CA1039512A - Cutter assembly for rotary lawn mower - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A cutter disc assembly for a rotary lawn mower in which the disc has a circular central portion and a peripheral portion with a shallow vertical wall in between penetrated by radial openings. A plastic pin is mounted cantilever-fashion in each opening. Each pin has a stiff shank protected by the disc and a stiffly resilient tip portion projecting beyond the periphery of the disc into cutting engagement with the grass. In the preferred embodiment the shank portion of the pin is protectively received in a groove. The groove has a rear wall against which the pin bends as the projecting tip of the pin strikes an obstruction as well as a front wall against which the pin bends upon rebound, the walls being curved in outwardly flaring shape thereby to support the shank of the bent pin substantially free of concentrated stress. Each groove has, in addition, a bridge or "ceiling" which serves as a guide surface to hold the pin in a downwardly-angled working position and to provide frictional damping. Protection of the tip portion of the pin in its bent state is offered by a ledge or radial extension on the disc either above or below the pin and which "wipes by" the obstruction, shielding the pin from abrading action. Upwardly swept radial vanes are provided above the periphery of the disc to generate air currents which agitate the grass as it is being cut and to provide a stream of air to move the clippings through the discharge chute.

Description

~)3~5~2 Many designs o~ mower blades have been devised, made of plastic or the like, for the purpose of overcoming the hazards of the conventional steel rotary mower blade.
Notwithstanding the fact that the cutter elements are made of plastic, the prior structures are capable of flinging missiles and capable of inflicting serious injury by direct impact upon the foot of the operator or upon the hand of a curious child. Thus there has been recent concentration upon weed cutters employing a thin, relatively limp whirling filament of plastic, namely nylon. It will suffice to say that filamentary cutters are ineffective in a thick stand of grass or against heavy or fiborus weed stalks and are subject to constant breakage.
It is accordingly an object of the present invention to provide a cutter disc assembly for a rotary mower Which reduces the hazards of steel blade cutter designs, which reduces the potential of serious injury either by missile or direct impact, and which is, at the same time, highly effective in cutting grass or weeds. It is a more specific object to employ a cutter disc with sockets for mounting cutter~elements in the form of plastic pins having relatively stiff shanks terminating in long flexible tip portions. The shank of each pin is anchored inwardly of the edge of the disc so that only `the flexible tip extends beyond the disc for severing grass and weeds with whiplash action but which, by reason of low mass, yields harmlessly when striking any more weighty object.
The disc itself, by reason of its circular shape, lS incapable of striking a blow. Consequently, the safety of the unit far exceeds that of conventional constructions.

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It is another object of the present invention to provide a cutter disc assembly which is, in addition, self protecting and in which the cutter elements, instead of being exposed and vulnerable, are shielded and fully protected against damage or breaking off, even under the most severe conditions, as, for example, encountered in the mowing of a wild area or a vacant lot strewn with heavy debris. It is a related object of the invention to provide a self-protecting cutter disc assembly in which the tip portions of the pins, upon striking obstructions are free to bend back toward, or into, the protection of the disc upon which ~hey are mounted, with the edge of the disc limiting the bending to safe degree.
It is a further related object of the invention to provide a safe cutter disc assembly having long flexible plastic pins which are mounted cantilever fashion inwardly o~ the disc periphery and in which each pin has means for insuring smooth bending of the shank to avoid concentration of stress. As a result, the service life of a pin is greatly extended, and the need for constant renewal, as in filamentary type cutters, is avoided.
It is a related object of the invention to provide a cutter disc assembly which is not only highly efficient and self-protecting, but which, by reason of the resilient yielding of the light, flexible cutter pins upon striking a pebblef piece of glass or similar foreign object, makes it substantially impossible for the object to be ejected, as a missile, from the mower housing. If ejection should, in rare circumstances, occur, the speed of ejection is in any event reduced to a :
level considerably less than with conventional blades.

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It is a specific object of the invention to provide a cutter assembly in which the shank of the pin is nested in a downwardly facin~ groove having a curved outwardly flaring rear wall against which the pin is bent upon striking an obstruction as well as a curved outwardly flaring front wall upon which the pin bends upon rebou:nd, the ef~ect in both cases being to distribute the bending to avoid concentrated stress which would result in eventual breakage. It is another specific and related object to provide a disc construction in which the ceiling of the groove is utilized to hold the tip portion of the pin in a downwardly-angled cutting position, with the engagement of the pin and ceiling serving to dampen pin movement.
Thus, the present invention is defined as a safe cutter disc assembly for a rotary lawn mower having a vertical drive shaft comprising, in combination, a disc having a central portion with provision for connection to the lower end of the drive shaft and a peripheral portion presenting a generally flat surface on its underside, at least one cutter pin on the disc arranged generally radially thereon, each pin being made of tough, resilient abrasion-resistant plastic and having a head and a stiff shank and terminating in a stiffly resilient tip portion, mounting means on the disc for engaging and supporting the shank of each pin cantilever-fashion adjacent the head so that only the tip portion of the pin projects radially out-wardly of the periphery for cutting of the grass as the disc is rotated, the mounting means being spaced sufficiently . inwardly of the periphery so that as the pin strikes a major : obstruction radially of the disc the pin may bend relatively harmlessly about its mounting means into an inwardly bent position in which the pin is increasingly shielded by the disc, and means for causing curvature to be smoothly distributed in the shank with avoidance of any sharply concentrated stress in ; ~ ~ 3 ~

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the pin as the tip portion of the pin strikes the obstruction, substantially the ~ntire shank of the pin being spacec~ upwardly from the underside of the peripheral portion of the disc and generally parallel thereto so that the shank of the pin is shielded against obstructions axially engaging the underside of the disc.
Other objects and advantages of the invention will become apparent upon reading the attached detailed description and upon reference to the drawings in which:
Figure 1 is a perspective view of a rotary mower including the present invention with a portion of the housing broken away to reveal the cutter disc assembly. ;
Fig. ~ is a perspective view of the underside of the mower of Figure 1.
Fig. 3 is a perspective top view of the cutter disc assembly.
Fig. 4 is a top view o the cutter disc assembly looking .
along the line 4-4 in Fig. 5.
Fig. 5 is a section taken along line 5-5 in Fig. 4.
Fig. 6 is an enlargement of a portion of Fig. 5.
Fig. 7 is an enlarged fragmentary underside view looking along line 7-7 in Pig. 6.

