Patent GB-757256-A (GB)
Title: Improvements in lockstitch sewing machines
IPC: D05B73/12
Filed: 1954-05-07
Abstract: 757,256. Sewing - machines. UNION SPECIAL MACHINE CO. May 12, 1954. [June 15, 1953], No. 13834/54. Class 112. Lock-stitching.-In a rotary hook sewing- machine the opening of the gap between shoulders on the bobbinholder and its retainer for passage of the needle - thread is produced by the inertia effect of a slight eccentricity of the centre of rotation of the bobbin-holder in relation to that of the hook body; this effect may be supplemented by that of arranging the centre of mass of the bobbin-holder eccentrically to its centre of rotation relative to the hook body. The centre of rotation of the bobbin-holder may be made eccentric by making the shaftreceiving bore in the hook body hub eccentric, by making the raceway eccentric in the hook body, or by making the hook-receiving end of the shaft eccentric; with the last-mentioned method, the direction of eccentricity in relation to the position of the hook beak may be altered by angular adjustment of the hook on the shaft, provided that compensating adjustment of the shaft relatively to its driving gear is made to preserve the timing of the hook in relation to the needle. The eccentricity is preferably about 0.01 inch, but may be between 0.015 and 0.005, or even less in certain cases. When the bobbin-holder has a pair of shoulders receiving between them a projection on the throat-plate or other fixed part, the direction of the eccentricity is preferably about 135 degrees in rear of the radius through the hook beak, but may be anywhere between 90 and 135 degrees in rear of the beak, or in certain conditions within wider limits. If the single projection is on the bobbin-holder and the two shoulders on the fixed part, the eccentricity should be between 30 degrees behind and 45 degrees in front of the beak, or under certain conditions within wider limits; the preferred direction is in line with the beak, but as the raceway is cut away here to allow the passage of the thread this arrangement is not practical, and the direction 45 degrees ahead of the beak is better. If the gap between the pair of shoulders in either case is so wide that the projection never moves into contact with one of them the permissible range for the direction of eccentricity is somewhat wider; in such cases one of the shoulders could be dispensed with, but is preferably retained to ensure correct placing of the projection. The offsetting of the centre of mass of the bobbin-holder from its geometrical centre may be produced by arranging extra metal at suitable points of its periphery, by inserts of heavy metal such as lead, by cutting away part of the bottom of the holder, or by making holes in its side wall; any of these methods may be used in combination. The amount of offset is between <1>/64 inch and “ inch, preferably about # inch; its direction is preferably opposite to that of the gap to be opened, but may be up to 45 degrees, or even 90 degrees in some cases, on either side of the preferred position. The raceway of a vertical axis hook body is closed partly by a flange on the body and partly by a half-annular retaining member; it is cut away for about 90 degrees in the neighbourhood of the beak. The bobbin-holder, in the form shown in Fig. 9, has a flange 62 at the top, cut away to form shoulders 63, 64 to engage a fixed rotationpreventing projection, and its bearing rib 75 is cut away at 76 for about 60 degrees to facilitate the passage of the needle-thread; the bottom is cut away, leaving only the portion 82 to displace the centre of mass to a point 79; the bobbin is held in place by a spring-urged arm 61b. Lubricating.-Lubricant is fed up an axial bore in the hook shaft from an adjacent reservoir by suitable pumping means, such as a helicallygrooved stationary rod in the bore, and passes thence through two radial passages to the raceway, one passage entering the raceway near its beginning and the other in a direction substantially the same as that of the eccentricity of the centre of rotation of the bobbinholder in the hook body. Specification 743,637 is referred to.