Patent GB-1007478-A (GB)
Title: Improvements in zig-zag sewing machines
IPC: D05B19/00
Filed: 1962-11-29
Abstract: 1,007,478. Sewing machines. FRATELLI BORLETTI S. P. G. Nov.29, 1962 [Dec. 2, 1961], No. 45221/62. Heading D1G. In a zig-zag sewing machine having a cam cooperating with a follower the movements of which are transmitted via a link to the needle bar for effecting transverse movements of the latter, and also having means for varying the stitch width, the follower lever is formed in two parts one carrying the follower and the other a fork for actuating the link, the relative angular position of the parts about a common pivot being variable against the bias of spring means tending to restore the parts to a predetermined relative position, and means are provided having a manual control and adapted to limit the movement of the part carrying the fork in one direction or the other so as to enable all or part of the preselected stitch width to be used for producing the bars and sides respectively of a buttonhole. A cam 3, driven by gears 4, 5 from the arm shaft 1 of a sewing machine, co-operates with a follower 8 which is carried by one arm of a twoarmed lever 9 pivoted on a fired pin 10, a spring 7 biasing follower 8 towards cam 3. One arm of a two-armed lever 12, also pivoted on pin 10, carries an adjustable stud 20 biased by a spring 23 against a lug 22 on the other arm of lever 9. Said arm of lever 12 is formed with a fork 17 which embraces a pin on a bracket 66 pivoting about a pin 65. A pin 64, slidably mounted in bracket 66, is connected by a link 18 to the needle bar gate, and is carried by a link 71 pivoted at 70 to one end of a lever 68 fulcrumed on a fired pin 69 and provided at its other end with a handle 67. Manipulation of lever 68 thereby serves to alter the distance Z between the axes of pins 64 and 65 for varying the stitch width. The other arm of lever 12 has adjustably secured thereto a fork 24 which embraces cams 25 and 28 fixed to a spindle 26 carrying a manually-operable knob 27. The latter is marked with symbols in four positions a, b, c, d displaced one from the other by 90 degrees and co-operating with a fired pointer 53. With knob 27 in position a, cam 25 engages the lower arm 24<SP>1</SP> of fork 24 to restrict the movement of follower 8 to the upper portions of the lobes 6 of cam 3, and cam 28 engages a leaf spring 29 carried by a follower lever 30 to engage the latter with that one of a pair of cams 31 controlling the reverse feed. The machine thereby sews the left hand side of a buttonhole. In position b, cams 25 and 28 are free from fork 24 and spring 29, whereby full stitch width is produced and a spring 33 engages follower lever 30 with the cam 31 controlling forward feed, for forming the top bearing stitches of the buttonhole. In position c, cam 38 is free from spring 29 and cam 25 engages the upper arm 24<SP>11</SP> of fork 24. Levers 9 and 12 thereby more together while follower 8 is engaging the lower portions of the lobes 6, lever 12 thereafter being arrested by cam 25 when lever 9 continues to move while follower 8 is engaged with the upper portions of the lobes 6, owing to the separation of lug 22 from stud 20 against the bias of spring 23. The right hand side of the buttonhole is thereby formed. In position d, cam 25 is free from fork 24 and cam 28 engages spring 29, for forming the bottom bearing stitches of the buttonhole. The arrangement is such that lever 9 performs half an oscillation for each revolution of shaft 1. With a twelve-lobed cam 3, as shown, shaft 1 performs 24 revolutions for 1 revolution of cam 3. Shaft 1 will perform two revolutions for one revolution of a single-lobed cam. In modifications the arms of the fork 24 are separately adjustable, and spring 29 is associated with a rigid strip to prevent over-flexing of the spring.