CA1198291A - Rotary flail cutter system - Google Patents
Rotary flail cutter systemInfo
- Publication number
- CA1198291A CA1198291A CA000316819A CA316819A CA1198291A CA 1198291 A CA1198291 A CA 1198291A CA 000316819 A CA000316819 A CA 000316819A CA 316819 A CA316819 A CA 316819A CA 1198291 A CA1198291 A CA 1198291A
- Authority
- CA
- Canada
- Prior art keywords
- spool
- filament
- rotary member
- rotation
- bearing surface
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
ABSTRACT OF THE DISCLOSURE
A spool upon which one or more lengths of filament are wound is provided and housed within a cylindrical cover having one or more generally radial openings formed through one wall portion thereof and the free ends of the filaments are threaded through the openings and extend outwardly there-from for flail-type cutting of vegetation thereby when the spool and housing are rotated as a single unit at high speed. The spool is controlably rotatable relative to the housing whereby the spool may be rotated in discrete controlable increments in a direction to unwind the filaments therefrom so as to renew the extended end portions of the filaments projecting outwardly of the housing by said predetermined increments as the extended ends of the filaments incur breakage. Latching structure is operatively associated with the spool and housing for releasably retaining the spool in adjusted angularly displaced position relative to the housing and the latching structure is remotely operable from a mounting structure relative to which the spool and housing may be rotated at high speed and during high speed rotation of the spool and housing relative to the mounting structure. In this manner, when breakage of the extended end portion of a filament occurs, a filament may be further extended during operation of the cutter so as to renew the extended end portion of the filament to the desired length.
A spool upon which one or more lengths of filament are wound is provided and housed within a cylindrical cover having one or more generally radial openings formed through one wall portion thereof and the free ends of the filaments are threaded through the openings and extend outwardly there-from for flail-type cutting of vegetation thereby when the spool and housing are rotated as a single unit at high speed. The spool is controlably rotatable relative to the housing whereby the spool may be rotated in discrete controlable increments in a direction to unwind the filaments therefrom so as to renew the extended end portions of the filaments projecting outwardly of the housing by said predetermined increments as the extended ends of the filaments incur breakage. Latching structure is operatively associated with the spool and housing for releasably retaining the spool in adjusted angularly displaced position relative to the housing and the latching structure is remotely operable from a mounting structure relative to which the spool and housing may be rotated at high speed and during high speed rotation of the spool and housing relative to the mounting structure. In this manner, when breakage of the extended end portion of a filament occurs, a filament may be further extended during operation of the cutter so as to renew the extended end portion of the filament to the desired length.
Description
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There are various forms of flail-type cutters being marketed for the purpose of performing cutting and similar functions such as light cultivation and edging by means of non-rigid filaments which extend generally radially outwardly from a cutter head rotated at high speeds. Desirable results are obtained by these filaments rotating at high speed under which they assume a tensioned condition due to centrifugal force. It has been found that these filaments can be used to cut grass and other delicate vegetation more safely and with a greater degree of flexibility than devices using rotating rigid blades.
The industry producing cutters of this type has generally avoided the use of either metallic or composite filaments inasmuch as it has seemed that filaments of this type exhibit inferior operating life characteristics when used with commonly available engines and electric motors. In particular, the metallic or composite filaments have been found to break more rapidly than plastic filaments.
However, I have found that the operating life characteristic of filements, whether plastic, metallic or composite, is more directly a function of the system employed to rotate and restrain the free end of the filement than a function of the filament material. Furthermore, prior devices have not addressed the fundamental problem of flail cutting which will be herein described. The disclosure of the nature and effect of several basic phenomena which occur and whose effects are interrelated, the statement of the basic problem, and the disclosure of a system which deals with that problem so as to accommodate and control the basic phenomena, will yield significant advances in the state of the art.
Hereinafter will be described the basic phenomena, the basic problem and a radically new, different and more productive search to the solution of the basic problem to yield substantial advancement of the art and enable the production of a new generation of filament cutters with characteristics far superior to those now available.
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In flail cutting a flexible filement is rotated at some angular velocity. The centrifugal force of rotation imposes an axial load on the filament. ~ach segment of the filament has a kinetic energy which is KE = 1/2 mv where m = mass of the segment v = velocity of the segment The velocity of each segment is a function of its distance from the center of rotation or v = rw where r = distance from center of rotation w = speed of rotation Therefore the kinetic energy of a segment is KE = 1/2 m (rw) This kinetic energy is available for instantaneous release when the filament encounters an obstacle such as a blade of grass. It is this eneregy release which effects cutting and other action which can be achieved in flail cutting.
Thus energy is stored in the filament and alternately released through impact and replenished by the power source, typically an electric motor or gasoline engine.
Cutting action improves as the ratio of stored kinetic energy to filament diameter is increased. This can be seen intuitively since for a given filament diameter a greater energy release will provide more effective cutting action.
Thus it would seem that higher rotational speed would be desirable. ~owever, rotational speed also imposes a centrifugal load on the filament which is C = mw r where m = mass w = speed of rotation r = distance from center of rotation Thus each filament segment exerts a force on every other segment nearer the center of rotation or point of restraint. Above a threshold speed, the summation of the forces acting on the e~tended filament yields a total force at the point of restraint such that at that point the tensile strength of the filament is exceeded producing failure.
In flail cutting the filament does not assume a straight radial position relative to the axis of rotation of the cuTtter head (even when not encountering obstructions) inasmuch as wind force acting upon the extended end portion of the filament imparts a drag thereon.
Thus, the extended end portion of the filament continuously curves rearward relative to the direction of rotation. As the filament encounters obstructions, phenomena occur which coact to shorten the operating life of the filament. These phenomena will be called impact shear, impact abrasion, impact heating and tensile fatigue.
When a segment of the filament, traveling at high veLocity, encounters an obstacle, the inertia of the free end of the filament and the inertia of the obstacle encountered acting in opposition to the inertia of the filament segment causes the filament to partially "wrap around" the obs-tacle. During this "wrap around" period the local Pilament segment experiences shear forces whose magnitude are a function of the contour of the obstruction, the mass of the obstruction, the velocity of the filament and the cross sectional mass and geometry of the filament. If the obstacle encountered has sufficient mass the filament will fail at the point of contact with the obstacle or at some adjacent point if there is a weakness in the filament. Impact shear occurs with every impact 90 that the filament encounters shear loading at very high frequency. ~ven where the individual impact does not produce instaneous failure, it induces localized damage making the filament more susceptible to future failure at that point. Thus, impact shear has an accumulative effect which is an important factor in the operating life e~pectancy of a given segment of the filament. Also, because the kinetic energy of a given segment increases with the square of its distance from the center of rotation, the outermost segments of the filament are most susceptible to failure in a shear mode.
Filament abrasion occurs when an obstruction has sufficient mass and geometry to actually cut away a portion of the filament. Thus, the filament may be "niched" or split at a given point but may not, at that instant, totally sever. This form of damage typically occurs when the filament encounters very dense obstacles such as rocks or curbing, asphalt and similar physical featurès and also has an accumulative effect in shortening the operating life of a filament segment. In the case of plastic filaments, this phenomenon frequently results in the "split end" condition where the tip of the filament splits into several small fibers. Of course, a plurality of smaller fibers, due to their greater flexibility and reduced inertia do not operate as efficiently in cutting vegetation. Many metallic and composite filaments exhibit shear and abrasion resistance superior to that obtainable from plastic filaments. Accordingly, metallic and composite fibers are less susceptible to failure due to abrasion and shear.
Impact heatillg is generated by the rubb;ng action which occurs when a filament section impacts with an obstruction and by hysteresis as the filament undergoea deformation as a result of impact. In general, insufficient heat is generated to melt a plastic filament segment at 8~
the point of impact, although heating as a result of impact becomes a more serious problem as larger diameter filaments are used.
It i.s obvious that an individual Eilament encounters a very high number of impacts per second. This induces very high frequency vibrations in the filament. Plastic filaments do not transmit vibrations as well as metallic filaments and a smaller percentage of the overall tensile load is transmitted to the point of restraint. The most severe tensile load on the filament occurs at the point where it is constrained. With conventional cutting heads this is either at the opening in the housing or hub or inside the hollsing or hub on the spool upon which the filament is wound, or a combination of the two.
Plastic, metallic and composite filaments are all subject to tensile failure at the point of constraint. Since the fatigue of the filament is a combined function of its angular velocity, its extended length and mass, the loading it encounters from impact with obstructions, and the structure by which it is restrained, if fatigue of the filament is suitably controlled, filaments utilized for cutting purposes can be employed with superior results.
Acceptance of the prior assertion requires a statement of the fundamental problem of flail cutting in the context of the present state of the art.
The present state oE the art is such that filament breakage is believed to be the fundamental problem. This is evidenced by the attention devoted to minimizing filament breakage. It has been recognized that breakage often occurs at the point of primary filament restraint which is typ:ically at the exit opening in the cover which houses one or more filament reservoirs. Various devices have been employed, such as the "curvilinear bearing surfaces" generally described in U.S. patents Nos. 3,708,967, 3,826,068 and 3,859,776, to reduce the incidence of such breakage.
However, it is asserted that filament breakage per se is not the Eundamental problem and that optimum system performance will result when the total breakage rate is sacrificed to obtain preferential breakage which will be hereinafter explained.
The fundamental problem, with the present state of the art, is that filament breakage causes inconvenience and greatly reduces the productivity of the cutting system. This stems from the necessity of stopping the rotating filament reservoir in order to activate the various mechanisms which have been devices to enable additional filament to be extended. There is an inherent attendant drawback in that the user becomes accustomed to frequent physical contact with portions of the cutting system which are capable of imparting injury.
