Improvements in Machines for Sharpening the Blades of Lawn Mowers

1,195,869. Sharpening lawn mower blades. J. W. HARTLEY. 14 Oct., 1968 [14 Oct., 1967], No. 46952/67. Heading B3D. A machine for grinding the blades of lawn mowers of the type having a cylindrical cutter drum with a plurality of non-radial blades comprises :- (i) a main frame for supporting a traversing rotary grinding wheel; (ii) a sub-frame for supporting the cutting cylinder carrying the cutting blades; (iii) means for adjusting the position of the sub-frame vertically and transversely of the main frame; (iv) means for rotating the cylinder for trueing up the blades ; and (v) means for rotating the cylinder by hand during backing-off so that the grinding wheel traverses the whole length of each blade in turn to apply a bevel or taper on the trailing edge of each blade. A machine for grinding the blades a on a cutting cylinder A of a lawn mower A1 has a frame A2 on which a sub-frame b is adjustable both vertically, by a handle b4 and gearing b1, and transversely, by a handle b41 and a screw b42. Bars B, B1 have their ends located in slots b13 in the sub-frame, and are secured together by slotted arms and U-bolts. A lawn mower has the gear case, bottom knife plate, front roller and chain sprocket on the cutting cylinder removed and the mower is inverted and mounted with the rear roller resting on the bar B1. Brackets B2 are clamped by U-bolts b10 to the bar B and the mower is secured by bolts b2 passing through slots b3 in the brackets B2 and through the holes for the front roller of the mower. The driving spindle of the cutting cylinder is aligned with a head stock C and coupled thereto by a coupling c2. The main frame A2 supports a screw b5 driven by a belt 611 and engaging a split nut b6 on a bracket b7 supporting a carriage b8 travelling on rails b9 on the frame A2. A grinding wheel C1 mounted in the bracket b7 is driven by a motor c1. The grinding wheel C1 is positioned to engage a blade a on the cylinder A and the headstock rotates the cylinder, e.g. at 16 r.p.m. The grinding wheel C1 is traversed and grinds each blade to render all the blades truly cylindrical. The sub-frame is then raised and moved transversely. During backing off of each blade to reduce the width of the cutting edge the cylinder A is rotated by hand, e.g. by trimming one end c3 of the coupling c2, to maintain the trailing edge of each blade in turn in contact with the grinding wheel as it traverses. The cylinder may be removed from the mower and mounted in V-bearings affixed to th