US3871307A

US3871307A - Placket forming machine

Info

Publication number: US3871307A
Application number: US348267A
Authority: US
Inventors: Rollo L Scott; Robert F Overby
Original assignee: Munsingwear Inc
Current assignee: Munsingwear Inc
Priority date: 1973-04-05
Filing date: 1973-04-05
Publication date: 1975-03-18
Anticipated expiration: 1992-03-18

Abstract

Apparatus for use in forming a placket in a fabric workpiece. The apparatus comprises a sewing machine having spaced reciprocating needles acting in conjunction with looper mechanisms to form two parallel lines of chain stitches. A cutter blade is disposed between the needles and reciprocates with them to slit the fabric between the lines of stitches. The fabric workpiece is held in position and advanced relative to the sewing machine by a clamping device which moves over a track at a regulated rate. Following completion of the sewing operation, a pair of horizontal knives are automatically extended to pick up the stitch forming threads and retracted relative to stationary members to sever the threads in shearing fashion.

Description

nited States Patet [191 Scott et a1.

[451 Mar. 18, 1975 PLACKET FORMING MACHINE [75] Inventors: Rollo L. Scott, Minneapolis; Robert F. Overby, Bloomington, both of Minn.

[73] Assignee: Munsingwear, Inc., Minneapolis,

Minn.

[22] Filed: Apr. 5, 1973 [21] Appl. No.: 348,267

[52] U.S. Cl. 112/l2l.15, 112/252 [51] 1nt. Cl D051) 21/00 [58] Field 0fSearch..... l12/121.15,121.12, 121.11, 112/2, 252, 65, 68, 7O

[56] References Cited UNITED STATES PATENTS 3,139,849 7/1964 Cohen et a1. 112/252 3,354,852 11/1967 Kennedy et al... 3,401,655 9/1968 Johnson et a1 112/2 3,424,117 l/l969 Schopf 112/252 3,489,115 l/l970 Marforio 112/254 3,532,065 10/1970 Marforio 112/252 3,653,345 4/1972 Bianchi l12/121.1l

Nicolay et al 112/65 Champney et a1 ll2/l2l.l2

Attorney, Agent, or Firm-Merchant, Gould, Smith &

Edell [57] ABSTRACT Apparatus for use in forming a placket in a fabric workpiece. The apparatus comprises a sewing machine having spaced reciprocating needles acting in conjunction with looper mechanisms to form two parallel lines of chain stitches. A cutter blade is disposed between the needles and reciprocates with them to slit the fabric between the lines of stitches. The fabric workpiece is held in position and advanced relative to the sewing machine by a clamping device which moves over a track at a regulated rate. Following completion of the sewing operation, a pair of horizontal knives are automatically extended to pick up the stitch forming threads and retracted relative to stationary members to sever the threads in shearing fashion.

7 Claims, 9 Drawing Figures :JENTED I 3,871,307

sum 1' [IF 4 PATENTEU 3,871,307"

- sumanrg I PLACKET FORMING MACHINE The invention is directed to apparatus for use in forming a placket in a fabric workpiece.

The nature of some garments requires the formation of a slit opening or placket for conveniently putting the garment on. An example of such a garment is the slipover shirt, in which the placket ordinarily extends downwardly from a center point at the top and front of the neck opening. In making such garments, formation of the placket usually involves placement of additional layers of material and/or stiffeners over the primary fabric layer, cutting the slot opening through all layers in the proper position and sewing along each side of the opening through all of the layers.

Obviously, due to the number and complexity of steps involved in forming a placket, it behooves the garment manufacturer to utilize automatic equipment to every extent possible to reduce the amount of time spent on the garment. Unfortunately, to the best of our knowledge, fully automatic placket forming machines are not available to the garment manufacturer. Typically, plackets are formed by an operator using a conventional sewing machine which has dual spaced needles for making the parallel lines of stitches, and which may include a reciprocating cutter blade for simultaneously sheaving the material between the stitch lines. However, this procedure still involves assembly of the several cloth layers by the operator, placement of the layers in a proper position on the machine, controlling operation of the machine and position of the fabric workpiece as stitching and sheaving take place, determining the stopping point for the stitching and sheaving operation, severing all threads and removing the workpiece from the machine. It will be appreciated that this procedure is at best only semiautomatic, and requires considerable time on the part of the operator in proper formation of the placket.

