US2822657A - Blade mounting for rotary lawnmowers - Google Patents

Description

Feb. M, 958 J. E. HAFFEE BLADE MOUNTING FOR ROTARY LAWNMOWRRS Filed March s, 195e n n n l l l l n I nite rates This invention relates to new and useful improvements in rotary lawn mowers, and has particular reference to the mounting means for attaching the blade or blade-carrying bar on the power driven shaft.

One important object of the present invention is the provision of `a blade mounting which, although made up and secured by a single screw threaded axially into the arent power shaft, does not depend on said screw to retain the Y blade in centered and balanced relation to the shaft. Instead the blade is centered on a relatively heavy portion of the mounting, independently of the screw. In previous mountings wherein the relatively weak screw itself provided lateral support of the blade, the screw often was bent if the blade struck an obstruction, with resultant unbalance of the blade. Such unbalance of the blade caused violent and often destructive vibration on continued rotation of the blade.

Another important object of the present invention is the provision of a blade mounting of the class described wherein the blade is permitted to rotate in its mounting, or vice versa, if the blade strikes an obstruction or if the drive shaft should turn in a reverse direction as on kickback of a gasoline engine driving the same, without loosening the screw. In previous mountings such loosening of the screw could occur, with the resultant consequences that the screw could become entirely disengaged and permit the blade to be thrown outwardly with danger to any bystander. This feature also reduces the possibility that the drive shaft itself will be bent by shocks thereto which occur when a blade strikes an obstruction.

A still further important object is the provision of a blade mounting of `the character described which is yieldably fracturable or bendable in response to certain types of shocks or blows to the blade caused by striking rocks, stumps, sidewalks, etc., in such a manner as to prevent the bending of the drive shaft. The blades and mounting are relatively inexpensive and easily replaced, while a bent drive shaft necessitates costly major repairs.

Other objects are simplicity and economy of construction, eiiiciency and dependability of operation, and adaptability for use with many types and sizes of blades.

With these -objects in view, as well as other objects which will appear in the course of the specification, reference will be had to the drawing, wherein:

Fig. 1 isa central vertical sectional view through a rotary laWnmOWer, with parts leftrin elevation, showing a blade mounting embodying the present invention.

Fig. 2 is an enlarged, foreshortened sectional view taken on line lI-II of Fig. 1, and

Fig. 3 is an enlarged fragmentary sectional view taken on line III-Ill of Fig. 2.

Like reference numerals apply to similar parts throughout the several views, and the numeral 2 applies to the frame of a rotary lawnmower, said frame being of inverted dish-shape and being formed of metal or other suitable material. Attached rigidly to the upper side of said frame, as by adjusting screws 4, is a power unit 6, which may be either an electric motor or an internal combustion engine. The drive shaft 8 of said power unit extends vertically downwardly through a hole 10 formed therefor in said frame, and has a cutter bar or blade 12 attached to the lower end thereof by means of a mounting device embodying the present invention and designated generally by the numeral 14. Said blade normally has the form of an elongated flat bar, secured at its mid-point in mounting l-i and disposed symmetrically thereto whereby it is dynamically balanced relative to `drive shaft 8. Blade 12 has lits opposite lateral edges sharpened respectively at opposite ends thereof, as indicated at 16, to form cutting edges. engaging wheels, not shown, whereby blade 12 is supported at mowing elevation above the ground, and with suitable propelling or guiding means, also not shown.

Blade mounting i4 comprises a tubular metal body member 18 adapted to tit snugly over the lower end of drive shaft 8 in coaxial relation therewith. Said body is provided with an internal shoulder 2i) limiting the insertion of the drive shaft, and is secured against rotation on said drive shaft by a key 22. The lower end of drive shaft S is axially drilled and tapped as at 24 to receive a screw 25 as will be described hereinbelow. Body member 18 is provided with an integral peripheral ange 26 disposed in spaced relation above the lower end of the, body, the lower face of said flange being disposed accurately at right angles to the axis of the mounting. Said flange is provided `at its peripheral edge with an upstanding integral lip 28, and body i8, ilange 26 and lip 28 are joined by a plurality yof Iangularly spaced radial fins 30 extending between said body and said lip and formed integrally therewith.

The portion of body 18 'extending below flange 26 forms a circular boss 32-over which blade 12 is tted, a hole 34 being formed centrally in the blade for this purpose. This hole should t closely but freely over the boss. A planar washer 36 having the same diameter as ilange 26 1s secured against the lower face of boss 32 by screw 25, the face of said boss being smooth and unbroken except for the hole 3S formed therethrough to receive said screw, 1n order to insure a broad metal-to-metal contact between the boss and the washer. Washer 36 may thus be considered as a flange attached to the body and corresponding to ange 26, except that it is disposed below instead of above the blade. Also disposed 4on boss 32 are a pair of compressible rubber washers lil disposed respectively between blade 12 and ilange 26, and between blade 12 and washer 36. Said rubber washers are of such `density and thickness that they are compressed as washer 36 is drawn up tight against boss 32 by screw 25. A second washer 42 is also carried on screw 25, between washer 36 and the head of the screw. It is smaller in diameter than washer 36, and may be equal to or slightly larger than the diameter of boss 32.

The mounting as described is believed clearly to accomplish the objects firstly above outlined. Firstly, it is apparent that the blade is centered and balanced on boss 32 of the relatively large and strong body member, `and does not depend in -any way on the relatively small and weak screw 25 for lateral support. Thus the blade is much more strongly supported against being knocked oil? center relative to the drive shaft if said blade should strike a rock or other obstruction. In previous mountings wherein the blade is centered on the screw, any such lateral blow could comparatively easily bend the screw and thus unbalance the blade, with the result that continued operation would cause a radical and often destructive vibration.