The user approaches physical contact with a rigid steel lawnmower or edger blade with caution on the relatively infrequent occasions when it is necessary. However, presently available flail cutting systems require such contact with a frequency which tends to invite carelessness.
In addition, the inconvenience inherent in present filament storage and feed systems inhibits the user in applying the systems to heavy growth and almost totally precludes their use in other applications, such as lawnmowers, where it would be impractical to advance additional Eilament using present feed systems.
Thus, it i9 asserted that the basic pro'blem i8 not one of filament breakage. 'l'he basic problem is to provide a system which controls filament breakage while providing a safe and effective means for dispensing additional filament from the reservoir to replenish segments which are lost.
l`he desirability of an improved dispensing system, particularly one which can be activated and controlled while the device is in continuous ~ ~9~2~
operation, should be obvious. The desirable elements of controlled breakage are as follows.
The filament is an expendable element of the system. However, there are clearly preferred breakage modes. Since the tip segment effects the greatest cutting action, it is abraided and worn away most rapidly. Therefore, the most preferred breakage area is near the end of the extended fiber.
Conversely, the least preferred areas are those segments near the point of restraint, or worse, beyond the point of restraint into the storage area This should be obvious since, if the filament breaks farther from the tip of the cutting end, a greater portion is lost with no commensurate benefit.
Loss of short segments at the tip is much preferred.
There are three approaches which can be used to reduce breakage at the root of the filament. These approaches are reduced operating speed (which reduces the fundamental vibratory frequency and the tensile load), distribution of restraint forces over greater filament lengths (to reduce load concentration), or special restraint of the filament in such a manner as to control the fundamental "breaking" process.
The reduction of speecl tends to reduce the cutting effectiveness because such effectiveness is a direct function of the kinetic energy stored in a segment of the filament. Therefore, lowering the rotational speed is not a desirable approach to reducing filament breakage, because overall performance of the system suffers.
Much has been attributed to the importance of "curvilinear"
bearing surfaces parallel to the axis of rotation at the point of restraint of the filament. These "curvilinear" bearing surfaces have been provided as a means for distributing loading over a greater filament length so as to thereby extend operating life of the filament.
Curvilinear surfaces are disclosed in U.S. patent Nos. 3,708,967, 3,826,068 and 3,859,776. However, the precise contour and function of these "curvilinear" bearing surfaces have not been defined nor has the ~L~g~
effect of their particular contour been precisely explained. The utilization of "curvilinear" bearing surfaces has apparently been adopted as a result oE observation that a sharp corner at the bearing surface results in rapid filament breakage at the point of restraint.
This would be expected due to excess shear and vibratory load concentrations on the filament at that point.
While the use of a "curvilinear" bearing surface eliminates the rapid filament breakage which occurs when a sharp angle at the bearin8 surface is utilized, it still does not actively contribute to selective breakage outwardly of the bearing surface. When breakage of the filament occurs at the bearing surface the filament end will often be retracted within the housing surrounding the spool and it is therefore extremely difficult to extend the desired length of filament from the spool and requires access to the interior of the housing in order to thread the end of the filament to be extended through the opening in the housing for the spool definincg the bearing surface.
~ lowever, if a bearing surface which causes controlled angular deformation oE the filament at the bearing surface is provided and structure enabling selective increment feed of the filament from the spool during operation of the associated cutter is provided, each time a new aection of filament is engaged with the bearing surface that section is subject to tensile and vibratory loading and is therefore partially weakened.
Rcepeated increment feeding of the filament during operation of ttle cutter thereby produces a free end portion oE the filament which has longitudinally spaced weakened zones therealong. These longitudinally spaced weakened zones are, as well as intermediate portions of the filament, subject to impact with the material being cut and impact shear and abrasion and friction heating as a result thereof. These phenomena tend to further weaken the spaced pre-wealcened zones more rapidly than the "virgin" filament there-between and the outermost weakened zone is of course more severely weakened than the preweakened zones spaced inwardly thereof. This results in asubstantial majority of the breakage of the filament as a result of its use in cutting vegetation occurring at the outer end portion of the free end thereof. Therefore, inasmuch as the filament should be considered as an expendable item, a cutter including means for increment feed of the filament during operation of the cutter and also means for pre-weakening the filament in the zones thereof successively with the bearing surface of the housing is operable in a substantially contimlous manner through repeated increment feeding of the filament in order to renew the outer end portions thereof which are repeatedly broken therefrom. During operation of the cutter, as successive segments of filament are broken from the free end thereof and the filament is fed in increments from the spool, the localized weakened zones disposed outwardly of the bearing surface experience cumulative stress concentration and their tensile properties degenerate. Thus, a weakened zone toward the free end of the filament, having experienced more impact with the vegetation being cut than weakened zones closer to the bearing surface, is weaker and more likely to sever. This yields selective severing or breakage of the filament with a higher incidence of breakage near the tip of the filament. Therefore, increment feeding of the filament may be continued during operation of the cutter with a substantial reduction of unwanted breakage of the filament at the bearing surface or inwardly thereof necessita-ting operation of the cutter to be terminated in order to manually extend a new length of filament from the housing.
The preferred geometry of the bearing surface is a function of the filament geometry, material properties, the extended filament length and the average speed of rotation. ~lowever, it has been determined that for various availab]e metallic, non-metallic and composite filaments, and for speeds of rotation between lO00 and 10,000 rpm a bearing surface with at least one angular break where the included angle is not greater than 178 nor less than 100 will produce localized filament compression and weakening to _g _ `` 1~9~g~
achieve the deslrec] reslllt of selective hrea'~.age. ~here multiple angular surfaces are employed they may be separated by straight or curved surface segments without noticeable diEference but the distance between pairs of relatively angulated surface should be substantially less than the lenoth of the increment of filament extended by one acdvance of the feed mechanism so as to insure that the e:ctended seg-ment of the filament has discrete leakened zones.
The cutter system of the instant invention utilizes a rotary cutter head including a coaxial spool from which a filament l~ound on the spool may be fed in increments therefrcm and the spool is enclosed witilin a housing stucture defining an opening therein through ihich the end of tlle f:ilament extends with the surfaces of the housing de-fining the trailing surace of the opening including at least one angular surface for pre-wealcening, to a slight degree, of that portion of the filament engaged with the bearing surface so that each time a new increment of fila-ment is feed from the spool a new spaced weakened ~one of the filament will be added to the end portion thereof pro-jecting outwardly of the opening.
The nnechanism by which the fiLament may be fed in increments from the spool is operable during operation oE
the~ cutter wilell the spc)ol :is rotatin~ at high speeds.
The mechanisnl wherel)y the Eilament may be fecl in :increments Erom the SpOO 1 i.S also deeme(l to be ne~. Thus the l~loadest deillit:ion of tile present :inventiorl may be seen to T)rovi~le an appnr.l~us or cutting vegetatic)n atld the lil;c E
32~
comprisinp, a support, a rotary member journa]led from the support for rotation at hioh speed in a cutting plane, having storage means and including a support portion definino a peripherally located bearing surface, at least one elongated flexiE)le flail member having storage and free end portions, the storage end portion being supported from the storage means for feeding oE the free end portion therefrom~ the free end portion extending outwardly from the axis of rotation of the rotary member and being tr~ined across the bearing surface, means for driving the rotary melnber in one direction of rotation, the bearing s~rface facin~ ~enerally in the direction of rotation of the rotary member, the storage means includino spool means llpon which the storage end portion is wound, the spool means being supported frorn the rotary member for rotation relative thereto, the spool means being disposed substantially concentric ~lith the axis of rotation member and rotatable relative to the support portion, a dr:ive member mounted on the rotary member for rotation therewith and axially shiftable thereon for movement between first and second posit:ions, the drive member and spool including coactino portions engageable with each other to drive the spool, in the one direction, w-itEl the drive melllber when said drive member is in the first position and operat;ve to allow first an(l second pre(leterllline(l ang~llar rotatioll, only, oE the spooL in thc opposite (I:irection relative to the rotary 1nem-ber as 1 reslllt of sllifting of the dr:ive mel!lber from tEle ~:~98;~
first position to the second position and then back to the first pos;tion from the second position.
The present invention also may be considered as providing the method oE feeding monofilament from the rotary head of a filament trimmer in a manner to enhance breakage of the filament outwardly of the hea(l during high speed ro-tation of the latter and to thus enhance centrifugal feed-ing of the filament by reducing brealcage thereof closely adjacent the head, the method comprising sequentially longitudinally feeding the nlonofilament from a storage loca-tion within the head in short increments while the mono-filament is trained arross bearing surface edge means facing in a direction extending outwardly from the axis oE rotation of the head inclined in the direction of rotation thereof and with the bearing surace of a configuration such to cause pre-wealcening in the area of the monofilament engaged with the bearing surface edge means after a predetermined time of operation of the trimmer, whereby successive pre-weakened areas of the monofilament may be fed outwardly of the bearing surface e`dge means and the cumu]ative further weakening of the areas due to impact with vegetation and the greater impact of tlle outermost end portion of the monofila-ment will cause controlled brealcage of the monofilament out-wardly from the bearing sur~ace edge mean9 rather than Qd jacent or :inwarclly tht!reof.