My invention is directed to an automatic machine which requires the operator only to place the layers in a predetermined position, to initiate operation of the machine and to remove the finished product. More specifically, my invention contemplates a conventional sewing machine having dual needles and a cutter blade in combination with clamping apparatus for automatically securing the fabric workpiece and advancing it over a worktable relative to the reciprocating needles and cutter at a regulated rate. The apparatus further comprises a pair of thread severing knives horizontally mounted below the worktable. Upon completion of the cutting and sewing, these knives are automatically extended to pick up thread and retracted to sever the thread in shearing fashion. A significant feature of the inventive apparatus is maintaining the thread at a predetermined tension to permit proper thread pick up by the knives, and slackening the thread to preclude damage to the last made stitch and prevent disengagement of the threads from the sewing machine as the knives are retracted. The control apparatus for the machine automatically returns the clamping apparatus to its starting point and releases the fabric workpiece after the threads have been severed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view in top plan of a machine embodying the inventive principle;

FIG. 2 is an enlarged view of a portion of the machine as seen from the line 2--2 of FIG. 1;

FIG. 3 is a view in side elevation of the machine as seen from the line 33 of FIG. 1;

FIG. 4 is an enlarged fragmentary sectional view of the machine taken along the line 44 of FIG. 1;

FIG. 5 is an enlarged fragmentary sectional view taken generally along the line 55 of FIG. 2;

FIG. 6 is an enlarged fragmentary sectional view taken along the line 6-6 of FIG. 2;

FIG. 7 is a fragmentary sectional view taken along the line 7-7 of FIG. 2;

FIG. 8 is a fragmentary perspective view of the stitch forming and thread severing structure of the machine; and

FIG. 9 is a view in top plan of the work product of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT With initial reference to FIGS. 1-3, a machine embodying the inventive concept is represented generally by numeral 11. Generally, machine 11 comprises a supporting frame 12, a sewing machine 13, a worktable l4, advancing apparatus 15 and control apparatus 16.

Frame 12 includes leg members 17 and cross members 18 which provide support to a tabletop 19.

Sewing machine 13 is mounted on tabletop 19 toward its front, and is operated by driving apparatus consisting ofa drive motor 21 and

drive pulleys

22, 23 acting through V-

belts

24, 25. Operation of drive motor 21 is by control apparatus 16 through a control line (not shown) and a control device 26 mounted on the housing of drive motor 21. Associated with drive pulley 23 is an automatic positioning device 27 which senses the operating position of sewing machine 13 whenever it is stopped and automatically returns it to a predetermined beginning point. Device 27 thus ensures complete and proper operation from the predetermined beginning point in the formation of a placket.

Sewing machine 13 itself is conventional in nature, with the exception of certain modifications as pointed out below. The sewing machine disclosed is a Union Special model 56700, made by the Union Special Machine Company of Chicago, Illinois, and reference is made to the technical publications relating to such machines for structural and operational details not discussed herein.

With specific reference to FIGS. 4 and 6, sewing machine 13 includes a reciprocating needle bar 28 upon which a needle holder 29 is mounted. Needle holder 29 carries a pair of needles 31 in spaced, side-by-side relation, together with a cutter 32 which is disposed precisely between needles 31 and slightly rearwardly thereof to cut fabric as it is sewed. Machine 13 further includes the usual presser bar or foot 33 which is moved between the fabric clamping position shown and an elevated non-clamping position by a pneumatic cylinder 40 in the usual manner (FIG. 3). Thread 34 is supplied to each of the needles 31 through a tension regulator 35 and oppositely reciprocating

thread advancing mechanisms

36, 37. Threads 34 are also threaded through a pivotal arm 38 the position of which is controlled by a pneumatic cylinder 39. As indicated by the arrows, actuation of the pneumatic cylinder 39 rotates the pivotal arm 38 counterclockwise to strip" additional thread from the thread source for a purpose described in detail below.

With additional reference to FIG. 8, sewing machine 13 further includes a looper 41 for each needle 31 which operates in conjunction therewith to form stitches. As best shown in FIG. 6, each of the loopers 41 is carried by a looper rocker 42 which is reciprocated by a mechanism not shown from right to left relative to the associated needle 31, and also from a point behind the needle 31 to a point in front of it. As shown in FIGS. 4 and 8, the loopers 41 each receive a separate thread 43 from the tension regulator 35, through a second tension device 44 and

guides

45, 46. The enlarged representation of FIG. 8 shows the looper 41 to have two eyes 47 connected by an elongated groove through which the thread 43 is threaded.

