Abstract:
An improved head for a flexible line trimmer apparatus is provided. The improved head includes a metal tubing that extends through the head and surrounds a cutting line of selected length. The tubing is provided with a flared exit portal increasing the efficiency of the head. The contact surface eliminates the possibility of the cutting line fusing to plastic surfaces due to heating caused by friction. The head is surrounded with an interior perimeter counterweight to store kinetic energy on each end having a parabolic surface of revolution concentric with the axis of the tubing. A replaceable cartridge is provided to increase the ease of maintenance and the useful life of the head.

Description:
FIELD OF THE INVENTION 
   This invention relates to flexible rotary line trimmers. In particular, this invention relates to a balanced head for a rotary line trimmer in which a metal tube is provided in the head surrounding the trimming line to prevent frictional welding and premature failure of the line and the head. Further the invention relates to a removable cartridge that creates a path for the trimming cutting line and which may be easily removed for cleaning and periodic maintenance. 
   BACKGROUND OF THE INVENTION 
   Rotary line trimmers are widely used for cutting grass, weeds and other plants in the upkeep of lawns and generally clearing vegetation. Line trimmers are typically characterized by a flexible nylon trimming line attached to a rotatable head. The head is attached to a motor shaft which is rotated at high speeds, typically by trigger operation of a small gasoline engine or electric motor. When the head is rotated, the rotating trimming line serves as a cutting blade to cut grass, weeds or other vegetation. The length of the cutting line extending from the head determines the overall diameter of the cutting path. 
   During use of line trimmers the cutting line often becomes worn and breaks off, eventually requiring replacement. Often the cutting line fails at the point where the cutting line extends from the head. One cause is the scoring of the cutting line from sharp or discontinuous surfaces on the head itself. Another cause is stress fractures caused by repeated bending of the cutting line during use. Still another cause is heating of the cutting line due to repeated bending, resulting in softening of the cutting line. Additionally, the heating of the cutting line can fuse the cutting line to the plastic surfaces of the head requiring replacement of the head or dismantling the head to remove the fused cutting line. 
   An additional problem in the prior art occurs after extended use of the line trimmer. The inventor has observed that after extended use, the line trimmer head collects a substantial amount of dirt, debris and plant matter both on the outside and inside of the trimming head. The problem is exacerbated by the presence of lubricating oils and greases typically used in line trimmers and which have a tendency to build up at the line trimming head. In most cases, the debris builds up to the point where it interferes with the mechanical operation of the trimming head. 
   An additional problem in the prior art occurs because the internal working components of the head are generally exposed to the external environment in which the line trimmer is operating. The external environment can include corrosive salt water, sand and salt residue typically found in coastal environments in which line trimmers are often used. Exposure to caustic environments can cause premature failure of the internal working components because of corrosion and salt residue buildup. 
   In prior art examples which include locking blades, the button used to bias the cutting line clamp becomes inoperable as its freedom of movement is blocked by a buildup of debris or corrosion. As the old soiled cutting line is removed from the head, one end must be pulled through the head. As the used cutting line is pulled through the head, dirt, excess vegetation and salt debris are pulled through the head as well. The debris is dislodged inside the head, it eventually blocks the movement of the locking blades requiring tedious cleaning of the internal parts or complete replacement of the entire head. 
   Still a further problem involves excessive wear of the plastic edges where the cutting line contacts the head. After prolonged use, the contact point(s) where the cutting line exits the line trimming head become jagged. The jagged edges wear the cutting line rapidly causing frequent failure and excess welding of the cutting line to the head. In most cases, the failures of the cutting line became so frequent that the entire head must be discarded. 
   Still another problem is friction caused by rotational imbalance in the line trimmer head. Various line trimmers in the prior art have not been adequately balanced about the axis of rotation of the line trimmer shaft. The imbalance results in vibration in the head which further results in additional friction at the exit portal for the cutting line. Additional friction results in premature wear of the head and premature failure of the cutting line. 
   Still a further problem in prior art trimming heads is insubstantial weight of the head. Line trimmers derive a significant amount of their effectiveness from the high speed of rotation of the trimming head. Maintaining the high speed during use requires a significant amount of energy. In use, cutting vegetation absorbs energy and has a tendency to slow the rotation of the head forcing the user to repeatedly back away from cutting to reestablish sufficient rotational speed. Maintaining sufficient rotational speed during use therefore requires larger engines and fuel tanks. However, most line trimmer heads of the prior art are made from injected molded plastic and therefore are of significantly light weight. The light weight of the prior art heads reduces the amount of rotational inertia needed to store energy. Some line trimmer heads of the prior art are provided with counterweights; however, the positioning of the counterweights has not been ideal or sufficient and has lead to other problems such as vibration. 
   Rotary line trimmer apparatus incorporating single length cutting lines having heads of various designs are known in the art. 
   U.S. Pat. No. 5,303,476 to Tuggle discloses a line head for a rotary line trimmer apparatus that securely holds a single cutting line. The apparatus includes a head with raised portions on its underside that define two channels. A bail including a clasp and a lip is recessed in the first channel. A length of cutting line is recessed in the second channel. The bail rotates between an open position facilitating insertion of the cutting line and a closed position designed to hold the cutting line during operation. While this apparatus secures a cutting line, it does not prevent premature cutting line breakage or minimize failure from accumulated debris. 
