Abstract:
A cutting blade assembly incorporating two lawnmower cutting blades and a holder configured to hold the lawnmower cutting blades in perpendicular orientation with respect to each other. The holder does not occupy any space on the lawnmower blade mounting shaft and results in less rotational inertia than conventional mounting hub designs.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to the field of lawnmowers. More specifically, the invention comprises a lawnmower blade assembly which can be attached to a conventional lawnmower shaft. 
   2. Description of the Related Art 
   The overall design of the gas-powered and electric-powered lawnmower cutting system has remained unchanged in recent decades. The overall design uses an electric or gas motor to turn a shaft which extends in the direction of the ground beneath the motor. The shaft extends through a hole into the blade housing where a blade is attached to the shaft. The motor drives the shaft causing angular rotation of the blade within the housing. Grass that extends above the height of the blade is cut and discharged from the housing. 
   Various lawnmower replacement blades are known in the art. The designs of the replacements blades vary significantly and have been the subject of many U.S. patents. Although great efforts have been made to improve the design of replacement lawnmower blades, these designs have their shortcomings. 
   As an example, most commercially available blades are ineffective at neatly cutting grass when the grass is wet, tall, or thick. The rotation of a conventional blade slows down under these conditions as the lawn provides greater resistance to cutting. This resistance can often escalate as the rotation of the cutting blade continues to slow until the blade eventually stops. The escalation of resistance occurs because, as the blade slows down, the force at which the cut grass is ejected decreases. This results in the accumulation of cut grass in the housing which increases the force required to turn the blade. 
   Even under ideal cutting conditions, conventional blades are ineffective at “cutting” the grass. As a conventional blade begins to dull, more grass is “torn” than “cut.” As the blade strikes the grass, some of the grass is pulled by the blade until it breaks. This “tearing” of the grass results in increased cellular damage to the grass. This often causes the tip of the blade of grass to appear brown. It has also been noted that the increased cellular damage causes the grass to grow more quickly which requires more frequent mowing. 
   In order to address these disadvantages, some have proposed mounting two or more cutting blades on a common hub. In such an embodiment, the resistance provided by the lawn is spread out across twice as many cutting blades. In addition, each blade cuts approximately half as much grass as in the standard single blade mower, thus slowing the blade wear. These multiple blade designs can be more effective at cutting grass when the grass is wet, tall, or thick. 
   There are also disadvantages associated with using a mounting hub, however. First, mounting hubs take up space on the blade mounting shaft. Some shafts may not be long enough to accommodate the combination of two cutting blades, a mounting hub, and clamping collar. Also, many prior art hub designs can lose clamping force over time, allowing the blades to tilt or otherwise come out of alignment. Hubbed designs also tend to result in a flywheel effect—owing to the increase in rotational mass—which can cause the blades to bend when the blades strike a rock, ant hill, or root. 
   Thus, it would be desirable to provide an improved lawn mower blade assembly capable of realizing the advantages of multiple blade designs while avoiding the disadvantages associated with the use of a mounting hub. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention is a cutting blade assembly incorporating two lawnmower cutting blades and a holder configured to hold the lawnmower cutting blades in perpendicular orientation with respect to each other. The holder does not occupy any space on the lawnmower blade mounting shaft and results in less rotational inertia than conventional mounting hub designs. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is a perspective view, showing a holder. 
       FIG. 2  is a perspective view, showing a cutting blade assembly. 
       FIG. 3  is a section view, showing the cutting blade assembly attached to a mounting shaft. 
       FIG. 4  is a perspective view, showing a holder. 
   

   REFERENCE NUMERALS IN THE DRAWINGS 
   
     
       
             
             
             
             
           
         
             
                 
             
           
           
             
               10 
               holder 
               12 
               top support member 
             
             
               14 
               bottom support member 
               16 
               spacer 
             
             
               18 
               top cutting blade 
               20 
               bottom cutting blade 
             
             
               22 
               mounting bore 
               24 
               mating edge 
             
             
               26 
               mating edge 
               28 
               mounting shaft 
             
             
               30 
               boss 
               32 
               collar 
             
             
               34 
               arcuate relief 
             
             
                 
             
           
        
       
     
   
   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention, holder  10 , which may be used to stabilize a pair of cutting blades on a lawnmower blade mounting shaft, is illustrated in  FIG. 1 . Holder  10  includes a pair of top support member  12  which are attached at their ends to a pair of bottom support members  14  at their ends. Spacers  16  are provided at each corner so that the bottom surfaces of top support members  12  are vertically offset relative to the top surfaces of bottom support members  14 . Although top support members  12 , bottom support members  14 , spacers  16  are shown as discrete components in  FIG. 1 , holder  10  may be cast or milled as a single, integrated component. It is preferred that holder  10  be constructed of a durable metal alloy. 
   A blade assembly employing holder  10  is illustrated in  FIG. 2 . Holder  10  is actually sandwiched between top cutting blade  18  and bottom cutting blade  20  when assembled as shown. Top cutting blade  18  and bottom cutting blade  20  are positioned such that mounting bores  22  are aligned. Bottom cutting blade  20  is positioned between bottom support members  14  such that the edge of bottom cutting blade  20  mates with mating edge  26 . Top cutting blade  18  is positioned between top support members  12  such that the edge of top cutting blade  18  mates with mating edge  24 . 
   Turning to  FIG. 3 , the assembly is shown attached to the shaft of a lawnmower. The assembly shown in  FIG. 2  is attached to mounting shaft  28  of a lawnmower by the clamping force of boss  30  and collar  32 . In many applications, mounting shaft  28  contains male threading which engages female threading on collar  32 . Thus, after placing the blade assembly on mounting shaft  28 , the user would rotate collar  32  about mounting shaft  28  until the cutting blades and holder are tightly clamped between collar  32  and boss  30 . When clamped, the bottom surface of top cutting blade  18  mates with the top surface of bottom cutting blade  20  and the top surfaces of bottom support members  14 . In addition to mating with the bottom surface of top cutting blade  18 , the top surface of bottom cutting blade  20  also mates with the bottom surfaces of top support members  12 . As mentioned previously the edge of top cutting blade  18  mates with mating edge  24  of top support member  12 . The edge of bottom cutting blade  20  mates with mating edge  26  of bottom support member  14 . 
   The reader should now appreciate that holder  10  holds top cutting blade  18  and bottom cutting blade  20  at perpendicular orientation with respect to each other. When the components are tightly attached to mounting shaft  28 , the contacting surfaces of bottom cutting blade  20 , top cutting blade  18 , top support members  12 , and bottom support members  14  reduce the stress exerted on the corners of holder  10  when one of the cutting blades strikes a hard object. The reader will also appreciate that, unlike hub-type blade assemblies, holder  10  does not occupy any space on mounting shaft  28 . 
   An alternate embodiment of the present invention is shown in  FIG. 4 . In this embodiment, arcuate relief  34  is provided on each top support member  12 . This feature provides for greater clearance where a lawnmower employs a larger boss than the example shown in  FIG. 3 . 
   The preceding description contains significant detail regarding the novel aspects of the present invention. It should not be construed, however, as limiting the scope of the invention but rather as providing illustrations of the preferred embodiments of the invention. Thus, the scope of the invention should be fixed by the following claims, rather than by the examples given.