Patent GB-697370-A (GB)
Title: Improvements in sharpening devices
IPC: B24B3/54
Filed: 1951-11-16
Abstract: 697,370. Sharpening knives and scissors. MUNIZ, A. J. Nov. 16; 1951, No. 26848/51. Class 60. In apparatus for sharpening knives and scissors an abrasive disc carried by a motor shaft projecting beyond a.motor housing is protected by a cover provided with a pair of openings for the insertion of the blade of a knife first with one side and then with the other side against the disc and a further opening for the insertion of a blade of a pair of scissors, the openings extending at a predetermined angle to the tangent plane of the effective surface of the disc and having a length such that the line of contact between a blade to be sharpened and the disc is not longer than the radius of the disc. A housing 2, having a carrying handle 4 and rubber feet 5, encloses a motor 3 the shaft 11 of which projects through the front wall 8 of the housing. The abrasive disc comprises two disc parts 16, 17 supported on the cylindrical part 15 of a carrier 14 having a collar 13 mounted on reduced part 12 of the shaft; the parts are secured together by a disc 18 having a metallic hub 19 screwed on the end of the shaft. Plates 21, 22 together form an exterior stationary cover. Plate 21 is semi-circular and has a base 23 fixed by screws 24 to a platform on the front wall 8; plate 22 is fixed to plate 21 by screws. For the insertion of the blades of knives, a pair of openings 27, 28 are provided in the plates 22, 21; in the plate 22 is another opening 29 for the insertion of the blades of scissors. The openings 27, 28 are made in that quadrant of the cover at which the disc runs clockwise and upwardly so that the edge of an inserted knife blade is contacted from the cutting edge upwards; the opening 29 is placed in that quadrant of the cover in which the disc travels downwardly so that the blade is attacked towards the edge. The edges of the openings are fitted with small plates 30 of hard metal, such as cemented steel, secured by screws 31. The discs 16, 17 have annular abrasive surfaces 27', 28<SP>1</SP>; the edges of the openings 27, 28 extend along lines forming a predetermined angle with the tangent plane of the surfaces 27<SP>1</SP>, 28<SP>1</SP> so that a knife introduced into an opening contacts an abrasive surface at the cutting angle, e.g. between 4 degrees and 25 degrees. The cutting angle presented by the opening 29 is approximately 22 degrees. The openings extend between the periphery of the cover and a point near its centre so that a blade being sharpened may enter into contact with the discs 16, 17 to an extent not greater than the radius of the discs and preferably approximately onehalf the radius. The discs have openings or recesses 32 which allow the passage of a current of air to avoid excessive heating of the blades during shapening. The shaft may have a polygonal or other non- circular projection 33 for the coupling of any instrument which might require rotative motive power. The rear end of the apparatus has a base plug 34 so that the apparatus can be used with the shaft disposed vertically. A detachable screw or other plug 35 is provided to enable dust loosened from the abrasive discs to be removed from the base of the cover 21, 22.