US3491710A

US3491710A - Sewing machine with improved throat plate and feed dog construction

Info

Publication number: US3491710A
Application number: US605733A
Authority: US
Inventors: Richard E Bowin
Original assignee: Union Special Machine Co
Current assignee: Union Special Machine Co
Priority date: 1966-12-29
Filing date: 1966-12-29
Publication date: 1970-01-27
Anticipated expiration: 1987-01-27
Also published as: FR1550655A

Description

5 Sheets-Sheet 1 EZI-g R. E. BowlN FEED DOG CONSTRUCTION Jan. 27,1970

Filed Dec. 29, 1966 Jan. 27, 1970 R. E. BowlN 3,491,710

SEWING MACHINE WITH IMPROVED O'T PLATE AND FEE D DOG CONSTRUCT N Filed Deo. 29, 1966 5 Sheets-Sheet 2 Jan. 27, 1970 R. E. BowlN 3,491,710

' SEWING MACHINE WITH IMPROVED THROATPLATE AND FEED DOG CONSTRUCTION Filed DGO. 29, 1966 5 Sheets-Sheet 3 FlG-4A. F'IG-E. 45C 5.2? 5,2 4.59

.Elliannum Jam 21, 1970 R. E. Bowm '3,491,710

, SEWING MACHINE WITH IMPROVED THROAT PLATE AND FEED DOG CONSTRUCTION Filed Dec. 29, 1966 5 Sheets-Sheet 4 F165. l' ma@ I Jan. 27, 1970 4 R. E. BowlN 3,491,710

SEWING MACHINE WITH IMPRGVED THROATPLA'TE AND FEED DOG CONSTRUCTION Filed D90. 29. 1956 5 Sheets-Sheet 5 United States Patent O 3,491,710 SEWING MACHINE WITH IMPROVED THROAT PLATE AND FEED DOG CONSTRUCTION Richard E. Bowin, Chicago, Ill., assignor to Union Special Machine Company, Chicago, lll., a corporation of Illinois Filed Dec. 29, 1966, Ser. N0. 605,733 Int. Cl. Db 27/00, 75/00 U.S. Cl. 112-215 14 Claims ABSTRACT OF THE` DISCLOSURE A special throat plate and four-'motion feed dog combination for sewing machines, particularly for such machines that are adapted to produce a zigzag line of stitching. An important aspect of the construction is its provision of maximum support of the work being stitched in the region in which the stitching takes place and closely adjacent thereto. A further important aspect of the construction is that it provides for feeding of the work as close as possible to the region in which the formation of stitches occurs. In addition, the construction is such that it includes a stitch tongue rigidly connected with the feed dog, thus enabling the proper formation of stitches, and the shedding thereof from the stitch tongue, in the course of back-tacking as well as during the forward movement of the work. In achieving the foregoing objectives, the throat plate and feed dog cooperate in an effective manner with other elements of the machine, such as a reciprocatory and oscillatory needle, a cooperating looper, and a spreader or retainer hook for loops of thread entering into the line of stitching. By virtue of the particular construction and cooperation of the various parts, certain difficulties heretofore encountered, such as skipping of stitches, puckering of the work, or failure of the feed mechanism to advance the work, have been overcome.

DESCRIPTION OF THE INVENTION This invention relates to an improved combination of a throat plate and a four-motion feed dog for use in a sewing machine. It is concerned with such a combination adapted to overcome certain difficulties heretofore encountered in connection with the advance of the work to be stitched, and particularly in zigzag sewing machines.

In sewing machines as heretofore constructed, involving a throat plate along which work is advanced by a four-motion feed dog that rises upwardly through and is advanced along slots or openings provided in the throat plate, and involving a reciprocatory needle which passes downwardly through the work and through an opening in the throat plate to cooperate `with a complementary stitch-forming device vbeneath the throat plate, it has been found that difficulties are frequently encountered by virtue of the fact that portions of the work are forced downwardly into the needle passage opening in the throat plate by the impact of the point of the needle against the work. Such downwardly forced portions of the work are then pulled upwardly again by the upward movement of the needle, since the presser foot does not vprevent such return movement, at least to the top of the throat plate. This is frequently referred to as flagging and often leads to skipping of stitches by virtue of the fact that such downward and upward movement of the work prevents the proper formation of a loop in the needle thread that is arranged to be seized by the complementary stitchforming element, such as a looper.

