US3577944A

US3577944A - Undertrimmer mechanism for sewing machines

Info

Publication number: US3577944A
Application number: US864447A
Authority: US
Inventors: Erich M Willenbacher; Ulrich Schmedtkord; Dieter K Gabler
Original assignee: Singer Co
Current assignee: SSMC Inc
Priority date: 1969-10-07
Filing date: 1969-10-07
Publication date: 1971-05-11
Anticipated expiration: 1988-05-11
Also published as: DE7033547U; GB1321246A; FR2065015A5; DE2048502A1

Abstract

A trimming mechanism for a sewing machine for severing the marginal edge of the lower ply of material being seamed. Oscillatory movement is imparted to the trimming blade by a series of arms driven off an eccentric on the sewing machine bed shaft. An operator-controlled cam member is operatively connected through its follower to mechanism which changes the relative position of the arms to vary the stroke of the trimming blade and also change its vertical elevation so that the blade at the bottom of its cutting stroke is at the same elevation for any stroke selected.

Description

United States Patent [72] Inventors Erich M. Willenbacher Karlsruhe; Ulrich Schmedtkord, Badenwuerttemberg; Dieter K. Gabler, Neudorl, Germany 864,447 Oct. 7, 1969 May 1 l, 197 1 The Singer Company 1 New York, N.Y.

[21 Appl. No. [22] Filed [45] Patented [73] Assignee [54] UNDERTRIMMER MECHANISM FOR SEWING MACHINES 11 Claims, 14 Drawing Figs.

[52] US. Cl 112/127 [51] Int. (1 D05b 37/02 [50] Field of Search 112/127,

[56] References Cited UNITED STATES PATENTS 2,064,598 12/ 1936 Fabian et al. 1l2/l27 2,475,758 12/1949 Seaman l 12/127 Primary Examiner-H. Hampton Hunter Attorneys-Marshall .l. Breen, Chester A. Williams, Jr. and

Robert E. Smith ABSTRACT: A trimming mechanism for a sewing machine for severing the marginal edge of the lower ply of material being seamed. Oscillatory movement is imparted to the trimming blade by a series of arms driven off an eccentric on the sewing machine bed shaft. An operator-controlled cam member is operatively connected through its follower to mechanism which changes the relative position of the arms to vary the stroke of the trimming blade and also change its vertical elevation so that the blade at the bottom of its cutting stroke is at the same elevation for any stroke selected.

PATENTEUMAH 1|97l 3" 577' 944 sum 1 or 4 INVENTORS Erich M- Willenbacher WITNESS Ulrich Schmadfkord.

Dieter K. Gab/er Z/l I V BY yAiTTORNEY I PATENTED MAY] 1 I97l 3,577,944

SHEEI 3 OF 4 BYWW -V TTORNE Y PATENTEU m1 1 19m SHEET UF 4 Fig.Hd

Fig.l|o- Fig.llb

INVENTORS Erich M. Willanbacher Ulrigh Schmedfkord Dieter K. Gab/er BY QM @w WITNESS ATTORNEY UNDERTRIMMER MECHANISM FOR SEWING MACHINES BACKGROUND OF THE INVENTION This invention relates to trimming mechanism for sewing machines and more particularly to a trimming mechanism for severing the lower ply of fabric as it is being seamed at a position proximate'to the seam line.

Certain operations in the manufacture of textile products require simultaneously stitching the seam and trimming the marginal edge of one ply of the stitched material. During later operations performed thereon, the wider edge is folded about the trimmed edge and an additional line of stitching is applied thereto so as to produce a neat and strong seam in which each of the trimmed edges is concealed. In sewing machines adapted for these operations it is desirable for the operator to be able to have the capability to adjust the bite of the trimmer blade for various purposes, e.g., for trimming different thicknesses of material, to coordinate the trimmer with the stitch length, etc. For the highest speed of operation of the machine, however, it is necessary that the total stroke of the trimmer be as short as possible under these circumstances so as to minimize vibration. The present invention allows the operator to adjust the stroke of the trimmer blade while simultaneously varying its vertical elevationso that substantially all the variation in the stroke goes into increasing the bite of the blade.

SUMMARY OF THE INVENTION The primary object of this invention is to provide an improved trimming mechanism for use in a sewing machine which is adapted to trim a marginal edge of fabric being sewn simultaneously with the stitching thereof.