Specifically, the cooperative movement of each needle 3l-looper 41 pair may be assumed to begin with the needle 31 in its down position and looper 41 behind the needle and toward the right. As the needle 31 begins to move upward, looper 41 moves to the left (remaining behind the needle) and picks up the loop deposited by the needle. As the needle 31 reaches its uppermost point, looper 41 reaches its extreme left position and moves to the forward side of the needle, which is the position shown in FIG. 8. At this point, the loop of thread 34 on the looper 41 and the thread 43 extending from the previously made stitch and the tip of looper 41 together define an opening 48 through which the needle 31 passes on its downward stroke. Simultaneously, looper 41 begins its return trip to the right, and as soon as the looper tip clears the needle 31, looper 41 moves back to the initial position behind the needle 31. The result is the formation of a double locked chain stitch which is well known in the art.

With continued reference to FIG. 7 as well as FIG. 8, a pneumatic cylinder 51 mounted on the lower backside of sewing machine 13 carries a notched rod 52 disposed to project between the

guides

45, 46 and engage the threads 43 upon actuation of the cylinder 51. Similarly to the pneumatic cylinder 39, operation of the pneumatic cylinder 51 serves to strip or pull additional thread from the thread source as described in greater detail below.

With reference to FIGS. 3 and 4, worktable 14 comprises a tabletop 53 with a smooth upper surface and is spaced above the tabletop 19 of frame 12 by a plurality of U-shaped supporting brackets 54. The height of tabletop 53 is chosen to permit optimum operation of the needle 3l-looper 41 pairs. A work light 50 is mounted below table 14 to assist the operator in his use of the machine.

Broadly speaking, advancing apparatus comprises a fabric clamping device 55 which is slideably mounted on a track on the tabletop 53 for movement relative to the sewing machine 13. With reference to FIGS. 1, 2, 5 and 6, the track for clamping device 55 comprises a pair of elongated members 56 of I-cross section which are mounted in parallel, spaced relation. Clamping device 55 includes a pair of horizontally disposed and forwardly projecting guide members 57 which cooperate in sliding relation with the inside channels defined by the track members 56. Guide members 57 are commonly connected at their rearward most end by an uprightsupport 58. A horizontal bracket strap 59 is secured to the rear face of support 58 and carries at each of its extreme ends a forwardly projecting elongated stay member 61. The leading tip of each stay member 61 curves upwardly to receive material thereunder as described in greater detail below.

As best shown in FIG. 2, clamping device 55 further comprises a clamping portion including a pair of parallel spaced support bars 62 interconnected by a transverse strap 63. Each of the support bars 62 has a downwardly projecting ear 64 which is pivotally connected to the upright support 58 by a screw 65. Each of the support bars 62 carries a clamping bar 66 the underside of which has an elongated strip 67 of foam rubber or the like adhesively secured thereto.

The clamping bars 66 are respectively disposed above the guide members 57 for clamping relation therewith in the lowered position. As shown in FIGS. 2, 5 and 6 the clamping bars are normally urged to this lower clamping position by a pair of coil springs 68 which are mounted in tension between each support bar 62 and a portion of the upright support 58.

The interconnecting strap 63 has a tail 69 projecting rearwardly therefrom, and a pneumatic cylinder 71 having an extensible actuator member 72 disposed so that the tail portion 69 can be engaged to swing the clamping bar 66 upwardly to the position of FIG. 2.

Clamping device 55 further comprises a support block 73 mounted on the upright support 58 which carries a horizontally disposed, spring loaded pin 74 for actuating a switch 75 (FIG. 1), as discussed more fully below. As shown in FIGS. 4 and 5, a switch mounted on the machine 13 is disposed to be engaged by the upright support 58 as the clamping device 55 moves to its extreme forward position.