Fig~lre 1 is a fraglllent~ry s:ide e]evat:ional view of the cutter ~ysteln oE tl~e inst-lllt invention ~ith portiolls of the cllttc~r beinp brc)lcen a\~.ay an(l i]lustrQtetl in verticaL
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s e c t i o n s ;
Figure 2 is an enlarged hor-izontal sectional view taken substantially ' .~,1 llb :iLiL98Z~l upon the plane indicated by the section line 2 2 oE Figure 1, Figure 3 is a fragmentary enlarged transverse vertical sectional view taken substantially upon the plane indicated by the section line 3-3 of Figure l;
Figure 4 is a horizontal sectional view taken substantially upon the plane indicated by the section line 4-4 of Figure 3;
~ igure 5 is a horizontal sectional view taken substantially upon the plane indicated by the section line 5-5 of Figure 3;
E'igure 6 is an enlarged horizontal sectional view of the portion of the spool enclosing housing having the feed opening formed therein and illustrating the manner in which the filament is deflected by the juncture of relatively angulated surfaces defining the feed opening; and Figure 7 is a fragmentary schematic view illustrating the manner in which increment feeding of the filament from the spool is accomplished.
Referring now more specifically to the drawings the numeral 10 generally designates the flail-type cutter of the instant invention. The cutter 10 includes an upwardly and outwardly inclined main handle 12 from ~Jhose lower end a lightweight gasoline engine 14 is supported. The engine 14 includes a downwardly directed rotary output shaft 16 and the upper end of the handle includes a horizontally directed portion 18 having a hand-grip 20 disposed thereon.
The en8ine 14 includes an air intake 22 to which the discharge end of an inlet hose 2~ i8 connected and the outlet end of the discharge hose 24 is connected to a branch tube 26 which opens into the interior of the lower end of the hollow tubular handle 12. The free end of the upper end portion 18 is open and has an air filter assembly 28 secured thereover. AccordinglyJ ai.r is supplied to the air inlet 22 through the tubular handle 12, it being understood that the air inlet 22 leads into the air and fuel passages of a carburetor (not shown) of the ~91~
engine 14.
A second tubular handle 30 is disposed forwardly of, generally parallels and is supported from the handle 20 by means of suitable brackets 32. The upper end of the handle 30 includes a horizontal forwardly directed portion 34 having a second handgrip 36 mounted thereon and the forward end of the portion 34 is closed by means of a removable cap 38. The handle 30 defines a fuel tank and the lower end thereof is closed and the inlet end of a gasoline feed line 40 opens into the lower end of the handle 30, the outlet end of the gasoline feed line 40 opening into the fuel chamber of the carburetor (not shown) of the engine 14.
The engine 14 is of the manual start type and includes a pull cable 42 slidably received through an outer housing 44 extending upwardly along the handle 12 and 30 and having its upper end supported from a bracket 46 anchored relative to the handles 12 and 30. The upper end of the cable 42 has a pull handle 48 mounted thereon whereby the engine 14 may be started from the upper ends of the handles 12 and 30.
A guard plate 50 is secured beneath the horizontally forwardly directed lower end portion 52 of the handle 12 and includes a rearwardly and outwardly flared as well as downwardly curved rear portion 54.
The guard plate 50, handle and engine 14 may all be considered parts of a support from which the shaft 16 of the engine 14 i8 rotatably journalled.
With attention now invited more specifically to Figures 2, 3, 4 and 5 of the drawings it may be seen that the shaft 16 includes a tapered lower end portion 56 having a blind threaded bore 58 formed therein. The lower end portion 56 is snugly seated in the tapering inner end portion 60 of an upwardly opening counterbore 62 formed in the upper end of an upstanding sleeve 64. The sleeve 64 has an axial bore 66 formed therethrough and the lower end of the bore 66 includes 30 first and second counterbores 68 and 70, the counterbore 68 being smooth and terminating inwardly at the lower end of the bore 66 and the counterbore 70 being slightly larger in diameter than the counter-bore 68 and threaded. The sleeve 64 is secured on the shaft 16 by means of a bolt 72 having its head seated in the counterbore 68 and its threaded shank portion passed through the bore 66 and t.hreaded in the blind bore 58. The upper end of the sleeve 64 includes a diametrically enlarged terminal end 74.
The sleeve 64 has a pair of opposite side longitudinally extending flats 76 formed thereon and a hub sleeve 78 is mounted on the sleeve 64 and keyed thereto for rotation therewith by means of the flats 75. The hub sleeve 78 includes diametrically opposite radially outwardly projecting pins 80 and the lower end of the hub sleeve 78 is diametrically reduced as at 82 and defines a downwardly opening circumferential seat 84 in which to seatingly receive the upper end of a compression spring 86. In addition, a lower terminal end of the hub sleeve 78 includes a downwardly opening counterbore 88 defining a downwardly facing circumferential rib 90 on the lower end of the hub sleeve 78 for a purpose to be hereinafter more fully set forth.
The upper end of the hub sleeve 78 has a thrust washer defining annulus 92 recessed therein and the diametrically enlarged upper terminal end 74 of the sleeve 64 overlies and abuts the inner periphery of the thrust washer defining annulus 92.
A hori~ontally disposed storage spool 94 including upper and lower flanges 96 and 98 is mounted on the hub sleeve 78 for rotation relative thereto and the upper flange 96 includes an inner peripheral portion 100 which seats against an upwardly facing annular shoulder 102 defined adjacent the upper end of the hub sleeve 78. Additionally, the lower flange g8 includes an inner peripheral portion 104 which snugly receives the lower end of the hub sleeve 78 therethrough and ~;3L98Z9~
against which the lower end of the compression spring 86 bears.
A housing referred to in general by the reference numeral 106 is provided and includes a cylindrical wall portion 108 disposed in upstanding position and closed at its lower end by means of a lower end wall 110 having a central opening 112 formed therethrough. The housing opens upwardly and has a sleeve 114 secured in the opening 12 and keyed to the lower end portion of the sleeve 64 which is also provided with diametrically opposite flats 116 corresponding to the flats 76. The upwardly opening housing 106 snugly but rotatably receives the spool 94 therein and the cylindrical wall portion 108 of the housing 106 includes a pair of diametrically opposite radial openings 118 formed therethrough in which metal grommets 120 are secured.
Two lengths o plastic monofilament 122 have one end of each wound on the spool 94 between the flanges 96 and 98 and anchored relative to the spool 94 as at 124. The free ends of the filaments 122 extend tangentially away from the hub 126 of the spool 94 and pass outwardly through the grommets 120 and include free end portions 128.
The spool 94 is formed of upper and lower halves which are assembled and welded together in any convenient manner. The inner surface of the hub 126 of the spool 94 includes a circumferentially extending inwardly opening groove 130 (see Figure 7) and the lower half 132 of the spool 94 includes circumferentially spaced ribs 134 which project upwardly into the lower half of the groove 130 while the upper half 136 of the spool 94 includes ribs 138 which project downwardly into the upper half of the groove 130. The ribs 134 and 138 are spaced circumferentially centrally between adjacent ribs 138 and 134, respectively, whereby the groove 130 is transformed into a serpentine passage. The outer ends of the pins 80 are received in the serpentine passage and the compression spring 86 normally biases the hub sleeve 78 upwardly along the sleeve 64 to the uppermost position thereof illustrated in Figure 3 with the thrust washer defining amlulus 92 abutted against the underside of the diametrically ~15-z~
enlarged upper terminal end 74 of the sleeve 64 and the outer ends of the pins 80 received in the corresponding upper portions of the groove 130 between adjacent ribs 138.
A retaining cup referred to in general by the reference numeral 140 ~see Figure 3~ is provided with a central threaded attaching stud 142 and the cup 140 is secured to the underside of the housing 106 by means of the threaded stud 142 being threadedly engaged in the threaded counterbore 70, a compression spring 144 being disposed about the threaded stud 142 and bet.ween the lower end of the sleeve 64 and the opposing upwardly facing central inner surfaces of the cup or cap 140.
The outer periphery of the lower end wall 110 is relieved as at 146 to minimize the area of contact 148 of the lower end wall 110 of the housing 106 with the underside of the lower flange 98 of the spool 94 and the central area of the lower end wall 110 is further relieved as at 150 to receive the rib 90 therein when the hub sleeve 78 is urged do~lwardly against the biasing action of the compression spring 86.
A mounting block 152 i5 secured to the underside of the shield or plate 50 by means of attaching fasteners 154 and a bifurcated actuating lever 156 is pivotally supported from the mounting block 152 as at 158 and has its furcations 160 disposed immediately above the thrust washer defining annulus 92 outwardly of the diametrically enlarged upper terminal end 74 of the sleeve 64. The free end of the lever 156 has one end of a Bowden cable assembly generally referred to by the reference numeral 162 anchored relative thereto and the other end of the Bowden cable assembly 162 is anchored to a control lever 164 pivotally supported Erom the upper end portion 18 of the handle 12 as at 166.
It iB to be noted that upon an upward pull on the lever 164 the Bowden cable assembly 162 will exert an upward pull on the associated end of the lever 156 so as to swing the furcations 160 of the lever 156 downwardly into contact with the thrust washer defining annulus 92 of the hub sleeve ~98~
78. This of course will cause the hub sleeve 78 to be shifted downwardly relative to the sleeve 64 against the biasing action of the compression spring 68 and the pins to shift from the upper half of the groove 130 to the lower half of the groove 130.
With attention now invited more specifically to Figure 6 of the drawings, it may be seen that the outer portions of the grom~ets 120 are bevelled as at 168 so as to define spaced first and second inner and outer corner bearing surfaces or edges 170 and 172 in the outer end of each grommet 120, the grommets 120 being substantially cylindrical in cross sectional shape.
In operation, the cutter 10 is used to cut vegetation 176 in the manner illustrated in Figure 1 of the drawings during operation of the engine 14 to spin the spool 94 and housing 106 at high speeds.