Secondly, the mounting as shown will permit rotation of the blade in its mounting without loosening screw 25. Screw 25 has a right-handed thread, and the blade turns in a clockwise direction as viewed from above, so that Patented Feb. 11, 1958 Mower frame 2 is provided with suitable ground-r any normalrresistance to rotation of the blade will tend to tighten the screw. Nevertheless, -under certain circumstances, such as when a kick-back or reverse rotation occursV in power unit 6, if said unit isa gasoline engine, or when the blade rebounds in a reverse direction after striking an obstruction, there may be a pronounced tendency for the blade rotation to be transmitted through washer 36 to the screw, and to loosen the screw, with the danger that the screw will eventually be disengaged and the blade thrown. 'This will not occur in the present device since the blade is held only frictionally between rubber washers, and will slip therebetween before sutiicient torque strain is built up to cause washer 36 to turn relative to boss 32, since the contact between said washer and boss is metal-to-rnetal and may be very tight. The proper frictional grip on the blade provided by rubber washers 40 may be regulated by providing washers of the proper yieldability and thickness, although this has not been found particularly critical. The mounting can easily be adapted to use with thicker or thinner blades by the substitution therein of thicker or thinner rubber washers. Also, the frictional blade mounting permits the shaft 8 to continue rotation, at least for a short time, in the event the movement of the blade is arrested by striking an obstruction. This has been found to reduce substantially the possibility that such an impact might cause bending of shaft 8.

Thirdly, it will be seen that if either end of the blade is deflected forcibly upwardly or downwardly by striking an obstruction, `and this has been found to be an occurrence commoner by far than the simple stoppage of the blade by a square impact, the upward or downward strain of the blade will be transmitted either to flange 26 of the body member, or to the flange constituted by the rim portion of washer 36. The strength of these flanges, relative to shaft 8, is such that they will yield, either by bending or cracking, before shaft 8 is strained sufficiently to be permanently bent. Continued upward or downward deflection of the blade will of course bend the blade, but the transverse line of bend of the blade will then be located directly at the periphery of body 18 (or the periphery of washer 42), and not at the periphery of flange 26 or washer 36. The bending force on the blade will thus have a much smaller moment tending to bend shaft 8, and the shaft will be protected against damage. it would of course be possible to protect shaft 8 against damage in these circumstances by using a lighter, thinner blade, or by notching or otherwise weakening the blade, but this is objectionable as the blade is then much less rugged and l serviceable. The present construction permits the use of a rugged, heavy blade without endangering the shaft. A square impact of the blade against an obstruction, without upward or downward deflection, might still cause bending of the shaft. However, as previously stated, this has been found to be a relatively rare occurrence and even in such rare cases the likelihood of bending the shaft is materially reduced by the fact that the shaft may continue to turn `due to its frictional attachment to said blade.

The inventor has heretofore formed body 18 and flange 26, of a light, inexpensive, but relatively Weak metal such as produced by die-casting or the like, in order to render the replacement thereof when damaged as inexpensive as possible. With such metal, it has been found desirable to reinforce flange 26 by webs 30. The yield- `ability and strength of the flange may be regulated by varying the size, number and spacing of these webs. However, this is not an essential feature, and if the body and its flange were formed of steel or other stronger metal as is washer 36, such reinforcement would be unnecessary. The use of additional washer 42 prevents the possibility` that if washer 36 were bent downwardly by the blade as described above, it might bend at screw 2S. This could loosen washer 36 from boss 32, permit ting relative rotation thereof, and might also bind or crimp the screw so that it would turn with the washer 36, with consequent danger that the screw might become disengaged from the shaft. Washer 42 confines the bending of Washer 36 to an area outside of the contact area between washer 36 and boss 32, and thereby prevents the occurrence just describe-d. The same result could be accomplished by thickening the central portion of washer 36, but the use of two simple planar washers is more economical.

Although I have shown and described a specic embodiment of my invention, it will be readily apparent that numerous changes of structure and operation could be made without departing from the spirit of the invention as defined by the scope of the appended claims.

What I claim as new and desire to protect by Letters Patent is:

l. In combination with -a lawnmower including a power driven vertical drive shaft, a mounting body having a socket formed in the upper end thereof in which the lower end of said drive shaft is engaged, an elongated blade bar having a central aperture formed therethrough through which said body extends, a fixed ange carried by said body above said blade bar, a screw extending upwardly through said body and threaded into said drive shaft, a detachable ilange constituting a planar washer secured against the lower end of said body by said screw, said washer being held in non-rotating relation to said body by reason of metal-to-metal contact therebetween, and a pair of friction washers disposed respectively between said blade bar and said fixed flange and between said blade bar and said detachable ange, said anges pressing said friction washers against said blade bar whereby rotation of said blade bar relative to said body is yieldably resisted.

2. The structure as recited in claim 1 with the addition of means reinforcing the central portion of said detachable flange washer against bending, and wherein the edge portion of said washer and said xed flange are suiciently thin in a direction parallel to the axis of the drive shaft to possess substantially less bending strength than said drive shaft, whereby upward or downward force on either extended end portion of said blade bar will cause bending of one or the other of said flanges, rather than bending of said drive shaft.

References Cited in the file of this patent UNITED STATES PATENTS 2,651,530 Blydenburgh Sept. 8, 1953 2,707,362 Thelander May 3, 1955 2,721,438 OMalley Oct. 25, 1955

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