GB402223A - Improvements in or relating to lawn-mowers - Google Patents

Abstract

402,223. Lawn-mowers. BERGWALL, E., Võrnamo, Sweden. Oct. 7, 1932, No. 27916. Convention date, Dec. 3, 1931. [Class 6 (ii).] A lawn-mower comprises cutting blades 1a, 1b, 1c mounted on arms 6-9 on a shaft 3 and forming a cutter wheel 1 adapted to rotate in such a direction that the blades approach a fixed cutter 5 towards its bottom face. The blades 1a. are plane or substantially plane and each has such a position in a plane intersecting the axis of rotation of the cutters at an acute angle that their plane sides at each point along the cutter edge form an acute angle with that tangent to the surface of rotation drawn in a direction from said point reverse to said direction of rotation and lying in the plane of rotation of said point. The cutter edges are thus formed by intersection of the planes of the blades with the surface of rotation and are thus curved corresponding to conic sections. Where such surface is cylindrical, each cutter must lio entirely within the quadrant of an ellipse. The angle of inclination of the blades to the tangent is preferably less than'60‹ and may vary from 15‹ at one end of a blade to 35‹ at the other end. The blades 1a ... are mounted on pairs of the arms 6-9 by screws 13, 14, Fig. 6, on the arms having flattened necks 16 adapted to engage keyhole slots 11, 12 in the blades. Springs 15 are inserted between the blades and the arms, forked ends of the springs engaging the necks 16 and a projection 19 registering with an aperture 18 on the blade. The resilience of the mounting may be increased by lengthening the necks 16. That edge of a blade which first meets the fixed cutter may be rounded. When the blades are rectangular, the arms 6-9 are relatively displaced angularly in order to provide the inclintion of the blades. Blades in the form of truncated triangles may be provided thus obviating this displacement. The blades may be reversible, having cutting edges on opposite edges. The fixed cutter may be formed of invertable blades arranged in steps and having concave edges curved to correspond with the surface of rotation.