   U.S. Pat. No. 6,401,344 to Moore et al. discloses a head for a line trimming apparatus that includes a sliding cutting line clamp and generously curved cutting line contact points. The apparatus defines a pair of clamp arms that extend through a cutting line channel and secure a cutting line in the cutting line channel. The cutting line clamp is normally biased with a spring in the clamping position whereby the clamp arms press the cutting line against the cutting line channel. While the &#39;344 patent discloses a method to more easily replace a trimming cutting line it does not address the issue of premature cutting line breakage due to heating or the issue of fusing of the cutting line to the internal plastic parts of the head. 
   U.S. Pat. No. 7,111,403 to Moore also discloses a head for a line trimming apparatus with a set metal inserts partially forming a cutting line channel. The inserts are sandwiched between upper and lower body sections of the head and provide a partial contact surface for the cutting line&#39;s lateral surfaces. A problem with the design disclosed in the &#39;403 patent is that the cutting line tends to fuse to the internal plastic surfaces above and below the metal inserts. Also the minute gap that exists between inserts and the internal plastic surfaces creates a discontinuity in the cutting line channel which generates friction with the cutting line during use and results in the cutting line fusing itself to that gap and the internal plastic surfaces. The discontinuities also invite fouling and corrosion due to their tendency to scrape off dirt and debris from the cutting line inside the head. 
   SUMMARY OF THE INVENTION 
   The present invention provides an improved head for a flexible line trimmer that addresses the premature breaking and fusing of the cutting line due to the cutting line&#39;s increased temperature caused by the friction between the cutting line and the rotating head. The present invention also addresses the problem of excessive debris build up and premature failure of the head by damage to the cutting line exit portal. 
   The present invention also addresses the problem of insufficient head weight and injected molded plastic housings and imperfections in the counterweight balance which leads to inefficient cutting and vibration. 
   A preferred embodiment is characterized by a molded plastic housing including continuous metal tubing that extends through the head and receives a trimming cutting line of selected length. The cutting line is releasably clamped in the tube and extends out from opposite sides of the head. At the cutting line insertion point leading the cutting line into the tube is a convex frustroconical shaped eyelet. The eyelet engages the cutting line during rotation of the head and prevents excessively acute or sharp bending of the cutting line. The combination of the eyelet and the tubing creates a continuous metal surface surrounding the cutting line isolating the internal parts of the head from the environment and the cutting line from contact with the plastic portions of the head. The tube and eyelet eliminates the possibility of the cutting line fusing to the plastic surfaces of the head due to heating caused by friction. The metal eyelet also prevents the opening edges from becoming uneven and prematurely damaging the cutting line. 
   The head is also characterized by a pair of matched perimeter counterweights. The even distribution of mass at the perimeter of the rotating head effectively stores kinetic energy and allows a smaller diameter head to function as if it were bigger and/or heavier. The smaller diameter head provides for an increased length of cutting line to be exposed during operation, which ultimately prolongs operating time between replacements and provides a greater cutting area than previously possible with similarly sized heads of the prior art. The weighted interior perimeter counterbalance also allows for the use of a lighter, more economical, less powerful engine to rotate the head. Further, smaller, lighter fuel tanks are necessary thereby decreasing the overall operational weight of the line trimmer. The interior perimeter counterbalance also serves to dissipate the heat generated by the friction between the cutting line and the opening in the head which further reduces wear and premature failure of the cutting line. 
   In one embodiment, the metal tubing is characterized by a removable cartridge. The removable cartridge can be replaced when the exit ports become worn thereby extending the useful life of the head. The removable cartridge also serves to prevent fouling of the integral components of the head by effectively isolating the interior of the head from debris and promotes efficient cleaning of the head after prolonged use. 
   The present invention also provides a head for a line trimmer characterized by a body and a cover which are typically secured to a motor shaft of a line trimmer and encloses a sliding cutting line clamp which receives a trimming cutting line of selected length and thickness. 
   In one embodiment the cutting line clamp is characterized by a single clamp arm which extends from a clamp base through the metal tube in which the cutting line resides. The cutting line clamp has a clamp slot and is normally biased in a clamping position in which the clamp arm presses the trimming cutting line against the interior of the metal tube. The clamp slot is of varying radii to accommodate different styles of cutting line. 
   In another embodiment of a head in accordance with the invention, the cutting line clamp comprises two spaced apart clamp arms that are engageable with a cutting line to forcibly urge the cutting line against the interior of the metal tube. Both clamp arms have a clamp slot through which the cutting line passes. A spring biases the cutting line clamp in a clamping position in which the clamp arms press the cutting line against the interior of the metal tube such that the cutting line is secured. 
   In another embodiment of this invention a head for a rotary line trimmer is provided that includes a convex funnel shaped eyelet incorporated into the exit portals of the metal tube or into the perimeter counterweight that guides the cutting line during rotation of the head preventing the cutting line from contacting exterior plastic surfaces of the head during operation and fusing. 