It is a further object of this invention to provide in a sewing machine, a trimming mechanism in .which the stroke of the trimming blade can be selectively adjusted by the-operator to meet various conditions of operation and in which the trimming blade can be stopped completely while the machine continues to sew.

A still further object of this invention is the provision of a trimming device adapted for use in a sewing machine in which the vertical elevation of the trimming blade is automatically adjusted when the stroke of the blade is adjusted by the operator so that substantially all of the increase in stoke goes into in.- creasing the bite of the trimming blade, thus minimizing wasted motion of the blade, and minimizing vibration.

These and other objects are achieved by providing cam means selectively operated by the operator to move acontrol shaft to adjust the stroke of the trimmer blade to the character of the work being trimmed and simultaneously to effect the vertical elevation of the trimmer blade. The trimmer blade is driven through a driving lever from an eccentric on the bed shaft. The driving lever is slidably mounted at one end in a carrier frame. Movement of the control shaft varies the location of the fulcrum of the trimmer blade-to change its vertical elevation and also varies the direction of oscillation of the driving lever by changing the angular position of t the carrier frame to thus change the stroke of the trimmer blade.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the nature and objects of the invention reference should be had for the following description taken in connection with the accompanying drawings1 in which:

FIG. 1 is a perspective view of the trimming mechanism of this invention partially in section and shown in the maximum cuttingposition;

FIG. 2 is a cross-sectional view through the bed of a sewing machine incorporating the present invention taken substantially along line 2-2 of FIG. 1 and showing a fragmented portion of the standard in elevation;

FIG. 3 is a cross-sectional view through the bed of the sewing machine taken substantially along line 3-3 of FIG. I;

FIG. 4 is a cross-sectional view taken throughthe bed of the sewing machine taken substantially along line 4-4 of FIG. I and showing the ply deflector used with the present trimming mechanism;

FIG. 5 is a bottom plan view of the sewing machine with a portion of the feed mechanism broken away and a portion of the frame in section;

FIG. 6 is a view in bottom plan of the trimmer blade and its support elements as shown in FIG. 5 but removed therefrom for clarity;

FIG. 7 is an enlarged fragmented top plan view of the throat area of the sewing machine showing the position of the trimmer blade in relation thereto and showing the ply separator in phantom;

FIG. 8 is a view similar to-FIG. 7 but on an even larger. scale and with the accessory plate partiallyv broken away;

FIG. 9 is a cross-sectional view taken along line 9-9 of FIG. 8 showing the trimmer blade at the top of its stroke prior to the taking of a cut and further showing the ply separator positioned between the two plys-of fabric;

FIG. 10-is a cross-sectional view similar to FIG. 9 taken along line 10-10 of FIG. 8 but showing thetrimmer blade in its position subsequent to the cutting of the lower ply of fabric;

FIGS. Ila-11d are end views, partially broken away, showing the position of the trimmer blade relative to the'throat plate of the sewing machine for various settings of the operator controlled lever; FIG. Ila being the no-cut position, FIG. Ilb showing the trimmer blade at the top and bottom of its stroke for the first cutting position, FIG. 11c showing the trimmer blade at the top and bottom of its stoke for thesecond cutting position and FIG. 11d. showing the trimmer blade at the top and bottom of its stroke for the maximum cutting positron.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawing, the invention is illustrated as applied to a zigzag sewing machine having a bed 10 and including a bedplate 11 to theupper surface of which is secured an, acces sory plate Ila and a throat plate 12 provided with the usual openings to accommodate a feed dog 13; Rising from the bed at one end of the, bed is a standard 14, the upper end ofwhich has an overhanging bracket arm (not shown) extending above the bedplate I1. and terminating in a head at its outer extremity (not shown) as is well known in the art. Slidably joumaled in the head for endwise reciprocation and for zigzag jogging movement is a needle bar 15 which carries at its lower extremity a needle .16. Needle jogging means of any conventional form is adapted to jog the needle in adirection-longitudinally of the-bed 10. Further joumaled-in the head is a presser bar 17 which carries at its lower end a presser foot 18 cooperating with the feed dog 13 to hold and feed the work in the usual manner in a direction transversely of the bed. A slotted needle aperture 12a extendinglongitudinally of the bed is provided in the throat plate 12. Cooperating with the needle in the usual manner for forming lock stitches isa rotary loop taker I9 driven by shaft20 by means of gearing (not shown) within gear boxes 21 and 22. Driving the gearing within the gear boxes is a rotary bed shaft 23 deriving its-motion from a pulley 24' on its right end, as viewed in FIG. 5, which in turn, is driven by a belt 25 from a main. shaft (not shown) in timed relation with the needle bar. The feed dog 13 is given feed motion by means of the feed bars. 26, 26a which are connected to the triangularly shaped feed advance bar 27 driven offthe bed shaft 23 by means of feed advance rock arm 28. An eccentric (not shown) on bed shaft 23 imparts motion to an arm 29 which in turn, drives the rock arm 28. An eccentric (not shown) on stud shaft 30 imparts feed lift motion to the feed bars. The feed mechanism not forming any part of this invention is well known in the art and need not be described any further at this time. 1