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Fig. 8 is an enlarged fragmentary top view looking along line 8-8 in Fig. 6 and showing th~ b~nding back of a cutter pin into the protection of the disc upon striking of a weighty obstruction.
Fig. 9 is a partial section similar to Fig. 6 but showing a modified structure.
Figs. 10 and 11 correspond to Figs. 6 and 8 but show substitution of a straight-sided pin as a modification of the invention.
Fig. 12 is a perspective view of the underside of a mower employing a modified form of cutting assembly.
Fig. 13 shows the top side of a cutter disc of Fig.
12.
Fig. 14 is a cross section of the cutter disc taken along the line 14-14 of Fig. 13 with a cutter pin in place.
` Fig. 15 is a fragmentary elevation of the cutter disc looking along line 15-15 in Fig. 13.
Fig. 16 is a fragment showing the underside of the disc at one of the pin positions with the pin shown both in its extended and bent condition. ~
Fig. 17 is a fragmentary elevation looking along the line 17-17 in Fig. 13 showing the overhanging ledge providing protection for a pin in bent condition.
Fig. 18 is a view similar to Fig. 16 but showing a modified form of the invention.
Fig. 19 is a fragmentary top view of th~ disc taken at one of the groove positions.
Fig. 20 is a radial section looking along line 20~20 in Fig. 19.

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Figs. 21-2~ are a series of parallel, trans-radial sections taken on corresponding section lines in Fig. 19.
Fig. 25 shows the underside of the portion of the disc shown in Fig. 1~.
Fig. 26 shows a preferred form of pin employed with the structure shown in Figs. 19-25.
Fig. 27 is an end view of the pin of Fig. 26.
Fig. 28 is a sectional view similar to Fig. 20 and showing the cooperating dies employed to form the disc.
Fig. 29 is a vertical section looking along line 29-29 in Fig. 28.
Fig. 30 is a view similar to Fig. 25 and showing the projected area relationships.
Fig. 31 is a fragmentary vertical section of a modified form of disc looking along linP 31-31 in Fig. 32.
Fig. 32 is a fragmentary top view looking along the line 32-32 in Fig. 31.
` Fig. 32a is a fragmentary section looking along line 32a-32a in Fig. 32.
Fig. 33 is a fragmentary perspective of a further modification of the invention.
Fig. 34 is a vertical section looking along line 34-34 in Fig. 33.
Fig. 35 is a vertical fragmentary section of a still further modification of disc looking along line 35-35 -; in Fig. 36.
Fig. 36 is a fragmentary top view looking along the line 36-36 in Fig. 35.
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1~)39S12 While the invention will be described primarily in connection with a preferred embodiment, it will be understood that we do not intend to be limited to the particular embodi~
ments shown but intend, on the contrary, to cover the ~arious alternative and equivalent constructions included within the spirit and scope of the appended claims.
Turning to Figures 1 and 2, there i5 shown a type of rotary mower in common use and to which the present invention is applicable. It includes a frame 11 in the form of a shallow inverted enclosure having an encircling sidewall 12, a set of wheels 13, a handle 14 to provide guidance, and an engine 15 which may, alternatively, be an electric motor, having a vertical drive shaft 16 which is conventionally tapped for receiving a clamping screw 17. A discharge chute 18 projects from one side of the housing to dispose of the clippings.
Secured to the drive shaft in horizontal position is a cutter disc 20 which carries the cutting elements. Such a disc, which is preferably molded of a durable and resiliently deformable plastic, has a circular central portion 21 (Figs.

3-5), a shallow wall or offset portion 22 and an annular outer portion 23. ~ecured axially in the center portion 21, to provide durability, is a metallic hub 25 which may, for example, be made of aluminum alloy. The hub, in addition to a central opening 26, has a set of peripheral openings 27 registering with projections 28 formed in the molded piece for locking the hub in place. Evenly spaced, radially extending openings, or sockets, 31, 32 are formed in the shallow wall 22 for receiving cutter pins 33, 34, respectively.

1~39512 Referrin~ to a typical cutter pin 33, as shown in Fig. 6, it includes a head 35, a shank 36 and a long tapering flexible tip portion 37 terminatillg in an outer tip 38. The shank portion 36 of the pin is di~nensioned to fit snugly, cantilever fashion~ in the radial opening 31. The opening 31 serves as a mounting means holding the pin in a position in which it is spaced upwardly from the undersurface of the outer portion of the disc. More specifically, the opening 31 is formed in the lower portion of the shallow wall or offset 22 so that the annular outer portion 23 of the disc closely underlies and protects the relatively stiff shank portion of the pin while the tip portion of the pin projects beyond the periphery 24 of the disc into cutting engagement with the grass G. Because the shank 36 of the pin 33 is spaced well inwardly of the periphery 24 of the disc, approximately one-half of the length of the pin being included within the disc perimeter, the shank of the pin is completely shielded against radially encountered obstructions, the tip portion 37 of the pin being free to bend incr~asingly into the protection afforded by the disc upon stri~ing of an obstruction. At the same time, the shank of the pin, by reason of its position above the underside of the disc, is shielded against obstructions which engage the disc axially. ~hile about one-half of the length of the pin extends beyond the perimeter of the disc, preferably the - length of the pin is at least one and one-half times the radial width of the outer portion of the disc utilizing the - pin. In any event the pin should project from the dlsc at ~ least a half inch and preferably at least two inches.
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In accordance with one of the aspects of the present invention, there are located adjacent the radial openings 31, 32, upstanding radial backstops 41, 42, respectively, securely joined to the disc and having a retreating curvature for engaging and providing lengthwise-distributed support for the associated pin during its backward bend and serving as air vanes.
Thus, taking the backstop 41 by way of example (Fig. 6), it has a lower edge 43 which is integrally joined with respect to the peripheral portion 23 of th~ disc and an inner edge 44 which is integrally joined with respect to the shallow wall 22 to provide radial reinforcement.
In carrying out the invention, the backstop is shaped to present a curved face 45 (Figs. 7 and 8) lying adjacent the pin 33 and which terminates in an end 46 which is spaced inwardly from the periphery 24 by a clearanee distance shown at D in Fig. 8.
Thus when an obstruction is encountered, for example, in the form of a rock or pebble R, its mass applies reaction force against the pin 33, causing the pin to be bent back-in the most extreme case to the curved position shown "dot-dash"
in Fig. 8. Only the tip portion of the pin 33 is accessible to the rock or pebble, and since it is highly resilient, and of low mass, the backward bending takes place to relieve the foree before the force, indicated at F, can increase to a degree which might ereate a dangerous missile. ~
For the purpose of promoting radial air flow so that the elippings are blown clear of the disc, sector shaped through-openings 61 (Fig. 4a) may be formed in the eentral - portion 21 of the dise defined by radially extending spokes 62.

