Abstract:
A chisel with a bi-material blade comprising a main body of low grade steel and a cutting portion of higher grade steel. The cutting portion of higher grade steel provides longer life and decreases the need for frequent sharpening. The main body and cutting portion are connected using an arcuate interface. Additionally, the main body and cutting portion may have a radiussed cross-sectional connection. The arcuate interface and radiussed cross-section help absorb the shear and impact forces applied to the tool.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    The present invention is generally related to chisels. More particularly, the application relates to chisels having an improved cutting insert. 
         [0003]    2. Description of Related Art 
         [0004]    Chisels typically include a blade with a sharp cutting edge for carving, shaving, or cutting work pieces. The sharpened edge of the blade becomes dull with continuous use, requiring the craftsman to re-sharpen and re-hone the blade edge regularly in order to produce a satisfactory and predictable performance. 
         [0005]    Prior art has attempted to alleviate the craftsman&#39;s need to sharpen the blade by providing a replaceable chisel blade. These blades are removable from the tool shank and allow the craftsman to replace the blade when needed. 
         [0006]    Other chisels attempt to lengthen the life of the blade by constructing a blade of relatively harder metallic material. Specifically, it is known to provide a chisel blade made of two different steel materials, a lower grade, less costly base steel portion, and a higher grade, harder, and more costly steel portion for forming the cutting edge. 
         [0007]    However, in such bi-material blade structures, the connection of the blade edge portion to the base metal portion is subject to stress and strain. 
         [0008]    There is a need in the art to improve upon the known chisels of the prior art. 
       SUMMARY OF THE INVENTION 
       [0009]    One embodiment comprises a chisel comprising a handle, an elongated working portion, and a shank portion. The elongated working portion and a shank portion are joined with the handle. The elongate working portion has a main body portion and cutting portion. The main body portion is formed from a relatively lower grade steel, and the cutting portion is formed from a relatively higher grade steel in comparison with the lower grade steel of the main body portion. The cutting portion has a sharpened cutting edge at one end thereof and an arcuate force receiving surface disposed in spaced relation from the cutting edge. The main body portion has a driving engagement surface with an arcuate shape that mates with the arcuate configuration of the force receiving surface of the cutting portion. 
         [0010]    In an embodiment, the arcuate configuration of the force receiving surface and the arcuate shape of the driving engagement surface may form a portion of an arc. Alternatively, the arcuate configuration of the force receiving surface and the arcuate shape of the driving engagement surface may form one of a sinusoidal, parabolic, or elliptical configuration. 
         [0011]    The main body portion may have a reduced thickness region defining a recess for receiving the cutting portion. The main body portion may have a larger thickness region adjacent to the reduced thickness region, and the combined thickness of the reduced thickness region and the cutting portion may be configured to provide a generally flush transition with the larger thickness region. 
         [0012]    The driving engagement surface may define a transitioning surface between the larger thickness region and the reduced thickness region. Further, the driving engagement surface may generally slope rearwardly as it extends from the larger thickness region towards the reduced thickness region. A juncture between the driving engagement surface and the reduced thickness region may define a radiussed cross-sectional configuration. 
         [0013]    In another embodiment, a chisel comprises a handle, an elongated working portion, and a shank portion. The elongated working portion and shank portion are joined with the handle. The working portion has a main body portion and cutting portion. The main body portion is formed from a relatively lower grade steel, and the cutting portion is formed from a relatively higher grade steel in comparison with the lower grade steel of the main body portion. The cutting portion has a sharpened cutting edge at one end thereof and a force receiving surface disposed in spaced relation from the cutting edge. The main body portion has a recess with a driving engagement surface for receiving the force receiving surface of the cutting portion. The driving engagement surface of the main body portion has a radiussed cross-sectional configuration that generally slopes rearwardly when it mates with the force receiving surface of the cutting portion. 
         [0014]    The recess may be defined by a reduced thickness region. The main body portion may have a larger thickness region adjacent to the reduced thickness region, and the combined thickness of the reduced thickness region and the cutting portion may be configured to provide a generally flush transition with the larger thickness region. The driving engagement surface has an arcuate shape that mates with the arcuate configuration of the force receiving surface of the cutting portion. 
