Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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In the original form of rotary lawn mower, a steel blade
having sharpened edges is rotated at high speed parallel to the
ground for cutting of grass, weeds and the like. It has long
been recognized that a steel blade with a sharp edge and high
inherent inertia constitutes a severe safety hazard, and consid-
eration has been fiven to reducing this hazard by replacing steel
with flexible plastic. Joyner patent 3,156,082 which issued in
November, 1964, for example, shows substitution of polyethylene
or the like. Ely in patent 3,302,377 which issued in February of
1967 teaches use of a molded rubber blade reinforced by fibers.
Wixson in patent 3,303,637 which issued in February of 1967
shows replacement of the arms of a metal blade with loops of `
resilient wire. Ely in patent 3,340,682 which issued in September
of 1967 and Freedlander et al. in patent 3,389,541 which issued in
June of 1968 are further examples of conventionally shaped blades
formed of elastomeric material.
Voigt patent 3,104,510 which issued in September of 1963
is an example of a blade of conventional rectangular form used
with a "whip" and in which a resileint bumper extends along the
leading edge the full length of the "whip" for improving efficiency
in the cutting of grass or weeds growing adjacent a fixed ob-
stacle. The "whip" is flat-sided with transverse grooves or
serrations.
~ o overcome the disadvantages of a conventional blade,
Daggett in patent 2,557,598 which issued in June of 1951 dis-
closes use of a disc having replaceable, radially-projecting
wires. Use of radially-projecting wires is also proposed in
the Dunlap et al. patent 3,208,209 which issued in September
of 1965.
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In an effort to reduce the hazard presented by a conventional fixed
cutter, various inventors have disclosed the use of pivoted flailing elements.
Wire flails are proposed in Boggs patent 2,538,230 which issued in January
of 1971 and in Diesterweg patent 3,018,602 which issued in January of
1962, both of these devices being intended for trimming purposes. The
use of a disc having sharpened metal blades is shown in Kirk patent
~3~ 320~ 732 which issued in May of 1967, Zweegers patent 3,389~ 539 which
issued in June of 1968 and Geier patent 3~ 905~ 182 which issued in September
of 1975.
Frick in patent 3~ 474~ 608 which issued in October of 1969 shows
use of a rotated carrier of "snail" shape having plastic cutting elements
52 mounted along the edge which may be either freely pivoted or crimped
in place. The leading edge of the carrier in such construction is capable
of striking a hammer blow, and most of the cutting will be done, not by
the cutting elements, but by the leading edge of the snail which, extending
to a point of maximum radius, is first to engage the standing grass or
weeds~
As a separate line of development, inventors became intrigued
with the possibilities of cutting grass and weeds using a whirling filament
of nylon or the like. An early example of the use of a whirling filament
occurs in French Naveau patent 1, 281J 450 which issued in December of
1961 and in French Reber patent 6~ 914,884 which issued in May of 1969.
A similar line of development occurred in Germany as evidenced by
Langenstein German patents 6, 919, 841, 6, 919, 842 and 6~ 919,844 which
issued in April of 1969, 6~ 938~ 165 which issued in September of 1969
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and the Vogelenzang patent 1,657, C39 whlch issued in October of 1970. The
latter patent shows ~mwinding of filamentary cutters from central spools
- but does not specify the material of which the filament is made. A more
recent German design is the Adlus "UFO" trimmer in which a filament is
led outwardly between rounded surfaces on adjacent buttons on the under-
side of a rotating disc.
- In the U. S., the use of rubber flails impacting vegetation near fence
posts or other obstructions is disclosed in Huff et al. patent 3, 44 4,674
which issued in May of 1969. Curtis et al. patent 3, 410, 064 which issued
in November of 1968 shows a "plant knocker" utilizing strips of tire casing.
The use of thin whirling filaments is disclosed in all of the following U. S.
patents: Geist patent 3, 708, 967 which issued in January of 1973,
Voglesonger patent 3, 831, 278 which issued in August of 1974 and Ballas
patent 3, 826, OB8 which issued in July of 1974 and 3, 859, 776 which issued
in January of 1975.
; All of the above }tDwer patents are directed toward cutting of grass
while attempting to reduce the hazard presented by a sharpened, whirling
rectangular steel blade. Sufficient time has now elapsed to be able to
form a judgment as to whether the aspirations of the inventors in these ;
and similar patents have been realized. It is apparent that the problem
of a weighty blade delivering a solid hammer-like blow has not been
avoided in the patents issued to Joyner, Ely, Freedlander and Voigt.