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:1'039S~2 The radially extending surfaces of the openings may be beveled as shown at 63 so t~at air is forced through the center portion of the disc by scooping action.
While the function has been described in connection with backstop ~1, it will be understood that backstop 42, which is diametrically opposite, acts in the same way. In the pre-ferred form of the invention two cutter pins 33, 34 are used.
However, the invention is not limited to use of two cutter pins and either a single cutter pin may be used or additional cutter pins may be spaced about the periphery of the disc, for example, cutter pins 33a, 34a with their associated backstops 41a, 42a (Fig. 4).
As one of the features of the present construction, the annular outer portion 23 of the disc, and the openings (for example opening 31) which register the pins, are not oriented perfectly horizontally but are, instead, angled downwardly at a shallow angle. The bottom surface of the disc may be angled downwardly by an angle ~ (Fig. 6) of at least 1 degree but preferably 2 degrees or more to form a shallow conical surface, while the opening 31, and hence the pin which it contains, is angled downwardly by a slightly greater angle ~ which may be on the order of 2 to 8 degrees, and preferably 4 to 5 degrees, the difference between ~ and preferably being no greater than 3 degreesO As a result, the outer tips of the pins lie at a lower level than the periphery 24 of the disc, to insure that cutting takes place at lower than disc level. Thus it is not necessary for the dlsc to dxag or brush against the standing blades of grass ~ in the cut condition. This, in turn, reduces the effort -~- 30 required to push the mower.
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It is a further feature of the present invention that the pins are angled with slight retreat, that is, opposite to the direction o~ rotation of the disc, b~ an angle ~ with respect to the radius as shown in Fig. 7, which angle is in the range of from 1 to 9" and preferably on the order of 6.
It will be apparent in view of the above that the cutting pins are protected in at least two different ways.
Because of the closely underlying annular portion 23 of the disc, any obstructions which may be encountered by the mower either radially or axially of the disc are prevented from having access to the shank portions of the pins which are relatively stiff and thus subject to breakage, if unprotected. Conversely any obstruction is limited to engagement by tke light, stiffly resilient tip portion of the pin which, bending backwardly about its backstop and into the radial confines of the disc, simply lets the object go by without developing a force capable of converting the object into a hazardous missile. To minimize transfer of momentum from the flexible cutting element, the weight of the projecting tip portion should be kept low, for example, below about 2 grams.
While a pin made of durable plastic, inherently protected by the disclosed disc construction, may be expected to have a long life, it is one of the features of the present invention that any pin may be replaced, without special tools, in a few seconds time. The head 35 of the pin, protected in its recess 39, may simply be pushed inwardly by grasping the outer end of the pin, without use of tools, or may be pried by any edged tool such as a screwdriver toward the dotted c . - . ..

~395:12 position shown in Fig. 6. Once the shank portion 3~ has been loosened, the pin may be retracted radially inwardly by the fingertips, and a new pin substituted.
Also in the preferred form of the invention, and to facilitate replacement of the pins when replacement becomes necessary, the outer, or peripheral, portion 23 of the disc is shown in the drawings and stated to be at a lower level than the circular central portion 21. In the broader aspect of the invention it is not essential that these two portions be at a different level and they may, indeed, be at the same level and form a radial continuation of one another provided that there is an axially offset portion at the junction between the central portion and outer portion providing a plurality of radially extending openings for registration of tapered pins, with the shanks of the pins being held, cantilever fashion adjacent the head, in a protected position extending just above the outer portion of the disc and with the pins being of tapered construction to secure smooth curvature and freedom from concentrated stress. Such a structure is shown in Fig. 9 in which the same reference numerals as in Fig. 6 have been used to designate similar parts with addition o~
subscript "c". Such construction may be used without a backstop.
The version shown in Fig. 9 possesses ~he same general advantages as the earlier version except that the pins are not quite so readily replaceable, requiring removal of the disc;
such captivity may be considered as an advantage in some applications. The wall 22c is preferably annular~
One of the features of the preferred form of the - - invention, emphasized above, has been the fact that each pin is of tapexed configuration, providing a high degree of ., .

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1~39512 flexibility and low mass at the tip but with a shank of relatively lar~er diameter resultin~ in a natural cantilever bending curvature which increases from shank to tip. However, it is understood that the invention may be practiced, if - desired, employing a cutter pin which is of substantially constant thickness, with a curved backstop to prevent concentration of bending stress. Such a "parallel~sided"
pin is illustrated in Figs. 10 and 11 which correspond to Figs. 6, 7 and ~ of the earlier embodiment, similar reference numerals being employed with addition of subscript "d". As in the earlier embodiments, the tip is protected hy bending retreatingly toward, or into, the confines of the disc periphery, the main difference being that the very tip of the pin tends to remain more straight than in the case of the tapered pin. One advantage of the parallel-sided pin is that the pins may be produced easily and cheaply by extrusion, with the head being formed, for anchoring purposes, by a separate terminal "heading"
operation. A further advantage is that there is more material available for wear and abrasion at the tip, which may be desirable when using the mower for heavy weeds, brush and the like, either with or without an increase in driving horsepower.
Turning to Fig. 12, there is shown another major embodiment of the present invention. Secured to the drive shaft in a horizontal position is a cutter disc 120 which carries the cutting elements. Such disc has a circular central portion 121 ~see also Figs. 13 and 14), an axially offset, or wall, portion 122, and a peripheral portion 123 of relatively thin average cross section extending from a dropoff 124 and presenting an outer edge 125. Centered in the disc is a mounting hole 126 :

