GB888971A - Device for sewing button-holes - Google Patents

Abstract

888,971. Sewing machines. SDRUZENI PODNIKU TEXTILNIHO STRAJIRENSTUI. April 28, 1959 [April 28, 1958], No. 14479/59. Class 112 A zig-zag sewing machine adapted to sew buttonholes comprises a first driven cam serving to oscillate the needle bar via a linkage system, an element located within an arcuate groove in one of the links and adjustable therein by means of a second driven cam and also by manual control means to vary the stitch width, and a third driven cam adapted to vary the mean position of the stitches, the arrangement being such that the profiles of the second and third cams determine the relative lateral proportions of the buttonhole, and the size of the buttonhole can be varied by the hand control means without altering said relative proportions. A three-lobed cam 2, carried by a rotary shaft 43, is embraced by a fork 3 on a bar 4. One end of bar 4 is connected by a link 7 to one end of a curved arm 9 pivoted at a fixed point 11. The other end of bar 4 is pivoted to one arm of a bellcrank lever 19 pivoted at a fixed point 20, the other arm of lever 19 carrying a roller 18 biased by a spring 21 into engagement with a cam 17. Arm 9 is formed by a spring 21 into engagement with a cam 17. Arm 9 is formed with a slot 10 slidably holding a pin 12 connected by a link 13 to one end of a two-armed lever 14, the other end of which is connected by a linkage 15, 16 to the pivoted gate of the needle bar 1. Pin 12 is embraced by a fork 30 on one arm of a lever 29 pivoted at 31 to one end of a bar 32 slidable in a fixed guide 33. The other arm of lever 29 carries a pin 28 embraced by a fork 27 on a lever 24 pivoted at a fixed point 25. Lever 24 carries a roller 23 biased by a spring 26 into engagement with a cam 22. The other end of bar 32 carries a pin 34 embraced by a fork 35 at one end of a two-armed lever 36 pivoted at 37. The other end of lever 36 has a fork 38 embracing a pin 39 on a block 40 adapted to be moved linearly by means of a screw 41 turned by a knob 42. Rotation of cam 2 serves to oscillate arm 9 about its pivot 11 for swinging the needle bar gate via the linkage 13, 14, 15, 16. Adjustment of cam 17 for altering the angular position of lever 19 serves to alter the mean angular position of arm 9 for varying the centre line of the stitches. Adjustment of cam 22 for altering the angular position of lever 24 serves to alter the angular position of lever 29 and thereby to move pin 12 along slot 10 for varying the stitch width. Moving block 40 by means of knob 42 swings lever 36 and thereby shifts the pivot 31 of lever 29 along the guideway 33. Pin 12 is thereby moved along slot 10 for varying the basic width of the stitches. The machine is adapted for sewing the form of buttonhole shown in Fig. 8. With the cams 17 and 22 in the positions shown in Fig. 3 the left hand stitches O<SP>1</SP> of the buttonhole are sewn, the centre of the stitches being on the line A. Cam 17 then moves the centre line to the position C and cam 22 increases the stitch width to O<SP>3</SP> for sewing the rear barring stitches. Cam 17 then shifts the centre line to the position B and cam 22 returns to its original position for sewing the right hand stitches O<SP>2</SP>. Finally the cams move to positions appropriate for sewing the front barring stitches.