The outer end portions 128 of the filaments 122 cut with a flail action on the vegetation 1i6 during rapid spinning of the spool 94 and housing 106.
As indicated in Figure 7 of the drawings the pins 80 move in the direction of the arrows 178 and thus bear against diametrically opposite ribs 138 of the upper half 136 of the spool 94 and cause the latter to move in the direction of the arrow 180. However, when the lever 164 is actuated, the lever 156 forces the hub spool 78 downwardly so as to shift the pins 80 from the solid line position thereof illustrated in Figure 7 to the phanto~
line position 182 of Figure 7 in the lower half of the groove 130. Then, because of the windage drag and centrifugal force acting on the outer end portions 128 of the filaments lZ2 and the air drag on the upwardly projecting radial vanes 184 carried by the upper flange 96 of the spool 94, the spool 94 lags in rotation relative to the housing in order that the pins 80 may assume the positions thereof illuatrated in phantom lines as at 186 in Figure 7 to thereby extend a first increment of monofilament 122 from the spool 94 through the grommet 120. Thereafter, when the lever 164 is released, the hub ~:~9~
s]eeve 78 shifts back up to the posit;on thereof illustrated in Figure 3 under the biasing action of spring 86 so as to raise the pins 80 to the phantom line positions 187 in the upper half of the groove 130 and air drag and centrifugal force acting on the filament end portions 128 and the vanes 184 causes the spool 94 to further lag in rotation whereby the pins 80 assume the phantom line positions 188 in Figure 7 to extend or feed further segments of filaments 122 from the spool 9~. Thus, upward swinging of the lever 164 causes a first increment of each filaMent 122 to be fed or extended from the spool 94 through the corresponding grommet 120 and release of the lever 164 causes a second increment of each filament 122 to be extended or fed from the spool 94 through the corresponding grommet 120. The increment feeding of filaments 122 from the spool 94 may of course be carried out during operation of the cutter 10. Further, the successive angle edges 170 and 172 cause localized loading of the filaments 122 and thus those points of contact of the filaments 122 with the grommets 120 are weakened. However, upon initial operation of the cutter 10 successive segments of filament are fed from the spool 94 by actuation of the lever 164 and the extended end portions 128 of the filaments 122 disposed outwardly of the grommets 120 thereby include longitudinally spaced areas thereof which are weakened. Inasmuch as the outermost weakened areas travel at higher peripheral speeds, they impact the vegetation 176 with greater force and are more rapidly further weakened.
This results in breakage of the filaments 122 most likely occurring at the outermost weakened areas thereof.
Thus, the incidence of breakage of the filaments 122 adjacent or inwardly of the grommets 120 is substantially reduced and continuous operation o the cutter 10 may be carried out. Shoulcl the fi.laments 122 exit from the hou~ing 106 along a large radius curvilinear bearing surface as has been practiced heretofore, sufficient localized loading of the filaments at the bearing surfaces to support controlled breakage of the filaments outwardly of the point they exit from the housing 106 does not occur. Rather, breakage of 9~
the filaments 122 may occur inwardly of the housing 106 at the points of constrainment of the filaments on the spool. When such brea~age occurs the free ends of the filaments 122 will attain positions inwardly of the grommets 120 thereby rendering the feed mechanism of the filaments 122 inoperative and necessitating that operation of the cutter 110 be terminated so that the cup 1~0 and housing 106 may be removed in order to thread the free end portions of the filaments 122 outwardly through the grommet 120.
In addition to providing localized loading on the filaments 122 as the latter are fed through the grommets 120, the angle edges 170 and 172 tend to absorb the tension forces on the filaments 122 due to centrifugal forces acting upon the free ends 128 thereof and to thereby prevent such tension forces from being transmitted inwardly of the housing 106 and excessive abrasion of the outer convolutions of the filaments 122 with adjacent convolutions thereof and subsequent breakage of the filaments 122 within the housing 106.
It is important that the openings through the cylindrical wall portion 108 of the housing 106 through which the filaments 122 extend be substantially circular in cross sectional shape as accomplished by the grommets 120. In this manner, inasmush as the free ends 128 of the filaments 122 can vibrate considerably in vertical directions, excessive loading of the filaments 122 at the outer ends of the grommets 120 does not occur and breakage of the filaments 122 at their exit points from the grommets 120 is maintained at a minimum. Further, localized loading of the filaments 122 at the outer end of the grommets 120 may be effected by a single angular edge at either 170 or 172. However, in some instances it has been found to be beneficial to provide a pair of successive angular edges as at 170 and 172 It will also be noted from Figure 4 of the drawings that each filament 122 is deflected in opposite directions by its passage through the grommet 120. Although this successive opposite deflection of the il29~
monofilament 122 is not necessary, it does reduce excess tension forces acting upon the monofilament 122 inwardly of the grommet 120 and thereby greatly reduces abrasion of the outer convoLution of the monofilament 122 within the housing 106 against adjacent convolutions of the monofilament 122.
Those surfaces of the ribs 134 and 138 which face in the direction opposite to the directions 178 and 180 may be inclined toward the center of the groove 130 either in the direction of the arrows 178 and 180 or opposite to the direction of the arrows 178 and 180, depending upon the strength of the spring 86 and the expected wind drag forces tending to retard rotation of the spool 94 relative to the hub sleeve 78.
The filaments may be of metallic materials, non-metallic materials or composite materials and only one filament need be used to perform a cutting operation. Further, the specific configuration of the bearing surface or surfaces is determined by the material of which the filaments are constructed, the expected rotational speed of the housing, and the inertia generated by the extended ends of the filaments at that speed. However, the configuration of the bearing surfaces is such to attain the aforementioned controlled breakage of the filaments adjacent their outer free ends rather than adjacent or inwardly of the bearing surfaces therefor.
There are various forms of flail-type cutters being marketed for the purpose of performing cutting and similar functions such as light cultivation and edging by means of non-rigid filaments which extend generally radially outwardly from a cutter head rotated at high speeds. Desirable results are obtained by these filaments rotating at high speed under which they assume a tensioned condition due to centrifugal force. It has been found that these filaments can be used to cut grass and other delicate vegetation more safely and with a greater degree of flexibility than devices using rotating rigid blades.
The industry producing cutters of this type has generally avoided the use of either metallic or composite filaments inasmuch as it has seemed that filaments of this type exhibit inferior operating life characteristics when used with commonly available engines and electric motors. In particular, the metallic or composite filaments have been found to break more rapidly than plastic filaments.
However, I have found that the operating life characteristic of filements, whether plastic, metallic or composite, is more directly a function of the system employed to rotate and restrain the free end of the filement than a function of the filament material. Furthermore, prior devices have not addressed the fundamental problem of flail cutting which will be herein described. The disclosure of the nature and effect of several basic phenomena which occur and whose effects are interrelated, the statement of the basic problem, and the disclosure of a system which deals with that problem so as to accommodate and control the basic phenomena, will yield significant advances in the state of the art.
Hereinafter will be described the basic phenomena, the basic problem and a radically new, different and more productive search to the solution of the basic problem to yield substantial advancement of the art and enable the production of a new generation of filament cutters with characteristics far superior to those now available.
z~
In flail cutting a flexible filement is rotated at some angular velocity. The centrifugal force of rotation imposes an axial load on the filament. ~ach segment of the filament has a kinetic energy which is KE = 1/2 mv where m = mass of the segment v = velocity of the segment The velocity of each segment is a function of its distance from the center of rotation or v = rw where r = distance from center of rotation w = speed of rotation Therefore the kinetic energy of a segment is KE = 1/2 m (rw) This kinetic energy is available for instantaneous release when the filament encounters an obstacle such as a blade of grass. It is this eneregy release which effects cutting and other action which can be achieved in flail cutting.
Thus energy is stored in the filament and alternately released through impact and replenished by the power source, typically an electric motor or gasoline engine.
Cutting action improves as the ratio of stored kinetic energy to filament diameter is increased. This can be seen intuitively since for a given filament diameter a greater energy release will provide more effective cutting action.
Thus it would seem that higher rotational speed would be desirable. ~owever, rotational speed also imposes a centrifugal load on the filament which is C = mw r where m = mass w = speed of rotation r = distance from center of rotation Thus each filament segment exerts a force on every other segment nearer the center of rotation or point of restraint. Above a threshold speed, the summation of the forces acting on the e~tended filament yields a total force at the point of restraint such that at that point the tensile strength of the filament is exceeded producing failure.
In flail cutting the filament does not assume a straight radial position relative to the axis of rotation of the cuTtter head (even when not encountering obstructions) inasmuch as wind force acting upon the extended end portion of the filament imparts a drag thereon.
Thus, the extended end portion of the filament continuously curves rearward relative to the direction of rotation. As the filament encounters obstructions, phenomena occur which coact to shorten the operating life of the filament. These phenomena will be called impact shear, impact abrasion, impact heating and tensile fatigue.
When a segment of the filament, traveling at high veLocity, encounters an obstacle, the inertia of the free end of the filament and the inertia of the obstacle encountered acting in opposition to the inertia of the filament segment causes the filament to partially "wrap around" the obs-tacle. During this "wrap around" period the local Pilament segment experiences shear forces whose magnitude are a function of the contour of the obstruction, the mass of the obstruction, the velocity of the filament and the cross sectional mass and geometry of the filament. If the obstacle encountered has sufficient mass the filament will fail at the point of contact with the obstacle or at some adjacent point if there is a weakness in the filament. Impact shear occurs with every impact 90 that the filament encounters shear loading at very high frequency. ~ven where the individual impact does not produce instaneous failure, it induces localized damage making the filament more susceptible to future failure at that point. Thus, impact shear has an accumulative effect which is an important factor in the operating life e~pectancy of a given segment of the filament. Also, because the kinetic energy of a given segment increases with the square of its distance from the center of rotation, the outermost segments of the filament are most susceptible to failure in a shear mode.