The trimmer mechanism of this invention will now be described with'particular reference to FIGS. 1-5. As best seen in FIG. 1, mounted on the bed shaft 23 is an eccentric 31 and a balance wheel 23a. An eccentric strap connection 32 having a pitman extension 33 transmits oscillating motion to a driving lever 34. The driving lever comprises two parallel wall sections 35 and 35a joined together by a bottom section 36 and two braces 37 and 37a. The pitman extension 33 is pinned between the walls 35 and 35a. At either end of the driving lever is a forked

portion

38 and 39 between the walls 35 and 35a. Joumaled within the fork 38 is a cylindrical slide 40 having an aperture 41 therethrough. A pin 42 set in a carrier frame or yolk member 43 is adapted to pass through the aperture 41 in the slide. The carrier frame 43 is essentially a boxshaped element having one end open for the passage therethrough of the driving lever 34. As seen in FIGS. 1 and 5, attached to end walls 44 and 44a of the carrier frame are

shafts

45 and 46 which are joumaled within the bed of the machine as at 47 and 48. Joumaled at 39a within the fork 39 of the driving lever 34 is a crank arm 49 formed at its free end with a split sleeve portion which is secured by means of screw 51 onto a short rock shaft 52 having a step portion 53 journaled within the frame of the machine as shown at 54 in FIG. 5. Fixed onto the shaft 53 is the hub of a crank arm 55 whose free end is pinned at 56 to a lever 57. The lever 57 is'in turn pin connected at 58 to one arm 59 of a bellcrank 60 fulcrumed at 61 as will be later described. The other arm 62 of the bellcrank 60 is bent at a right angle 63 remote from the pivot 61 and has an upstanding portion 64 thereon. A trimming element 65 is connected to the portion 64 as by

screws

66 and 67. A slot 67a in the element 65 allows adjustment of the lateral movement of the trimming mechanism of the trimming element 65.

Joumaled in the bed plate at the standard end of the machine is a pin 68, the top of which has a disc 69 connected thereto by means of a set screw 70. A lever 71 having an operator control knob 72 is fixed within the disc 69. The pin 68 passes through a plate 73 which rests on the bed plate 10. Beneath the bed plate the pin is fixed into a cam element 74 and locked to the hub thereof by a set screw 75. The cam 74 has a cam track 76 thereon comprising a series of

notches

76a, 76b, 76c and 76d corresponding to the stroke of the trimmer selected. The notch 76d corresponds to the no-cut position or the setting where the trimmer blade does not oscillate. Of course, any number of notches more or less than the four shown can be used and is within the scope of this invention.

In contact with the cam track is a follower pin 77 integral with a follower arm 78 having a split sleeve 79 at its opposite end thereof. The sleeve passes about a control shaft 80 and is locked thereon by means of a screw 81 in such relation that the pin 77 is always in contact with the cam track 76. The control shaft further passes through the split sleeve 82 of a crank arm 83, the sleeve being fixedly secured to the control shaft 80 by means of a screw 84. The lower end of the crank arm 83 is pin connected at 85 to one end of a lever 86 whose free end is pin-connected at 87 to the carrier member 43 below the shaft 46. A moment arm is thus created between the shaft 46 and the connection 87 on the member 43. It is, therefore, clear that movement of the lever knob 72 by the operator will cause the control shaft 80 to turn in a given direction, causing the carrier frame 43 to change its angular relationship.

