Abstract:
A method of constructing a bed knife blade assembly for a reel-type lawn mower having a frame rotatably supporting a cutting reel. The bed knife blade assembly comprises a clamp plate having a flange with a locking surface, and a blade insert having a tab cooperating with the locking surface to restrict movement of the blade insert relative to the clamp plate. The clamp plate is adapted to be coupled to the frame such that the flange biasedly engages the tab to further restrict movement of the blade insert relative to the clamp plate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 09/521,497 filed on Mar. 9, 2000, now U.S. Pat. No. 6,301,867. The disclosure(s) of the above application(s) is (are) incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention generally pertains to turf care equipment, such as lawn mowers and the like. More particularly, the present invention relates to a bed knife blade for a reel-type lawn mower. 
     2. Discussion 
     Commercial turf care equipment often employ reel-type lawn mowers for mowing golf greens. These reel-type mowers typically include a frame having a rotatably mounted cutting reel and a bed knife blade positioned in close proximity to the cutting reel. As the cutting reel is rotated, the blades of grass projecting between the cutting reel and the bed knife blade are cut at a desired height. In order to repeatedly cut blades of grass in this manner, it is advantageous to maintain sharp edges on both the cutting reel blades and the bed knife blade for as long a duration as possible. Accordingly, most bed knife blades are constructed from materials such as heat treated high carbon steel in order to maintain a sharp edge over time. 
     Unfortunately, even though the bed knife is heat treated, the blade typically requires frequent sharpening and eventual replacement. Because the entire conventional bed knife blade is constructed from high carbon steel, manufacture and replacement of such a blade is expensive. Specifically, costly carbide cutting tools are required to rough machine a hot formed, high carbon steel blank. The blank is next heat treated and ground on two surfaces to produce a knife edge. 
     In addition to high manufacturing process costs, the current bed knife blade design is also costly to manufacture due to the type of raw material which must be used. Specifically, in order to resist impact and bending loads at the mounting location, material toughness is required. Furthermore, to provide a long lasting cutting edge, high hardness is beneficial. Currently, expensive steel alloys exhibiting both toughness and hardenability are selected for use in this application. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a bed knife blade assembly having an economically advantageous replaceable blade insert. 
     It is another object of the present invention to maintain the current ease of sharpening and/or replacement of the bed knife blade assembly. 
     The present invention pertains to a bed knife blade assembly for a reel mower having a frame rotatably supporting a cutting reel. The bed knife blade assembly comprises a clamp plate having a flange with a locking surface, and a blade insert having a tab cooperating with the locking surface to restrict movement of the blade insert relative to the clamp plate. The clamp plate is adapted to be coupled to the frame such that the flange biasingly engages the tab to further restrict movement of the blade insert relative to the clamp plate. 
     Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from a reading of the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of an exemplary reel mower having a bed knife constructed in accordance with the teachings of the present invention; 
     FIG. 2 is a side elevational view of a clamp plate of the present invention; 
     FIG. 3 is a side elevational view of a blade insert of the present invention; 
     FIG. 4 is a side elevational view of the bed knife blade of the present invention; 
     FIG. 4A is an enlarged view of the interconnection of the clamp plate and the blade insert of the present invention; 
     FIG. 5 is a perspective view of a second embodiment of the bed knife blade assembly of the present invention; 
     FIG. 6 is a side elevational view of a second embodiment of the clamp plate of the present invention; and 
     FIG. 7 is a side elevational view of a second embodiment of the blade insert of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With initial reference to FIG. 1, a bed knife blade constructed in accordance with the teachings of an embodiment of the present invention is generally identified at reference numeral  10 . The bed knife blade  10  is shown operatively associated with an exemplary mower  12  having a cutting reel  14  rotatably mounted to a frame  16 . A backing plate  18  is also coupled to the frame  16  for receiving and mounting the bed knife blade assembly  10  thereto. An adjustment mechanism  20  cooperates with the frame  16  and the backing plate  18  for positioning the bed knife blade assembly  10  relative to the cutting reel  14 . One skilled in the art will appreciate that proper cutting or shearing of grass blades is accomplished by maintaining a minimal clearance between the rotating cutting reel  14  and the bed knife blade assembly  10 . Specifically, the cutting reel  14  includes a plurality of helical blades providing individual shear interfaces along the entire length of bed knife blade assembly  10 . 