The structures in such patents, even though more yielding than a con-
ventional steel blade, are nevertheless fully capable of hammering stones
and other debris from the mower at high speeds.
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In the Daggett and Dunlap et al. patents which teach the use of a
disc with radially extending wires, missile throwing capabi'ities are re-
duced, but the wires are subject to concentrated stress, with breaka-ge
and bending. The same is true of the devices in the Boggs and Diesterweg
patents .
The idea of using a disc with pivotally mounted metal blades or
flails as shown in the patents to Kirk, Zweegers and Geier has reduced,
but only in minor degree, the hazards inherent in a sharpened steel blade
rotated at high speed, while raising the possibility that a blade may become
stuck in a rotated, non-cutting position. The device in the Frick patent
is considered to be relatively dangerous and ineffective.
The remaining patents which employ a thin filament, uncoiled from
a spool or the like, sacrifice cutting efficiency almost entirely to con-
siderations of safety to the point where the devices are not capable of
production cutting of a lawn or other area. The devices rely upon
centrifugal force to maintain the cutting elements extended, and since
such force is limited, the cutting elements tend to lay back into an
ineffective position when cutting all but the lightest vegetation. As a
result, cutters of the filamentary type have not been employed, as a
practical matter, in full sized rotary mowers, and their use has been
limited to light trimming operations. Even where used only for light
trimming and edging, a filament is subject to a high degree of wear and
almost constant breakage, which explains why such filaments are con-
ventionally supplied in continuous form from a supply spool from which
new filament is payed out as required. Sometimes instead of breaking
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off the ends will "split" or "brush" which further reduces cutting
efficiency~
While efforts to achieve a cutting efficiency comparable to that
of a steel blade combined with improved safety, both in the striking of an
obstruction and in the throwing of missiles, have brought about a pro-
liferation of cutter designs, no design, as far as is known, has been able
to achieve the desired goal as shown by practical testing, as indicated
by absence of mowers of such designs in the commercial market, and
by tne continued widespread use of the original rectangular steel cutter
blades, notwithstanding their recognized hazards.
It is an object of the present invention to provide, as an article
of manufacture, a cutter pin made of durable resilient plastic which may
be radially mounted, cantilever fashion, in an opening formed in a disc,
with the tip portion of the pin projecting radially outward from the disc
to provide a cutting edge which is effective in the cutting of vegetation
; but which is capable of yielding upon striking a weighty obstruction to
reduce the likelihood of damage or injury. It is a more specific object
of the present invention to provide a cutter pin for a rotary mower which
is safer than the sharpened steel blade normally employed and which, upon
striking the hand or foot of the operator, tends to bend or yield to an out-
of-the-way position for protective purposes. It is a related object of the
¦( invention to provide a plastic cutter pin for a rotary mower which is
sufficiently stiff to cut vegetation but which is sufficiently yielding and
resilient so that upon striking a stone or other piece of debris, tne debris
does not tend to turn into a high-speed missile capable of producing injury
at a distance.
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It is a general object of the present invention to
provide a plastic cutter pin for a rotary mower which is of
such tapered construction as to bend with gradual and distributed
curvature thereby to reduce concentration of stress to secure a
long life without breakage due to wear, "notching", or fatigue.
It is a related object to provide a cutter pin which resists
abrasion by impact with obstacles as well as wearing away at the
tip, thereby maintaining initial cutting effectiveness. It is
a still further object of the invention to provide a plastic cutter
pin which is not only inherently long wearing but which may be
replaced at the cost of only a few cents whenever the degree of
wear makes replaeement neeessary.
Broadly stated, the present invention provides an
artiele of manufaeture for use in the cutter disc of a rotary
lawn mower having cantilever anchoring means for a cutter pin,
a cutter pin of durable resilient plastic comprising, in com-
bination, a relatively thick shank, the shank terminating at
its outer end in a relatively thin but stiffly resilient tip
portion providing a cutting edge, the shank having a head at
its inner end for retaining the pin in the anchoring means and
the pin being of tapered construetion so that upon striking a
weighty obstruetion, the pin yields by bending baekwardly with
smoothly distributed eurvature.