   Those skilled in the art will further appreciate the above-mentioned features and advantages of the invention together with other important aspects thereof upon reading the detailed description that follows in conjunction with the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the detailed description of the preferred embodiments presented below, reference is made to the accompanying drawings. 
       FIG. 1  is an elevation view of an assembled head of a preferred embodiment of the invention including upper and lower covers. 
       FIG. 2  is a plan view of the lower cover of the preferred embodiment of the invention. 
       FIG. 3  is a plan view of the upper cover of the preferred embodiment of the invention shown in  FIG. 1 . 
       FIG. 4  is an isometric view of the arbor. 
       FIG. 5  is an isometric view of a dual locking blade, a spring, and a button. 
       FIG. 6  is an isometric view of the underside of a button. 
       FIG. 7  is an isometric view of a locking blade. 
       FIG. 8  is a plan view of the lower cover of an alternate embodiment of the invention. 
       FIG. 9  is the plan view of the upper cover of the embodiment shown in  FIG. 8 . 
       FIG. 10  is a plan view of the lower cover of an alternate embodiment of the invention. 
       FIG. 11  is the plan view of the upper cover of the embodiment shown in  FIG. 10 . 
       FIG. 12  is a plan view of a lower cover of an alternate embodiment of the invention showing a replaceable modular section. 
       FIG. 13  is an isometric view of the replaceable cartridge. 
       FIG. 14  is the plan view of the upper cover of the embodiment shown in  FIG. 12 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIGS. 1 ,  2  and  3 , a preferred embodiment of a head for a rotary line trimmer is shown. Head  100  has a generally disk-like housing formed by upper cover  105  and lower cover  106 . The housing in the preferred embodiment is constructed of injection molded nylon. Other materials with suitable strength and rigidity to maintain the positions of internal parts can be used such as fiberglass and polypropylene. Head  100  has two diametrically opposed openings where the single cutting line protrudes. Head  100  mounts on the threaded rotating drive shaft of a typical rotary line trimmer by way of an arbor  400 . Arbor  400  is provided with an arbor hole  420  and is threaded to accept the lower portion of the line trimmer drive shaft. In an alternate embodiment the drive shaft passes through the head by way of a shaft hole and is secured to the head with a shoulder bolt (not shown). Upper cover  105  has a rounded exterior shape and a generally flat top surface including arbor hub  109  defining a circular opening through which arbor  400  extends. Button opening  814  and button indention  824  when mated with button opening  114  and button indention  124  create a depressed, rectangular aperture through which button  210  extends. 
   Lower cover  106  has a rounded exterior shape defined by housing  108  and a generally domed surface including four stanchion holes  119 . Lower cover  106  includes two diametrically opposed eyelet slots  134  and  135 , each forming a semicircular impression. Eyelet support ribs  136  and  137  are also provided. The eyelet slots and support ribs also form seats for the arcuate counterweights. In  FIG. 1  a single arcuate counterweight is shown so that the details of eyelet slots and support ribs can be seen. In the preferred embodiment, two identical arcuate counterweights are provided mounted at opposite sides of the head and providing diametrically opposing eyelet openings. Arcuate counterweight  101  includes eyelet  102  and arcuate projections  104  and  115 . The arcuate projections can be provided with fins  196  and  197  on their internal surfaces to aid in dissipation of heat generated by friction of the cutting line. Eyelet opening  103  is defined by a convex frustroconical surface leading to the cutting line channel. The arcuate counterweights in the preferred embodiment are cast metal parts constructed of an iron alloy. Furthermore, in the preferred embodiment, each arcuate counterweight weighs approximately 4 to 8 ounces. Other alloys will suffice, such as steel, aluminum, iron, copper, bronze or titanium. 
   Cutting line tubing sections  110  and  111  are seated in the channel formed by channel walls  160 ,  161 ,  162  and  163  and are adjacent to and share a central axis with both eyelets of the diametrically opposed pair of arcuate counterweights. Cutting line tubing sections  110  and  111  are hollow tubes made of aluminum, steel, brass or copper. In the preferred embodiment the tubing sections are about 0.060 inch thick and of sufficient inside diameter to receive cutting line having a diameter of up to about 0.155 inches. The eyelets provide a smooth convex frustroconical surface at the exits for the line on opposing sides of head  100 . The smooth surfaces surround the cutting line during operation eliminating any material discontinuity and irregular surface from contacting the cutting line. A channel hole  199  is provided through arbor  400  which, in cooperation with the tubing, forms a complete and circumferentially continuous metallic channel for the cutting line from one eyelet to the other. In addition to forming the channel which houses cutting line tubing sections  110  and  111 , channel walls  160 ,  161 ,  162  and  163  add rigidity and structure to lower cover  106 . Channel walls  160  and  161  abut button guide  191  and housing support  180  at generally right angles. Channel walls  160  and  163  abut housing support  181  and button guide  190  at generally right angles. Housing supports  180  and  181  are adjacent to counterweights  170  and are integrally formed with housing  108 . Button guides  190  and  191  are generally perpendicular to the channel walls and form a support track on which button  210  travels. Locking blade receiving supports  130  and  131  for a support track on which locking blade  300  moves. Three counterweights  170  are equidistant from each other and extend upwards into upper cover  105 . In between counterweights  170  are counterweight receiving slots  178 . 