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which may be optionally rein~orced b~ a metal reinforcing disc either secured to or molded in the disc structure.
- Evenly spaced openings 127, 128, 129 are provided in the wall portion 122 of the disc Eor receiving outwardly extending cutter pins 130. Each pin includes a head 131, a shank 132 and a stiffly resilient tip portion 133 terminating in an outer tip 134. The shank portion 132 is dimensioned to fit snugly, cantilever fashion, in a radial opening, for example, the opening 127.
In accordance with one aspect of the present invention, the annular outer portion 123 is formed, on its underside, with radially extending grooves in register with the respective openings for receiving the shanks of the pins, each groove having a downwardly angled "ceiling", a narrow neck portion, and a curved, outwardly flaring rear wall against which the pin bends as the projecting tip strikes an obstruction as well as a curved outwardly flaring front wall against which the pin may bend upon rebound, thereby to support the shank of the pin with the bending distributed along the length thereof for avoidance of concentrated stress.
Referring to Figs. 12-16, the grooves are indicated at 137, 138, 139 in respective alinement with the pin receiving ~ `
openings 127, 128, 129. Taking the groove 137 as representative, - -and referring to Figs. 13-16, the groove has a relatively narrow neck 141 having a width d which just slightly exceeds the diameter of the shank of a pin 130. The groove has a curved, outwardly ~ i -~ flaring rear wall 142 which is of increasing curvature and i which is tangentially faired into the periphery of the disc~

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~)395~2 The rear wall serves as a support or backstop for the shank of the pin as the tip portion of the pin strikes an obstruction, for example, in the form of a rock or other weighty piece of debris, R (Fig. 16), with the bending of the pin a~ainst the curved wall serving to distribute the bend smoothly in the shank of the pin so as to avoid the setting up of concentrated stress. The groove, in addition, has a front wall 143 adjacent the pin which is curved and outwardly flaring so that when the pin 130 is released, tending, because of its resilience, to rebound in the forward direction through an angle ~ , the pin bends about the curved front wall 143 with the bending, again, being distributed along the length dimension of the pin for avoidance of concentrated stress. The flaring curvature and the narrowness of the throat 141 produce a groove profile which, viewed vertically, is of "trumpet" shape. Since the curvature of the rear wall 142 causes it to merge smoothly into the periphery 125 of the disc, there is no abrupt discontinuity and the outer portion of the pin lS supported, in bent condition, upon the periphery.
In accordance with the present invention a substantially horizontal bridge is provided closely overlying the pin at the periphery of the disc, for the purpose of providing a ceiling surface for holding the pin in downwardly angled working position - over its range of lateral motion. Thus each groove includes an inclined but substantially flat "ceiling" 144 which is oriented outwardly and downwardly at a shallow angle thereby to provide a superimposed guide surface for not only holding the pin to the work but also for damping the lateral movement of the pinO
The angling of the ceiling from the horizontal, indicated at ~ in Fig. 14, is preferably within the range of 2 to 8.
' ~39S12 The projection of the tlp portion of the pin below disc level tends to insure that the cut grass will not drag on the bottom surface of the disc. The ceiling of the groove, - by its contact with the pin, overcomes the tendency of the pin to ride at a higher level, that is, to straighten out horizontally as a result of centrifugal force, tending to keep the tip portion of the pin at a desired cutting level in spite `
of variations in the centrifugal force. The ceiling is preferably of such height _ (Fig. 4), i.e. the groove 137 has such axial depth, as to contain the shank of the pin 130 and thus shield and protect it against abrasion from the underside which occurs when the rapidly rotating disc is, during the course of mowing, brought against some sharp projection on the surface of the ground. -In accordance with one of the aspects of the present invention the ceiling surfaces 144 of the respective grooves - 137, 138, 139 are formed by integral reinforcing "bridges"
` 147, 148, 149. Taking the groove 137, and its bridge 147, ~-as representative, it will be seen in Fig. 15 that the bridge 147 is a region of the outer portion 123 of the disc where the -disc has augmented thickness t. The region of augmented thickness extends peripherally over a length L which substantially overlaps the side walls of the groove, and extends radially from the dro-off 124 to the outer edge 125 of the disc. Each bridge thus serves to reinforce the disc to make it uniformly strong.
Referring to Figs. 13, 14 and 15, vanes 147, 158, , 159 extend from the central portion of the disc radLally outwardly for joining at their outer ends to the trailing edges of the respective bridges. The vanes are of special upwardly-swept ., , '. ~

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1(~39S12 cross section (Fig. 15) so as to create upward movement of the air in the immediate vicinity of the pins. Where the disc has no through-openings the vanes tend to cause a partial vacuum above the disc which causes the grass to be agitated as it is being cut. The vanes not only create desired air flow as the disc rotates at high speed, but also insure that the disc is reinforced in multiple directions, the bridges j providing peripheral reinforcement while the connected vanes provide radial reinforcement.
Lightness is enhanced hy specially constructing the wall portion 122 of the disc. Preferably the wall portion 122 is relieved by forming therein a circular groove 160 to define two ribs 122', 122" (see Fig. 14) which are concentric and radially spaced from one another over most of their length with alined openings so that the shank of the pin is ~ripped at longitudinally spaced regions to provide firm cantilevered support with a minimum of supporting structure.
However, to practice the invention it is not necessary for the wall 122 to be continuous or for there to be a single central recess for removal and replacement of the pinsO If desired, the wall portion 122, in which the pins are retalned, may be discontinuous and the wall may be formed of separate segments 165 formed at one end of an individual radial recess - 166 provided for each of the pins (see Fig. 18).
- In accordance with a further feature of the present invention there is provided, at the point where the rear wall 2 merges with the periphery 125 of the disc, a ledge which ` overlies the tip portion of the pin 130 as it is bent backwardly upon striking of an obstruction, the ledge merging at its .. . ....

