referring first to fig1 the illustrated sewing machine 1 is a commercial two - needle sewing machine with a needle holder 3 carrying two spaced needles 4 and secured on a vertically reciprocable needle bar 2 . needles 4 cooperate with respective loopers ( not shown ) arranged under a stitch plate 5 , for the formation of two independent seams n , shown in fig6 . a ripping knife 6 works between needles 4 to form the elongated slot l , shown in fig6 and 7 , and is secured on a knife bar 7 which can be longitudinally displaced in the casing of sewing machine 1 and which can be coupled , in a known manner , with a constantly driven swing lever . in the casing of sewing machine 1 , there is also arranged a vertically displaceable and resiliently pre - stressed presser bar 8 which bears , by spring action , on the sewing material resting on stitch plate 5 . by means of a screw 9 , a presser foot 10 , with two sole parts 11 and 12 , is secured on presser bar 8 , and has a passage 13 , as shown in fig7 for the raised edges r of braid strip p to be sewn on cut garment piece w and between which ripping knife 6 works . on a post or mounting plate 14 of work support plate 15 of sewing machine 1 , there is secured a supporting plate 16 , shown in fig1 and 2 , for the cutting device for making the corner cuts e and f , shown in fig6 . the free left end of supporting plate 16 is forked and has two bored arms 17 and 18 , as best seen in fig2 . a supporting bar 19 extends through the bores of arms 17 and 18 , for rotation and longitudinal displacement . an angle cross - section cutting knife 20 is secured to the upper end of supporting bar 19 by means of a screw 21 . a gear 22 is arranged on supporting bar 19 and is held and guided between arms 17 and 18 of supporting plate 16 , and supporting bar 19 has a guide slot 23 extending parallel to its longitudinal axis and in which there is engaged a guide pin 24 secured in gear 22 . a rack 25 meshes with gear 22 and is secured on piston rod 26 of a compressed air cylinder 27 having connections 28 and 29 . the bottom end of supporting bar 19 has a journal 30 whose diameter is smaller than that of bar 19 , and journal 30 rotatably mounts an index ring 31 , shown in fig2 and 4 , and which is secured against axial displacement by a safety ring 32 . index ring 31 is formed with two flat surfaces 33 and 34 serving as guide surfaces and embraced by arms 35 , 36 of the forked end of a swing lever 37 which is pivotally mounted on supporting plate 16 for pivoting about a bolt or pin 38 . two pins , 39 and 40 , are secured in index ring 31 at diametrically opposite locations , and engage guide slots 41 and 42 , respectively , of arms 35 and 36 , respectively . swing lever 37 is an angle lever having a bent end 43 to which is articulated a fork 46 secured on piston rod 44 of a compressed air cylinder 45 which has connections 47 and 48 , as shown in fig1 and which is mounted , by means of a mounting ring 50 provided with a journal 49 and rotatably received in supporting plate 16 , for pivotal movement about journal 49 . a stop pin 51 , shown in fig2 and 3 , is pressed , with a press - fit , into rack 25 , and engages an elongated slot 52 in supporting plate 16 , and the end faces 53 and 54 ( fig3 ) of slot 52 form counter - stops for stop pin 51 . instead of the end faces 53 and 54 of an elongated slot 52 serving as counter - stops , adjustable stop cams could be provided on supporting plate 16 in the path of motion of stop pin 51 in order to enable adjustment and fixing of the end positions of rack 25 and the angular positions , defined by it , of angle cross - section cutting knife 20 secured on supporting bar 19 . stitch plate 5 of sewing machine 1 has a recess 55 , shown in fig2 and through which angle cross - section cutting knife 20 is pushed upward to make the corner cuts e and f , shown in fig6 . stitch plate 5 also has a slot 56 , shown in fig2 for the passage of the toothed webs of a cloth feed 57 of sewing machine 1 performing a rectilinear movement , and is formed with stitch holes 58 for needles 4 . it should be mentioned that cloth feed 57 can displace the sewing material by shifting a known stitch adjustor , both in the feeding direction , indicated by arrow v , and in the opposite direction , for example , in order to lock the seams n at the beginning and at the end , these seams having been formed during displacement of the sewing material in the feeding direction v . since only the first corner cut e can be made with the above - described corner cutting means during the sewing operation , it is necessary to bring the sewing material , after the completion of the sewing operation , that is , after the seams n have been locked , by