIMMING DEVICE FOR SEWING MACHINES Inventor: Gunter Kroll, Munich, Germany The Singer Company, New York, NY.

Filed: Aug. 14, 1972 Appl. N0.: 280,701

Assignee:

US. Cl. 112/252 Int. Cl D05b 65/00 Field of Search 112/65, 70, 122,

References Cited 1 1 UNITED STATES PATENTS 2,376,417 5/1945 Chudner 112/252 2,826,160 3/1958 Adams 112/252 2,358,878 9/1944 Pikul 112/252 2,707,927 5/1955 Artzt et a] 1 12/252 3,084,647 4/1963 Matchett et al. 112/252 3,118,405 1/1964 Schenkengel 112/252 3,391,665 7/1968 Kozuka 112/252 Primary Examiner--Warner H. Schroeder Attorney- Marshall J. Breen, Chester A. Williams J r.

and Robert E. Smith 1 Claim, 6 Drawing Figures sfiesma PATENTED JAN 81974 UNDERBED THREAD TRIMMING DEVICE FOR SEWING MACHINES BACKGROUND OF THE INVENTION In lockstitch sewing machines and particularly those organized for cyclic sewing to produce predetermined groups of stitchesas for attaching buttons or sewing tacks, and the like, known thread trimming devices have the shortcoming that they leave objectionably long ends of the severed thread hanging from the work, which shortcoming cannot be overcome by moving the known thread trimming instrumentalities closer to the stitching point because this would interfere with thread manipulation during stitch formation.

BRIEF SUMMARY'GF THE INVENTION The present invention provides a thread trimming mechanism for simultaneously severing the bobbin thread and one limb of the thread loop in a lockstitch sewing machine which mechanism is capable of severing threads extremely close to the stitches which are set in the work. The object of this invention is attained by tron.

DESCRIPTION OF THE DRAWINGS In the accompanying drawings of a preferred embodiment:

FIG. 1 represents a side elevational view of a portion of a sewing machine havingthe thread trimming device of this invention applied thereto,

FIG. 2 is 'a bottom plan view of the sewing machine throat plate with the thread trimming device of this invention illustrated in solid lines in an at-rest position and in dotted lines in a position for picking up the bob bin thread of the sewing machine,

FIG. 3 is a bottom plan view of the sewing machine throat plate similar to' FlG...2 and showing the thread trimming mechanism of this invention in solid lines in a position for picking up the needle thread loop and in dotted lines in the final thread severing position,

FIG. 4 is a top plan view of the movable knife blade assembled onto the thread manipulating plate,

FIG. 5 is an enlarged perspective view of the throat plate insert formed with the ledger blade and of the movable thread severing knife of this invention, and

FIG. 6 is a perspective view of a sewing machine loop taker, the thread, manipulating plate, and the throat plate insert showing the arrangement of threads prior to trimming. I

FIG. 1 illustrates a conventional lockstitch cyclic sewing machine of the type adapted to produce repetitive stitched tacks such as may be used to sew buttons, snaps or the like to garments. The sewing'machine includes a work supporting bed 11 in which a loop taker 12 is supported. A throat plate 13 is secured on the work supporting bed to sustain work fabrics against the thrust of a thread carrying needle 14 which is endwise reciprocable in a bracket arm 15 which forms part of the sewing machine frame and is rigidly supported relatively to the sewing machine bed 11. A work clamp 16 is carried by the sewing machine frame and is shiftably supported between the bed and the bracket arm to carry work fabrics in a predetermined path relatively to the stitching point as determined by the needle and the loop taker.

Although not illustrated in the accompanying drawings, group stitch sewing machines such as that illustrated in FIG. 1 conventionally include cam devices for shifting the work clamp, stopping the machine after completion of a predetermined number of stitches, or operating ancillary devices. It is also conventional in this type of group stitch sewing machine to provide operator influenced mechanisms for effecting various operations incidental to the performance of the machine. Any of the known conventional cam devices as well as a manually operable device may be utilized to shift a thread trimmer operating rod 20 which is carried beneath the sewing machine throat plate 13 as shown in FIGS. 1 and 3. The operating rod is formed with a rack 21 constrained in mesh with a gear segment 22 journaled on a stud shaft 23 supported in the throat plate and in a bracket 24 secured by a fastening screw 25 beneath the throat plate. The gear segment which is thus rotatable on a vertical axis beneath the throat plate on the stud, is secured to rotate with a knife supporting arm 26 which extends radially outward from the. stud shaft 23 and is formed with a downturned positioning flange 27 at the free extremity and with a threaded boss 28. A thread manipulating plate 30 is formed with an aperture 31 which embraces the boss 28 and a slot 32 which embraces the positioning flange 27 so as to orient the thread manipulating plate with respect to the supporting arm 26. A securing screw 33 threaded in the threaded hole 28 clamps the thread manipulating plate 30 securely in place on the supporting arm. The thread manipulating plate overhangs a circular recess 34 formed in the underside of the throat plate 13 and as shown in FIGS. 2 and 3 is formed with a pair of converging tapered

thread deflecting fingers

35 and 36 which terminate beneath the circular recess 34. A teardrop shaped slot 37 is formed between the tapered converging

fingers

35 and 36 which slot 37 is located directly beneath the circular recess 34.

Extending radially forwardly and outward from the thread deflecting finger 36 is an arched thread deflecting finger 38 which terminates in a radially inwardly bent extremity 39 extending transversely across the circular recess 34 beneath the throat plate.