         [0015]    In an embodiment, the arcuate shape of the driving engagement surface and the arcuate configuration of the force receiving surface form a portion of an arc. Alternatively, the arcuate shape of the driving engagement surface and the arcuate configuration of the force receiving surface form one of a sinusoidal, parabolic, or elliptical configuration. 
         [0016]    Another embodiment provides a method of assembling a chisel, comprising: forming a main body portion of a lower grade steel with a driving engagement surface of arcuate shape; forming a cutting portion of a higher grade steel in comparison with the lower grade steel of the main body portion with an arcuate force receiving surface disposed in a spaced relation to a cutting edge; mating the driving engagement surface of the main body portion and force receiving surface of the cutting portion to form a chisel blade; and connecting the chisel blade with a handle. 
         [0017]    The method may further comprise forming a transitioning surface on the driving engagement surface that generally slopes rearwardly. The method may also comprise forming the driving engagement surface and the force receiving surface with a radiussed cross-sectional configuration. 
         [0018]    In an embodiment, the higher grade steel of the cutting portion has a hardness range of 57 to 62 HRC and the lower grade steel of the main body portion has a hardness range of 35 to 45 HRC. 
         [0019]    Other objects, features, and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  shows an exploded perspective view of one embodiment of a chisel in accordance with the present invention; 
           [0021]      FIG. 2  shows a perspective view of the chisel of  FIG. 1  with the main body portion and cutting portion connected; 
           [0022]      FIG. 3  shows a top view of the of the chisel blade; 
           [0023]      FIG. 4  shows a bottom view of the chisel blade, illustrating an arcuate connection between the main body and cutting portion; 
           [0024]      FIG. 5  shows a side view of the chisel blade, illustrating a radiussed cross-sectional juncture; and 
           [0025]      FIG. 6  shows a detail view of the mating of the main body portion and the cutting portion of  FIG. 5 , particularly a radiussed juncture with a rearward slope. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    Referring now more particularly to the drawings,  FIG. 1  is an exploded perspective view and  FIG. 2  is an assembled perspective view of a chisel  100  in accordance with one embodiment of the invention. The chisel  100  includes a blade  10  and a handle  12  that are connected to one another. Handle  12  comprises an opening  17  for receiving shank portion  16  of chisel blade  10 . In an alternate embodiment, handle  12  may be molded around shank portion  16 . Handle  12  may also comprise an end cap  18  for striking by another tool, such as a hammer. Handle  12  and end cap  18  are made of materials known to withstand impact. For example, handle  12  may be made of a polymer, and end cap  18  may be made of steel. Handle  12  may be contoured, shock absorbent, ergonomic, or other type of handle known in the art. 
         [0027]    Chisel blade  10  comprises an elongate working portion  14  that is joined with a shank portion  16 . The joining of the shank portion  16  and handle  12  form a hand-held chisel  100  that may be used to carve, shave, or cut work pieces made of wood, for example. The elongate working portion  14  of chisel blade  10  is formed from main body portion  20  and cutting portion  30 . 
         [0028]    As seen in  FIG. 2  and the top plan view of  FIG. 3 , the cutting portion  30  has a cutting edge  32  that extends beyond the body portion  20  and defines the leading surface of the blade  10 . 
         [0029]    In one embodiment, body portion  20  is made of a lower grade carbon steel in comparison with cutting portion  30 , thus forming a bimetallic blade. An exemplary embodiment would include a main body portion  20  made of carbon steel having a Rockwell Hardness (HRC) in the range of 35 to 45 HRC, and a cutting portion  30  made of carbon steel having a Rockwell Hardness (HRC) in the range of 57 to 62 HRC. The use of the lower grade steel for main body portion  20  provides a cost effective base material, while the more expensive cutting portion  30  provides longer edge life and a reduced need for sharpening. 
         [0030]    Main body portion  20  defines reduced thickness region  22  toward a forward portion thereof, while the rearward longitudinal portion defines a larger thickness region  26 . Larger thickness region  26  is adjacent to the reduced thickness region  22 . As best seen in  FIGS. 1 ,  5 , and  6 , the forward longitudinal portion of reduced thickness region  22  defines a recess  27  in main body portion  20  for receiving cutting portion  30 . The recess  27  has a major surface  29  for engaging a back surface  31  of cutting portion  30 . Also as shown in the Figures, the main body portion  20  includes a surface  24  defining a transition surface between larger thickness region  26  and reduced thickness region  22 . 