Further secured to the control shaft as by a latch member 88 is a lever element 89. It is seen in FIG. 6 that the latch member 88 has two

cars

90 and 91, through which pass a screw 92. A finger 93 at the top of the latch member is forced into engagement with a step 94 on the lever element 89 when the screw is tightened into these ears. The bellcrank 60 is thus fulcrumed at 61 between

fork elements

95 and 95a of the lever element 89 for pivotal movement relative thereto. A bracket 96 at the bottom of the bed is connected by means, for example, of a bolt 97 to a cylinder 98. Within the cylinder 98 a spring (not shown) biases a pin 99 against the bottom of the lever element 89, so as to maintain the same upwardly. Between the split sleeve 82 and the lever element 89 the control shaft passes through and is concentric with the rock shaft 52 and acts to further journal the rock shaft for oscillatory movement.

A spring 100 secured as by a pin 101 to the bed of the machine at one end, engages a pin 101a on the carrier frame 43 so as to bias the carrier frame towards its maximum inclination as shown in FIG. 1. This in turn, by means of lever 86 and crank arm 83, tends to keep the follower pin 77 against the cam track 76. At the standard end of the bed, a bracket 102 is secured beneath the bedplate to a bed by a screw 103. A slot 104 in the bracket allows lateral shifting of the bracket relative to the bed. An upstanding portion 105 of the bracket receives the end of the control shaft 80 within an aperture therein. For purposes later described, a spring 106, between the portion 105 and the split sleeve 79 biases the control shaft and the elements secured thereto to the left, as viewed in FIG. 5.

Bushings

107 and 108 in the bed of the machine and rock shaft 52 rotatably support the control shaft 80 which extends therethrough.

As can be seen in FIG. 5, the cam track 76 does not extend entirely about the cam 74, but terminates at

edges

109 and 110. A stop pin 111 protruding from the bed of the machine is adapted to extend into this region between 109 and 110, clockwise of 109 in FIG. 5, thus limiting the movement of the cam between these edges. The pin 111 engages edge 109 at the maximum cutting position, as shown, and edge at the no-cut position so that the operator may easily go to either of these extremes.

Attached to a boss on the bedplate 11 as by an adjustable screw 112 is a fabric ply separator 113 which, as best seen in FIGS. 9 and 10, acts to separate the top ply from the lower ply as the latter is being trimmed. As clearly shown in FIG. 8, the ply separator 113 has a cutout portion 114 to provide clearance for the trimmer blade during the latters upward stroke. There is further provided a tapered upper surface 115 and a hooked position 116 on the ply separator so as to allow the same to intervene between the top ply 117 and the bottom ply 118 as close to the stitching point as possible without deflecting the upper ply in such manner as to interfere with the sewing operation.

The trimmer element 65 comprises a trimmer blade 119 having a wedge-shaped cutting edge 120. The trimming action is accomplished by a scissors-type movement of the cutting edge against a ledger blade 121 as shown in FIGS. 9 and 10. The bias supplied by spring 106 maintain the trimmer blade 119 against the ledger blade for proper cutting. The movement of the trimmer blade takes place in a vertical plane which passes normal to the fabric being trimmed. This plane is the plane of the paper in FIG. 11. The oscillating movement of the bellcrank 60 about fulcrum 61 also creates movement of the trimmer blade in a slightly arcuate path within this vertical plane.

With the present arrangement, as the stroke of the trimmer blade is adjusted by the operator, the elevation of the lever element 89 is changed, thus changing the location of the fulcrum 61 relative to the throat plate 12. The center of oscillation of the trimmer blade is therefore varied simultaneously and automatically with the stroke. In FIG. 11b11d, the location of the trimmer blade is shown in solid at the top of its stroke and is dotted at the bottom of its stroke. It is thus seen that the bottom of the stroke is always at the same level, which is also the zero stroke position, for any stroke selected. The

- adjustment in stroke, therefore, goes to increase or decrease the effective cutting stroke or bite of the blade, thus substantially eliminating wasted motion of the blade.

In operation when the operator desires to select a particular bite of the trimmer blade, he merely moves the knob 72 until the cam follow pin 77 engages one of the

notches

76a, 76b, or 76c on the cam track 76. There can be indicia on the bedplate of the machine to indicate the selected stroke if desired. The follower arm 78 being fast on control shaft 80 thus turns this shaft through an angle determined by the notch or stoke selected. Since crank arm 83 and lever element 89 are also fast on shaft 80, they too are rotated therewith.