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forward end with the periphery of the disc to facilitate the disc's "wiping by" the obstruction. Referring particularly to Figs. 13, 16 and 17 it will be noted that the bridge 147, along its trailing edge, is extended radially outward to form an overhanging ledge 161 which projects beyond the periphery 125 by an amount indicated at r (Fig. 13) which approximates the thickness of the pin at the point of exit. The briage 147 is preferably smoothly faired with respect to the periphexy of the disc at its leading edge indicated at 165 to insure that the obstruction is "cammed away" from the pin so that the pin is protected from radial abrasion. Since the amount of ~- material which forms the periphery of the disc is substantially ' greater than the amount of material used in the tip portion of the pin, the disc is well able to absorb the impact and forces of abrasion while imparting to the pin a much longer life in the face of rough usage.
While the shanks of the pins are protectivel~ enclosed in downwardly facing grooves, it is found that grooves remain free of crushed grass and other debris which might affect the freedom of the pin to bend backwardly and forwardly under stress.
The reason for such freedom is believed to be the fact that each pin, in the normal operation of the mowerj constantly works back and forth and the grooves, being of flaring shape, are inherently self-shedding.
In addition to holding the cutter pin 130 (Fig. 14) in a downwardly angled position, so that the cutting tends to take place below disc level, the ceiling 144 of the groove performs the function of damping the movement of the pin.
High speed movies taken under actual operating conditions ,~

1~3~S12 show that the pin 130 upon being released from an obstruction does indeed swing forwardly, due to its resilience and with a snake-like action, until it contacts the ~ront wall 143 of the groove just as illust~rated in Fi~. 16. Contact between the upper surface of the pin and the ceiling 144 of the groove, particularly in the region of the periphery, is assured because of the leveling action of centrifugal force, that is, the tendency of centrifugal force to radially aline the pin with its point of attachment. The force of the pin against the ceiling is not great enough to cause aggravated wear but is great enough to produce a frictional drag which inherently inhibits oscillation of the pin through a wide angle after striking an obstruction by reason of the pin's inherent resilience. The result is to produce a more even and consistent cutting action in spite of striking of obstructions and in spite of the uneven growth of the grass being cut.
It is one of the specific features of the present invention that the wall portion 122 which is divided by the annular groove 160 to form concentric ribs 122', 122" is ~ -intersected by radially spaced recesses in the top surface of the disc and which extend downwardly to form radially -alined saddle openings in the ribs. Thus referring to Figs.
~` 19 and 20, the disc, at each pin locatlon, has recesses 171, 172 which penetrate downwardly into the ribs 122', 122" to form alined, pin-receiving saddle openings 173, 174. The recesses 171, 172 are shown in profile in Figs. 21, 23. To reinforce the pin-receiving openings 173, 174, the annular groove 160 is radially "bridged" at each pin position by reinforcing walls 175, 176. In order to achieve clearance ., 1 1~3~5~Z
of the pin between the reinforcing walls, the underside of the groove is provided with an upwardly extending recess 181, shown in section in Fig. 22, and which a~ially overlaps the recesses 171, 172 to define a through-opening for the pin having the profile illustrated at 182, in Fig. 24.
While the bottoms of the recesses 171, 172 and 181 may be circularly profiled for reception of a pin of circular cross section, it is preferred to employ a pin of non-circular cross section as indicated at 190 in Figs. 26 and 27. As here - 10 shown the pin is of fluted construction having axially extending ribs 191-194, and provided with a head 195 and terminating in -a tip 196. Such a ribbed pin has a number of advantages, but it will suffice for present purposes to say that the pin shown in Fig. 26, registered in the ribbed opening 182 shown in Fig.
24, is non-rotatable in the opening so that the pin maintains a constant and predetermined orientation to provide a relatively narrow line of impact with the grass, while being reversible through 180. By use of alined saddle openings the pin may be positively anchored, and tightly cantilevered, using a minimum amount of material in the disc. Moreover, because of the saddle openings, the pin is gripped over only a limited amount of area, and on opposite sides, so that replacement of the pin is much easier than where the pin is wedged tight in an opening which encircles the pin. Finally, the access provided through the lower recess 81 permits entry of a prying tool for pin removal in those instances where the head of the pin has become damaged.
- The recesses 171, 172 and 181 can be readily formed in a two piece mold having mold sections Ml, M2 tFig. 18).
The mold section Ml is provided with projections 171a, 172a ~; -19-.: - - .
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while the lower section has a projection l~la, corresponding to -the similarly numbered recesses. It is preferred that the tips of the projections be of scaLloped profile to produce a cruciform opening (182 in Fig. ~4) for keyed reception of the cross section of the pin, but the tips of the projections may be circularly profiled if desired.
In describing the preferred form of the invention (which utilizes a notch of trumpet proile with a ceiling 144 in between) no mention has been made of the total area of the ceiling. In accordance with one of the aspects of the present invention the ceiling area is limited so that it is no more than about two to three times the area of the pin projected upon the ceiling. Thus, referring to Fig. 30, where the total cross hatched area of the ceiling is indicated at 144, such area should preferably not exceed the doubly cross hatched area of the pin 130 by a factor of more than 2 to 3. The result is - to produce a notch which is sufficiently wide for adequate flexing of the pin as it striXes an obstruction, and upon ` rebound, yet sufficiently small so that the notch is not capable of serving as a pocket or pouch for catapulting small stones and other debris.
In the preferred form of the invention the pin is recessed, as described, in a groove formed in the underside of the peripheral portion of the disc. However, ln accordance with the broader aspects of the invention it is not essential to provide a groove, and the invention may be employed in modified form as illustrated in Figs. 31, 32 and 32a where -corresponding numerals have been employed with addition of subscript "a". Thus the disc has a disc-shaped body including ~1)395~L2 a central portion 121a and a peripheral portion 123a, the central portion having a rotary drive connection 117a. Means indicated at 122a are provided for anchoring the pin 130a in a radially extendin~ opening 127a which is angled downwardly at a shallow angle, with the tip portion of the pin projecting radially beyond and below the periphery of the disc. A backstop surface 142a (Fig. 32) is arranged in the path of hending movement of the shank portion of the pin to support the pin as the projecting tip portion strikes an obstruction, and a corresponding frontstop surface 143a, preferably curved, is placed in the path of forward movement of the pin to support it upon rebound. A bridge~ indicated at 147a, closely overlies the pin at the periphery of the disc. The bridge serves to hold the pin in a downwardly-angled working position notwith-standing the elevating effect of the centrifugal force, while producing a dampening effect upon the pin by reason of frictional engagement with the ceiling surface 144a as the pin bends back-wardly and forwardly below the bridge.
It is further within the scope of the present invention to provide the groove 141 of the preferred embodiment, and in which the pin is recessed, with a "floor" thereby enclosing the groove on the underside. Such structure is illustrated in FigsO 33 and 34, in which the "floor" surface is indicated at 200 opposed to the ceiling surface 144b, and with all other corresponding elements being designated by corresponding reference numerals with addition of subscript "b". By enclosing the groove on the underside, the groove 3 iS converted into a radially extending recess, completely enclosing the pin, while permitting swinging movement thereof , .