Other objeets and advantages of the invention will
beeome apparent upon reading the attaehed detailed description
and upon referenee to the drawings in whieh:
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Fig. 1 is a perspective view of a plastic cutter pin constructed in
accordance with the present invention;
Figs. 2 and 3 are plan and elevational views, respectively, of the
cutter pin shown in Fig. 1;
Fig. 4 is an end view;
Fig. 5 is a section taken through the thickest portion of the shanl;
and looking along line 5-5 in Fig. 2;
Fig. 6 shows, in perspective, a typical rotary mower in which
the improved pin is employed;
Fig. 7 is a perspective view of the under side of the mower of
Fig. 6 showing the disc in which the pins are mounted;
Fig. 8 shows a fragment of the peripheral portion of the disc shown
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in Fig. 7 and illustrating the flexing of the cutter element which may
occur with the elen-lent in uC e.
Fig. 9 shows the test set-up used for determining initial bending
modulus;
Fig. 9a is an end view looking along line 9a-9a in Fig. 9;
Fig. 10 shows a test set-up for determining the force which,
normally applied, is required to bring about a 90 bend with the pin
supported cantilever fashion adjacent the head but with the shank being
otherwise unsupported;
Fig. lOa is a fragmentary section taken along line lOa-lOa in
Fig. 10.
While the invention has been described in connection with a pre-
ferred embodiment, it will be understood that we do not intend to be
limited to such embodiment but intend, on the contrary, to cover the
various alternative and equivalent forms of the invention included within
the spirit and scope of the appended claims.
i Turning now to Figs. 1-5 there is shown, somewhat enlarged, a
i cutter pin 10 constructed in accordance with the invention having a shank
11 with a head 12 integrally formed at one end and a tip portion 13 terminat- I
ing in a tip 14.
The pin is smoothly tapered and is distinguished, in the preferred
i, embodiment, by a set of evenly spaced grooves which extend longitudinally
over a substantial portion of the length of the pin, the grooves being indicatedat 21-24 in Fig. 4. The grooves are, as shown in that figure, arcuately
bottomed so as to avoid any sharp discontinuities with resulting concentration
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of stress, and have a radial depth which is approximately proportioned to
the thickness, being a maximum at the head and reduced to zero as the
point of the pin is approached. The grooves 21-24 define between them a
set of longitudinally extending ribs 31-34. It has been found that pins
having a length between two inches and eight inches produce an acceptable
cut, proportioned to the size of the carrier in which it is mounted. The
pin is preferably about four to seven inches in length with a maximum
shank diameter in the range of 1/4 to 1/2 inch and a tip having a minimum
diameter of 1/16 to 3/16 inch. A pin having the following overall dimensions
has been found to work particularly well: Length--6 inches, maximum
diameter of shank adjacent head--3/8 inch, tip diameter--1/8 inch.
The ribs have a width, at the face, which is approximately equal
to the thickness of the tip of the pin. Preferably, also, the material of
the pin is symmetrically disposed about the pin axis, for example, as
shown in Figs. 4 and 5, so that the tapered portion is sharply conical,
with the shank having a material cross sectional area at least about twice
the cross sectional area of the tip and a total cross sectional area, including
flute area, of at least about four times the cross sectional area of the tip.
While pins of the present construction can be used in various
, 20 forms of rotary carriers, there is set forth in Figs. 6, 7 and 8 an
exemplary environment in which the pins may be employed to take
advantage of a combination of hlgh cutting efficiency and improved safety.
The mower in the present instance includes a frame 41 in the form of a
shallow inverted enclosure having an encircling sidewall 42, a set of
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wheels 43, a handle 44 for propulsion and guidance and an engine 45 whichmay alternatively be an elect.ic motor having a vertical drive shaft 46
which is conventionally threaded for receiving a clamping screw 47. A
discharge chute 48 projects tangentially from one side of the housing
to dispose of the clippings.
Secured to the drive shaft in horizontal position is a cutter disc
50 which carries the cutting elements. Such a disc, which is preferably
molded of durable and resiliently deformable plastic, has a circular
central portion 51, an axially off-set, or wall, portion 52 and a peripheral
portion 53 of relatively thin average cross section. Evenly spaced
openings 57, 58, 59 are provided in the wall portion 52 of the disc for
receiving pins in outwardly extending position. While it is preferred to
employ a total of three pins in symmetrical positions, it will be under-
stood that the invention is not limited thereto and that the invention may
be practiced using only a single pin, or as many as four or five pins as
a practical upper limit. The openings are dimensioned for a snug fit,
so that the shank of each pin is supported, adjacent the head, cantilever
fashion. Preferably forty to sixty percent of the length of each pin extends
outboard of the disc.