Various other difficulties, that the present invention has been developed to overcome, very frequently arise.

One of these occurs in dealing with relatively limp or,

highly flexible fabrics. Another difficulty overcome by 3,491,710 Patented Jan. 27, 1970 the present invention arises from dealing with low friction producing fabrics formed in substantial part of smooth synthetic fibers. A further difficulty overcome by this invention is the heretofore frequently encountered tendency of lumps contained in the work to c-reate a non-feed condition.

In the case of limp fabrics it has been found that portions thereof have a tendency to follow the downward movement of the feed dog in the region of needle operation and to then have an undesired reverse feed action imparted thereto by the reverse movement of the feed dog. The danger of having this happen is substantially eliminated by the present invention through the special construction of the throat plate and the feed dog.

When low friction producing fabrics are being stitched together, it has been found difficult to insure the desired advance of the upper layer of fabric along with the lower layer that is being advanced by the feed dog. This is because the friction created between the two layers is usually less than that existing between the upper layer and the usual presser foot which urges the work toward the throat plate. As a result of this condition the upper layer of fabric has a tendency to lag behind the lower layer as the latter is being advanced by the feed dog. While the stitching together of portions of the two layers in a region which has already passed through the stitching zone serves to assist in pulling the top layer along with the bottom layer, this frequently leads to temporary stretching of the upper layer and then contraction thereof to produce buckling or puckering of the lower layer between successive stitches.

The difficulty with respect to lumps in the work serving to interfere with the feeding of the work arises when a lump happens to come into a position between the toothed sections of a feed dog. When this occurs, the lump acting between the surface of the throat plate and the bottom of the presser foot serves to hold the latter in such an elevated position that the toothed sections of the feed dog are not able to force the work against the presser foot to bring about an effective feed action. Lumps of the character mentioned may be developed in the regular performance of various stitching operations, such asV when an overedge line of stitching is provided along a side edge of a work piece and another edge adjoining said side edge is folded over to form a hem, or when a hem crosses a bulgy seam, such as a lap seam, which involves the stitching operation in which the lump trouble arises.

The present invention serves to substantially eliminate all of the foregoing difficulties heretofore encountered. This is achieved by the inclusion of a number of special features in the throat plate and feed dog combination. An important feature is the reduction to a minimum of the size of the openings through the throat plate which leave the work wholly unsupported in the course of its advance along the upper surface of thethroat plate. This is done in part by reducing the size of the openings through the throat plate to just the extent needed for the passage of the needle therethrough and the movement of sections of the feed dog therein. It is further accomplished by insuring partial support of the work by the upper surfaces of certain portions of the feed dog in the regions of the openings through the throat plate. Another important feature of the invention is the provision of active work engaging surfaces on the feed dog in direct alignment with the opening through which the needle is reciprocated, such alignment being provided. on both the upstream and downstream sides of the line offeed of the work over said needle opening. These active work engaging surfaces extend quite close to said needle opening, and in fact at least the upstream work engaging surface is adapted to move longitudinally within said needle opening in the course of advancing the work. This workengaging surface preferably has a smooth topped extension which always remains Within the needle opening.

An aspect of the foregoing feature is that the upstream section of the feed dog, referred to above, is arranged to serve as a stitch tongue to temporarily receive and retain portions of the thread entering into the stitch being formed. This is important in the formation of zig-zag stitching in order to insure the production of a at seam. By having the stitch tongue on the feed dog, rather than the throat plate, the mechanism is adapted for reverse feed movement of the work, as in back-tacking at the end of a seam. The movement of the feed dog toward the front of the machine at this time will bring about the desired shedding of the loop of thread from the stitch tongue to enable completion of a stitch.

It should be noted in connection with the foregoing that the features of the present invention are especially desirable and beneficial in a machine adapted to form zigzag stitching because in such machines the needle opening is relatively large, and therefore more likely to lead to difficulties of the type mentioned above. It must be large enough to enable the needle to pass through the work and the supporting throat plate as the needle is reciprocated along the two different paths on successive operations. The provision of the stitch tongue on the feed dog so as to reciprocate back and forth along a path between the two paths of the needle has been found particularly helpful in insuring proper stitch formation Without -any of the objectionable results mentioned above. Also it has been found highly desirable to include in the overall structure a spreader bar or retainer hook of the character shown in the patent to Schoij et al. No. 3,068,- 8,18, granted Dec. 18, 1962. Such a bar or retainer assists in the proper functioning of the needle and looper in cooperation with the stitch tongue carried by the feed dog.