Filament abrasion occurs when an obstruction has sufficient mass and geometry to actually cut away a portion of the filament. Thus, the filament may be "niched" or split at a given point but may not, at that instant, totally sever. This form of damage typically occurs when the filament encounters very dense obstacles such as rocks or curbing, asphalt and similar physical featurès and also has an accumulative effect in shortening the operating life of a filament segment. In the case of plastic filaments, this phenomenon frequently results in the "split end" condition where the tip of the filament splits into several small fibers. Of course, a plurality of smaller fibers, due to their greater flexibility and reduced inertia do not operate as efficiently in cutting vegetation. Many metallic and composite filaments exhibit shear and abrasion resistance superior to that obtainable from plastic filaments. Accordingly, metallic and composite fibers are less susceptible to failure due to abrasion and shear.
Impact heatillg is generated by the rubb;ng action which occurs when a filament section impacts with an obstruction and by hysteresis as the filament undergoea deformation as a result of impact. In general, insufficient heat is generated to melt a plastic filament segment at 8~
the point of impact, although heating as a result of impact becomes a more serious problem as larger diameter filaments are used.
It i.s obvious that an individual Eilament encounters a very high number of impacts per second. This induces very high frequency vibrations in the filament. Plastic filaments do not transmit vibrations as well as metallic filaments and a smaller percentage of the overall tensile load is transmitted to the point of restraint. The most severe tensile load on the filament occurs at the point where it is constrained. With conventional cutting heads this is either at the opening in the housing or hub or inside the hollsing or hub on the spool upon which the filament is wound, or a combination of the two.
Plastic, metallic and composite filaments are all subject to tensile failure at the point of constraint. Since the fatigue of the filament is a combined function of its angular velocity, its extended length and mass, the loading it encounters from impact with obstructions, and the structure by which it is restrained, if fatigue of the filament is suitably controlled, filaments utilized for cutting purposes can be employed with superior results.
Acceptance of the prior assertion requires a statement of the fundamental problem of flail cutting in the context of the present state of the art.
The present state oE the art is such that filament breakage is believed to be the fundamental problem. This is evidenced by the attention devoted to minimizing filament breakage. It has been recognized that breakage often occurs at the point of primary filament restraint which is typ:ically at the exit opening in the cover which houses one or more filament reservoirs. Various devices have been employed, such as the "curvilinear bearing surfaces" generally described in U.S. patents Nos. 3,708,967, 3,826,068 and 3,859,776, to reduce the incidence of such breakage.
However, it is asserted that filament breakage per se is not the Eundamental problem and that optimum system performance will result when the total breakage rate is sacrificed to obtain preferential breakage which will be hereinafter explained.
The fundamental problem, with the present state of the art, is that filament breakage causes inconvenience and greatly reduces the productivity of the cutting system. This stems from the necessity of stopping the rotating filament reservoir in order to activate the various mechanisms which have been devices to enable additional filament to be extended. There is an inherent attendant drawback in that the user becomes accustomed to frequent physical contact with portions of the cutting system which are capable of imparting injury.
The user approaches physical contact with a rigid steel lawnmower or edger blade with caution on the relatively infrequent occasions when it is necessary. However, presently available flail cutting systems require such contact with a frequency which tends to invite carelessness.
In addition, the inconvenience inherent in present filament storage and feed systems inhibits the user in applying the systems to heavy growth and almost totally precludes their use in other applications, such as lawnmowers, where it would be impractical to advance additional Eilament using present feed systems.
Thus, it i9 asserted that the basic pro'blem i8 not one of filament breakage. 'l'he basic problem is to provide a system which controls filament breakage while providing a safe and effective means for dispensing additional filament from the reservoir to replenish segments which are lost.
l`he desirability of an improved dispensing system, particularly one which can be activated and controlled while the device is in continuous ~ ~9~2~
operation, should be obvious. The desirable elements of controlled breakage are as follows.
The filament is an expendable element of the system. However, there are clearly preferred breakage modes. Since the tip segment effects the greatest cutting action, it is abraided and worn away most rapidly. Therefore, the most preferred breakage area is near the end of the extended fiber.
Conversely, the least preferred areas are those segments near the point of restraint, or worse, beyond the point of restraint into the storage area This should be obvious since, if the filament breaks farther from the tip of the cutting end, a greater portion is lost with no commensurate benefit.
Loss of short segments at the tip is much preferred.
There are three approaches which can be used to reduce breakage at the root of the filament. These approaches are reduced operating speed (which reduces the fundamental vibratory frequency and the tensile load), distribution of restraint forces over greater filament lengths (to reduce load concentration), or special restraint of the filament in such a manner as to control the fundamental "breaking" process.
The reduction of speecl tends to reduce the cutting effectiveness because such effectiveness is a direct function of the kinetic energy stored in a segment of the filament. Therefore, lowering the rotational speed is not a desirable approach to reducing filament breakage, because overall performance of the system suffers.
Much has been attributed to the importance of "curvilinear"
bearing surfaces parallel to the axis of rotation at the point of restraint of the filament. These "curvilinear" bearing surfaces have been provided as a means for distributing loading over a greater filament length so as to thereby extend operating life of the filament.
Curvilinear surfaces are disclosed in U.S. patent Nos. 3,708,967, 3,826,068 and 3,859,776. However, the precise contour and function of these "curvilinear" bearing surfaces have not been defined nor has the ~L~g~
effect of their particular contour been precisely explained. The utilization of "curvilinear" bearing surfaces has apparently been adopted as a result oE observation that a sharp corner at the bearing surface results in rapid filament breakage at the point of restraint.
This would be expected due to excess shear and vibratory load concentrations on the filament at that point.
While the use of a "curvilinear" bearing surface eliminates the rapid filament breakage which occurs when a sharp angle at the bearin8 surface is utilized, it still does not actively contribute to selective breakage outwardly of the bearing surface. When breakage of the filament occurs at the bearing surface the filament end will often be retracted within the housing surrounding the spool and it is therefore extremely difficult to extend the desired length of filament from the spool and requires access to the interior of the housing in order to thread the end of the filament to be extended through the opening in the housing for the spool definincg the bearing surface.
~ lowever, if a bearing surface which causes controlled angular deformation oE the filament at the bearing surface is provided and structure enabling selective increment feed of the filament from the spool during operation of the associated cutter is provided, each time a new aection of filament is engaged with the bearing surface that section is subject to tensile and vibratory loading and is therefore partially weakened.
Rcepeated increment feeding of the filament during operation of ttle cutter thereby produces a free end portion oE the filament which has longitudinally spaced weakened zones therealong. These longitudinally spaced weakened zones are, as well as intermediate portions of the filament, subject to impact with the material being cut and impact shear and abrasion and friction heating as a result thereof. These phenomena tend to further weaken the spaced pre-wealcened zones more rapidly than the "virgin" filament there-between and the outermost weakened zone is of course more severely weakened than the preweakened zones spaced inwardly thereof. This results in asubstantial majority of the breakage of the filament as a result of its use in cutting vegetation occurring at the outer end portion of the free end thereof. Therefore, inasmuch as the filament should be considered as an expendable item, a cutter including means for increment feed of the filament during operation of the cutter and also means for pre-weakening the filament in the zones thereof successively with the bearing surface of the housing is operable in a substantially contimlous manner through repeated increment feeding of the filament in order to renew the outer end portions thereof which are repeatedly broken therefrom. During operation of the cutter, as successive segments of filament are broken from the free end thereof and the filament is fed in increments from the spool, the localized weakened zones disposed outwardly of the bearing surface experience cumulative stress concentration and their tensile properties degenerate. Thus, a weakened zone toward the free end of the filament, having experienced more impact with the vegetation being cut than weakened zones closer to the bearing surface, is weaker and more likely to sever. This yields selective severing or breakage of the filament with a higher incidence of breakage near the tip of the filament. Therefore, increment feeding of the filament may be continued during operation of the cutter with a substantial reduction of unwanted breakage of the filament at the bearing surface or inwardly thereof necessita-ting operation of the cutter to be terminated in order to manually extend a new length of filament from the housing.
The preferred geometry of the bearing surface is a function of the filament geometry, material properties, the extended filament length and the average speed of rotation. ~lowever, it has been determined that for various availab]e metallic, non-metallic and composite filaments, and for speeds of rotation between lO00 and 10,000 rpm a bearing surface with at least one angular break where the included angle is not greater than 178 nor less than 100 will produce localized filament compression and weakening to _g _ `` 1~9~g~
achieve the deslrec] reslllt of selective hrea'~.age. ~here multiple angular surfaces are employed they may be separated by straight or curved surface segments without noticeable diEference but the distance between pairs of relatively angulated surface should be substantially less than the lenoth of the increment of filament extended by one acdvance of the feed mechanism so as to insure that the e:ctended seg-ment of the filament has discrete leakened zones.
The cutter system of the instant invention utilizes a rotary cutter head including a coaxial spool from which a filament l~ound on the spool may be fed in increments therefrcm and the spool is enclosed witilin a housing stucture defining an opening therein through ihich the end of tlle f:ilament extends with the surfaces of the housing de-fining the trailing surace of the opening including at least one angular surface for pre-wealcening, to a slight degree, of that portion of the filament engaged with the bearing surface so that each time a new increment of fila-ment is feed from the spool a new spaced weakened ~one of the filament will be added to the end portion thereof pro-jecting outwardly of the opening.
