Patent Application
20120055031
The invention relates generally to cutting tools such as cutting pliers and more particularly to an improved cutting edge for such tools.
Cutting tools such as cutting pliers are known to be used to cut articles such as wire. The typical cutting tool comprises a first jaw connected to a second jaw at a pivot such that the jaws may be moved toward and away from one another. The jaws include cutting edges that are disposed opposite to one another such that the cutting edges engage one another when the jaws are closed. A handle may be connected to each jaw where the handles act as levers to close the jaws when the handles are squeezed by an end user. An article may be located between the jaws and the jaws closed such that the cutting edges engage and sever the article.
A cutting tool comprises a first cutting edge and a second cutting edge where the cutting edges are movable into engagement with one another. At least one of the cutting edges comprises an edge tip extending along at least a portion of the cutting edge. The edge tip, in cross-section, has a curved outer surface that is within a range bounded by a first line defined by the equation y=74x2 where x is within the range −0.023 inches≦x≦0.023 inches and a second line defined by the equation y=294x2 where x is within the range −0.012 inches≦x≦0.012 inches.
The edge tip defines a plane that extends through the first cutting edge and the second cutting edge and the edge tip may be symmetrical about the plane. The first cutting edge may be formed on a first jaw and the first jaw may be operatively connected to a first lever arm and the second cutting edge may be formed on the second jaw and the second jaw may be operatively connected to a second lever arm. The second cutting edge may have a second curved surface that is the same as the curved surface of the first cutting edge. The second cutting edge may also comprise a second edge tip extending along at least a portion of the second cutting edge where the second edge tip has a curved surface that is also within the range bounded by lines defined by the equation y=74x2 where x is within the range −0.023 inches≦x≦0.023 inches and the equation y=294x2 where x is within the range −0.012 inches≦x≦0.012 inches. The first jaw and second jaw may also comprise gripping surfaces. The first cutting edge may extend for the length of the first jaw and the second cutting edge may extend for the length of the second jaw. The geometry of the outer surface may extend for 0.040 inches from the distal end of the edge tip.
Referring to
The invention relates to a cutting edge geometry for use in such cutting tools. The cutting force required to cut soft materials, such as electrical cable, is lowered by the geometry of the cutting edge. Cutting edges on such cutting tools may be damaged through use and abuse. The damage is often the result of cutting hard materials such as cable, wire, bolts or screws and may deform the cutting edges. The cutting edge geometry of the invention comprises an edge tip that lowers the cutting force required to cut through materials while providing an edge that is resistant to damage.
The shape of edge tip 502 will be described with Reference to
Referring to
The edge tip 502 has a curved outer surface 502b that may extend for the length of the cutting edge 500. The outer surface 502b comprises a rounded distal end 502a that is the apex of the curve that forms the outer surface 502b. The distal end 502a forms the leading edge of the edge tip 502 and is the line of contact between the two jaws. In cross-section the outer surface of the edge tip 502 has a curved shape that is parabolic or approximately parabolic. To describe the shape of the edge tip 502 reference is made to
The outer surface 502b of the edge tip 502, in cross-section, lies within the range bounded by Line A-A defined by the equation y=74x2 where x is within the range (−0.023 inches≦x≦0.023 inches) and Line C-C defined by the equation y=294x2 where x is within the range (−0.012 inches≦x≦0.012 inches). The outer surface 502b of the edge tip 502 may be within this range where the outer surface has a curved shape that approximates the shapes of lines A-A and C-C. The outer surface of the edge tip 502 falls within the area bounded by the line A-A and the line C-C along the length of the edge tip. A preferred outer surface 502b of the edge tip 502, in cross-section, lies on the line B-B defined by the equation y=136x2 where x is within the range (−0.017 inches≦x≦0.017 inches) Because the tip 502 has a height A of approximately 0.040 inches the scale of the tip is relatively small such that there will be some variation in the curve that defines the tip due to manufacturing tolerances. Thus, an edge tip that has a curved surface that has a cross-sectional shape approximating the parabolic shape of the described curves and that has a cross-sectional area similar to the cross-sectional area of the described edge tip will provide the desired performance. It has been found that a curved outer surface having a shape similar to that described that has cross-sectional area beneath surface 502b from distal end 502a to a transverse line d-d that is 0.040 inches from distal end 502a that is approximately 0.001 square inches provides the improved cutting performance and durability of the invention.