` Other objects, features and advantages of the invention will appear from the following detailed description of various embodiments of the invention, given in connection with the accompanying drawings in which:

FIG. 1 is a vertical, sectional view taken lengthwise through the frame of a zigzag sewing machine embodying the invention;

I FIG. 2 is a plan view of a part of the base portion of the machine with the top, work supporting member of the base removed to show the mechanism within the base;

FIGS. 3A-D are schematic views showing the relationship between the throat plate, the feed dog, the presser foot and a reciprocatory needle at different stages in a cycle of operation of the machine;

FIGS. 4A-D are plan views of the throat plate and feed dog, illustrating these in different relationships assumed during a cycle of operation of the machine;

FIG. 5 is a plan View of the throat plate, showing certain features in greater detail;

FIG. 6 is a cross-sectional view through the throat plate taken along the line 6-6 of FIG. 5;

FIG. 7 is a cross-sectional view through the throat plate taken alonge the line 7--7 of FIG. 5;

FIG. 8 is a side elevational view of the feed dog of an illustrative embodiment of the invention;

FIG. 9 is an end View of the feed dog as seen from the right in FIG. 8;

FIG. 10 is a plan view of the feed dog; and

FIG. l1 is a perspective view showing the relationship between portions of the throat plate, the feed dog, the needle, a looper, and a spreader or retainer hook incorporated in the illustrative embodiment of the invention.

Referring to the drawings, they illustrate the various features of the invention as incorporated in a chain stitch sewing machine of the general type disclosed in the patents to Hayes et al, No. 2,792,797, granted May 2l, 1957, and Schoij et al, No. 3,068,818, granted Dec. 18, 1962. Reference may be had to those patents for details of certain devices incorporated in the machine embodying the present invention, and the mode of operating such devices.

The machine illustrated comprises a frame having a base portion 10, a vertical standard 11, and an overhanging arm 12, carrying at its outer end a head 13. Extending longitudinally of the base portion of the frame is a main drive shaft 14 which is provided with suitable connections therefrom for operating the various devices incorporated in the machine. Shaft 14 extends outwardly from the frame and has secured to its outer end a combined pulley and hand wheel 15 by which the sewing machine is driven.

Suitably mounted within the head 13 of the frame is an oscillatory and reciprocatory needle bar 17, carrying at its lower end a thread carrying needle 16. The needle bar 17 is mounted for vertical movement in an arm 18 of an L-shaped member rockable about a pivot 19 adjacent the upper end of the head 13. The other part of the rockable member being described in an arm 20 extending longitudinally of the overhanging arm of the frame of the machine. At its right end, FIG. 1, the arm 20` carries a ball stud 21 which is connected with a vertically extending pitman 22 within the vertical standard 11 of the frame. By suitable mechanism generally designated as 23, the link 22 is arranged to be moved upwardly upon one revolution of the drive shaft 14 and downwardly upon the next revolution of the drive shaft 14. This arrangement is such that during alternate cycles of operation of the machine the needle bar 17 will be reciprocated along one line of movement, and upon the cycles of operation of the machine occurring between said alternate cycles the needle bar will be reciprocated along a different line, which is inclined at a slight angle to that along which it was reciprocated during the first mentioned cycle.

For retaining the work against the Work supporting surface of the base 10 of the machine frame, there is provided a presser foot 31 secured to the lower end of a vertically shiftable presser bar 30. The latter is normally urged downwardly by a suitable spring, not herein shown but of the type disclosed in the Hayes et al. and Schoij et al. patents mentioned above. Means are provided for lifting the presser bar whenever desired, as when a new piece of work is to be introduced or a completed workpiece is to be removed, or when it is desired to facilitate manual movement of the work in the direction opposite to that in which it is normally fed, to enable back-tacking. For this purpose a bellcrank lever 32 is provided, this normally being urged in a counterclockwise direction (FIG. 1) by a spring 33. Rocking of the bellcrank 32 to bring about lifting of the presser bar may be accomplished by a knee press member suitably connected with a link 34. The means for this purpose may suitably be of the character disclosed in the Hayes et al. and Schoij et al. patents mentioned above.