In order to provide additional lateral support for the pin upon
striking of an obstruction, the outer portion 53 of the disc is formed, its
underside, with radially extending grooves in register with the openings.
Referring to the drawings, the grooves are indicated at 67, 68, 69 in
respective alignment with the pin receiving openings 57, 58, 59. Taking
the groove 67 as representative, and referring to Fig. 8, the groove has
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a relatively narrow neck 71 having a width which just slightly
exceeds the diameter of the shank of the pin as well as a curved,
outwardly flaring rear wall 72. The latter is of increasing curv-
ature, tangenitally faired or merged into the periphery of the
disc, and serves as a support or back-stop for the shank of
the pin as the tip portion of the pin strikes an obstruction,
for example, in the form of a large stone or other piece of
debris D (Fig. 6). The bending of the pin against the curved
wall serves to insure that the bend is distributed longitudinally
of the pin so as to avoid the setting up of concentrated stress.
The groove, in addition, has a front wall 73 adjacent the pin
which is curved and outwardly flaring so that when the pin 10
is released tending, because of its resilience, to rebound in
the forward direction, bending is distributed for avoidance of
concentrated stress. Reference is made to copending application
Serial No. 260,658, filed Sept. 7, 1976 for a more complete
discussion of the advantages in employing the present type of
pin with a narrow groove of flaring, or trumpet, shape, but it
will be understood by one ski]led in the art that the improved
pin, which is defined herein, has an inherent combination of
advantages not possessed by prior pins making it possible to
employ the pin, as an article of manufacture, in various types
of rotary mower structures, either with or without a backstop
surface.
The plastic material which the pin is made is preferably
a "high performance" resilient plastic such as nylon, delrin
and the like including such recently formulated materials as -
those identified as Z-801, Z-101, Z-71 and Z-42, all of such
materials being available from E.I. Dupont de Nemours of Wil-
mington, Delaware. The materials are defined in data
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sheets accompanying the present application. Z-801 is preferred because
of its strength, resiliency, and relative freedom from abrasion and
"notching". "Notching" is a term of art used to describe the tendency
of a plastic material to break, by reason of concentrated stress, at a
notch or similar surface injury which may occur during hard usage in
the presence of ground obstructions, and resistance to notching in a
material is defined by the "Izod Impact Strength" of the material
- (ASTM Method D-256). In the preferred embodiment, it is desirable
to use a material for the pin which has a high Izod Impact Strength, for
example, 10 foot-pounds per inch or greater, with the minimum preferred
Impact Strength being about 2 foot-pounds/inch as determined in accord-
ance with ASTM Method D-256 under conditions of 73F and 50 percent
relative humidity.
Since the stress-strain characteristics may vary with the type
of material, in addition to thickness and degree of taper, it is accordingly
desirable to define the invention in terms of the "bending modulus" of
the pin. The bending modulus is a well-known parameter used in defining
beam characteristics and can be used to predict deflection of a beam
, under loaded conditions. Bending modulus defines the deflection
characteristics of a cantilever beam in terms of the moment of inertia
of the beam structure ana the flexual modulus of the beam material.
Bending modulus is the product of the second area moment of inertia (I)
multiplied by the flexual modulus. Moment of inertia is determined from
the cross section of the beam at a specific location on the beam in
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accordance with the formula I =J o y2dA, where "dA" is a small discreet -
area within the cross section and "y" is the distance of dA from the
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neutral axis of the beam. The flexual modulus is a material property
and can be determined in accordance with A. S. T.M. test method
D-790 at 50 percent relative humidity and 73F.
It has been determined that the pins should be of such cross
section and taper so as to exhibit a minimum bending modulus of
50 in. -lb. in the shank (see Fig. 5) and a maximum bending modulus
of 30 in. 2-lb. adjacent the tip. It is preferred that the pin have a
minimum bending modulus of 70 in. 2-lb. in the shank and a maximum
bending modulus of 10 in. 2-lb. adjacent the tip. Also, the bending
modulus from the shank to the tip should essentially smoothly
continuously decrease, showing that the pin is gradually more flexible
in progressing from the shank to the tip.