Movement imparted by crank 83 is transmitted through lever 86 to the carrier frame 43, thus causing the carrier frame and pin 42 to assume a predetermined angular relationship due to the joumaled relationship of the

shafts

45 and 46 in the frame. Rotary motion of the bed shaft 23 is converted into oscillatory motion by the eccentric 31, strap 32 and pitman 33. The driving lever 34 is thus always given an oscillatory movement, but the path of oscillation is variable. When the pin 42 is in the neutral or vertical position, the slider 40 and hence the lever 34 merely idle up and down along pin 42 about the pivotal connection 390 with the arm 49, and substantially no horizontal motion is transmitted to the arm 49 to oscillate shaft 52. If the pin 42 was bent at a radius equal to the length of lever 34,. then no horizontal motion at all would be transmitted to arm 49. However, when the carrier frame 43 and hence the pin 42 is placed at an angle to the vertical, the slider 40 has a horizontal component. The driving lever 34 is thus given this component of motion which in turn oscillates the rock shaft 52 through the crank 49, which in turn oscillates bellcrank 60 about fulcrum 61 by way of lever 57. The amplitude of oscillation transmitted to the rock shaft 52 and thus to the trimmer blade 119 is therefore controlled by the angular relationship of the carrier frame 43 as established by the control shaft 80.

The angle through which lever element 89 is turned determines the elevational position of fulcrum 61, and thus the center of oscillation of the bellcrank 60 and trimmer blade 119.

When it is desired to sew without trimming, the operator selects notch 76d which sets the carrier frame 43 and pin 42 vertically. In this position, no horizontal component of motion is transmitted to the lever 49 and the blade does not oscillate. The control shaft 80 in this position also lowers the blade 119 to the position shown in FIG. 11a.

The timing of the trimmer blade oscillation is such that it moves up when the needle is driven upwardly as seen in FIG. 9, and it moves down to sever a marginal edge 122 of the lower ply when the needle is driven downwardly, as seen in FIG. 10.

We claim:

1. In a sewing machine having a frame, and stitch forming instrumentalities including a reciprocating needle mounted in said frame for forming a seam at a stitching location, an improved trimming mechanism including a trimmer blade mounted for cooperation with a ledger blade adjacent to said stitching location for selectively severing a marginal edge of material being seamed and capable of varying the bite of the trimmer blade while the machine is sewing, comprising a control shaft rotatably mounted in said frame, operator-controlled means in operative engagement with the control shaft for selectively turning said shaft a controlled amount, means for pivotally mounting said trimmer blade for movement with said shaft, oscillatory means operatively connected to said pivotable mounting means for oscillating said trimmer blade in timed relation to said needle reciprocation, and means interconnectingthe control shaft andsaid oscillatory means for changing the amplitude of oscillation imparted to said trimmer blade.

2. In a sewing machine as recited in claim 1 including a rotating bed shaft driven in timed relationship to the needle reciprocation, wherein said oscillatory means comprises means for converting the rotational motion of the bed shaft into oscillatory motion, a driving lever connected to said motion converting means to be oscillated thereby, means operatively connecting said driving lever to said pivotable mounting means for pivotably oscillating said trimmer blade, and means on the driving lever for joining the driving lever to said interconnecting means.

shaft.

3. In a sewing machine as recited in claim 2 wherein said interconnecting means comprises a carrier frame joumaled for pivotal movement in the sewing machine frame, guide means mounted in said carrier frame interconnecting said carrier frame with the drivin lever joining means for controlling the path of oscillation 0 said dnvrng ever, and means mounted on said control shaft operably connected to said carrier frame for selectively'pivoting the same when the control shaft is turned to thereby change the angular relationship of the guide means.

4. In a sewing machine as recited in claim 3 wherein the means for connecting the driving lever to the trimmer blade mounting means comprises a rock shaft, first and second crank arms on said rock shaft, the first of said crank arms being pivotably connected to said driving lever to be selectively oscillated thereby, the second of said crank arms operably connected to said trimmer blade mounting means to oscillate said trimmer blade when said first crank arm is oscillated.

5. In a sewing machine as recited in claim 3 wherein said driving lever joining means comprises a slide member pivotably mounted on said driving lever, said slide member including means defining a hole, said guide means comprising a pin mounted at each of its ends in the carrier frame and passing through said hole such that said slide member is constrained to slidably oscillate along said pin, said driving lever being oscillated along a path determined by the angular relationship of said pin.