The work supporting base of the machine is provided with a cover plate 10a, which may be readily removable to provide access to the mechanism within the base. Beneath this cover plate there is provided a spreader or retainer hook 40 (FIGS. 1 and 11) having a hooked portion 40a at its free end. This spreader or retainer hook is slidably mounted within a turnable pivot element 41 (FIG. 2) carried by a plate -42 secured to the base portion of the frame of the machine. At its right end (FIG. 2) the spreader 40 is suitably connected with a screw stud 43b eccentrically mounted on a disk 43a carried by a shaft 43. The latter is suitably journaled in the base portion of the frame of the machine and has secured thereto adjacent its lower end a gear 44 which cooperates with a gear carried by the main drive shaft 14. By this gearing the shaft 43 is given one revolution for each revolution of shaft 14. For further details as to the construction and mode of operation of the spreader or retainer hook reference `may be had to the Hayes et al, and Schoij et al. patents hereinabove referred to.

Turning now to the Work feeding mechanism, this in.-

cludes a feed dog 45 which is shown in detail in FIGS. 8-10 inclusive. It is also shown in combination with other elements of the machine in various other views. This feed dog is arranged to be given four-motion movements, i.e. an upward movement, a rearward movement, a downward movement, and a forward movement to its starting position, =by mechanism of the character disclosed in the above-mentioned Hayes et al. and Schoij et al. patents. Briefly it comprises a feed bar 46 having its rearward end pivotally or rockably mounted on the upper portion of a vertically disposed feed rocker 47. The feed dog 45 has a downwardly extending portion 45a provided with an elongated opening 45b therein adapted to receive a screw or bolt by which the feed dog may be adjustably attached to the forward end of the feed bar 46. Means of the character shown in FIG. 2 of the above-mentioned Schoij et al. patent may be provided for imparting lifting and lowering movements to the forward end of the feed bar, and hence to the feed dog secured to said bar. For imparting longitudinal movements to the feed bar, and hence the feed dog, the feed rocker 47 is provided with a laterally extending pin 48 about midway between the top and bottom of the feed rocker. To the end of the pin 48 there is clamped an arm 49 which, at its forward end, is pivotally connected with the lower end of a pitman 50. The upper portion of the pitman 50 cooperates with an adjustable eccentric 51 carried by the main drive shaft 14. It will be understood that the eccentric 51 may be suitably adjusted to impart the desired feed aand return movements to the feed dog.

Set within an opening in the top plate a and secured to the base of the frame of the machine is a throat plate 52. This is in the region of stitch formation, and more particularly in the area in which the feed dog is located and given its four-motion movements. As best shown 1n FIGS. 5-7, the throat plate 52 has elongated

slots

52a and 52b extending through the same and disposed in the direction of movement of the feed dog. Also the throat plate is provided with

wider openings

52e and 52d for cooperation with broader toothed portions of the feed dog. Interconnecting the

openings

52e and 52d are

narrow slots

52e and 52f, having at an intermediate point a wider opening 52g for the passage of the needle in the course of its reciprocation along the two paths mentioned hereinbefore. This arrangement is such that in the region in which the needle contacts the work the latter is well-supported except for the relatively small area of the slots and

opening

52e, 521, and 52g, As will be explained, the work is prevented from any substantial downward movement even in this area, since it is supported there, to a substantial extent, by portions of the feed dog to be described. As shown in FIG. 7 the wall of the opening 52g on the right hand side is preferably curved, as indicated at 52h. If desired the opposite wall of the opening may be similarly curved outwardly so as to widen the opening from top to bottom. This insures proper' cooperation with the needle as the latter is tilted in the two directions in the course of its reciprocation for the production of zigzag stitching.

