Patent Publication Number: US-2021162520-A1

Title: Variable radius gash

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of pending U.S. Provisional Application No. 62/716,615 filed Aug. 9, 2018, which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     High-performance rotary cutting tools, such as end mills, may incorporate various geometrical designs, including symmetrical (or equal) geometry designs and variable (or unequal) geometry designs. Symmetrical, equal geometry designs may resonate at natural frequencies during use, and thus vibrate, known as “chatter” in machining terms and which can cause damage to the tool and unacceptable surface finish to the work piece. To control chatter in such standard, non-variable geometry cutting tools, cutting rates need to be reduced, sometimes significantly, thus hindering productivity. 
     Thus, modern high-performance rotary cutting tools may incorporate variable or unequal geometry designs. Exemplary variable geometry designs include, but are not limited to, unequal flute indexing, variable helix, variable rake, variable edge treatment, etc., and high-performance cutting tools may include one or more of these variable design features. By disrupting the natural frequencies that occur with equal, symmetrical geometry designs, the variable or unequal geometry designs reduce or eliminate “chatter” which can cause improve tool life and surface finish. However, variable geometry designs may subject the tool to varying chip loads, which may result in irregular wear of the cutting edges of the cutting tool. 
     SUMMARY 
     In accordance with the present disclosure, a variable radius gash geometry is provided. The variable radius gash geometry may be utilized in a variety of rotary cutting tools having cutting faces at an axial end of the rotary cutting tool. In some examples, the variable radius gash geometry may include a plurality of gash grinds each associated with an end cutting edge, wherein each of the gash grinds is defined by a unique radius such that the end cutting edges have equal length. In some of these examples, each of the gash grinds may be a full radius gash grind that is tangent to an axial rake face and a clearance face; and in some of these examples, the axial rake face and the clearance face associated with each of the plurality of gash grinds may be formed via the gash grind associated therewith. In some examples, the end cutting edges are each formed via the gash grind associated therewith. In some examples, each of the end cutting edges is associated with a flute, the flutes having an unequal flute indexing arrangement. 
     Also disclosed herein is a variable radius gash geometry for a rotary cutting tool. In some examples, the variable radius gash geometry may include a plurality of gash grinds each associated with an end cutting edge and each tangent to an axial rake face and a clearance face, wherein each of the gash grinds develops the end cutting edge associated therewith with a length equal to the other end cutting edges. In some of these examples, each of the gash grinds may be defined by a unique radius that is different from the other gash grinds. In some examples, the axial rake face and the clearance face associated with each of the plurality of gash grinds may be formed via the gash grind associated therewith. In some examples, the end cutting edges may each be formed via the gash grind associated therewith. In some examples, each of the end cutting edges is associated with a flute, and the flutes may have an unequal flute indexing arrangement. In some examples, each of the gash grinds defines a full radius providing a gash surface having continuous curvature equal to the full radius. 
     Also disclosed herein is a rotary cutting tool. In these examples, the rotary cutting tool includes a cylindrical body having a cutting portion that extends longitudinally along an axis of the cylindrical body towards an axial end of the cylindrical body; and a cutting face provided at the axial end, the cutting face having a plurality of end cutting edges that are each developed by a gash grind in the cutting face, wherein each gash grind is defined by a different radius that equalizes length of the end cutting edges. 
     Also disclosed herein is a method of providing a variable radius gash geometry on a cutting face of a rotary cutting tool. This method may include plunging a plurality of grinding wheels into the cutting face, wherein each grinding wheel has a different radius; and grinding a gash into the cutting face with each of the grinding wheels, wherein each of the gashes is defined by a unique radius that corresponds to the different radius of the grinding wheel associated therewith and that develops an associated end cutting edge such that each of the associated end cutting edges have equal length. In some examples, this method may include forming a full radius gash into the cutting face with each of the grinding wheels, wherein each full radius gash is tangent to an axial rake face and a clearance face associated with the full radius gash. In some examples, the method is a method of radius gash grinding that provides an axial rake face and a clearance face tangent to a radius of a gash interposing the axial rake face and clearance face. 
     Also disclosed herein is a method of equalizing length of end cutting edges on a cutting face of a rotary cutting tool having variable flute indexing. This method may include plunging a plurality of grinding wheels into the cutting face, wherein each grinding wheel has a different radius; and grinding gash grinds that each have a unique radius corresponding with the different radius of the grinding wheel utilized to form the gash grind, wherein the gash grinds develop the end cutting edges having equal lengths. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following figures are included to illustrate certain aspects of the present disclosure, and should not be viewed as exclusive embodiments. The subject matter disclosed is capable of considerable modifications, alterations, combinations, and equivalents in form and function, without departing from the scope of this disclosure. 