A pin such as shown in Fig. 1 having a shank diameter of 3/8
inch and a tip diameter of 1/8 inch which is made of the above mentioned
Z-801 material has a bending modulus of about 85. 2 in. 2-lb. in the
shank and 0. 48 in. -lb. adjacent the tip. The moment of inertia in
the shank is 5. 68 x 10-4 in 4 and adjacent the tip is 3. 22 x 10-6 in 4.
The flexual modulus of material Z-801 at 50 percent RH and 73 F is
150, 000 PSI. A pin having the same shape made from the above-
mentioned material Z-42, which has a flexual modulus of 175, 000
PSI, has a bending modulus of 99. 4 in. 2-lb. in the shank and 0. 56
in. -lb. adjacent the tip.
The bending modulus within a particular range defines a pin
having the necessary degree of stiffness to insure efficient cutting of
, grass and weeds combined with sufficient resilience, or flexibility,
to yield in the face of an obstruction to reduce damage or injury.
Thus protection is afforded upon striking of an obstruction as a stake,
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root, or rock anchored in the ground, or upon the striking of
the inadvertently interposed hand or foot of the user. The factor
of yieldability, combined with an extremely narrow profile and low
mass, is also important in reducing the size, velocity, and number
of the stones or the like which may be ejected from the mower either
through the chute or from below the enclosure.
Several other parameters which may be used to define
characteristics of the pin are termed "initial deflection modulus"
and "90 bending force". The initial defection modulus is the ratio
of the deflection of the free end of the pin to the force applied per-
pendicularly to the axis of the pin at the free end to produce such
deflection, expressed in units of inches per pound. The 90 bending
force is the force in pounds required to bend a pin in a 90 arc as
shown in Fig. 10.
The initial deflection modulus and 90 bendlng force may
be conveniently specified by use of jigs of fixtures of the type set
' forth respectively in Figs. 9 and 10. In Fig. 9 the pin 10 is gripped
cantilever fashion adjacent the head 12, and over a distance of about
an inch, by means of a clamp 80 having separable mated halves 81,
81 (see Fig. 9a) and which is clamped upon a vertical support 83 by
means of screws 84. Inscribed upon the support is a scale 85 which,
while arcuateJ is calibrated in terms of units of vertical deflection.
The initial deflection modulus can be determined by hanging
a weight Wl from the tip 14 of the pin to produce an initial deflection.
The deflection produced, the amount of weight required, and the
projecting length of the pin can then be used to calculate the initial
deflection modulus for that pin. It has been found that in pins made
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of ~,-801 nylon at 50 percent RH and 73F, having a shank diameter
of 0. 375, a tip diameter of 0.125, and a taper and cross section as
shown in Fig. 1, with a projecting length of five inches, a weight Wl
of 0. 2 pounds hung from the tip of the pin, the pin deflects about
0. 28 inch, whereby the initial deflection modulus is 1. 4 inches per
pound. It has been determined that the pins preferably should be
of such cross section and taper so as to exhibit an initial deflection
modulus in the range of 0. 5 to 3. 0 inches per pound. Preferably
the initial deflection modulus is within the stated range measured
in all transaxial directions.
For determining the 90 bending force which characterizes
the present invention a test fixture is preferred as set forth in Fig.
10. Here the same clamp 80 may be employed as is used in the
fixture Fig. 9 but rotated at 90 so that the pin projects vertically.
For applying force to the pin a horizontally extending arm
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90 is used, horizontally pinned at 91 to a bracket 92. The arm 90 has
a groove 93 formed in its underside. At the outer, or right hand, end
Il of the arm 90 is a reference index 95 which cooperates with the lower
edge of the arm and which is horizontally aligned with the arm pivot
91. Both the arm pivot and the index are preferably located above
the clamp 80 by a distance which is related to length L of the pin, speci-
fically, the amount 2L/~. Moreover, means are provided for applying
force downwardly upon the arm at a point which is spaced horizontally
by a distance 2L/5~ from the initial location of the pin axis. For apply-
ing the force, indicated at W2, a yoke 96 is used which is pinned to the
arm by a transversely extending pin 97 (Fig. lOa).