Sliding movement of the clamping device 55 on the elongated track members 56 is effected by the pneumatic cylinder 76 (FIG. 3) which is mounted on the tabletop 19 by brackets 77. Pneumatic cylinder 76 has an extensible actuator rod 78 the extreme end of which is threaded and is secured to the upright support 58 of clamping device 55 by a pair of lock nuts 79. Operating in association with pneumatic cylinder 76 is a hydraulic cylinder 81, which is carried by brackets 82 mounted on the brackets 77. Hydraulic cylinder 81 also has an actuator rod 83 which is similarly connected to the upright support 58. An accumulator 84 communicates with one end of the hydraulic cylinder 81 and also with one end ofa hydraulic line 85. The opposite end of line 85 is connected to the opposite end of hydraulic cylinder 81, thus establishing a flow loop for hydraulic fluid as the internal piston of cylinder 81 is moved from end to end. A restriction (not shown) is included in this hydraulic loop to restrict flow therethrough at a regulated rate. Consequently, as the pneumatic cylinder 76 is actuated to slide clamping device 55 over the worktable 14, the actuator 83 of hydraulic cylinder 81 is carried therewith, thus causing hydraulic fluid to flow through the hydraulic loop. Movement of the clamping device 53 is therefore regulated in accordance with the sewing rate of machine 13 and smoothly controlled by the restricted flow within the hydraulic loop as discussed above.

FIGS. 6-8 disclose a pair of extensible and retractable knives 86 respectively disposed relative to each needle 31-looper 41 pair for severing the

threads

34, 43 after stitching has been completed. Each of the knives 86 has a point 87 which moves along a horizontal line to which the associated vertically disposed needle 31 transversely projects. The respective knives 86 are also notched, as shown at 88, rearwardly of the knife point 87. It will thus be appreciated that the smooth knife edge between point 87 and notch 88 guides the

threads

34 and 43 into the notch 88 as the knife 86 is extended.

The knives 86 are each slideably mounted between a pair of flat members 89 mounted on the underside of machine 13, and each is extensible and retractable by a pneumatic cylinder 91. As best shown in FIG. 6, the knives 86 are disposed at essentially the same level as the extreme tops of the loopers 41. As shown in FIG. 8, in the cycle of machine operation, each of the knives 86 is extended when the looper 41 has swung to the left and is on the front side of needle 31. At this point, as discussed above, looper 41 has formed a loop in the thread 34 by projecting therethrough, and it has also carried its own thread 43 through such loop. Accordingly, as knife 86 is extended, it projects through the loop of thread 34 and past the thread 43, guiding single strands of both into the notch 88. Upon retraction of the knives 86, the

threads

34 and 43 are carried therewith and severed by the shearing action of the knife 86 relative to the members 89. g

The successful operation of the knives 86 in severing the

threads

34 and 43 cannot be accomplished unless tension on the

threads

34 and 43 is proper at the time the knives are extended. If there is slack in either of the

threads

34 or 43, the knife point 87 may miss one or both of them and the thread cutting is precluded. To ensure that proper tension in the

threads

34 and 43 exists at the time that the knives 86 are extended, the control apparatus 16 operates the pneumatic cylinder 76 to cause the clamping device 55 and fabric workpiece to advance slightly or creep approximately oneeighth of an inch after the sewing operation has been completed and stopped. As shown in FIG. 8, this creep of the fabric workpiece draws the

threads

34 and 43 taut and allows the knife 86 to project through in the proper manner described above.

It is also necessary, for successful cutting of the

threads

34 and 43, to prevent the respective knives 86 from pulling out the last formed chain stitch and from disengaging the-

threads

34, 43 from the respective needles 31 and looper 41. This is avoided through actuation of the

pneumatic cylinders

39 and 51 by control apparatus 16, the effect of which is to swing pivotal arm 38 down and back to strip additional lengths of the threads 34, and to extend and retract the notched rod 52 to strip additional lengths of the threads 43. These additional lengths provide slack in all threads which is taken up to some extent as the knives 86 retract and shear the thread in half, thus preventing undesirable tension from pulling on the last formed stitch or disengaging the threads.

FIG. 9 shows the fabric workpiece to comprise a bottom fabric layer 92, a stiffener 93 and a top fabric layer 94. With reference to FIGS. 5 and 6, prior to operation of the machine, the operator slips the bottom fabric layer 92 underneath the stay members 61 but on top of the track members 56, the clamping bars 66 being up (see FIG. 2) when the machine is stopped. The stiffener 93 and top fabric layer 94 are then respectively and centrally placed on top of the bottom layer 92 essentially as shown in FIGS. 5 and 9.