6. In a sewing machine as defined in claim 5 wherein said operator controlled means comprises a cam member pivotally mounted on said sewing machine frame, a follower member on said control shaft in contact with said cam, and operator biased means in engagement with said cam for selectively pivoting said cam to force said follower to turn the control shaft :1 controlled amount.

7. In a sewing machine as recited in claim 6 wherein the means for connecting the driving lever to the trimmer blade mounting means comprises a rock shaft, first and second crank arms on said rock shaft, the first of said crank arms being pivotably connected to said driving lever to be selectively oscillated thereby, the second of said crank anns operably connected to said trimmer blade mounting means to oscillate said trimmer blade when said first crank arm is oscillated.

8. In a sewing machine as defined in claim 7 wherein said cam member comprises a cam track having a plurality of discrete notches, each of said notches corresponding to a different amplitude of oscillation of said trimmer blade, one of said notches corresponding to a zero oscillation of said trimmer blade.

9. In a sewing machine as defined in claim 8 wherein said trimmer blade mounting means comprises a lever element on said control shaft, a bellcrank lever pivotably mounted on said lever element for oscillatory movement relative thereto, and means to secure the trimmer blade to one arm of said bellcrank, the other arm of said bellcrank being operably connected to the second of said crank arms.

[0. in a sewing machine as defined in claim 9 wherein said rock shaft is concentric with and joumaled on said control 11. In combination with a sewing machine as defined in claim 10, a material ply separator for intervening between the lower ply and an upper ply of material being seamed together so that the trimmer blade may act on and sever the lower ply only, comprising a member having a cutaway portion for providing clearance for said trimmer blade, and means to mount said separator on the sewing machine frame proximate to said stitching location in contact with the underside of said upper ply so as to prevent said upper ply from being contacted by said trimmer blade.

Claims

1. In a sewing machine having a frame, and stitch forming instrumentalities including a reciprocating needle mounted in said frame for forming a seam at a stitching location, an improved trimming mechanism including a trimmer blade mounted for cooperation with a ledger blade adjacent to said stitching location for selectively severing a marginal edge of material being seamed and capable of varying the bite of the trimmer blade while the machine is sewing, comprising a control shaft rotatably mounted in said frame, operator-controlled means in operative engagement with the control shaft for selectively turning said shaft a controlled amount, means for pivotally mounting said trimmer blade for movement with said shaft, oscillatory means operatively connected to said pivotable mounting means for oscillating said trimmer blade in timed relation to said needle reciprocation, and means interconnecting the control shaft and said oscillatory means for changing the amplitude of oscillation imparted to said trimmer blade.

3. In a sewing machine as recited in claim 2 wherein said interconnecting means comprises a carrier frame journaled for pivotal movement in the sewing machine frame, guide means mounted in said carrier frame interconnecting said carrier frame with the driving lever joining means for controlling the path of oscillation of said driving lever, and means mounted on said control shaft operably connected to said carrier frame for selectively pivoting the same when the control shaft is turned to thereby change the angular relationship of the guide means.

6. In a sewing machine as defined in claim 5 wherein said operator controlled means comprises a cam member pivotally mounted on said sewing machine frame, a follower member on said control shaft in contact with said cam, and operator biased means in engagement with said cam for selectively pivoting said cam to force said follower to turn the control shaft a controlled amount.

7. In a sewing machine as recited in claim 6 wherein the means for connecting the driving lever to the trimmer blade mounting means comprises a rock shaft, first and second crank arms on said rock shaft, the first of said crank arms being pivotably connected to said driving lever to be selectively oscillated thereby, the second of said crank arms operably connected to said trimmer blade mounting means to oscillate said trimmer blade when said first crank arm is oscillated.

10. In a sewing machine as defined in claim 9 wherein said rock shaft is concentric with and journaled on said control shaft.

11. In combination with a sewing machine as defined in claim 10, a material ply separator for intervening between the lower ply and an upper ply of material being seamed together so that the trimmer blade may act on and sever the lower ply only, comprising a member having a cutaway portion for providing clearance for said trimmer blade, and means to mount said separator on the sewing machine frame proximate to said stitching location in contact with the underside of said upper ply so as to prevent said upper ply from being contacted by said trimmer blade.