The nnechanism by which the fiLament may be fed in increments from the spool is operable during operation oE
the~ cutter wilell the spc)ol :is rotatin~ at high speeds.
The mechanisnl wherel)y the Eilament may be fecl in :increments Erom the SpOO 1 i.S also deeme(l to be ne~. Thus the l~loadest deillit:ion of tile present :inventiorl may be seen to T)rovi~le an appnr.l~us or cutting vegetatic)n atld the lil;c E
32~
comprisinp, a support, a rotary member journa]led from the support for rotation at hioh speed in a cutting plane, having storage means and including a support portion definino a peripherally located bearing surface, at least one elongated flexiE)le flail member having storage and free end portions, the storage end portion being supported from the storage means for feeding oE the free end portion therefrom~ the free end portion extending outwardly from the axis of rotation of the rotary member and being tr~ined across the bearing surface, means for driving the rotary melnber in one direction of rotation, the bearing s~rface facin~ ~enerally in the direction of rotation of the rotary member, the storage means includino spool means llpon which the storage end portion is wound, the spool means being supported frorn the rotary member for rotation relative thereto, the spool means being disposed substantially concentric ~lith the axis of rotation member and rotatable relative to the support portion, a dr:ive member mounted on the rotary member for rotation therewith and axially shiftable thereon for movement between first and second posit:ions, the drive member and spool including coactino portions engageable with each other to drive the spool, in the one direction, w-itEl the drive melllber when said drive member is in the first position and operat;ve to allow first an(l second pre(leterllline(l ang~llar rotatioll, only, oE the spooL in thc opposite (I:irection relative to the rotary 1nem-ber as 1 reslllt of sllifting of the dr:ive mel!lber from tEle ~:~98;~
first position to the second position and then back to the first pos;tion from the second position.
The present invention also may be considered as providing the method oE feeding monofilament from the rotary head of a filament trimmer in a manner to enhance breakage of the filament outwardly of the hea(l during high speed ro-tation of the latter and to thus enhance centrifugal feed-ing of the filament by reducing brealcage thereof closely adjacent the head, the method comprising sequentially longitudinally feeding the nlonofilament from a storage loca-tion within the head in short increments while the mono-filament is trained arross bearing surface edge means facing in a direction extending outwardly from the axis oE rotation of the head inclined in the direction of rotation thereof and with the bearing surace of a configuration such to cause pre-wealcening in the area of the monofilament engaged with the bearing surface edge means after a predetermined time of operation of the trimmer, whereby successive pre-weakened areas of the monofilament may be fed outwardly of the bearing surface e`dge means and the cumu]ative further weakening of the areas due to impact with vegetation and the greater impact of tlle outermost end portion of the monofila-ment will cause controlled brealcage of the monofilament out-wardly from the bearing sur~ace edge mean9 rather than Qd jacent or :inwarclly tht!reof.
Fig~lre 1 is a fraglllent~ry s:ide e]evat:ional view of the cutter ~ysteln oE tl~e inst-lllt invention ~ith portiolls of the cllttc~r beinp brc)lcen a\~.ay an(l i]lustrQtetl in verticaL
~'l]a ~1~8Z~:~
s e c t i o n s ;
Figure 2 is an enlarged hor-izontal sectional view taken substantially ' .~,1 llb :iLiL98Z~l upon the plane indicated by the section line 2 2 oE Figure 1, Figure 3 is a fragmentary enlarged transverse vertical sectional view taken substantially upon the plane indicated by the section line 3-3 of Figure l;
Figure 4 is a horizontal sectional view taken substantially upon the plane indicated by the section line 4-4 of Figure 3;
~ igure 5 is a horizontal sectional view taken substantially upon the plane indicated by the section line 5-5 of Figure 3;
E'igure 6 is an enlarged horizontal sectional view of the portion of the spool enclosing housing having the feed opening formed therein and illustrating the manner in which the filament is deflected by the juncture of relatively angulated surfaces defining the feed opening; and Figure 7 is a fragmentary schematic view illustrating the manner in which increment feeding of the filament from the spool is accomplished.
Referring now more specifically to the drawings the numeral 10 generally designates the flail-type cutter of the instant invention. The cutter 10 includes an upwardly and outwardly inclined main handle 12 from ~Jhose lower end a lightweight gasoline engine 14 is supported. The engine 14 includes a downwardly directed rotary output shaft 16 and the upper end of the handle includes a horizontally directed portion 18 having a hand-grip 20 disposed thereon.
The en8ine 14 includes an air intake 22 to which the discharge end of an inlet hose 2~ i8 connected and the outlet end of the discharge hose 24 is connected to a branch tube 26 which opens into the interior of the lower end of the hollow tubular handle 12. The free end of the upper end portion 18 is open and has an air filter assembly 28 secured thereover. AccordinglyJ ai.r is supplied to the air inlet 22 through the tubular handle 12, it being understood that the air inlet 22 leads into the air and fuel passages of a carburetor (not shown) of the ~91~
engine 14.
A second tubular handle 30 is disposed forwardly of, generally parallels and is supported from the handle 20 by means of suitable brackets 32. The upper end of the handle 30 includes a horizontal forwardly directed portion 34 having a second handgrip 36 mounted thereon and the forward end of the portion 34 is closed by means of a removable cap 38. The handle 30 defines a fuel tank and the lower end thereof is closed and the inlet end of a gasoline feed line 40 opens into the lower end of the handle 30, the outlet end of the gasoline feed line 40 opening into the fuel chamber of the carburetor (not shown) of the engine 14.
The engine 14 is of the manual start type and includes a pull cable 42 slidably received through an outer housing 44 extending upwardly along the handle 12 and 30 and having its upper end supported from a bracket 46 anchored relative to the handles 12 and 30. The upper end of the cable 42 has a pull handle 48 mounted thereon whereby the engine 14 may be started from the upper ends of the handles 12 and 30.
A guard plate 50 is secured beneath the horizontally forwardly directed lower end portion 52 of the handle 12 and includes a rearwardly and outwardly flared as well as downwardly curved rear portion 54.
The guard plate 50, handle and engine 14 may all be considered parts of a support from which the shaft 16 of the engine 14 i8 rotatably journalled.
With attention now invited more specifically to Figures 2, 3, 4 and 5 of the drawings it may be seen that the shaft 16 includes a tapered lower end portion 56 having a blind threaded bore 58 formed therein. The lower end portion 56 is snugly seated in the tapering inner end portion 60 of an upwardly opening counterbore 62 formed in the upper end of an upstanding sleeve 64. The sleeve 64 has an axial bore 66 formed therethrough and the lower end of the bore 66 includes 30 first and second counterbores 68 and 70, the counterbore 68 being smooth and terminating inwardly at the lower end of the bore 66 and the counterbore 70 being slightly larger in diameter than the counter-bore 68 and threaded. The sleeve 64 is secured on the shaft 16 by means of a bolt 72 having its head seated in the counterbore 68 and its threaded shank portion passed through the bore 66 and t.hreaded in the blind bore 58. The upper end of the sleeve 64 includes a diametrically enlarged terminal end 74.
The sleeve 64 has a pair of opposite side longitudinally extending flats 76 formed thereon and a hub sleeve 78 is mounted on the sleeve 64 and keyed thereto for rotation therewith by means of the flats 75. The hub sleeve 78 includes diametrically opposite radially outwardly projecting pins 80 and the lower end of the hub sleeve 78 is diametrically reduced as at 82 and defines a downwardly opening circumferential seat 84 in which to seatingly receive the upper end of a compression spring 86. In addition, a lower terminal end of the hub sleeve 78 includes a downwardly opening counterbore 88 defining a downwardly facing circumferential rib 90 on the lower end of the hub sleeve 78 for a purpose to be hereinafter more fully set forth.
The upper end of the hub sleeve 78 has a thrust washer defining annulus 92 recessed therein and the diametrically enlarged upper terminal end 74 of the sleeve 64 overlies and abuts the inner periphery of the thrust washer defining annulus 92.
A hori~ontally disposed storage spool 94 including upper and lower flanges 96 and 98 is mounted on the hub sleeve 78 for rotation relative thereto and the upper flange 96 includes an inner peripheral portion 100 which seats against an upwardly facing annular shoulder 102 defined adjacent the upper end of the hub sleeve 78. Additionally, the lower flange g8 includes an inner peripheral portion 104 which snugly receives the lower end of the hub sleeve 78 therethrough and ~;3L98Z9~
against which the lower end of the compression spring 86 bears.
A housing referred to in general by the reference numeral 106 is provided and includes a cylindrical wall portion 108 disposed in upstanding position and closed at its lower end by means of a lower end wall 110 having a central opening 112 formed therethrough. The housing opens upwardly and has a sleeve 114 secured in the opening 12 and keyed to the lower end portion of the sleeve 64 which is also provided with diametrically opposite flats 116 corresponding to the flats 76. The upwardly opening housing 106 snugly but rotatably receives the spool 94 therein and the cylindrical wall portion 108 of the housing 106 includes a pair of diametrically opposite radial openings 118 formed therethrough in which metal grommets 120 are secured.
Two lengths o plastic monofilament 122 have one end of each wound on the spool 94 between the flanges 96 and 98 and anchored relative to the spool 94 as at 124. The free ends of the filaments 122 extend tangentially away from the hub 126 of the spool 94 and pass outwardly through the grommets 120 and include free end portions 128.