   Lower cover  106  also includes four stanchions  139  located in each quadrant of lower cover  106  and each with stanchion hole  119 . When assembled, self locking screws fit through stanchion holes  119  and into stanchion  839  in upper cover  105 . The self-locking screws are a self-tapping, PLASTITE® screw provided, in the preferred embodiment, by Textron Fastener Systems, Inc. of Decorah, Iowa. Stanchions  839  are not threaded, and upon assembly of upper cover  105  and lower cover  106 , seal around the self-locking screws to prevent the screws from backing out during operation of the head. 
   Still referring to  FIGS. 1 ,  2  and  3  and further to  FIGS. 5 ,  6 , and  7 , button  210  and locking blade  300  are shown. Button  210  includes button shoulders  211 , locking blade receiving slot  215 , spring receiving slot  221 , and holes  222 . In the preferred embodiment, locking blade  300  is a U-shaped metal piece, which can also be formed of a metal laminate or alloy. Stainless steel or titanium is used in the preferred embodiment. Locking blade  300  includes arms  302  and  304  and a top  303 . In the preferred embodiment, arms  302  and  304  and top  303  are formed in one piece. Each arm is provided with clamp slots  305  and  306 . The clamp slots are concentrically aligned. Clamp slot  305  is comprised of a first radius  330  and a second radius  335  placed at opposite ends of clamp slot  305 . Clamp slot  306  is comprised of a first radius  331  and a second radius  336 . The length of the slots is determined by the diameter of cutting line tubing sections  110  and  111 . In the preferred embodiment the slots are about 0.25 inches in length. First radii  330  and  331  and second radii  335  and  336  are connected by angular indentions  340  and  341 , respectively, and locking surfaces  345  and  346 , respectively. The locking surfaces create angular steps from the first radii to the second radii. The first radii are larger than the second radii by approximately thirty percent. In the preferred embodiment, the first radii are 0.093 inches and the second radii are 0.037 inches. In the preferred embodiment, angular indentions  340  and  341  make an angle of thirty-four to thirty-six degrees from the long axis of the arm in which it is placed, but other oblique angles will also function properly. The purpose of the stair step locking surfaced and angular indention is to accommodate differing sizes of cutting line when the head is assembled. 
   When assembled, spring  220  fits in spring receiving slot  221  of button  210 . The arms  302  and  304  of locking blade  300  slide along locking blade guides  830  and  831  of upper cover  105  and locking blade receiving supports  130  and  131  of lower cover  106 . When the housing is assembled, spring seat  118  and spring seat  818  form a single shelf capable of supporting the bias force of spring  220 . One end of spring  220  is placed in the shelf and the other end is fitted into spring receiver slot  221  on the bottom. Spring  220  biases the shelf against button  210  forcing button shoulders  211  against the insides of button opening  814  and button opening  114  when upper cover  105  and lower cover  106  are assembled. The first radii of each clamp slot is placed in concentric alignment with the axes of cutting line tubing sections  110  and  111 . The bias provided by spring  220  forces angular indentions  340  and  341  to engage the cutting line in cutting line tubing sections  110  and  111  and force it against channel hole  199  of arbor  400  and the interior of cutting line tubing sections  110  and  111  thereby preventing movement of the cutting line along its axis with respect to the head. 
   Referring now to  FIG. 4 , the preferred embodiment of the head also includes an arbor  400  having a positioning seat  405 , a channel hole  199 , flat diametrically opposed faces  415 , arbor hole  420  and arbor hole  425 . When assembled, arbor  400  is seated on arbor positioning shelf  126  of lower cover  106  and directly below arbor hole  825  in upper cover  105 . When assembled, positioning seat  405  fits snugly against arbor positioning shelf  826  on upper cover  105 . A self-tapping and self-locking screw fits through lower cover  106  and into arbor hole  425  in arbor  400  to hold arbor  400  firmly in place. Diametrically opposed faces  415  cooperate with arbor positioning faces  815  in upper cover  105  and the opposing inside surfaces of locking blade receiving supports  130  and  131  in lower cover  106  to prevent rotation of the arbor in the head. Channel hole  199  is in concentric alignment with cutting line tubing sections  110  and  111  and the eyelets in the arcuate counterweights. Channel hole  199  is sized to match the inner diameter of the cutting line tubing sections. 