1~3~5~Z
between a backstop surface 142b and a ~ront wall 1~3b. The "floor" not only prevents entry of small stones which conceivably could become missiles, but it also provides additional frictional damping for the pin, while preventing the shank portion o~ the pin from moving downwardly beyond the undersurface of the disc.
In snort, the floor insures that the pin is at all times contained and fully protected in all directions. Finally, it will be understood that the integral floor 200 serves to further strengthen the disc structure. If desired, the floor may be extended radially outward to provide a lower protective ledge havina the same profile of the ledge 161 (Fig. 13).
In the various embodiments of the invention described ~ ;
above, the pin has an enlarged head and is intended to be inserted "from the inside out". In accordance with one of the aspects of the present invention provision is made for inserting a pin "from the outside in" by avoiding an enlarged head and by providing latching members, for example, in the disc structure.
Such a modified embodiment is shown in Figs. 35 and 36 in which c~rresponding reference numerals, with addition of subscript "c", are employed to indicate corresponding parts. In this embodiment the head 131c of the pin has the same diameter as the shank. The pin is engaged and retained by a pair of resilient latch members 201, 202 which may either be separate or integrally formed when ;
molding the disc and which are oriented in inwardly~sprung positions engaging a reduced section 203 of the pin immediately under the head 131c.
Upon insertion head first, when the head strikes the latch members 201, 202 they are cammed outwardly and then snap ~nto the reduced section 203 to hold the pin firmly in place .

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1~39~i1Z
against the effects of centrifugal force. When pin replacement is necessary, the old pin may be squarely severed at the periphery of the disc and tapped inwardly by means of a dri~t pin or the like, thereby freeing the opening for insertion of a new pin. This may be accomplished without having access to the top of the disc so that the disc need not be removed from the mower for pin replacement. The other features and advantages provided by the structures shown in Figs. 33-36 are equivalent to the features and advantages of the preferred embodiment.
While it is preferred to employ a wall 22, 122 for mounting the pins which is of continuous, annular shape, it - will be understood by one skilled in the art that the wall may be non-circular, for example, of polygonal shape if desired.
Also the wall may be discontinuous, that is, in the form of a short segment of a circle or polygon and either curved or straight without departing from the invention. Thus the term `
"circular center portion" of the disc refers generally to that portion which immediately surrounds the hub and which need not be circularly bounded by the wall. Indeed, the term "wall"
refers to any upstanding structural means on the disc, either -integral with the disc or not, for engaging and thus rigidly securing to the disc, in generally radial position, the shanks of the respective pins. Similarly, the term "annular outer portion" of the disc is directed to a portion having an outer edge which has a sufficiently gradual curvature so that it is impossible for the outer edge of the rotating element to strike a hammer blow against a pebble or piece of debris sufficient to turn the same into a missile. The term "disc" and "disc assembly" refers to a shape which sufficiently approaches a 1~3951~
smooth circular shape so tha~ the member is incapable of being blocked by, or striking a direct hammer blow against, a concentrated obstruction.
The term "stiffly resilient" has been used to characterize the long, flexible tip portion of the cutter pin.
This term has been used in order to distinguish over rigid and relatively non-yielding, or backed-up, cutting elements which have been used in the prior art and which are capable of inflicting serious injury upon the hand or foot of the operator. -The term is also used to distinguish over filamentary cuttingelements, for example formed of nylon, which are relatively limp, which tend to sag under their own weight or rely upon centrifugal force to keep it in a cutting posture. Indeed, the pin is stiff enough so that the tip remains downwardly angled, to cut at or slightly below disc level in spite of the elevating, or leveling, effect of centrifugal force~ It is nevertheless of sufficiently low mass, and sufficiently resilient and yielding so as to retreat to an out-of-the-way position upon striking an obstruction including the hand or foot of the operator.
While the tip is capable of applying a painful blow to an exposed limb, severe injury-of the type inflicted by a steel blade is avoided.
It has been found preferable to use a type of plastic for the cutter pins which has a resilient, elastic nature, which is flexible in thin section, which resists surface abrasion, which has a high impact strength, and which resists notching and is capable of repeated stressing without fatigue. ~`~
Various forms of nylon manufactured, for example, by E. I.
duPont de Nemours possess the above characteristics in desired :. . ~ . ,. ~ .