         [0031]    The surface  24  engages a rearward surface  34  of the cutting portion  30 . When the end of handle  12  receives an impact (e.g., from a hammer), force is transmitted through the main body surface  24  to the rearward cutting portion surface  34 . Thus, the surface  24  can be considered to be a driving engagement surface while the surface  34  can be considered to be a force receiving surface. 
         [0032]    Cutting portion  30  is an insert that may be attached to main body portion  20  by metal bonding adhesive, electric resistance welding or brazing, induction welding or brazing, or electron beam welding for adjoining or engaging surfaces, for example. The force receiving surface  34  is disposed in a spaced relation from cutting edge  32 , but is not necessarily at the rearwardmost end of the cutting portion  30 . For example, in one embodiment (not shown), a discrete rearwardmost portion of the cutting portion  30  may project rearwardly of the main force receiving surface  34 , and not engage the driving surface  24 , although such a configuration is not preferred. 
         [0033]    The thickness of cutting portion  30  in one embodiment is configured in relation to main body portion  20  to provide a smooth, transitional fit. That is, when cutting portion  30  is inserted into recess  27  and attached to main body portion  20 , the combined thickness of reduced thickness region  22  of main body  20  and the thickness of cutting portion  30  (at least the rearward portions thereof) are configured to provide a generally flush transition with larger thickness region  26 . 
         [0034]    As shown in  FIG. 4 , the driving engagement surface  24  and the force receiving surface  34  meet at an arcuate interface  36 . Specifically, the two mating surfaces  24  and  34  have a corresponding mating arcuate shape or configuration when extending laterally from one side of the blade to the other side of the blade, as seen in the bottom plan view of  FIG. 4 . The arcuate surface interface of the cutting portion and main body portion is designed to spread the shear and impact force over a relatively larger surface area in comparison with a linear interface. 
         [0035]    In one embodiment, the arcuate shape of the driving engagement surface and the arcuate configuration of the force receiving surface form a portion of an arc. In another embodiment, the arcuate shape may be of a circular, sinusoidal, parabolic, or elliptical configuration. The use of an arcuate shape for mating is an advantage to the user or craftsman in that the arcuate shape provides a larger surface area which assists in the absorption of shock and shear loads and forces that are created axial to the tool handle during use (such as impact from a hammer). 
         [0036]    The side view of  FIG. 5  illustrates also that the interface between the main body portion  20  and the rearward portion of cutting portion  30  defines a radiussed cross-sectional juncture.  FIG. 6  shows a detailed view of the juncture in a longitudinal cross section. As shown, driving engagement surface  24  is shown as generally sloping rearwardly (i.e., towards the handle) as it extends from larger thickness region  26  towards reduced thickness region  22 . The rearward slope is, in one embodiment, at an angle θ of between 5° and 60° with respect to a plane that is perpendicular to the longitudinal axis A of the blade. As also seen in  FIG. 6 , the juncture between driving engagement surface  24  and reduced thickness region  22  defines a radius of curvature at the rounded corner  40  of the engagement. In one embodiment, the radius of curvature has a dimension of 0.010 inches. The engaging radius between the main body portion  20  and cutting portion  30  further helps to absorb the shear and impact load that will be present when the tool is impacted with a load axial to the tool handle. 
         [0037]    The combination of the arcuate lateral interface and radiussed longitudinal, and each individually, at the interface between the cutting portion  30  and the body portion  20  function to reduce stress and strain of the interface driving impact in comparison with a linear, square cornered interface. 
         [0038]    While the principles of the invention have been made clear in the illustrative embodiments set forth above, it will be apparent to those skilled in the art that various modifications may be made to the structure, arrangement, proportion, elements, materials, and components used in the practice of the invention. 
         [0039]    It will thus be seen that the objects of this invention have been fully and effectively accomplished. It will be realized, however, that the foregoing preferred specific embodiments have been shown and described for the purpose of illustrating the functional and structural principles of this invention and are subject to change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.