   Referring to  FIG. 3 , it can be seen that the shape of upper cover  105  defined by housing  801  is generally a mirror image of lower cover  106 . When assembled, the two covers will enclose and hold in place the arcuate counterweights, button  210 , spring  220 , locking blade  300 , and arbor  400 . Upper cover  105  includes channel walls  860 ,  861 ,  862  and  863  which form the channel that seats cutting line tubing sections  110  and  111 . Upper cover  105  also includes two diametrically opposed eyelet slots  834  and  835 , each forming a semicircular impression in upper cover  106  and each divided with eyelet support ribs  837  and  836 , respectively. Eyelet slots  834  and  835  both seat an eyelet of the pair of arcuate counterweights. The channel walls abut locking blade guides  830  and  831  at approximate right angles. When the housing is assembled, the inside surfaces of locking blade guides  830  and  831  provide flat surfaces which abut the flat diametrically opposed faces  415  of arbor  400  and prevent the arbor from rotating during operation. Arbor support  808  is a support with an arcuate shaped interior surface that aligns and positions arbor  400 . Upper cover  105  further includes four stanchions  839  which are additionally supported by stanchion ribs  841  and which correspond to stanchions  139 . Additionally, upper cover  105  includes four structural counterweights  870  and defines counterweight receiving slots  878 . Arbor positioning shelf  826  defines the opening of arbor hole  825 . 
   Housing  801  of upper cover  105  cooperates with housing  108  of lower cover  106  to form the enclosure for the internal working components of the assembled head. When upper cover  105  and lower cover  106  are assembled, counterweights  170  matingly interface with counterweights  870 . Counterweights  870  and counterweights  170  serve a dual purpose. The counterweights offset the weight of locking blade  300  and button  210  and also structurally support the outside of upper cover  105  and lower cover  106 . The position of the counterweights prevents sagging or bulging of upper cover  105  and lower cover  106  during operation. 
   When assembled, each stanchion  839  comes in contact with its stanchion counterpart  119 . After assembled, arbor hole  420  of arbor  400  is visible through arbor hub  109 . Arbor hole  420  is then secured onto the threaded receiving shaft of a rotary line trimmer. 
   When the head is assembled, the parabolic shape of the inside of each eyelet prevents wearing and heating of the cutting line from bending when the head is in operation. The eyelets completely surround the cutting line with a circumferentially continuous metal surface and eliminate fusing of the cutting line to head  100  during operation. In use, the arcuate counterweights evenly distribute extra mass to the perimeter of head  100  and thus increase the angular momentum of the head. The additional angular momentum allows the use of a smaller, lighter, and more economical engine or motor to rotate the head without sacrificing cutting performance. The projections provided on the arcuate counterweights also dissipate heat thereby reducing the operational temperature of the cutting line and lengthening the useful life of the cutting line. 
   In operation, button  210  extends through button openings  814  and  114  and is depressed by the user thereby compressing spring  220  until the central axis of cutting line tubing sections  110  and  111  is aligned with the first radii of the clamp slots in locking blade. A cutting line is inserted through eyelet  102 , into cutting line tubing section  110 , through a first clamp slot  305 , through arbor  400  via channel hole  199 , through second clamp slot  306  and cutting line tubing section  111 , passing through the second opposing eyelet and exiting the head until the cutting line is evenly exposed out of both diametrically opposed openings in head  100 . The user then releases button  210  which allows spring  220  to force button  210  radially outward, in turn moving locking blade  300  radially outward. Clamp slots  305  and  306  engage the cutting line and force it against the inside of channel hole  199  clamping it securely against angular indentions  340  and  341 . Each angular indention of each clamp slot engages the cutting line at two distinct points. Locking blade  300  holds the cutting line in place and once the head is rotated, the centrifugal force tends to force locking blade  300  radially outward further securing the cutting line. 
     FIG. 8  shows the lower cover of an alternate embodiment of the present invention. Cover  800  is generally circular in shape defined by housing  501  and includes channel retaining walls  580 ,  581 ,  582  and  583  which support and locate cutting line tubing sections  502  and  504 . Cutting line tubing sections  502  and  504  are metal tubes that have flared ends at channel openings  507  and  508  and opposite ends  598  and  599  that abut locking blade  506 . The flared ends form parabolic surfaces of revolution about the axis of the tubing sections. In a preferred embodiment, cutting line tubing sections  502  and  504  are made of a metal material such as aluminum, steel or titanium. Other metals such as copper or brass will suffice. Cover  800  structural supports include stanchions  539 , counterweights  570  and trimmer shaft hub support  523 . Cover  800  has four stanchions  539  located in the four quadrants of the head and each defining a stanchion hole  519 . Cover  800  has four counterweights  570  integrally formed with housing  501  spaced equidistant from each other and define counterweight receiving slots  578 . Trimmer shaft hub support  523  defines the circular opening trimmer shaft hole  522 . The outside surface of cover  800  also includes button indention  524  and button stops  525  that define button opening  514 . Button opening  514  is rectangular in shape and when mated with button opening  914  of cover  900  form a rectangular aperture through which button  510  extends. Button  510  has button shoulders  511  and also includes a single locking blade  506 . Locking blade  506  is preferably made of a metal such as aluminum or steel and is generally perpendicular to the support member that defines button shoulders  511 . Locking blade  506  is aligned along the diameter that diametrically opposes channel openings  507  and includes clamp slot  509 . Clamp slot  509  is similar in dimensions and function to clamp slots  305  and  306  shown in  FIG. 7 . Spring seat  518  is adjacent to channel retaining walls  581  and  582  and is bisected by locking blade  506 . In another embodiment, as shown in  FIG. 2 , cover  800  can be fitted with a pair of diametrically opposed arcuate counterweights with opposing eyelets concentrically arranged with the axis of cutting line tubing sections  502  and  504 . 