~'1)3951Z
; combination. However, it is found that nylon is not the only material which can be successfully employed and delron (acetyl homopolymer), also manufactured by duPont, may be successfully used. Lexan (polycarbonate) and Nor~l (phenylene oxide), both manufactured by General Electric Company, are also plastics having high performance characteristics and which may be expected to have a long life in the present usage. Common varieties of polyethylene and polypropylene will also serve and have the advantage of economy. The plastic materials which have thus far been acceptable for cutter pins have the following approximate minimum mechanical properties: tensile strength 8,000 psi.; compressive strength 11,000 pse.; flexural yield strength 6,000 psi.; and flexural modulus 100,000 psi.
While it is preferred to employ a pin having an enlarged head with a cylindrical shank portion adjacent thereto and a flexible tip portion of constant taper, it will be apparent to one skilled in the art that the invention is not limited to the particular shape which is disclosed. Indeed, instead of using a constant taper resulting in a sharp conical shape, with straight, convergent sides, the sides may be slightly concaved, or even slightly convexed if desired. Because of the variations in shape the terms "shank portion" and "tip portion", as applied to a given structure, may shift or overlap. ~enerally stated, the shank portion is the portion which is permanently -- within the confines of the disc whereas the tip portion may be defined as that portion which normally extends beyond the disc.
By "taper" is meant gradual reduction in area free of any abrupt changes in cross section. The diameter of the tip portion, near 1~395~Z
the outer extremity of the pin, is, for the most common size of mower, on the order of 0.050 to 0.125 inch, preferably about 0.09 inch, providing a cross sectional area of about .0064 square inch. Pins having a shank diameter of about 0.250 to 0.375 inch have been used, corresponding to a cross sectional area of about 0.0~9 to about 0.110 square inch. The average thickness of the pin should preferably be greater than 0.20 _ inch. In the case of a tapered pin, the shank of the pin should have a cross sectional area which is at least four, and preferably about five to ten, times that at the tip. The size of the pin may be scaled downwardly, in proportion, for a hand held weed trimmer, or may be scaled upwardly, for heavy work, where higher horsepower is available.
The invention is not limited to any particular - cross section, and the cross section may be round, oval, star-shaped, square, or even somewhat rectangular, provided there is sufficient cross section so that the pin can be characterized as "stiffly resilient". The term "head", is not necessarily ;
limited to an enlargement and is intended, more generally, to denote the inner end of the pin, provided that suitable retaining means are used to hold the pin anchored in the disc. Thus it is possible, within the scope of the invention, even though not preferred, for the head portion of the pin to be threadedly retained in its registering opening. The term "plastic'l includes tough flexible materials having a density which is characteristic of synthetic plastics in general, exhibiting abrasion resistance comparable to the high performance synthetic materials already mentioned and capabIe of self-restoration to substantially radial position after bending at right angles around a curved .
backstop.

_ . . . _ ., .

In carrying out the invention~ the disc itself has been manufactured from plastic materials having characteristics similar to those materials used in the cutter pins and capable of resisting abrasion while resiliently deforming, for purposes of self-protection, in the face of suddenly applied impact as, for example~ upon the striking of a sharp embedded object when rotating at rated speed. However, durable materials other than plastic, for example, steel, may be used for the disc. A
typical disc, in a push type mower powered by a 3 horsepower engine and designed to cut a 20 inch wide swath, is 14 inches in diameter with cutter pins mounted in the disc as shown in Figs.
2 and 12, each pin being about six inches long. Such disc and pin assembly will have rotational inertia equal to or somewhat less than that of the usual unitary steel blade. A disc, with pins installed to make the effective cutting width 20 inches has been operated at a rotational speed on the order of 3,000 rpm.
and has been found capable, in heavy grass or weeds, of fully utilizing the rated horsepower of the usual (3-4 hp.) engine, with the pins automatically yielding under load to prevent lugging or stalling of the engine upon engagement of heavy wetted -vegetation. Thus the construction may be distinguished from the prior art in which stalling of the engine is a common occurrence. The construction is distinguished, by equal margin, over whirling filament cutters which are suited primarily to hand held trimmers.

, The invention has been described in connection with a rotary lawn mower where it finds greatest utility, being sufficiently versatile as to be used in rotary mowers already ~'~395~Z
in the field as well as in new designs of rotary mowers, replacing in each the sharpened steel blade which has for many years been used as a standard cutting element. Thus the term "mower" as used herein includes weed cuttexs, trimmers and edgers for example of the light hand-held type powered by an electric motor.

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Claims (38)

1. A safe cutter disc assembly for a rotary lawn mower having a vertical drive shaft comprising, in combination, a disc having a central portion with provision for connection to the lower end of the drive shaft and a peripheral portion presenting a generally flat surface on its underside, at least one cutter pin on said disc arranged generally radially thereon, each pin being made of tough, resilient abrasion-resistant plastic and having a head and a stiff shank and terminating in a stiffly resilient tip portion, mounting means on the disc for engaging and supporting the shank of each pin cantilever-fashion adjacent the head so that only the tip portion of the pin projects radially outwardly of the periphery for cutting of the grass as the disc is rotated, the mounting means being spaced sufficiently inwardly of the periphery so that as the pin strikes a major obstruction radially of the disc the pin may bend relatively harmlessly about its mounting means into an inwardly bent position in which the pin is increasingly shielded by the disc, and means for causing curvature to be smoothly distributed in the shank with avoidance of any sharply concentrated stress in the pin as the tip portion of the pin strikes the obstruction, substantially the entire shank of the pin being spaced upwardly from the underside of the peripheral portion of the disc and generally parallel thereto so that the shank of the pin is shielded against obstructions axially engaging the underside of the disc.

2. The combination as claimed in claim 1 in which the tip portion of the pin upon striking of a radial obstruction is free to bend to a protected position substantially within the extreme outer edge of the disc so that the abrading effect of the obstruction primarily occurs at the edge of the disc rather than at the surface of the pin.

3. The combination as claimed in claim 1 in which the central portion of the disc is offset axially from the peripheral portion to form a shallow vertically extending wall, the pin being fitted for cantilever support in a radial opening formed in the wall.

4. The combination as claimed in claim 3 in which the disc is recessed on its underside adjacent the head of the pin to provide access to the head of the pin enabling it to be inserted into and withdrawn from the opening.

5. The combination as claimed in claim 1 in which the cross section of the shank adjacent the head is non-circular and in which the opening is of registering non circular section to prevent twisting of the pin about its axis.

6. The combination as claimed in claim 5 in which the cross section is such as to permit insertion of the pin in two positions rotated about the pin axis 180°.