Secured by fastening screws 40 beneath the thread manipulating plate 30 is a thread severing blade 41 formed with a sharpened cutting edge 42 which extends substantially radially with respect to the stud shaft 23 about which the knife blade moves. The blade 41 is offset from the thread manipulating plate on which it is secured so that the cutting edge extends into close proximity to the throat plate in the circular recess 34 therein. The blade 41, further, is formed with a finger 43 which is upturned and projects within a guard aperture 44 in the thread manipulating plate and serves to prevent threads from slipping sideways out of the path of the cutting edge 42.

The throat plate is formed with a large counterbored aperture 50 beneath the path of reciprocation of the sewing machine needle 14 and a hardened insert 51 with a flange 52 is secured to the throat plate by screws 53 in a position filling the aperture 50. Preferably, as shown in FIG. 4, the lower extremity of the hardened insert 51 is formed with a slightly tapered face 55 onto which opens a needle aperture 56 which is formed through the hardened insert the juncture of the needle aperture 56 with the underface 55 of the insert is formed at one side with a substantially straight portion 57 extending substantially radially of the stud shaft 23 so as to define a stationary cutting edge or ledger blade for cooperation with the cutting edge 42 of the blade 41. The incline of the face 55 serves to flex the cutting blade 41 slightly as it passes beneath the hardened insert which insures close cooperation therebetween. As illustrated in FIGS. 2 and 4, a notch 60 is provided in the underface 55 of the insert leading from the needle aperture 56 on an angle radially inwardly. Any thread which is directed from the needle aperture radially outward will pass over the sharpened ledger blade edge 57 and will be cut when the cutting edge 42 of the knife passes. Any thread which is drawn radially inward beneath the needle aperture 56 will be accommodated in the notch 60 and will not be severed when the'knife cutting edge passes. The tapered converging

fingers

35 and 36 and the arched arm 38 of the thread manipulating plate serve selectively to urge the bobbin thread and each limb of a loop of needle thread relatively to the needle aperture 55 as will now be described so that the bobbin thread will be severed and only the work limb of the needle thread loop but not the supply limb thereof will be cut when the cutting edge 42 of the knife blade passes across the hardened insert 51.

In solid lines in FIG. 2 the parts of the thread trimming mechanism of this invention are illustrated in an at-rest position which the parts occupy during normal sewing operations of the sewing machine. ln dotted lines in FIG. 2 is illustrated an intermediate position of the thread manipulating plate 30 preferably derived as a result of the operation of a conventional cam in the sewing machine. In this intermediate position the arched arm 38 will have traversed the needle aperture 56 preferably at a time when no needle thread extends from the needle aperture. Consequently, the bobbin thread will be urged radially outwardly by the arched arm 38 positioning thebobbin thread away from the notch 60 so that the bobbin thread will be cut by the knife blade 41 after sufficient bobbin thread has been pulled off to insure a sufficiently long starting end for the next stitch group. ln solid lines in FIG. 3 is illustrated a second intermediate position of the thread manipulating plate 30, also preferably the result of the operation ofa conventional cam on the sewing machine in which the

tapered converging fingers

35 and 36 are shifted into a loop of needle thread being manipulated by the loop taker 12 of the sewing machine. This position of parts is also illustrated with the threads in FlG. 6. The limb of the needle thread loop N" which extends to the work will be deflected radially outwardly by the finger 36 so that this limb will be cut; while the limb of needle thread loop N which extends to the needle and to the thread supply will be deflected radially inwardly by the finger 35 so that this thread limb will enter the notch 60 and will not be severed by the knife blade 41. The bobbin thread B will be deflected radially outwardly by the arched arm 38 so that the bobbin thread will be cut. As shown in dotted lines in FIG. 3, the cutting position of the trimming mechanism of this invention, which is preferably attained by a manual operation of any conventional operator influenced device on the sewing machine causes the cutting edge 42 of the knife blade to traverse the ledger blade 57 and sever the bobbin thread B and the work limb N' of the needle thread loop.

Since the thickness of the hardened insert 51 provides the only limitation on the length of thread ends which will extend from the work after the threads have been severed by the device of this invention, it will be 7 apparent that by using this invention the length of these thread ends may be reduced to a minimum without interference with stitch formation.

Having set forth the nature of this invention, what is claimed herein is:

1. An underbed thread trimming device for simultaneously severing the bobbin thread arid one limb of the needle thread loop on a lock-stitch sewing machine and in which both a movable thread cutting blade and a cooperating stationary ledger blade are carried on the sewing machine work-supporting throat plate, characterized in that the movable thread cutting blade is formed with a sharpened edge arranged beneath and substantially parallel to the throat plate for cooperation with a similarly oriented stationary ledger blade provided along the bottom face of an insert secured in the throat plate through which insert a needle hole is formed, and in which the cooperative cutting engagement of said sharpened movable blade with said stationary ledger blade is interrupted at one side of said needle hole by a thread clearance notch formed in one of said blades, and a thread manipulating plate is carried with said movable blade and formed with thread deflecting fingers for positioning limbs of thread from said needle hole relatively to said thread clearance notch.

Claims

1. An underbed thread trimming device for simultaneously severing the bobbin thread and one Limb of the needle thread loop on a lock-stitch sewing machine and in which both a movable thread cutting blade and a cooperating stationary ledger blade are carried on the sewing machine work-supporting throat plate, characterized in that the movable thread cutting blade is formed with a sharpened edge arranged beneath and substantially parallel to the throat plate for cooperation with a similarly oriented stationary ledger blade provided along the bottom face of an insert secured in the throat plate through which insert a needle hole is formed, and in which the cooperative cutting engagement of said sharpened movable blade with said stationary ledger blade is interrupted at one side of said needle hole by a thread clearance notch formed in one of said blades, and a thread manipulating plate is carried with said movable blade and formed with thread deflecting fingers for positioning limbs of thread from said needle hole relatively to said thread clearance notch.