     FIG. 9  shows upper cover  900  which is designed to fit with lower cover  800 . Housing  901  defines the perimeter of cover  900  and cooperates with housing  501  of lower cover  800  to create a snub fit when assembled. Cover  900  includes structural support members channel retaining walls  980 ,  981 ,  982 , and  983 , stanchions  939 , counterweights  970 , trimmer shaft hub support  923 , and button indention  924 . Channel retaining walls  980 ,  981 ,  982  and  983  define a channel that locates and supports cutting line tubing sections  502  and  504  when the head is assembled. The channel mirrors the generally curved shape of channel retaining walls  580 ,  581 ,  582  and  583  and is adapted to form locking blade slot  950 . Locking blade slot  950  provides a space for locking blade  506  to pass between cutting line tubing sections  502  and  504 . 
   Stanchions  939  are located so as to cooperate with stanchions  519 . Each is supported by stanchion rib  941 . Counterweights  970  add structure and rigidity to the head once assembled and also promote even rotation as they offset the weight of button  510  located opposite of counterweights  970  in cover  900 . Counterweights  970  extend the full height of the assembled head and define counterweight receiving slots  978 . Located directly in the center of the generally circular shaped cover  900  is trimmer shaft hub support  923  that cooperates with trimmer shaft support hub  523  and defines aperture trimmer shaft hole  922 . 
   When assembled, button indention  924  and button opening  914  align with button indention  524  and button opening  514  to create a rectangular opening through which button  510  extends and in use is actuated by a user. Spring  520  abuts against spring seat  518  and in the resting position biases button  510  radially outward towards button opening  514  until button shoulders  511  strike button stops  525 . In operation, button  510  is depressed sliding locking blade  506  and clamp slot  509  until the first radius of the clamp slot is aligned with the axes of cutting line tubing sections  502  and  504 . A cutting line section is then inserted in channel opening  507 , through cutting line tubing sections  502  and  504  of the assembled head and exits out of the opposing channel opening  508  until roughly equal lengths of cutting line are exposed from each of channel openings  507  and  508 . Once the desired position of the cutting line is achieved, button  510  is released and spring  520  moves clamp slot  509  radially outward forcing the cutting line to be pinned against the inside surface of cutting line tubing sections  502  and  504 . 
   Referring to  FIG. 10 , the lower cover of an alternate embodiment of the present invention is shown. Cover  1000  has a generally disk-like shape defined by housing  601 . Two eyelet slots  634  and  635  are located on opposite sides of the perimeter of cover  1000 . Cover  1000  also includes structural members housing counterweight support  680 , counterweight  670 , molded counterweight  608 , channel retaining walls  681 ,  682 ,  683 ,  684 , and  685 , button stops  625 , trimmer shaft hub support  623 , and spring seat  618 . Molded counterweight  608  is integrally formed with cover  1000  and extends upwards into upper cover  1100 . It is formed in a shape to generally mirror the cutting line tubing sections  602 ,  603  and  604 . Its dimensions necessarily depend on the plastic chosen for the housing and the material chosen for the cutting line tubing sections in order to offset the weight of these sections. In the preferred embodiment, the cutting line sections are made of steel tubing and the lower housing is made of nylon. The dimension are such as needed to generate a weight in this embodiment of about 2 to 6 ounces. Eyelet slots  634  and  635  are semicircular shaped indentions bisected by eyelet support ribs  636  and  637  respectively. The eyelet support ribs and eyelet slots define seats for perimeter arcuate counterweights as shown in  FIG. 2 . The eyelets of the arcuate counterweights are concentrically aligned with the axes of cutting line tubing sections  602  and  604 . When assembled the eyelets of the arcuate counterweights and the cutting line tubing section form a circumferentially continuous channel for the cutting line. Channel retaining walls  681 ,  682 ,  683 ,  684 , and  685  define a channel that locates and supports cutting line tubing sections  602 ,  603 , and  604  and extends between each eyelet slot  634  and  635  in a curved manner bypassing trimmer shaft hole  622  defined by trimmer shaft hub support  623 . Spring seat  618  is located approximately perpendicular to and in between each arm of locking blade  606 . Each arm of locking blade  606  includes one clamp slot  607  or  609  located equal distances from an end of locking blade  606 . The channel retaining walls extend to the eyelet slots and abut the exterior surface of the arm of the locking blades. 
   Spring seat  618  is located between the blades of locking blade  606  and defines the portion of the channel that houses cutting line tubing section  603  opposite of channel retaining wall  685 . Abutting each end of the channel retaining walls at approximate right angles are locking blade guides  650  and  651 . Locking blade guides  650  and  651  form a seat on which the locking blade rests and is guided. Housing counterweight support  680  adds rigidity to cover  1000  and is approximately the same interior height as locking blade guides  650  and  651 . Molded counterweight support  608  is integrally formed with the lower cover and extends upward into the upper cover. Housing counterweight support  680  forms a generally rectangular shape enclosing and adjacent to counterweights  670 . Counterweights  670  are equidistant from each other and define spaces between each as counterweight receiving slots  678 . 