The spool 94 is formed of upper and lower halves which are assembled and welded together in any convenient manner. The inner surface of the hub 126 of the spool 94 includes a circumferentially extending inwardly opening groove 130 (see Figure 7) and the lower half 132 of the spool 94 includes circumferentially spaced ribs 134 which project upwardly into the lower half of the groove 130 while the upper half 136 of the spool 94 includes ribs 138 which project downwardly into the upper half of the groove 130. The ribs 134 and 138 are spaced circumferentially centrally between adjacent ribs 138 and 134, respectively, whereby the groove 130 is transformed into a serpentine passage. The outer ends of the pins 80 are received in the serpentine passage and the compression spring 86 normally biases the hub sleeve 78 upwardly along the sleeve 64 to the uppermost position thereof illustrated in Figure 3 with the thrust washer defining amlulus 92 abutted against the underside of the diametrically ~15-z~
enlarged upper terminal end 74 of the sleeve 64 and the outer ends of the pins 80 received in the corresponding upper portions of the groove 130 between adjacent ribs 138.
A retaining cup referred to in general by the reference numeral 140 ~see Figure 3~ is provided with a central threaded attaching stud 142 and the cup 140 is secured to the underside of the housing 106 by means of the threaded stud 142 being threadedly engaged in the threaded counterbore 70, a compression spring 144 being disposed about the threaded stud 142 and bet.ween the lower end of the sleeve 64 and the opposing upwardly facing central inner surfaces of the cup or cap 140.
The outer periphery of the lower end wall 110 is relieved as at 146 to minimize the area of contact 148 of the lower end wall 110 of the housing 106 with the underside of the lower flange 98 of the spool 94 and the central area of the lower end wall 110 is further relieved as at 150 to receive the rib 90 therein when the hub sleeve 78 is urged do~lwardly against the biasing action of the compression spring 86.
A mounting block 152 i5 secured to the underside of the shield or plate 50 by means of attaching fasteners 154 and a bifurcated actuating lever 156 is pivotally supported from the mounting block 152 as at 158 and has its furcations 160 disposed immediately above the thrust washer defining annulus 92 outwardly of the diametrically enlarged upper terminal end 74 of the sleeve 64. The free end of the lever 156 has one end of a Bowden cable assembly generally referred to by the reference numeral 162 anchored relative thereto and the other end of the Bowden cable assembly 162 is anchored to a control lever 164 pivotally supported Erom the upper end portion 18 of the handle 12 as at 166.
It iB to be noted that upon an upward pull on the lever 164 the Bowden cable assembly 162 will exert an upward pull on the associated end of the lever 156 so as to swing the furcations 160 of the lever 156 downwardly into contact with the thrust washer defining annulus 92 of the hub sleeve ~98~
78. This of course will cause the hub sleeve 78 to be shifted downwardly relative to the sleeve 64 against the biasing action of the compression spring 68 and the pins to shift from the upper half of the groove 130 to the lower half of the groove 130.
With attention now invited more specifically to Figure 6 of the drawings, it may be seen that the outer portions of the grom~ets 120 are bevelled as at 168 so as to define spaced first and second inner and outer corner bearing surfaces or edges 170 and 172 in the outer end of each grommet 120, the grommets 120 being substantially cylindrical in cross sectional shape.
In operation, the cutter 10 is used to cut vegetation 176 in the manner illustrated in Figure 1 of the drawings during operation of the engine 14 to spin the spool 94 and housing 106 at high speeds.
The outer end portions 128 of the filaments 122 cut with a flail action on the vegetation 1i6 during rapid spinning of the spool 94 and housing 106.
As indicated in Figure 7 of the drawings the pins 80 move in the direction of the arrows 178 and thus bear against diametrically opposite ribs 138 of the upper half 136 of the spool 94 and cause the latter to move in the direction of the arrow 180. However, when the lever 164 is actuated, the lever 156 forces the hub spool 78 downwardly so as to shift the pins 80 from the solid line position thereof illustrated in Figure 7 to the phanto~
line position 182 of Figure 7 in the lower half of the groove 130. Then, because of the windage drag and centrifugal force acting on the outer end portions 128 of the filaments lZ2 and the air drag on the upwardly projecting radial vanes 184 carried by the upper flange 96 of the spool 94, the spool 94 lags in rotation relative to the housing in order that the pins 80 may assume the positions thereof illuatrated in phantom lines as at 186 in Figure 7 to thereby extend a first increment of monofilament 122 from the spool 94 through the grommet 120. Thereafter, when the lever 164 is released, the hub ~:~9~
s]eeve 78 shifts back up to the posit;on thereof illustrated in Figure 3 under the biasing action of spring 86 so as to raise the pins 80 to the phantom line positions 187 in the upper half of the groove 130 and air drag and centrifugal force acting on the filament end portions 128 and the vanes 184 causes the spool 94 to further lag in rotation whereby the pins 80 assume the phantom line positions 188 in Figure 7 to extend or feed further segments of filaments 122 from the spool 9~. Thus, upward swinging of the lever 164 causes a first increment of each filaMent 122 to be fed or extended from the spool 94 through the corresponding grommet 120 and release of the lever 164 causes a second increment of each filament 122 to be extended or fed from the spool 94 through the corresponding grommet 120. The increment feeding of filaments 122 from the spool 94 may of course be carried out during operation of the cutter 10. Further, the successive angle edges 170 and 172 cause localized loading of the filaments 122 and thus those points of contact of the filaments 122 with the grommets 120 are weakened. However, upon initial operation of the cutter 10 successive segments of filament are fed from the spool 94 by actuation of the lever 164 and the extended end portions 128 of the filaments 122 disposed outwardly of the grommets 120 thereby include longitudinally spaced areas thereof which are weakened. Inasmuch as the outermost weakened areas travel at higher peripheral speeds, they impact the vegetation 176 with greater force and are more rapidly further weakened.
This results in breakage of the filaments 122 most likely occurring at the outermost weakened areas thereof.
Thus, the incidence of breakage of the filaments 122 adjacent or inwardly of the grommets 120 is substantially reduced and continuous operation o the cutter 10 may be carried out. Shoulcl the fi.laments 122 exit from the hou~ing 106 along a large radius curvilinear bearing surface as has been practiced heretofore, sufficient localized loading of the filaments at the bearing surfaces to support controlled breakage of the filaments outwardly of the point they exit from the housing 106 does not occur. Rather, breakage of 9~
the filaments 122 may occur inwardly of the housing 106 at the points of constrainment of the filaments on the spool. When such brea~age occurs the free ends of the filaments 122 will attain positions inwardly of the grommets 120 thereby rendering the feed mechanism of the filaments 122 inoperative and necessitating that operation of the cutter 110 be terminated so that the cup 1~0 and housing 106 may be removed in order to thread the free end portions of the filaments 122 outwardly through the grommet 120.
In addition to providing localized loading on the filaments 122 as the latter are fed through the grommets 120, the angle edges 170 and 172 tend to absorb the tension forces on the filaments 122 due to centrifugal forces acting upon the free ends 128 thereof and to thereby prevent such tension forces from being transmitted inwardly of the housing 106 and excessive abrasion of the outer convolutions of the filaments 122 with adjacent convolutions thereof and subsequent breakage of the filaments 122 within the housing 106.
It is important that the openings through the cylindrical wall portion 108 of the housing 106 through which the filaments 122 extend be substantially circular in cross sectional shape as accomplished by the grommets 120. In this manner, inasmush as the free ends 128 of the filaments 122 can vibrate considerably in vertical directions, excessive loading of the filaments 122 at the outer ends of the grommets 120 does not occur and breakage of the filaments 122 at their exit points from the grommets 120 is maintained at a minimum. Further, localized loading of the filaments 122 at the outer end of the grommets 120 may be effected by a single angular edge at either 170 or 172. However, in some instances it has been found to be beneficial to provide a pair of successive angular edges as at 170 and 172 It will also be noted from Figure 4 of the drawings that each filament 122 is deflected in opposite directions by its passage through the grommet 120. Although this successive opposite deflection of the il29~
monofilament 122 is not necessary, it does reduce excess tension forces acting upon the monofilament 122 inwardly of the grommet 120 and thereby greatly reduces abrasion of the outer convoLution of the monofilament 122 within the housing 106 against adjacent convolutions of the monofilament 122.
Those surfaces of the ribs 134 and 138 which face in the direction opposite to the directions 178 and 180 may be inclined toward the center of the groove 130 either in the direction of the arrows 178 and 180 or opposite to the direction of the arrows 178 and 180, depending upon the strength of the spring 86 and the expected wind drag forces tending to retard rotation of the spool 94 relative to the hub sleeve 78.
The filaments may be of metallic materials, non-metallic materials or composite materials and only one filament need be used to perform a cutting operation. Further, the specific configuration of the bearing surface or surfaces is determined by the material of which the filaments are constructed, the expected rotational speed of the housing, and the inertia generated by the extended ends of the filaments at that speed. However, the configuration of the bearing surfaces is such to attain the aforementioned controlled breakage of the filaments adjacent their outer free ends rather than adjacent or inwardly of the bearing surfaces therefor.