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In use, the groove 93 is lubricated and the arm is swung clock-
wise engaging the tip of the pin in the groove. Weight is added at W2
in increments until the arm is horizontal, that is, until the underside
of the arm coincides with the index 95. This is the force required to
bend the pin through an angle of 90 or, alternatively, to bend the pin
so that its effective length, measured parallel to the axis of the
unstressed pin, is reduced to 2L/ " . It is found that a pin as described
above has a 90 bending force of 3. 75 pounds and that a pin should,
in accordance with the present invention, have a 90 force character-
istic which lies between 1. 5 and 10. 0 pounds.
It may be noted that the test fixtures set forth in Figs. 9 and
10 do not employ any backstop or frontstop of the type provided in the
exemplary form of the disc earlier described. The reason for this
is that the pins having the characteristics of the present invention need
not, necessarily, be employed in structures having the particular
backstop and frontstop provisions shown, for example, in Fig. 8.
Indeed, pins having the characteristics of the present invention may
be successfully used if desired with pure cantilevered, or concentrated,
support as contrasted with the distributed support shown in Fig. 8.
While it is preferred to make the pin of cruciform cross
section, it will be apparent that the invention is not limited thereto;
for example, one or more of the grooves 21-24 may be omitted without
departing from the invention. Thus the pin may have just one rib--or
a groove and rib may be added to make a total of five ribs. Where the
shank is of non-circular section, the head 12 is preferably enlarged and
'~latted" (Fig. 4) or the like for registration purposes, that is, to
insure that a rib is oriented forwardly to present a relatively con-
centrated cutting edge.
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It will be understood by one skilled in the art that pins
constructed in accordance with the invention, and having the
characteristics described above, are not claimed to provide a
perfect degree of safety. A pin, as defined, and rotated at normal
rotary mower speeds, striking a hand or foot is capable of deliver-
ing a painful blow. But the injury, instead of being severe, is more
likely to be of a superflcial nature. Indeed, where a hand is pro-
- tected by a glove or a foot is protected by a shoe any injury is
expected to be minimal. Nonetheless, it is found that pins defined
in accordance with the invention, and rotated at normal mower speeds,
have a high degree of grass cutting efficiency, an efficiency which
approaches that of a steel blade which has been in use for a period
of time. In short, when employing the present invention any sacrifice
in cutting efficiency is only a minor tradeoff for a large gain in safety.
The pin is self-protecting even when striking a fixed obstruction
because of its yieldability and because of the small amount of mass, or
momentum, which it possesses. Upon "wiping by" the obstruction there
may be some abrading action depending upon the degree of protection,
such as an overhanging ledge, provided on the supporting disc. But
even where a pin, constructed of high performance plastic, is relatively
unshielded, it is, by reason of its physical bending characteristics,
largely self-protected. Wear tends to be concentrated at the very tip
and tends to have a self-sharpening effect. Pins of the present type
may be employed for many hours of hard usage before the tip portion
becomes so short as to make replacement advisable.
While the taper of the pin is preferably linear over the entire ~;
length, the invention is not limited thereto, and the taper may be
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1079076
non-linear (slightly concave or convex) and may start at a point
separated from the head, if desired, without departing from the
invention, as long as the pin falls within the claimed ranges of bending
modulus. Thus by "smoothly tapered" is meant a gradual, but not
necessarily linear, variation in thicl~ness as a function of length
over the tapered range, and by "smoothly distributed curvature" is
meant freedom from sudden discontinuities of curvature. The term
"head" denotes the retaining means at the inner end of the pin,
whether enlarged or not. By "substantially straight" is meant
that the pin is free of the "curl" which distinguishes a filament
fed from a spool. The term "plastic" includes tough, flexible
organic materials having a density which is characteristic of
synthetic plastics in general, exhibiting abrasion resistance com-
- parable to the high performance synthetic materials already ~ -
mentioned and capable of self-restoration to a generally radial
position after bending at right angles.
The present pin is distinguished over plastic
cutter elements of the filamentary type by its freedom from
drooping under its own weight. In use, it is distinguished by the
fact that it will maintain a downwardly angled orientation, with
the head portion anchored cantilever-fashion and the tip pointed
outwardly and downwardly at a shallow angle from the disc or
other support, during rotation at cutting speed, notwithstanding
the tendency of centrifugal force to elevate the pin to the plane
of its region of attachment.
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