Operation of the machine 11 is controlled by two

switches

95 and 96 mounted on the front side of machine 13 (FIGS. 1 and 3). Switch 95 operates the pneumatic cylinder 71 to retract the actuating plunger 72 and permit the coil spring 68 to pull clamping bars 66 downwardly against guide members 57. This serves to hold the entire fabric workpiece in place for further sewing operations. Switch 96 is then depressed to initiate operation of the machine 11 through control apparatus 16. Such control consists of the simultaneous operation of sewing machine 13 and pneumatic advancing cylinder 76. With the operation of sewing machine 13, foot 33 is lowered, cutter blade 32 reciprocates to cut a slit 97 (FIG. 9) through both fabric layers 92 and 94 and stiffener 93, and needles 31 and loopers 41 operate in the manner described above to form lines of chain stitches 98. The actuation of pneumatic advancing cylinder 76, as regulated by hydraulic cylinder 81, advances clamping device 55 at a smooth, constant rate commensurate with operation of the needle 3l-looper 41 pair.

The operational movement of clamping device 55 is from the front to the back of the machine; i.e., the pneumatic advancing cylinder 76 actually pulls clamping device through the sewing operation. As clamping device 55 approaches the point at which sewing of the placket is completed, the spring loaded pin 74 strikes the switch 75, and the sequence of operation thereafter, as effected by control apparatus 16, is as follows. Drive motor 21 for sewing machine 13 is stopped, thus halting further movement of needles 31, cutter blade 32 and loopers 41. Automatic positioning device 27 then senses the position of the sewing elements and automatically positions the needles 31 at their uppermost point as shown in FIG. 8. Although sewing machine 13 is brought to a halt at this point, advancing cylinder 76 continues to provide the necessary creep" to the fabric workpiece and thereby place the

threads

34 and 43 under tension in preparation of the thread cutting operation.

Pneumatic cylinders

39 and 51 are operated at this point to strip additional thread to provide slack as described hereinabove, and knives 86 are then extended and retracted, through the actuation of pneu matic cylinders 91, to cut

threads

34 and 43.

Control apparatus 16 then actuates the foot lifter cylinder 40 to raise foot 33 to its highest position and subsequently operates advancing cylinder 76 in the opposite direction to return clamping device 55 to its starting point. As the clamping device 55 reaches this point, the upright support 58 strikes switch 80 to stop further extension of pneumatic cylinder 76. Pneumatic cylinder 71 is also actuated at this time to extend plunger 72, thereby overcoming the bias of coil springs 68 to raise clamping bars 66 and release the finished fabric workpiece. The cycle is repeated upon insertion of a new fabric workpiece.

We claim:

1. In sewing apparatus comprising a sewing machine having a first and second widely spaced needles, first and second thread carrying loopers arranged for cooperation severally with the first and second needles to comprise first and second needle and looper pairs, an independent tensioned supply of thread for each of the needles and loopers, and drive means energizable to cause coordinated sewing movement of said needles and loopers and effective when deenergized to return said needles and loopers to predetermined positions, combined with means for holding a multi-layer work piece and automatically drawing the work piece past the needles in a direction normal to the plane of the needles to produce a pair of widely spaced two-thread chain stitches along the work piece, the improvement which comprises:

means interrupting the energization of the sewing machine drive means at the end of a predetermined travel of the work piece while causing the work piece to creep slightly further whereby to ensure that the needle and looper threads beneath the work piece are taut and in predetermined locations;

a first cutter cooperating with a first needle and looper pair and a second cutter cooperating with the other needle and looper pair, each cutter comprising a movable knife member having a pointed end of reduced thickness and having a hooked recess along one edge thereof at a location spaced from the point, means reciprocating the knife member between a first, extended position and second, retracted position, and means cooperating with the knife member for shearing threads carried in said recess during retraction of the knife member;

and means mounting the cutters adjacent the loopers so that upon extension the point of each knife member moves close to the adjacent looper whereby the needle and looper threads from the stitch last made enter the recess in the knife, and upon retraction the threads are carried to the cooperating means for severing.

2. In sewing apparatus comprising a sewing machine having first and second widely spaced needles, first and second thread carrying loopers arranged for cooperation severally with the first and second needles to comprise first and second needle and looper pairs, an independent, tensioned supply of thread for each of the needles and loopers, and drive means energizable to cause coordinated sewing movement of said needles and loopers and effective when deenergized to return said needles and loopers to predetermined positions, combined with means for holding a multi-layer work piece and automatically drawing the work piece past the needles in a direction normal to the plane of the needles to produce a pair of widely spaced two-thread chain stitches along the work piece, the improvement which comprises:

means interrupting the energization of the sewing machine drive means at the end of a predetermined travel of the work piece while causing the work piece to creep slightly further, whereby to ensure that the needle and looper threads beneath the work piece are taut and in predetermined loca- 'tions;

a first cutter cooperating with a first needle and looper pair and a second cutter cooperating with the other needle and looper pair, each cutter comprising a movable knife member arranged for sliding movement between first and second fixed blades, each knife member having a pointed end of reduced thickness and having a hooked recess along one edge thereof at a location spaced from said point, and means reciprocating the knife member between a first, extended position and a second, retracted position relative to the fixed blades;

and means mounting the cutters adjacent the loopers so that upon extension the point of each knife member moves close to the adjacent looper whereby the needle and looper threads from the stitch last made enter the recess in the knife and upon retraction the threads are severed by shearing between a wall of the recess and a blade end.