Claims (7)
PROPRTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A filament type trimmer for cutting vegetation and the like, comprising:
a support having an axis;
a rotary member coupled with said support for high speed rotation about said axis in a cutting plane;
means for driving said rotary member;
a filament having storage and free end portions, said storage portion carried on said rotary member and said free end portion extending radially from said axis; and means for selectively feeding out incremental quantities of said storage portion of filament, said feeding means comprising:
a spool means for supporting the storage portion of filament in a wound condition said spool means being drivingly inter-engageable with said rotary member, and a pair of complementary means for controlling said driving inter-engagement between said spool means and said rotary member, one means disposed on said spool means and one means interposed between said spool means and said rotary member, one of said complementary means comprising at least two rows of spaced members, said rows of members being staggered, and the other means comprising at least one engagement member, and means for selectively shifting said engagement member between a first position in which said engagement member is aligned interchangeably with one of said rows of spaced members and a second position in interengageable alignment with the other rows of spaced members.
a support having an axis;
a rotary member coupled with said support for high speed rotation about said axis in a cutting plane;
means for driving said rotary member;
a filament having storage and free end portions, said storage portion carried on said rotary member and said free end portion extending radially from said axis; and means for selectively feeding out incremental quantities of said storage portion of filament, said feeding means comprising:
a spool means for supporting the storage portion of filament in a wound condition said spool means being drivingly inter-engageable with said rotary member, and a pair of complementary means for controlling said driving inter-engagement between said spool means and said rotary member, one means disposed on said spool means and one means interposed between said spool means and said rotary member, one of said complementary means comprising at least two rows of spaced members, said rows of members being staggered, and the other means comprising at least one engagement member, and means for selectively shifting said engagement member between a first position in which said engagement member is aligned interchangeably with one of said rows of spaced members and a second position in interengageable alignment with the other rows of spaced members.
2. An apparatus for cutting vegetation and the like comprising a support, a rotary member journalled from said support for rotation at high speed in a cutting plane, hav-ing storage means and including a support portion defining a peripherally located bearing surface, at least one elongated flexible flail member having storage and free end portions, said storage end portion being supported from said storage means for feeding of said free end portion therefrom, said free end portion extending outwardly from the axis of rota-tion of siad rotary member and being trained across said bearing surface, means for driving said rotary member in one direction of rotation, said storage means including spool means upon which said storage end portion is wound, said spool means being supported from said rotary member for rotation relative thereto, said spool means being disposed substantially concentric with the axis of rotation of said rotary member and rotatable relative to said support por-tion, a drive member mounted on said rotary member for rota-tion therewith and axially shiftable thereon for movement between first and second positions, said drive member and spool means including coacting portions engageable with each other to drive said spool means in said one direction, with said drive member, when said drive member is in said first position, and operative to allow first and second predeter-mined angular rotation, only, of said spool means in the op-posite direction relative to said rotary member as a result of shifting of said drive member from said first position to said second position and then back to said first position from said second position.
3. The combination of claim 2 wherein said spool means includes means defining an inwardly opening annular groove extending about said spool means concentric with said axis, said spool means including means defining abutments in axially opposite ends of said groove spaced alternately thereabout, said drive member including a portion disposed radially inwardly of said groove and having an abutment engageable member supported therefrom selectively shiftable into opposite ends of said groove for alternately abutting said abutments upon shifting of said drive member between said first and second positions.
4. An apparatus for cutting vegetation and the like comprising:
support means adapted to be moved about an outdoor area by an operator;
a rotary member carried by said support and mounted for rotation relative to said support, said rotary member including a support portion defining a peripherally located bearing surface;
means for driving said rotary member;
at least one flexible flail member having storage portion and a free end portion, said free end por-tion extending outwardly from said rotary member, being trained across said bearing surface, and adapted to be moved in a cutting plane upon rotation of said rotary member;
means within said rotary member for containing said storage portion, said means comprising spool means carried by said rotary member; and means for permitting said spool means to be driven with and to rotate relative to said rotary member, comprising complementary, inter-engageable means interposed between said drive means and said spool means, and means for selectively shifting at least one of said inter-engageable means between a first, driving position wherein said complementary means are inter-engaged to effect a driving interconnection between said spool means and said drive means and a second, disengagement position wherein said spool means is disconnected from said drive means; whereby said flail member is selectively fed from said spool means over said bearing surface during rotation of said rotary member;
said bearing surface defining an edge surface over which said flail member is trained of a configuration, dependent upon the physical characteristics of said flail member, such as to cause pre-weakening in the area of said flail member engaged with said edge surface after a pre-determined time of operation, whereby successive preweakened areas of said flail member may be fed outwardly of said bearing surface and the cumulative further weakening of said areas due to impact with vegetation and the greater impact of the outermost area with vegetation will cause controlled breakage of the flail member outwardly from said bearing surface rather than adjacent or inwardly thereof.
support means adapted to be moved about an outdoor area by an operator;
a rotary member carried by said support and mounted for rotation relative to said support, said rotary member including a support portion defining a peripherally located bearing surface;
means for driving said rotary member;
at least one flexible flail member having storage portion and a free end portion, said free end por-tion extending outwardly from said rotary member, being trained across said bearing surface, and adapted to be moved in a cutting plane upon rotation of said rotary member;
means within said rotary member for containing said storage portion, said means comprising spool means carried by said rotary member; and means for permitting said spool means to be driven with and to rotate relative to said rotary member, comprising complementary, inter-engageable means interposed between said drive means and said spool means, and means for selectively shifting at least one of said inter-engageable means between a first, driving position wherein said complementary means are inter-engaged to effect a driving interconnection between said spool means and said drive means and a second, disengagement position wherein said spool means is disconnected from said drive means; whereby said flail member is selectively fed from said spool means over said bearing surface during rotation of said rotary member;
said bearing surface defining an edge surface over which said flail member is trained of a configuration, dependent upon the physical characteristics of said flail member, such as to cause pre-weakening in the area of said flail member engaged with said edge surface after a pre-determined time of operation, whereby successive preweakened areas of said flail member may be fed outwardly of said bearing surface and the cumulative further weakening of said areas due to impact with vegetation and the greater impact of the outermost area with vegetation will cause controlled breakage of the flail member outwardly from said bearing surface rather than adjacent or inwardly thereof.
5. An apparatus for cutting vegetation and the like comprising a support, a rotary member journaled from said support for rotation at high speed in a cutting plane, hav-ing storage means and including a support portion defining a peripherally located bearing surface, at least one elongated flexible flail member having storage and free end portions, said storage end portion being supported from said storage means for feeding of said free end portion therefrom, said free end portion extending outwardly from the axis of rotation of said rotary member and being trained across said bearing surface, means for driving said rotary member in one direction of rotation, said storage means including selectively operable feed means for selectively feeding said flail member from said storage means over said bearing sur-face during rotation of said rotary member at high speed, said bearing surface defining an edge surface over which said flail member is trained of a configuration, dependent upon the physical characteristics of said flail member, such to cause preweakening in the area of said flail member engaged with said edge surface after a predetermined time of operation, whereby successive pre-weakened areas of said flail member may be fed outwardly of said bearing surface and the cumulative further weakening of said areas due to impact with vegetation and the greater impact of the outer-the flail member outwardly from said bearing surface rather than adjacent or inwardly thereof.
6. An apparatus for cutting vegetation and the like comprising a support, a rotary member journalled from said support for rotation at high speed in a cutting plane, having storage means and including a support portion defin-ing a peripherally located bearing surface, at least one elongated flexible flail member having storage and free end portions, said storage end portion being supported from said storage means for feeding of said free end portion there-from, said free end portion extending outwardly from the axis of rotation of said rotary member and being trained across said bearing surface, means for driving said rotary member in one direction of rotation, said storage means in-cluding spool means upon which said storage end portion is wound, said spool means being supported from said rotary member for rotation relative thereto, said spool means being disposed substantially concentric with the axis of rotation of said rotary member and rotatble relative to said support portion, a drive member mounted on said rotary member for rotation therewith and axially shiftable thereon for move-ment between first and second positions, said drive member and spool means including coacting portions engageable with each other to drive said spool means in said one direction, with said drive member, when said drive member is in said first position, and operative to allow first and second pre-determined angular rotation, only, of said spool means in the opposite direction relative to said rotary member as a result of shifting of said drive member from said first pos-ition to said second position and then back to said first position from said second position, said bearing surface defining an edge surface over which said flail member is trained of a configuration, dependent upon the physical characteristics of said flail member, such to cause pre-weakening in the area of said flail member engaged with said edge surface after a predetermined time of opertion, whereby successive pre-weakened areas of said flail member may be fed outwardly of said bearing surface and the cumulative further weakening of said areas due to impact with vegeta-tion and the greater impact of the outermost area with vegetation will cause controlled breakage of the flail mem-ber outwardly from said bearing surface rather than adjacent or inwardly thereof.
7. The method of feeding monofilament from the rotary head of a filament trimmer in a manner to enhance breakage of the filament outwardly of the head during high speed rotation of the latter and to thus enhance centrifugal feeding of said filament by reducing breakage thereof close-ly adjacent said head, said method comprising sequentially longitudinally feeding said monofilament from a storage location within said head in short increments while said monofilament is trained across bearing surface edge means facing in a direction extending outwardly from the axis of rotation of the head inclined in the direction of rotation thereof and with said hearing surface of a configuration such to cause pre-weakening in the area of said monofilament engaged with said bearing surface edge means after a pre-determined time of operation of said trimmer, whereby suc-cessive pre-weakened areas of said monofilament may be fed outwardly of said bearing surface edge means and the cumulative further weakening of said areas due to impact with vegetation and the greater impact of the outermost end portion of said monofilament will cause controlled breakage of the monofilament outwardly from said bearing surface edge means rather than adjacent or inwardly thereof.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000316819A CA1198291A (en) | 1978-11-24 | 1978-11-24 | Rotary flail cutter system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000316819A CA1198291A (en) | 1978-11-24 | 1978-11-24 | Rotary flail cutter system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1198291A true CA1198291A (en) | 1985-12-24 |
Family
ID=4113018
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000316819A Expired CA1198291A (en) | 1978-11-24 | 1978-11-24 | Rotary flail cutter system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1198291A (en) |
-
1978
- 1978-11-24 CA CA000316819A patent/CA1198291A/en not_active Expired
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