         FIG. 1  is a side view of an exemplary cutting tool that may incorporate the principles of the present disclosure. 
         FIG. 2  illustrates a cutting face of a tool having an exemplary center cutting design. 
         FIG. 3  illustrates an example plunge operation of the tool having the center-cutting design of  FIG. 2 . 
         FIG. 4  illustrates a cutting face of a tool having an exemplary non-center-cutting design. 
         FIG. 5  illustrates an example ramping operation of the tool having the non-center-cutting design of  FIG. 4 . 
         FIG. 6  is an isometric view of the cutting tool of  FIG. 1 . 
         FIG. 7  is a detailed side view of the axial end of the cutting tool of  FIG. 1 . 
         FIG. 8  illustrates the cutting face of a cutting tool having unequal flute indexing. 
         FIG. 9  illustrates the cutting face of  FIG. 8  having end cutting edges of varying lengths due to the unequal flute indexing. 
         FIG. 10  is an isometric view of a cutting tool incorporating variable radius gash geometry, according to one or more embodiments of the present disclosure. 
         FIG. 11  is a detailed side view of the axial end of the cutting tool of  FIG. 10 . 
         FIG. 12  illustrates the cutting face of a cutting tool with unequal flute indexing and incorporating variable radius gash geometry, according to one or more embodiments of the present disclosure. 
         FIG. 13  illustrates the cutting face of  FIG. 12  with end cutting edges of equal lengths due to the variable radius gash geometry. 
         FIG. 14  is a detailed perspective view of a cutting face of a cutting tool having a plurality of variable radius gash grinds, according to one or more embodiments of the present disclosure. 
         FIG. 15  is an alternate perspective view of  FIG. 14 . 
         FIG. 16  is a top view of a cutting face of a cutting tool having a plurality of variable radius gash grinds, according to one or more embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure is related to rotary cutting tools having variable radius geometries and, more particularly, to rotary cutting tools with variable radius gash geometries. 
     The embodiments described herein provide variable radius gash geometry for rotary cutting tools, such as end mills, that reduce or eliminate uneven wear of the cutting edges. 
       FIG. 1  is a side view of an example rotary cutting tool  100  (hereinafter, the “cutting tool  100 ”) that may be modified to incorporate the principles of the present disclosure. The depicted cutting tool  100  is just one example cutting tool that can suitably incorporate the principles of the present disclosure. Indeed, many alternative designs and configurations of the cutting tool  100  may be employed, without departing from the scope of this disclosure. For example, the principles of the present disclosure may be incorporated with various types of rotary cutting tools, such as end mills, drills, countersinks, counter bores, taps and dies, reamers, routers, etc. Thus, while the cutting tool  100  is illustrated and described as an end mill, it will nevertheless be appreciated that chip breaking features disclosed herein may be incorporated onto other types of rotary cutting tools without departing from the present disclosure. In the illustrated example, the cutting tool  100  is configured as an end mill having five (5) flutes and may be used to mill a variety of materials including ferrous type work piece materials such as steel, stainless steel, titanium, etc. However, the cutting tool  100  may be differently configured with more or less flutes, for example, a multi-flute router, used for routing CFRP and plastic type materials. In some examples, the cutting tool  100  may include seven (7) flutes or any other flute counts. Regardless, embodiments described herein may be utilized with any number of cutting tools, regardless of their flute count. Thus, embodiments described herein are not limited by the flute count of the cutting tool on which it is disposed. 
     As illustrated, the cutting tool  100  generally includes a cylindrical body  102  that extends longitudinally along an axis A 1  of the cylindrical body  102 . Here, the cylindrical body  102  includes a shank portion  104  and a cutting portion  106  that generally defines the length of cut of the cutting tool  100 , and the cutting portion  106  extends longitudinally along the axis A 1  to an axial face or axial end  108  of the cutting tool  100 . The cutting portion  106  is illustrated as having a generally cylindrical shaped periphery, but it may be configured with various other geometries without departing from the present disclosure, including but not limited to a frusto-conical shape or ball nose shape. 