   Button  610  extends through button opening  614  which is defined by button stops  625 . Button indention  624  defines a space that houses button  610  to follow the generally circular perimeter shape to continue while button is biased using spring  620  in an extended position during operation. Button  610  includes button shoulders  611  that during operation abut button stops  625  and prevent button  610  from dislodging from the assembled head. Cover  1000  also includes four stanchions  639  located approximately equidistant from each other in four corners of cover  1000 . Stanchions  639  each include and define stanchion holes  619 . 
     FIG. 11  shows the upper cover designed to mate with lower cover  1000 . Cover  1100  is generally a mirror image of cover  1000  shown in  FIG. 10  designed to fit together to form a line trimmer head and enclose and properly secure the arcuate counterweights, support button  610 , spring  620 , cutting line tubing sections  602 ,  603 , and  604 , and locking blade  606 . The generally circular shape of cover  1100  is defined by housing  1001 . Channel retaining walls  1081 ,  1082 ,  1083 ,  1084  and  1085  define a semicircular shaped channel that extends from opposite sides of cover  1100  and supports the cutting line tubing sections  602 ,  603 , and  604 . Eyelet slots  1034  and  1035  are located at diametrically opposite positions of cover  1100  and form seats for the arcuate counterweights (as shown in  FIG. 2 ). The channel formed by the channel retaining walls bypasses trimmer shaft hole  1022  defined by trimmer shaft hub support  1023 . The semicircular indentions that define eyelet slots  1034  and  1035  include eyelet support ribs  1037  and  1036 , respectively. Counterweights  1070  provide structure and opposing weight opposite the button mechanism to balance the head during operation. In between counterweights  1070  are counterweight receiving slots  1078  designed to accept counterweights  670  when covers  1000  and  1100  are joined to form an assembled line trimmer head. Locking blade guides  1050  and  1051  provide supports and guides for locking blade  606  and are located adjacent to trimmer shaft hub support  1023  on opposing sides. Locking blade guides  1050  and  1051  are approximately perpendicular to channel retaining wall  1085 . Similarly, button guides  1090  and  1091  provide supports for button  610  to slide on and are positioned approximately perpendicularly to spring seat  1018 , extending from spring seat  1018  to button stops  1025 . Spring seat  1018  defines one side of the channel that houses cutting line tubing section  603  opposite channel retaining wall  1085 . Button opening  1014  defined by button indention  1024  forms the opposite half of the aperture button  610  extends through when assembled with cover  1000  and button opening  614  from  FIG. 10 . Cover  1100  also includes stanchions  1039  located in the approximate four quadrants of cover  1100  and each is supported by stanchion rib  1041  connected to housing  1001 . 
   In operation, housing  601  of cover  1000  and housing  1001  of cover  1100  are fitted together enclosing the internal components arcuate counterweights, cutting line tubing sections  602 ,  603 , and  604 , button  610 , spring  620 , and locking blade  606 . Self-tapping screws are inserted through stanchions  639  and into stanchions  1039 . The assembled head is attached to a rotary line trimmer by inserting the shaft of the line trimmer through trimmer shaft holes  622  and  1022  and inserting a bolt into the end of the line trimmer shaft. In resting position, spring  620  biases button  610  against spring seats  618  and  1018  to extend through button openings  614  and  1014  until button shoulders  611  abut button stops  625  and  1025 . In this position, clamp slots  607  and  609  block the cutting line tubing. Depressing button  610  slides locking blade  606  over locking blade guides  650 ,  651 ,  1050 , and  1051  and positions clamp slots  607  and  609  such that a cutting line may pass through. Button  610  is released after inserting cutting line through the cutting line tubing and through the clamp slots. Spring  620  forces button  610  and locking blade  606  back to the resting position. Clamp slots  607  and  609  then press the cutting line against the interior surfaces of cutting line tubing sections  602 ,  603 , and  604  to securely hold the cutting line in place. 
     FIG. 12  shows the lower cover of an alternate embodiment of the present invention. Cover  1200  is generally disk like in shape defined by housing  701  with two cartridge channel openings  707  and  708  located on opposite sides of cover  1200 . Channel retaining walls  790  and  792  define a channel that seats removable cutting line tubing cartridge  702 . Molded counterweight  712  forms an angular structural shape and abuts channel retaining wall  792  at points on opposite sides of trimmer shaft hub support  723 . Molded counterweight  712  is generally shaped to match the angular shape of the replaceable cartridge and is provided with dimensions so that the weight of the plastic from which it is formed equals the weight of the replaceable cartridge. Molded counterweight  712  is formed integrally with lower cover  1200  and extends upwardly into upper cover  1400  when the housing is assembled. Trimmer shaft hub support  723  defines trimmer shaft hole  722 . Counterweights  770  are adjacent to housing support  780  and define spaces between counterweights  770  as counterweight receiving slots  778 . Four stanchions  739  located approximately in four corners of cover  1200  and equally spaced apart define stanchion holes  719 . Button  710  includes button shoulders  711 , spring  720 , and locking blade  706 . Button  710  extends through button opening  714  which is defined by button indention  724  and button stops  725 . Included on each blade of locking blade  706  is clamp slot  762  or  709  located an equal distance from the end of the locking blade. 