Returning to FIGS. 8-10, the feed dog, in its preferred form, is provided with toothed upwardly extending side sections 45C and 45d which fit rather snugly within the

openings

52a and 52b of the throat plate, with provision for longitudinal movement of the feed dog in accordance with the stitch length for which the machine may be set. At its forward end, the feed dog has a central portion 45e which is relatively broad and substantially fills the width of the opening 52e in the throat plate. Extending rearwardly from the wide section 45e is a narrow section 45f which may be toothed throughout its length or may be provided with only a few teeth adjacent the sectiony 45e and then provided with a flat top surface in the region 45g which is flush with the tops of the teeth. Preferably the lower surface of the narrow section in the region 45g is inclined slightly upwardly toward its free end, and the latter is slightly rounded on itsunderside. This facilitates shedding of the thread from this region of the section 45f which functions as a stitch tongue. The narrow section in the region 45g and a portion of the toothed section 45j are adapted to slidingly enter the opening 52e of the throat plate and preferably at all times extend throughout the front to rear length of the opening 52g. At the rear end of the feed dog a broad toothed section 45h is provided for sliding movement within the opening 52d of the throat plate. Forwardly of the section 45h there is provided a reduced width, toothed section 451 of the feed dog which is adapted to fit into and slide along the opening 52j in the throat plate. This arrangement in general is preferably such that a minimum of free opening is provided through the throat plate that is not occupied by sections of the feed dog. Of course some clearance must be provided in a lengthwise direction to permit the feed dog to be advanced longitudinally of the throat plate to effect feeding of the work through a stitch length upon each cycle of operation of the machine. It will be noted from FIGS. 8 and 10 that only a very small clearance, i.e. about the length of one tooth, is preferably provided between the free ends of the aligned central sections 45g and 451' of the feed dog. These various features of the construction of the feed dog and the cooperating throat plate have been found to substantially eliminate the difiiculties discussed hereinabove in connection with the operation of machines as heretofore constructed.

Turning now to FIGS. 3AD and FIGS. 4A-D of the drawings, these illustrate the relative positions of various portions of the throat plate and the feed dog, as well as the status of certain parts, i.e. their direction of movement, at different times during a cycle of operation of the machine, Thus FIGS. 3A and 4A illustrate the relationship between the various parts as the needle 16 is descending and is about to pass through an opening in the presser foot 31 and then through the opening 52g provided in the throat plate. FIG. 4A shows this relationship in plan view, while FIG. 3A may be regarded as a vertical sectional view taken along a broken line passing through the central openings 52e-52g in the throat plate and following close to the lower side of these openings as they are shown in FIG. 4A, so that the centrally disposed toothed portions of the feed dog are shown in elevation. As indicated by the arrow applied to the feed dog in FIG. 3A the latter is about to partake of a downward movement, having completed its feeding action in the direction toward the left in FIG. 3A. It will be noted that at this time the fiat-surfaced portion 45g of the feed dog extends through the opening 52g and into the passage 521c of the throat plate. At this time, the free end of portion 45g is at least two stitch lengths in rear of the plane in which the needle is shifted from one line of reciprocation to the other.

In FIGS. 3B and 4B the parts are shown in the relative positions which they assume after the feed dog has been lowered away from the work and has begun its return movement toward the right in FIG. 3B. At this time the flat-surfaced portion 45g of the feed dog will have been shifted slightly toward the right within the passage 52f, while the toothed section 451' of the feed dog will have entered the passage 52f to a somewhat greater extend than in the FIG. 4A position of the parts. Also, it will be noted that at this time the needle 16, which is positioned at the lower side of section 45g of the feed dog, as shown in FIG. 4B, has begun or is about to begin its upward movement.

In FIGS. 3C and 4C the feed dog is shown in its fully retracted position, i.e., the furthest to the right in these views but actually furthest toward the front of the machine, so that the section 45g of the feed dog is fully withdrawn from the passage 52j and may not quite completely extend across the opening 52g in the throat plate. At the same time the section 451' of the feed dog has been shifted further toward the right in the passage 52]c and its free end is closely adjacent to the opening 52g. At this time, furthermore, the feed dog is partaking of its upward movement and the needle is still moving upwardly and is above the work and the presser foot.

In FIGS. 3D and 4D the parts are shown in the relative positions assumed as the feed dog has just started its work feeding action. It has been moved slightly toward the left while in its raised position, engaged with the work, with the upper surface of the work being urged against the bottom of the presser foot 31. At this time the needle 16 has about reached its uppermost position and is ready to begin its downward movement very shortly. During the interval between the time that the needle is in the position shown in FIG. 3C and the time it reaches the position shown in FIG. 3D, or at least before the needle assumes the position shown in FIG. 3A, it will have been shifted by the swinging of the arm 18 (FIG. 1) to cause it to descend on the opposite side of the stitch tongue section 45g of the feed dog from that shown in FIG. 4B.