     The cutting portion  106  includes a plurality of blades  110  that are separated by a plurality of flutes  112 . Each of the blades  110  has a leading face surface  114 , a trailing face surface  116 , and at least one radial relief surface  118  that bridge the leading face surface  114  and trailing face surface  116 . As to each of the blades  110 , a cutting edge (or lateral or side cutting edge)  120  is formed at the intersection between the leading face surface  114  and the radial relief surface  118 . Here, the blades  110  and flutes  112  extend along the cutting portion  106 , helically about the axis A 1 . The blades  110  may be oriented at various helix angles that are measured with respect to the axis A 1 , and in other non-illustrated embodiments, the blades  110  and the flutes  112  may even be oriented parallel to the axis A 1 . During operation, the cutting tool  100  rotates in a direction R about the axis A 1 , and chips are removed from the work piece upward through the flutes  112  and towards the shank portion  104 . 
     The radial relief surface  118  may have various configurations. For example, the radial relief surface  118  may exhibit a generally cylindrical configuration, a generally planar configuration, a not-concave configuration, a faceted configuration, or an eccentric configuration when evaluated in cross section. Also, the radial relief surface  118  may include one or more relief surfaces that are oriented at one or more corresponding relief angles. For example, the radial relief surface  118  may include a primary relief surface disposed contiguous with the cutting edge  120  extending at a first relief angle relative to a tangential line drawn at the cutting edge  120 . In other examples, the radial relief surface  118  may include a secondary relief surface that is disposed on a side of the primary relief surface opposite of the cutting edge  120  at a second relief angle relative to the previously mentioned tangential line, where the magnitude of the second relief angle is greater than the magnitude of the first relief angle. In even other examples, the radial relief surface  118  may include additional relief surfaces, such as a tertiary portion disposed on a side of the second relief surface that is opposite of the first relief surface. These relief surfaces may be provided linearly, or may extend arcuately to blend into each other and/or the trailing face surface  116 . 
     In some examples, the cutting tool  100  has at least one end cutting edge extending beyond half a diameter of the cutting tool  100 , thereby allowing cutting across the entire diameter of the cutting tool. This is referred to as center-cutting end design, and  FIG. 2  illustrates an exemplary center cutting end design  200 , according to one or more embodiments. Here, the center cutting end design  200  includes two (2) flutes  202  that extend to (or beyond) a center  204  of a cutting diameter D of the tool, to thereby define center cutting edges  206  extending across the center  204 . Here, a pair of end cutting edges  208  that do not extend to (or stop short of) the center  204  of the cutting diameter D and are thus shorter than the center cutting edges  206 . The center cutting end design  200  enables the cutting tool  100  to do a direct plunge (axially) into a material to cut similar to a drilling operation.  FIG. 3  illustrates a plunge operation of a cutting tool having the center cutting end design  200  of  FIG. 2 . This results in a hole in the material from which the cutting tool  100  may then mill radially. Drill design, however, is more effective than end mill design for entering material axially to make a hole. And, although plunge milling with the cutting tool  100  having a center-cutting end design (e.g., such as the center cutting end design  200  of  FIGS. 2-3 ) is an effective operation, it is limited in use due to its aggressiveness, especially in difficult to machine materials. 
     In other examples, however, the cutting tool  100  may have a non-center-cutting end design.  FIG. 4  illustrates an exemplary non-center-cutting end design  400 , according to one or more examples. Here, the non-center cutting end design  400  includes five (5) flutes  402  that do not extend to a center  404  of the tool&#39;s cutting diameter D. While the non-center-cutting end design  400  may inhibit direct axial plunging due to its open design where the flutes  402  do not extend to or past the center  404 , the non-center-cutting end design  400  is effective at aggressively ramping into the material. In particular, the open design of the non-center-cutting end design  400  provides extra room for material or chip evacuation, thereby making the non-center-cutting end design  400  effective and/or efficient at ramping into a material.  FIG. 5  illustrates a ramping operation of a cutting tool having the non-center-cutting design of  FIG. 4 . The non-center-cutting end design  400  provides flexibility as the cutting tool  100  having such design may be manufactured from a carbide blank with a central hole that permits the cutting tool  100  to be utilized with a through the spindle coolant delivery system. 
     The cutting tool  100  also includes a gash (or gash relief or gash grind)  600  formed into the axial end  108  of the cutting tool  100 . The configuration of the gash  600  may determine whether the cutting tool  100  incorporates a center cutting end design or a non-center cutting end design, and may thus determine the axial feed capabilities of the cutting tool  100  (i.e., whether it may plunge into the material, and parameters at which it may plunge there-into, or whether it may ramp into the material, and the parameters at which it may ramp there-into). The gash  600  is more clearly illustrated in  FIGS. 6-7 , which are isometric and detailed side views of the cutting tool  100  of  FIG. 1 , respectively. The cutting tool  100  includes a cutting face  602  at the axial end  108  of the cutting tool  100  that engages and cuts the material when plunging or ramping into the material. The gash  600  is a notch or clearance that is ground or otherwise arranged on the cutting face  602 , between an axial rake face  604  and a clearance face  606 , so as to provide room for chip evacuation as the cutting tool  100  is plunging or ramping into the material. As more fully described herein, the axial rake face  604  and the clearance face  606  may be formed when grinding the gash  600 , for example, the axial rake face  604  and the clearance face  606  may be formed during radius gash grinding. The gash  600  is a grind that helps form or develop an end cutting edge  608  of the cutting tool  100  that engages material when feeding the cutting tool  100  into material in an axial direction along the axis A 1 . Thus, the end design of the cutting tool  100  may depend on the configuration of the gash  600 . 
