Patent GB-726638-A (GB)
Title: Improvements in or relating to sewing machines
IPC: D05B69/30
Filed: 1953-09-17
Abstract: 726,638. Eccentrics; connecting rods. UNION SPECIAL MACHINE CO. Sept. 17, 1953 [Sept. 18, 1952], No. 25675/53. Class 122 (1). [Also in Groups VII and XXXIV] An eccentric or crank mechanism in a sewing machine drives an oscillating member through a pitman and is such that the path of the driven end of the pitman has a component parallel with the axis of the shaft carrying the eccentric or crank, certain parts of the coacting surfaces of the pitman and the crank or eccentric being relieved to permit rocking of the pitman about an axis transverse to the shaft. Fig. 3 shows a pitman 40, for example for actuating a needle-operating lever, with a strap 52 surrounding a crank-pin 53 on the shaft 50, roller bearings 54 being interposed between the surfaces of the strap and the pin and being located axially by small flanges on the strap. The bearing surface of the pin is relieved at two portions 60 on one side and corresponding portions on the other side, so that lateral rocking of the pitman is permitted when its axis is in line with these portions; in the form shown, this is when the crank is horizontal, the mechanism being so arranged that when the pitman is at the ends of its stroke it is perpendicular to the shaft and thus those portions of the crank-pin surface taking the load at that time (at which the load, being mainly due to inertia, is a maximum) can be cylindrical, so providing the maximum load-carrying area. In a modification, Fig. 9, permitting somewhat greater rocking of the pitman, the crank-pin surface is cylindrical on its inner side, which takes the inertia load at the top or bottom of the stroke, and is relieved over the greater part of the remaining circumference. As an alternative to relieving the crank-pin surface, the surface of the pitman strap may be relieved, for example at the top on one side and at the bottom on the other side. The pitman strap has axial lugs engaging between the crank webs to prevent binding when it tilts. Similar means for allowing rocking of the pitman may be applied to an eccentric, as in Fig. 14, which shows a variable eccentric of the kind described in Specification 676,955, comprising inner and outer relatively-adjustable eccentric members 91, 92, the latter being angularly adjustable on the shaft to vary the stroke of the eccentric but being normally rotated with the shaft through a friction member 100 engaging it and a disc 98 fixed to the shaft. The disc 98 drives the eccentric member 91 by means of a flatsided head of a pin 103 engaging a notch in a flange 101 of the member (to allow for relative radial movement) ; the engaging parts are surrounded by a cover 97 fixed to the disc 98 and slidably engaging the flange 101 to locate the member 91 axially under the pressure of the spring 95 which maintains the members 92, 100, 98 in contact. The pitman is preferably formed of two tubular members 39, Fig. 2, having welded or otherwise secured to them caps a, b, the caps b being screw-threaded into the lower strap half 52 and the caps a receiving screws securing the strap 38 of the upper joint.