Patent GB-835386-A (GB)
Title: Improvements in or relating to sewing machines
IPC: D05B35/08
Filed: 1958-07-08
Abstract: 835,386. Sewing machines. UNION SPECIAL MACHINE CO. July 8, 1958 [July 25, 1957], No. 21838/58. Class 112 Differential fed by dogs. - A sewing machine comprises closely adjacent main and differential feed bars supported for pivotal and sliding movement at their rear ends, first eccentric means on a rotary shaft for imparting feed lift movements to the front ends of the feed bars, second eccentric means on said shaft, a forwardly extending pitman which co-operates with the second eccentric means and is directly connected to the main feed bar for imparting feed advance movements thereto, a rearwardly extending second pitman which co-operates with the second eccentric means, and connections between the rear end of the second pitman and the differential feed bar for imparting feed advance movements thereto and for enabling the stroke thereof to be varied relatively to that of the main feed bar. It is stated that the arrangement of opposed pitmans enables the stroke of the differential feed bar to be varied over a wide range. Tne main feed bar 25 in an overedge, differential feed sewing machine is formed at its rear end with a slot 32 slidably embracing a block 33 pivoted on a fixed pin 35, and is formed at its front end with a slot slidably embracing a block 39 journalled on an eccentric sleeve 40 provided on a rotary driving shaft 12. The differential feed bar 28 is similarly formed at its rear end with a slot slidably engaging a block pivoted on pin 35. The front end of bar 28 is slidably supported on a flange 51 projecting horizontally from bar 25, and is retained thereon by a block 52 secured adjustably to bar 25 by a screw 53. Eccentric 40 thereby imparts feed lift movements simultaneously to the feed bars. The main and differential feed dogs 20, 21 are secured to their respective feed bars by screws 24, 26a passing through vertical slots 23, 26, whereby the feed dogs may be adjusted vertically to effect a slight variation in their feeding strokes. An additional feed dog 22, secured adjustably by a screw 29, and slot 30, to the main feed bar, is arranged to co-operate with the thread chain formed between successive work pieces. A pitman 56 is journalled at its rear end on an eccentric sheave 56 on shaft 12, and is pivoted at its front end at 59 to the main feed bar 25 for imparting feed advance movements thereto. A pitman 61 is journalled at its front end on an eccentric sheave 60 on shaft 12, and its rear end is pivoted at 65 to a swinging arm 66 pivoted on a fixed pin 69. Arm 66 is formed with a curved slot 70 slidably receiving a block 71. A link 74 connects the latter to a pin 44 which extends from feed bar 28 through a slot 46 in bar 25. The position of block 71 in slot 70 thereby determines the amplitude of the feed advance movements of the differential feed bar 28. Block 71 is connected by a link 78 to one end of a lever 79 biased by a spring 83 to urge block 71 to the upper end of slot 70. The other end of lever 79 is connected by a chain to a treadle or the like. Eccentric sheaves 55, 60, are detachably connected, by means of Keyways formed therein and a key 54a, to an eccentric end portion 54 of shaft 12. The sheaves may thereby be replaced by other sheaves of greater or less eccentricity. Presser feet; presser bars, lifting; work guides. A presser bar 92, adapted to swing about respective horizontal and vertical axes, is biased downwardly by a spring- urged plunger 92a, and carries a presser foot 91 which co-operates with the main feed dog 20. A pin 93 on the presser bar enters a groove in the presser foot and is held releasably therein by a detent 94 pivoted on a screw 95 carried by the presser foot. A blade 96, co-operating with the differential feed dog 21 is carried by a horizontal bar 97 journalled in a bracket 98. Bar 97 is acted upon by a torsion spring to bias blade 96 downwardly, and carries an arm 107 connected by a chain to a treadle or the like for raising blade 96. Bracket 98 is pivoted under a plate 102 on a vertical bolt 101, and can thereby swing through 180 degrees after overcoming a spring detent 104. The edge of the work is guided by channel-shaped guide adjustably mounted on the work table. Folding guides. A guide for folding a strip of tape around the work edge is in the form of a channel member 113 provided at its inner end with an inwardlyextending flange 113a. Co-operating with the channel is a tubular guide 120 for an edge-reinforcing cord. Channel 113 is carried by a flat arm 114 secured adjustably to a flat arm 116 pivoted on a bolt 117 carried by plate 102. A spring mounted on bolt 117 biases arm 116 against plate 102. Arm 116 normally abuts a stop 119 on plate 102. Specifications 672,098, 691,894 and U.S.A. Specification 2,730,060 are referred to.