     Various parameters define the gash  600 . For example, the gash  600  may be arranged at a gash angle  702  (see  FIG. 7 ), which is the relief angle of the gash  600 . The gash angle  702  is measured from a gash surface  610  (i.e., a bottom surface  610  of the gash  600 ) to a cutting diameter D (i.e., margin to margin) of the cutting face  602 . As exemplified in  FIG. 7 , to measure the gash angle  702 , the axial or end cutting edge  608  is rotated to a centerline of the cutting tool  100  (i.e., the axis A 1 ), and the gash angle  702  is measured parallel to the centerline (i.e., axis A 1 ) of the cutting tool  100 . In addition, the gash  600  may have a depth parameter and a radius parameter. The gash angle, depth, and radius of the gash  600  may be designed and closely controlled to balance strength with efficient cutting of the cutting tool  100 . In some examples where the cutting tool  100  includes a plurality of gashes  600 , each of the gashes  600  may include the same gash angle, the same gash depth parameter, and the same gash radius parameter; however, in some examples, one or more of the gashes  600  may have one or more parameters different from one or more of the other gashes  600 . 
     When forming the gash  600  in the cutting tool  100 , the grinding wheel that produces the gash  600  enters the cutting face  602  of the cutting tool  100 , and “walks” laterally to provide the gash  600  with a width dimension W. Laterally “walking” the grinding tool to form the gash  600  in this manner imparts a square (or trapezoidal) shaped geometry on the gash  600  (i.e., a squarish gashing or trapezoidal gashing), as illustrated in  FIG. 6  and  FIG. 7 . Here, the squarish (or trapezoidal) gashing includes a generally flat gash surface  610  and the axial rake face  604  and the clearance face  606  extend therefrom at respective junctions  612 , 614  with the gash surface  610  (see  FIG. 7 ). Also, radiused corners are ground at the junction  612  between the gash surface  610  and the axial rake face  604  and at the junction  614  between the gash surface  610  and the clearance face  606 , and the radius of such radiused corners is equal to the radius of the grinding wheel (or other tool) utilized to grind the gashes  600 . In some examples, a single conventional grinding wheel is utilized to grind the gashes  600  (i.e., to form the gash  600  grinds). However, such squarish (trapezoidal) gashing creates a weak point (or weakness) that is susceptible to breakage or failure, for example, breakage or chipping a corner  616  at the axial end  108  of the cutting tool  100 . Also, gashes  600  formed in this manner often have equal widths W (i.e., the width W of the gash surface  610  is the same for each of the gashes  600  and flute  112  associated therewith) but, in examples where the cutting tool  100  has unequal indexing (or variable indexing), the gashes  600  formed (or ground) in that manner may result in the end cutting edges  608  having unequal (or different) lengths. 
       FIGS. 8-9  are exemplary end views of cutting tools having unequal (or variable) indexing of the blades  110  and the flutes  112 , wherein the end cutting edges  608  produced by the gash  600  grinds have unequal lengths. In particular,  FIG. 8  illustrates an example of the cutting face  602  having unequal flute indexing and  FIG. 9  illustrates how grinding (or forming) the gashes  600  on the cutting face  602  of  FIG. 8  that incorporates unequal flute indexing provides the end cutting edges  608  with unequal lengths. Here, the cutting tool  100  incorporates unequal flute indexing such that the flutes  112  are arranged at different index angles a°, b°, c°, d°, e° ( FIG. 8 ), and grinding the gashes  600  into the cutting face  602  such that the gashes  600  each have equal widths W results in the end cutting edges  608  having unequal lengths a, b, c, d, e ( FIG. 9 ). Thus, providing the gashes  600  with uniform dimensions (i.e., uniform dimensioned gashes  600 ) in a cutting tool  100  having unequal flute indexing may result in the end cutting edges  608  having varying (or different) lengths. However, this may result in irregular wear to the end cutting edges  608 , for example, during aggressive ramping operations, in addition to weakening of the corners  616  as mentioned above. 