     As mentioned earlier, proper function of the mower  12  also depends on maintaining the sharpness of the helical blades and the bed knife blade  10 . The longevity of blade sharpness depends on a variety of factors including cutting edge hardness and mower usage. As is commonly known, the carbon content of steel alloys may be increased for hardenability purposes. However, a trade-off generally exists whereby an increase in material hardenability results in a decrease in material toughness. However, certain steel alloys exist which exhibit high hardenability and adequate toughness. Unfortunately, these materials are expensive and difficult to machine in their annealed state, let alone after hardening. 
     Based on the aforementioned limitations, a standard bed knife blade is created by first hot forming a blank. Subsequently, the blank is rough machined. Finish machining occurs by drilling and counter-sinking holes in a portion of the blank. At least a portion of the blank is heat treated and subsequently ground to form a cutting edge. 
     With continued reference to FIG. 1, the bed knife blade assembly  10  of the present invention incorporates a multi-piece design including a blade insert  24  and a clamp plate  26 . The clamp plate  26  functions to couple the blade insert  24  to the backing plate  18  of the mower  12  but performs no cutting function. Accordingly, the clamp plate  26  is preferably constructed from a low cost, easily machined material exhibiting impact resistance and toughness. On the other hand, because the blade insert  24  cuts the grass and does not provide a mounting function, it is preferably constructed from a high carbon steel capable of achieving high hardness when heat treated. The hardened portion of the blade insert  24  is subsequently ground to a knife edge for cutting the blades of grass. 
     With reference to FIG. 2, the clamp plate  26  is an elongate structure having a body  28  and a flange  30  extending a distance “X” therefrom. The body  28  includes a mounting surface  32  for engagement with the backing plate  18 . The body  28  also includes a plurality of apertures  34  for receipt of fasteners such as threaded bolts or screws. In the preferred embodiment, the apertures  34  include a counter sink  36  thereby allowing the installed fastener to rest flush with a bottom surface  38 . 
     The flange  30  extends substantially along the entire length of the body  28  and includes a end face  40  and a locking surface  42  for engagement with the blade insert  24 . The locking surface  42  is positioned at an angle relative to the mounting surface  32  to effectively couple the blade insert  24  to the clamp plate  26  after assembly to the backing plate  18 . In the preferred embodiment, the locking surface  42  forms a small acute angle  43  with the mounting surface  32  in the range of 3-10 degrees. One skilled in the art will appreciate that the simple geometry of the clamp plate  26  may be created using a variety of cost effective manufacturing methods including roll forming, forging and casting. 
     Referring to FIGS. 1 and 3, the blade insert  24  functions to provide a cutting edge  44  in close relation to the helical blades  22  of the cutting reel  14  for cutting grass blades. The blade insert  24  includes a knife end  46  and a tab  48  extending a distance “Y” therefrom. The tab  48  includes a first clamping surface  50  and a second clamping surface  52  extending along the length of the tab  48 . It should be appreciated that the first clamping surface  50  and the second clamping surface  52  form an acute angle  53  preferably in the range of 2-9 degrees. Additionally, it should be appreciated that the angle  53  formed by the first clamping surface and the second clamping surface is preferably one degree less than the angle  43  formed between the locking surface  42  and the mounting surface  32  as will be described in greater detail hereinafter. The second clamping surface  52  terminates at a stop face  54 . Preferably, the second clamping surface  52  transitions to stop face  54  through a generous radius  56 . 