7. The combination as claimed in claim 2 in which the radial opening in the disc is formed by registering saddle recesses extending axially inwardly from opposite sides of the disc.

8. The combination as claimed in claim 3 in which the wall is in the form of a pair of annular reinforcing ribs and in which the pin is in register with aligned radial openings formed in the wall.

9. The combination as claimed in claim 1 in which the pin is telescoped into a radial opening in the disc and in which the shank of the pin is dimensioned for insertion of the pin radially inwardly, and a latch interposed between the disc and the head of the pin to retain it in the opening against the pull of centrifugal force.

10. The combination as claimed in claim 1 in which the disc provides a bridge above the pin adjacent the periphery of the disc, the bridge having a generally horizontal ceiling surface spaced closely to the shank of the pin and which extends peripherally permitting lateral swinging movement of the pin while inhibiting upward movement of the pin and thus holding the tip portion of the pin down to the work as the disc rotates.

11. The combination as claimed in claim 1 in which the pin is angled downwardly at a shallow angle so that the tip of the pin extends below the level of the disc.

12. The combination as claimed in claim 11 in which the shallow angle is between 2 and 8 degrees.

13. The combination as claimed in claim 1 in which the pin is angled downwardly at a shallow angle so that the tip of the pin extends below the level of the disc and in which the disc provides a bridge above the pin adjacent the periphery of the disc, the bridge having a horizontal ceiling surface spaced closely to the shank of the pin tending to hold the pin in its downwardly angled position notwithstanding the leveling effect of centrifugal force upon the pin as the disc rotates.

14. The combination as claimed in claim 10 in which the ceiling is bounded by backstop and frontstop surfaces in the path of bending movement of the pin upon striking of an obstruction.

15. The combination as claimed in claim 14 in which the backstop and frontstop surfaces are curved and out-wardly flaring.

16. The combination as claimed in claim 10 in which the bridge is provided with a ledge which extends beyond the radius of the disc to form a protective recess into which the tip portion of the pin bends upon striking an obstruction.

17. The combination as claimed in claim 1 in which the means for causing distribution of curvature in the shank includes a backstop mounted on the disc in the path of rearward bending movement of the shank as the tip portion of the pin strikes an obstruction.

18. The combination as claimed in claim 17 in which the backstop is smoothly curved in a retracting direction to provide support for the shank of the pin distributed along the length thereof.

19. The combination as claimed m claim 18 in which the backstop stops short of reaching the periphery of the disc so that the tip portion of the pin upon striking an obstruc-tion is free to move into the confines of the disc for protection thereby.

20. The combination as claimed in claim 18 in which the periphery of the disc is provided at the pin position with a ledge which extends beyond the radius of the remainder of the disc to form a protective recess into which the tip portion of the pin bends upon striking an obstruction.

21. The combination as claimed in claim 20 in which the ledge is an extension of a bridge beyond the radius of the disc.

22. The combination as claimed in claim 17 in which a frontstop is provided on the disc mounted in the path of forward movement of the shank of the pin to distribute the curvature thereof as the pin rebounds from the backstop after the striking of an obstruction.

23. The combination as claimed in claim 2 2 in which the frontstop is smoothly curved.

24. The combination as claimed in claim 1 in which the means for causing distribution of curvation in the shank includes a smoothly curved backstop and a smoothly curved front-stop located in the paths of opposite movement of the shank.

25. The combination as claimed in claim 1 in which the means for causing distribution of curvature in the shank resides in making the pin of tapering configuration, with the pin being of large cross section at the head and with the shank tapering to a thin cross section in the tip portion.

26, The combination as claimed in claim 25 in which the shank of the pin has a cross sectional area which is at least about four times as great as that of the tip of the pin.

27, The combination as claimed in claim 1 in which the cutter pin projects radially from the periphery a distance of one-half to three inches.

28. The combination as claimed in claim 1 in which two to four pins are provided spaced symmetrically on the disc.

29. The combination as claimed in claim 1 in which the pin occupies a radial groove formed on the underside of the disc, the groove having an arcurate dimension sufficient to permit substantial bending of the pin as the tip portion thereof strikes an obstruction.

30. The combination as claimed in claim 1 in which the disc includes a radially extending recess having out-wardly flaring beck and front walls in the path of movement of the shank of the pin serving as a backstop and frontstop for limiting and distributing the bending movement of the pin as the tip portion of the pin strikes an obstruction.

31. The combination as claimed in claim 30 in which the recess has a trumpet-shaped horizontal profile having a width at its throat just sufficient to accomodate the shank of the pin.

32. The combination as claimed in claim 29 in which the radial groove has a trumpet-shaped profile having a width at its inner end and having an axial depth just sufficient to accomodate the shank of the pin for shielding the shank of the pin against axially-engaged obstructions.

33. The combination as claimed in claim 29 in which the ceiling of the groove at the periphery of the disc engages the pin in its course of bending to dampen the movement of the pin.

34. The combination as claimed in claim 30 in which the recess has a ceiling which is angled downwardly by a shallow angle in the radial direction, the ceiling closely overlying and engaging the pin at the periphery of the disc thereby tending to hold the tip portion for cutting at a level below the bottom of the disc motwithstanding the leveling effect of centrifugal force upon the pin.

35. The combination as claimed in claim 1 in which upstanding, upwardly sweeping radial vanes are formed on the upper surface of the disc.

36. The combination as claimed in claim 1 including a step on the outer periphery of the disc, the step being adjacent the pin, the step being oriented so that the disc radius before the step is greater than the disc radius following the step as the disc is rotated in its intended manner, whereby the step forms a protective recess into which the tip portion of the pin bends upon striking an obstruction.

37. The combination as claimed in claim 10 in which the means for causing distribution of curvature in the shank includes a backstop mounted on the disc in the path of rearward bending movement of the shank as the tip portion of the pin strikes an obstruction.

38. The combination as claimed in claim 10 in which the means for causing distribution of curvature in the shank resides in the tapered configuration of the pin with the pin being of large cross section at the head and with the shank tapering to a thin cross section in the tip portion.