It will be understood that, in the course of forming a seam, the various elements discussed above will go repeatedly through the cycles of operation discussed to bring about the formation of a zigzag line of stitching.

FIG. 11 Shows how the needle 16, the looper 35, and spreader or retainer hook 40 cooperate in a manner to insure shedding of the stitch forming threads from the stitch tongue 45g, even in the course of back-tacking or other reverse feed sewing. While the machine as herein disclosed does not include any reverse feed mechanism, it will be understood that in the course of providing backtack stitching the operator will cause Ythe presser foot to be lifted by the operation of a knee press, or the like, and will then feed the work by hand in the direction required. If desired, however, the machine may be equipped with reverse feed ing mechanism, which may for example be of the general character disclosed in the patent to Daniel No. 3,033,141, granted May 8, 1962. Regardless of how the reverse feed is elfected, it will normally have a tendency to cause stitches to be partially retained and accumulated on the stitch tongue. This objectionable result is overcome by the present invention because of the provision of the stitch tongue on the feed dog which is given a retracting movement in the course of each stitch forming cycle, and which is of such form as to readily shed the stitches therefrom. Furthermore, the motion of the spreader or retainer hook is such as to assist in the shedding of stitches= This is because of the movement of the hooked end 40a, at a time in its cycle, in a direction toward the free end of the stitch tongue 45g.

While the invention has been shown and described in detail as applied to a zigzag sewing machine, because it has special advantages when applied to such a machine, it should be understood that there are certain features of the invention which will be highly benecial, when applied to single needle or multiple needle machines in which the needle or needles are reciprocated always along the same path or paths. Certain of the stitch forming difliculties mentioned in the foregoing, which frequently arise in machines adapted to form only straight stitching, as distinguished from zigzag stitching, are eliminated by the employment of various features of the present invention.

What is claimed is:

1. In a sewing machine having a frame provided with work supporting means, said frame having a member disposed above said work supporting means, a reciprocable needle bar carried by said member and arranged to reciprocate a thread carrying needle from a position above said work supporting means to a position in which a portion of said needle is disposed below the upper snrface of said work supporting means, complementary stitch forming means below the upper surface of said work supporting means adapted to cooperate with said needle to form stitches, and means for advancing work along said surface of the work supporting means across the path. of reciprocation of said needle, the combination which comprises a throat plate secured to said work supporting means in the region of said work advancing means and along the outer surface of which the work is advanced, said work advancing means comprising a fourmotion feed dog having a plurality of at least partially toothed portions in spaced parallel relation to each other, said throat plate having passages therethrough aligned with said toothed portions of said feed dog and enabling the latter to mc-ve upwardly through said throat plate and longitudinally thereof, said throat plate also having an opening therethrough in alignment with the path of movement of said needle, said passages and opening through said throat plate being of just suflicient dimension to enable the free movement of said needle and of said toothed portions of the feed dog in relation to said throat plate in the performance of their functions, certain of said toothed portions of said feed dog being directly aligned with said needle opening through said throat plate forwardly and rearwardly thereof, at least one of said at least partially toothed portions having a part thereof disposed constantly within said needle opening.

2. In a sewing machine, work supporting means, a throat plate carried by said work supporting means, said throat plate having a plurality of openings extending through the same with work supporting surfaces between said openings, a reciprocable needle bar adapted to carry a needle back and forth from a position above said throat plate to a position in which a portion of the needle extends through one of the openings in the throat plate to present a thread carrying eye of the needle below the throat plate, complementary stitch forming means cooperating with said needle when a portion thereof is below the throat plate to assist in producing a stitch, means for advancing Work along said work supporting surfaces of said throat plate through the path of reciprocation of said needle, said work advancing means comprising a spring urged presser foot serving to urge the work toward said throat plate and a four-motion feed dog having spaced parallel at least partially toothed sections adapted to be shifted upwardly through other of said openings in the throat plate into engagement with the work and then longitudinally within said openings, said toothed sections of the feed dog being arranged for subsequent downward movement away from the work and then a return movement in a direction opposite to that in which they are shifted longitudinaliy while engaged with the work, said sections of said feed dog substantially filling the openings in said throat plate through which they are lifted but being of sufficiently shorter length than said openings to permit said longitudinal movement of said sections, certain of said toothed sections being in direct alignment with said opening through which the needle is passed, one such section being upstream and another downstream from said opening, the upstream section extending at all times into said opening and having its free end closely adjacent the free end of the downstream section.