The equations set forth above define a smooth curve. The benefits of the cutting edge of the invention may be obtained even where the outer surface 502b of the cutting edge tip 502 is not a perfect curve. It is to be appreciated that a series of points along the curve can accurately define the curve even where the line between the points may or may not lie on the curve. Further, while the equations described above and the nodal points set forth below define the surface with a great degree of accuracy the outer surface of a cutting edge tip may vary slightly from these perfect curves. An approximation of the curve defined by the equations set forth above may be identified by identifying nodal points that adequately define the outer surface of the edge tip. A cutting edge tip having an outer surface 502b lying within the following x, y nodal points defines an outer surface having the cutting and durability benefits of the invention:
Positive x values in the table correlate to the positive range of the edge tip equations in all three cases. The equivalent negative x values with given y values may be used to correlate the negative range of the edge tip equation in all three cases. Table 1 is a series of seven nodal points that lie on the previously defined curve, y=74x2 and may be used as a measurement technique to ensure that the edge tip curvature is accurate. Table 2 is a series of seven nodal points that lie on the previously defined curve, y=136x2 and may be used as a measurement technique to ensure that the edge tip curvature is accurate. Table 3 is a series of seven nodal points that lie on the previously defined curve, y=294x2 and may be used as a measurement technique to ensure that the edge tip curvature is accurate.
The more nodal points that are used to define the curve of the outer surface of the edge tip, the more accurately the curve is represented. However, because the height dimension A of edge tip 502 is 0.040 inches, it has been found that the curve can be represented with the 7 nodal points to provide the cutting force characteristics and durability of the invention. Further, it has been found that the first 40 thousands of an inch extending from the distal end 502a of the edge tip 502 along the y-axis are most critical in providing the cutting force characteristics and durability of the cutting edge. Thus, a cutting edge that over the first 40 thousands of an inch (from distal end 502a) has a edge tip that comprises an outer surface having the geometry of the curve set forth herein provides desirable cutting force characteristics and durability. After the first 40 thousandths the tip may vary from the curves set forth above. In the example curves set forth in Tables 1 through 3, the distal end 502a is located at nodal point 0,0 such that the curves are described as a perfect tangent to the x-axis. In actual embodiments the distal end 502a may comprise a flat surface that extends along the x-axis a short distance, for example, 4 thousandths of an inch and still be considered to approximate the defined curve.
While the cutting edge of the invention has been described with respect to the diagonal pliers of
Referring to
A third lever assembly 420 is fixed to and pivoted relative to the first lever assembly 401 at a second pivot 422. The third lever assembly 420 is also connected to the second lever assembly 408 by a pin 430 formed on the third lever assembly 420 that engages a slot 432 formed on the stub 414 of the second lever assembly 408. The third lever assembly 420 comprises a handle 424 that extends generally opposite to the first handle 402. A user may press the handles toward one another such that the engagement of pin 430 with slot 432 rotates second lever assembly 408 to close the jaws 404 and 410.
The cutting tools described above are provided by way of example. The cutting edge of the invention may be used on any cutting tool where the cutting edge construction described herein provides the cutting force and durability advantages described herein.
A method of making a cutting tool comprises providing a first cutting edge and a second cutting edge where the first cutting edge and the second cutting edge are movable into engagement with one another (block 1001). One method of manufacturing a cutting edge is to forge the jaws pieces, machine the pieces, assemble the jaws together such as by a rivet, heat treat the jaws, and laser harden the edge. An edge tip is provided along at a least a portion of the first cutting edge (block 1002). The edge tip is shaped to have a curved surface that is within the range defined by a first line defined by the equation y=74x2 where x is within the range −0.023 inches≦x≦0.023 inches and a second line defined by the equation y=294x2 where x is within the range −0.012 inches≦x≦0.012 inches (block 1003). The edge tip shape can be ground into the desired shape before or after assembly of the pliers. It is also possible to create inserts that have the shaped cutting edges where the inserts are separately attached to the jaws. The inserts may be manufactured using various methods including EDM, machining, grinding, and investment casting. Alternatively, the jaws and cutting edges may be investment cast, machined and assembled. Another alternate method of manufacturing is to investment cast the jaws and use composite construction for the handles. The edge tip may be further shaped to have a curved surface that is defined by a third line defined by the equation y=136x2 where x is within the range −0.017 inches≦x≦0.017 inches (block 1004).
While embodiments of the invention are disclosed herein, various changes and modifications can be made without departing from the spirit and scope of the invention as set forth in the claims. One of ordinary skill in the art will recognize that the invention has other applications in other environments. Many embodiments are possible. The following claims are in no way intended to limit the scope of the invention to the specific embodiments described above.