sewing several stitches c , shown in fig6 in the displacement direction opposite to the feeding direction v , and after the threads have been cut off , so over the angle cross - section cutting knife 20 , before the second corncer cut is made , that the second corner cut f is made at the correct point of the elongated slot l . for this purpose , there is used a device which has a carrier 59 , shown in fig1 secured on the back of the machine casing and on which are arranged two parallel guide rods 60 and 61 for rotation about pivots 62 and 63 . at the opposite ends of the parallel guide rods 60 , 61 , and intermediate plate 66 is articulated thereto by pivots 64 , 65 . an angle lever 67 is arranged on intermediate plate 66 for swinging about a pivot 68 which is spaced from a pivot 70 for a guide rod 69 . angle lever 67 and guide rod 69 are articulated , by means of pivots 71 , 72 , respectively , on a shaft or web 73 of a sliding foot 74 arranged to engage the sewing material . at the free end of angle lever 67 , there is formed a bore 75 through which there passes a follower pin 76 secured on a fork 77 embracing the free end of lever 67 . the diameter of bore 75 is substantially greater than the diameter of pin 76 so that angle lever 67 can be moved relative to fork 77 . fork 77 , together with a suspension plate 78 , is secured on piston rod 79 of a compressed air cylinder 80 having connections 81 and 82 and which is mounted on a supporting arm 83 of intermediate plate 66 . in order to change the stroke of piston rod 79 , an adjusting nut 84 is screwed into the cylinder of air cylindeer 80 , and the piston rod 79 extends through nut 84 . a tension spring 85 is connected between suspension plate 78 and the free end of angle lever 67 to form an elastic coupling connection between the angle lever and its driving means , namely , the compressed air cylinder 80 . to raise and lower sliding foot 74 , there is provided a compressed air cylinder 86 having connections 87 and 88 and which is arranged on a supporting angle 89 secured on carrier 89 . a fork 91 is secured on piston rod 90 of compressed air cylinder 86 and embraces guide rod 60 to which it is connected by a pin 92 . between fork 91 and supporting angle 89 , there is arranged a compression spring 93 embracing piston rod 90 . in order to ensure the entrainment of sliding foot 74 in the sewing material , during its movement for locking the seams n at the end , the underside of the sole of sliding foot 74 is toothed . additionally , several hairpin springs 95 are provided on sliding foot 74 and have their bights engaged over retaining pins 94 , as shown in fig2 in sliding foot 74 . only one spring 95 is shown in fig2 and has an end 96 bearing on a pin 97 in sliding foot 74 as well as a downwardly bent end resiliently pre - stressed toward the sewing material on passing through a bore 99 in sliding foot 74 . sewing machine 1 , its various parts , and the compressed air cylinders 27 , 45 , 80 and 86 are controlled by a known program device utilizing electromagnetic valves , with a measuring wheel , equipped with hall generators , for scanning the workpiece and serving as a pulse transmitter for the control commands to be transmitted to the workpiece through an amplifier , the measuring wheel cooperating with stationary permanent magnets . the measuring wheel can be arranged , for example , on the cloth presser bar of the sewing machine . starting from the consideration that a cut garment piece w with a braid strip p fed through a folding sleeve and folded into an inverted t - form is under pressure foot 10 at a point where the locking seams b start , namely , the point a of fig6 and that angle cutting knife 20 is under stitch plate 5 in an annular position for the corner cut e , shown in solid lines in fig6 and determined by stop pin 51 and the end face 53 of elongated slot 52 , sliding foot 74 is lifted from the sewing material , ripping knife 6 is retracted and the measuring wheel is in contact with the sewing material , the device works in a manner which will now be described . with the electric program device activated , the motor driving the sewing machine is started by a starting switch and drives sewing machine 1 , at first , at a reduced speed until after the first corner cut e has been made , by displacing the sewing material in a direction opposite to the feeding direction v . a few locking stitches b are formed , starting at the point a after which the sliding direction of the work is reversed and the sewing material is displaced to form the seams n , in the direction of arrow v . at a point provided for this purpose , ripping knife 6 , working between the edges r ( fig7 ) of braid strip p is activated