3. Apparatus according to claim 2 together with means for stripping a predetermined short length of additional thread from each supply concurrently with movement of the knife members, to prevent pulling out the last stitch or unthreading the needles or loopers by allowing part of the additional thread to be drawn through the needles or loopers as the knives retract.

4. Apparatus according to claim 2 wherein the loopers oscillate in a common plane about separate axes aligned with the direction of movement of the work piece and spaced by the spacing between the needles, and in which the movements of the knives are substantially colinear, in opposite directions, in a line parallel to the plane of oscillation of the loopers.

5. Apparatus according to claim 3 in which the looper threads from the sources pass through a substantially common path near the loopers, and the stripping means includes normally inoperative means operable to displace both the looper threads laterally out of the common path.

6. Apparatus according to claim 3 in which the stripping means for needle threads is distinct from the stripping means for looper threads.

7. Apparatus according to claim 2 in which the sliding movement of the knife members in the blades is rectilinear.

Claims

1. In sewing apparatus comprising a sewing machine having a first and second widely spaced needles, first and second thread carrying loopers arranged for cooperation severally with the first and second needles to comprise first and second needle and looper pairs, an independent tensioned supply of thread for each of the needles and loopers, and drive means energizable to cause coordinated sewing movement of said needles and loopers and effective when deenergized to return said needles and loopers to predetermined positions, combined with means for holding a multilayer work piece and automatically drawing the work piece past the needles in a direction normal to the plane of the needles to produce a pair of widely spaced two-thread chain stitches along the work piece, the improvement which comprises: means interrupting the energization of the sewing machine drive means at the end of a predetermined travel of the work piece while causing the work piece to creep slightly further whereby to ensure that the needle and looper threads beneath the work piece are taut and in predetermined locations; a first cutter cooperating with a first needle and looper pair and a second cutter cooperating with the other needle and looper pair, each cutter comprising a movable knife member having a pointed end of reduced thickness and having a hooked recess along one edge thereof at a location spaced from the point, means reciprocating the knife member between a first, extended position and second, retracted position, and means cooperating with the knife member for shearing threads carried in said recess during retraction of the knife member; and means mounting the cutters adjacent the loopers so that upon extension the point of each knife member moves close to the adjacent looper whereby the needle and looper threads from the stitch last made enter the recess in the knife, and upon retraction the threads are carried to the cooperating means for severing.

2. In sewing apparatus comprising a sewing machine having first and second widely spaced needles, first and second thread carrying loopers arranged for cooperation severally with the first and second needles to comprise first and second needle and looper pairs, an independent, tensioned supply of thread for each of the needles and loopers, and drive means energizable to cause coordinated sewing movement of said needles and loopers and effective when deenergized to return said needles and loopers to predetermined positions, combined with means for holding a multi-layer work piece and automatically drawing the work piece past the needles in a direction normal to the plane of the needles to produce a paIr of widely spaced two-thread chain stitches along the work piece, the improvement which comprises: means interrupting the energization of the sewing machine drive means at the end of a predetermined travel of the work piece while causing the work piece to creep slightly further, whereby to ensure that the needle and looper threads beneath the work piece are taut and in predetermined locations; a first cutter cooperating with a first needle and looper pair and a second cutter cooperating with the other needle and looper pair, each cutter comprising a movable knife member arranged for sliding movement between first and second fixed blades, each knife member having a pointed end of reduced thickness and having a hooked recess along one edge thereof at a location spaced from said point, and means reciprocating the knife member between a first, extended position and a second, retracted position relative to the fixed blades; and means mounting the cutters adjacent the loopers so that upon extension the point of each knife member moves close to the adjacent looper whereby the needle and looper threads from the stitch last made enter the recess in the knife and upon retraction the threads are severed by shearing between a wall of the recess and a blade end.