     The knife end  46  of the blade insert  24  also includes a bottom surface  58  and a relief  60  formed along the entire length of the blade insert  24 . In the preferred embodiment, each of the surfaces defining the tab  48  and the body  46  are roll formed to their net shape shown. Accordingly, costly rough machining is eliminated. The body  46  also includes a first machined surface  62  intersecting a second machined surface  64  at the cutting edge  44 . Each of the first and second machine surfaces are ground after heat treatment of the blade insert  24  to produce a sharp cutting edge  44 . 
     Referring to FIGS. 1 and 4, the bed knife blade assembly  10  is assembled to the mower  12  by placing the tab  48  of the blade insert  24  in contact with the flange  30  of the clamp plate  26 . Specifically, the flange  30  extends the distance X from the body  28  while the tab  48  extends the lesser distance Y from the first end  46  of the blade insert  24 . Accordingly, the end face  40  abuts the stop face  54  once the bed knife blade assembly  10  is coupled to the backing plate  18 . One skilled in the art will appreciate that the abutment of end face  40  with stop face  54  assists in maintaining the position of the blade insert  24  relative to the backing plate  18  during operation. 
     With specific reference to FIGS. 1 and 4A it should also be appreciated that the locking surface  42  is positioned such that an interference zone  66  (shown in phantom line) is created when the first clamping surface  50  of the blade insert  24  is aligned with the mounting surface  32  of the clamp plate  26  as when clamped against the backing plate  18 . The tapered shape of the interference zone  66  in addition to the back angles  43  and  53  tend to bias the blade insert  24  towards the clamp plate  26  thereby closing the gap between the end face  40  and the stop face  54 . The clamp plate  26  is coupled to the backing plate  18  with a plurality of fasteners  68  (FIG. 1) disposed within the apertures  34 . As the fasteners  68  begin to exert clamping force, each of the tab  48  and the flange  30  compress in an attempt to account for the interference zone  66 . In addition, the flange  30  deflects to biasingly load the tab  48  against the backing plate  18 . Therefore, once the fasteners  68  have seated the mounting surface  32  against the backing plate  18 , the blade insert  24  is fixed in relation to the clamp plate  26 . 
     Referring to FIG. 5, a second embodiment of the bed knife of the present invention is depicted at  110 . It should be appreciated that the second embodiment of the bed knife  110  includes similar components and performs essentially the same function as the first embodiment  10 . Accordingly, like elements will be identified with like reference numerals. 
     With reference to FIG. 6, the clamp plate  126  includes a body  128  having a flange  130  extending a distance “X” therefrom. The flange  130  includes a first key  170  extending a distance  171  from the bottom surface  138  of the claim plate  126 . A first recess  172  is configured to interlock with a second key  174  and a second recess  176  of the blade insert  124 . With reference to FIG. 7, a blade insert  124  includes a knife end  146  and a tab  148  extending a distance “Y” therefrom. As mentioned earlier, the tab  148  includes the second key  174  for disposition within the first recess  172  and the second recess  176  for acceptance of the first key  170 . It should be appreciated that the second recess  176  is positioned a distance  180  from the first clamping surface  150  of the blade insert  124 . In order to provide the clamping retention feature of the blade insert  124  within the clamp plate  126  the sum of the distances  171  and  180  is greater than the total thickness of the clamp plate  182  (FIG.  6 ). In this manner, the flange  130  will be biasingly loaded against the tab  148  in similar fashion to the first embodiment. 
     Therefore, it should be appreciated that the configuration and operation of the bed knife blade assembly  10  provides a variety of advantages over the prior art. Specifically, the two-piece construction of the present invention reduces the cost of manufacturing by eliminating several rough machining steps and reducing the quantity of costly high carbon alloy steel. Additionally, a novel interlocking attachment method is used to couple the blade insert to the clamp plate. 
     The foregoing discussion discloses and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications and variations may be made therein without departing from the spirit and scope of the invention as defined in the following claims.