Note: Descriptions are shown in the official language in which they were submitted.
~)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
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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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~395~l~
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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~395~
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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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.
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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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1~395~1~
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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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
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~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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1~395~Z
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.
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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
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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
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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
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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
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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
,
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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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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
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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
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; 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
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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.
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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
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~'~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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