3. In a sewing machine as set forth in claim 2, said toothed sections in alignment with said opening through which the needle is passed having broadened portions in regions further upstream and downstream, respectively, from said opening than the adjacent ends of said sections.

4. In a sewing machine as set forth in claim 2, said toothed sections in alignment with said opening through which the needle is passed having broad portions in the regions furtherest removed upstream and downstream, respectively, from said opening and having narrower portions in regions closer to said opening, said narrower portion disposed upstream from said opening having a nontoothed, smooth-top extension which is at all times partially disposed in said opening and serves as a stitch tongue.

5. In a sewing machine as set forth in claim 2, said upstream section having at least a portion serving as a stitch tongue, said needle and said complementary stitch forming means being adapted to carry threads into cooperation with each other and place the same in engagement with said stitch tongue, and a longitudinally movable and laterally oscillatable retainer hook adapted to engage portions of said threads and shift the same in relation to said stitch tongue.

6. In a sewing machine as set forth in claim 5, the relative movements of said stitch tongue, said needle, said complementary stitch forming means and said retainer hook being so coordinated as to bring about shedding of the threadffrom said stitch tongue during reverse movement of the work in the course of applying back-tacking stitches to the work.

7. In asewing machine as set forth in claim 2, said complementary stitch forming means comprising a fourmotion looper adapted to enter a loop of needle thread cast outwardly from said needle, and adapted to present a loop of looper thread in the path of said needle.

8. In a sewing machine as set forth in claim 7, means for shifting said needle bar to carry the needle laterally of the direction of feed of the work and to thereby cause said needle to be reciprocated along two different paths alternately upon successive cycles of operation of the machine.

9. In a `sewing machine as set forth in claim 2, means for shifting said needle bar to cause said needle to be reciprocated along two different paths alternately upon successive cycles of operation of the machine, said two paths of th`e needle being at and closely adjacent to opposite sides of said upstream section of the feed dog in the regionfof said throat plate opening through which the needle is passed.

10. In a sewing machine as set forth in claim 5, means for shifting said needle bar to cause said needle to be reciprocated along two different paths alternately upon successive y,cycles of operation of the machine, said two paths of the needle being at and closely adjacent to opposite sides of said stitch tongue in the region of said throat plate opening through which the needle is passed.

11. In a sewing machine as set forth in claim 5, said complementary stitch forming means comprising an oscillatory looper, said retainer hook being positioned beneath said throat plate and above said looper and being arranged to pick up and shift both laterally of and forwardly of the stitch tongue a loop of needle thread and a cooperating portion of thread carried by said looper.

12. In a sewing machine as set forth in claim 11, means for shifting said needle bar to carry the needle laterally of the direction of feed of the work, thereby causing the needle to be reciprocated along two different paths alternately upon successive cycles of operation of the machine and thus forming a zigzag line of stitching.

13. In a sewing machine as set forth in claim 3, said throat plate having laterally inwardly extending work supporting portions in regions both upstream and downstream from that in which said opening for the passage of the needle is provided, said portions of the throat plate being restricted in length in the direction of movement of the toothed sections of the feed dog just suflicient to enable the longitudinal movement of said broadened portions of said toothed sections.

14. In a sewing machine as set forth in claim 13, at least one of said portions of the throat plate having its under surface sloped outwardly in the region of said opening through which the needle passes.

References Cited UNITED STATES PATENTS 597,663 1/1898 Woodward et al` 112-216 X 1,309,576 7/ 1919 Hill '112-158 2,792,797 5/1957 Hayes et al 112--158 2,884,883 5/1959 Reimer v 112-206 X 3,313,259 4/ 1967 Daniel 112-260 2,633,816 4/1953 Johnson et al. 112-215 FOREIGN PATENTS 8,539 1911 Great Britain.

RICHARD I. SCANLAN, IR., Primary Examiner U.S. Cl. X.R. 112-216, 260