     FIG. 13  is a perspective view of removable cutting line tubing cartridge  702 . Removable cutting line tubing cartridge  702  in the preferred embodiment is machined from steel and is removable from the assembled head. Other metals such as titanium, brass, copper or aluminum will also suffice. Removable cutting line tubing cartridge  702  is comprised of three guide sections  740 ,  741 , and  742 . Guide section  740  has concave rounded face  751  that defines cartridge opening  750 . Rounded face  751  has a concave frustroconical shaped interior surface lessening in diameter as it leads to cartridge channel  754 . Cartridge channel  754  connects to cartridge channel  753  which connects to cartridge channel  752  which leads to cartridge opening  755  to form one continuous circular shaped channel through the entire length of removable cutting line tubing cartridge  702 . Rounded face  749  defines cartridge opening  755  and is the same shape as rounded face  751 . Each of the cartridge openings comprises a parabolic surface of revolution about the axis of the cartridge channel. In another embodiment, the cartridge channel can be curved as it passes through the guide sections forming a smooth arcuate path for the cutting line. 
   Guide section  740  includes locking blade receiving slot  746 , which is sized appropriately to allow the blades of locking blade  706  to pass through removable cutting line tubing cartridge  702 . Guide section  740  is adjacent to guide section  741 . Guide section  741  is adjacent to guide section  742 . Guide section  742  includes locking blade receiving slot  744  that is sized to allow a blade of locking blade  706  to pass through removable cutting line tubing cartridge  702 . 
   Referring to  FIG. 14 , cover  1400  is an upper cover designed to mate with cover  1200  to form an assembled line trimmer head. Housing  1101  defines the generally circular shape of cover  1400 . Cover  1400  includes four stanchions  1139  that are supported by stanchion ribs  1141 . Counterweights  1170  add stiffness to cover  1400  and serve to offset the weight of button  710  and locking blade  706  located on the opposite side of the head when assembled. Counterweight receiving slots  1178  are gaps located in between counterweights  1170  and are sized to accept counterweights  770  when the head is assembled. Trimmer shaft hole  1122  is defined by trimmer shaft hub support  1123  and is sized to accept the trimmer shaft from a typical rotary line trimmer apparatus. Channel retaining walls  1190  and  1192  define a channel that runs through cover  1400  from opposing cartridge channel openings  1307  and  1308  located at opposite side of cover  1400 . Channel retaining walls  1190  and  1192  are each interrupted twice by locking blade slots  1126 . Locking blade slots  1126  are located on channel retaining walls  1190  and  1192  on opposite sides of trimmer shaft hole and are sized to accept the blades of locking blade  706 . Button opening  1114  and button indention  1124  when mated with button opening  714  and button indention  724  of cover  1200  create a depressed, rectangular aperture which button  710  extends through. Button stops  1125  located adjacent to button opening  1114  prevent button  710  from passing completely out of the assembled head. 
   When assembled, housing  701  of cover  1200  and housing  1101  of cover  1400  cooperate with each other to form the assembled head. Cover  1200  and cover  1400  are secured to each other with self-tapping screws inserted through stanchion holes  719  and into stanchions  1139 . A trimmer drive shaft from a typical rotary line trimmer is inserted through the head via trimmer shaft holes  722  and  1122 . A shoulder bolt (not shown) is inserted into the internally thread end of the trimmer shaft and tightened to secure the assembled head to the trimmer apparatus. In some embodiments, the shoulder bolt is fitted with a flat side to prevent rotation of the head with respect to the drive shaft. To insert a cutting line, button  710  is depressed and locking blade  706  is moved through locking blade receiving slots  744  and  746  of removable cutting line tubing cartridge  702 . Due to the bias of spring  720 , clamp slots  709  and  762  of locking blade  706  rest in the clamped position. Pressing button  710  moves clamp slots  709  and  762  into the open position ready to accept a cutting line. A cutting line is inserted at either opposing cartridge opening  750  or  755  and passed through the clamp slots while in the open position and out the opposite cartridge opening. When equal lengths of the cutting line extend out of opposing sides of the assembled head, button  710  is released and spring  720  forces button  710  and the clamp slots radially outward. The clamp slots force the cutting line against the cartridge channel and securely hold the cutting line in place during operation. To remove and replace a worn cutting line, button  710  is depressed sliding the clamp slots into the open position thereby releasing the cutting line from contact with the cutting line channel cartridge. After prolonged use and frequent cutting line replacements, the cutting line tubing cartridge may become worn or have excess buildup of dirt and debris. The cutting line tubing cartridge is then removed from the head and replaced easily. The angled shape of cutting line tubing cartridge keeps it in place during operation and allows for simple removal and installation. 
   It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.