and , during the sewing , cuts the elongated slot l in braid strip p and in cut garment piece w . with the sewing machine still operating at a reduced speed , the first corner cut e is made during the sewing by supplying compressed air to compressed air cylinder 45 through connection 48 , so that supporting rod 19 is pushed upwardly through the medium of index ring 31 and angle lever 37 . the angle cross - section cutting knife 20 passes through recess 55 in stitch plate 5 and makes the corner cut e . then , the supply of compressed air to connection 48 is interrupted , and the cylinder is exhausted , after which compressed air is supplied through connection 47 so that supporting bar 19 with angle cross - section knife 20 is retracted again into the starting position . supporting bar 19 , with angle knife 20 , is then turned through 180 ° to the angular position indicated by broken lines in fig2 for the preparation of the second corner cut f . this is effected by supplying compressed air to cylinder 27 through connection 28 and , in the end position for the second corner cut f , stop pin 55 secured in track 25 bears on end face 54 of slot 52 . sewing machine 1 can now be driven at a higher speed . ripping knife 6 is retracted or disconnected after cutting slot l to the required length and at the point provided for the second corner cut f , the sewing machine speed is reduced again and seams n are completed until the desired seam length is obtained . as soon as that point is reached where the sliding direction of the sewing material must be reversed for the formation of the end locking stitches c of the seams n , sliding foot 74 is lowered abruptly onto sewing material p and w through compressed air cylinder 86 to which compressed air is supplied through its connection 87 , and sliding foot 74 is held pressed against the sewing material , after exhausting of compressed air cylinder 86 , by compression spring 93 . in the following displacement of the sewing material in a direction opposite to the feeding direction v for the formation of end locking stitches c , sliding foot 74 is taken along by the sewing material up to the seam end d and tension spring 85 is tensioned . the entrainment of sliding foot 74 by the sewing material is made possible by the substantially large diameter of bore 75 in angle lever 67 , relative to the diameter of follower pin 76 , thus providing what may be termed a lost motion connection . in the last upward movement of needle bar 2 , the threads are cut off , pressure foot 10 is lifted from the sewing material , and sewing maching 1 is stopped with the needles at the upper position . by supplying air to air cylinder 80 through connection 81 , angle lever 67 is turned , through follower pin 76 , about pivot 68 in plate 66 until fork 77 , secured on piston rod 79 , bears on adjusting nut 84 . by providing the parallel guide rod 69 between plate 66 and shaft or web 73 of sliding foot 74 , the latter is displaced when angle lever 67 is actuated with the sewing material in the feeding direction v , into a position determined by adjusting nut 84 and fork 77 in which the sewing material is , together with the end of the elongated slot l above angle cross - section cutting knife 20 , which has been turned , in the meantime , through 180 ° about the axis of supporting bar 19 into the angular position shown in fig2 by broken lines . by a corresponding supply of compressed air over connections 47 and 48 of air cylinder 45 , supporting bar 19 , with cutting knife 20 , is then pushed briefly upward through angle lever 37 and index ring 31 to make the second corner cut f , is returned into the starting position , and the cutting knife is angularly displaced in the opposite direction for making the next corner cut e on a new workpiece by supplying compressed air through connection 29 of air cylinder 27 , the rotation being through 180 ° into the angular position shown in solid lines in fig2 and determined by pin 51 engaging end face 53 of elongated slot 52 . slidng foot 74 is then lifted from the sewing material by supplying compressed air through connection 88 to air cylinder 86 , so that the sliding foot 74 is lifted from the sewing table and a new workpiece is made ready under presser foot 10 , aligned according to optical markings , and a braid strip , folded in inverted t - form can be supplied , after which the above - described cycle can be started again after presser foot 10 has been lowered . while a specific embodiment of the invention has been shown and described in detail to illustrate the application of the principles of the invention , it will be understood that the invention may be embodied otherwise without departing from such principles .