     In other embodiments, the cutting tool  100  may include a variable radius gash geometry.  FIGS. 10-16  illustrate an exemplary variable radius gash geometry, according to one or more embodiments of the present disclosure. Variable radius gash geometry includes, or is defined by, a plurality of full radius gashes, each of unique size and each tangent to its neighboring axial rake face and clearance face. Thus, variable radius gash geometry is a grind feature that may include grinding each gash to have a unique or different radius to provide a plurality of variable radius gashes, and each such variable radius gash may be ground with a full radius (i.e., a continuous radius from the axial rake face to the clearance face) such that it is tangent to its associated axial rake face and the clearance face. This may be accomplished with a single angle form wheel utilized to cut gashes of different radii. Here, the single angle form wheel, that may vary in size according to the size of the cutting tool  100  being made or modified, generates the cutting face (axial rake face), the radius in the bottom of the gash, and the clearance face via multi-axis movements of the single angle form wheel controlled, for example, by a computer numerical control (“CNC”) grinding program. Thus, the axial rake face, the radius of the gash, and clearance face may all be formed during the radius gash grinding. However, in other examples, differently sized grinding wheels (i.e., multiple formed wheels) may be utilized to form the gashes of different radii, and in such latter examples, the differently sized grinding wheels may each cut an individual variable radius gash via an individual plunge grind operation. Accordingly, a gash surface of each such variable radius gash includes a continuous curvature extending between its neighboring axial rake face and clearance face. In addition, variable radius gash geometry described herein may be incorporated into cutting tools having center cutting end designs or a non-center cutting end design. 
     The dimensions of the different gash radii utilized in the variable radius gash geometry may depend on dimensions of the cutting tool, the flute indexing, and/or the desired length of the resulting end cutting edges. For example, the size of the variable radius gash may be dependent on the flute count and diameter of the particular cutting tool into which the variable radius gash geometry is to be incorporated. In some examples, the variable radius gashes each have the same depth into the cutting face as measured along the longitudinal axis, but in other examples, one or more of them may have a different depth. Also, each of the full radius gashes may have the same gash angle, or one or more of the full radius gashes may have a gash angle that is different from the gash angles of one or more of the other full radius gashes. The gash angle of one or more of the full radius gash grinds may be selected from a range of gash angles, positive or negative, and in some examples the gash angle of one or more of the full radius gash grinds is selected based on the material to be machined. In addition, the gash angle of the various radius gash grind may vary from flute to flute such that, for example, the various radius gash grind in a first flute may oriented a positive gash angle and the gash angle of the various radius gash grind in a second flute may be oriented at a different positive gash angle or at a negative gash angle, etc. In some examples, variable radius gash geometry utilizes full radius gashes oriented at the same or different gash angles. This will allow the cutting tools incorporating variable radius gash geometry to include variable axial rake, similar to how the variable radial rake is provided in the Z-CARB-AP series tools provided by KYOCERA SGS Precision Tools. The diameters of the variable radius gashes depend on the diameter and flute count of each tool and may thus include any number of dimensions depending on those parameters. 
     By grinding a plurality of full radius gashes, each of unique size and tangent to the neighboring axial rake and clearance faces, the lengths of the end cutting edge will be the same. Thus, variable radius gash geometry may be incorporated into cutting tools having unequal flute indexing to equalize the lengths of the end cutting edges formed by the gash grind, and thereby improve ramping ability and overall performance. In addition, because the gashes of the variable radius gash geometry have a full radius (rather than “walking” the grinding wheel to form squarish or trapezoidal gashing), the corners of the cutting tool are significantly strengthened. Indeed, load testing has shown that the variable radius gash geometry may increase the strength of the corners up to three (3) times compared to conventional gash geometry. The increased strength provided by the variable radius gash geometry also stabilizes the cutting tool during heavy milling, which promotes tool life. 
     The variable radius gash geometry may be provided on various types of rotary cutting tools, such as the cutting tool  100  described with reference to  FIGS. 1-9 . Thus, the variable radius gash geometry described herein may be incorporated into end mills, drills, countersinks, counter bores, taps and dies, reamers, routers, etc. However, while the variable radius gash geometry is described and illustrated with reference to an end mill, it will nevertheless be appreciated that the variable radius gash geometry disclosed herein may be incorporated onto other types of rotary cutting tools without departing from the present disclosure. In addition, the variable radius gash geometry may be incorporated into cutting tools with unequal flute indexing as mentioned above, but may also be incorporated into cutting tools having other types of flute indexing. 
       FIG. 10  is an isometric view of a cutting tool  1000  incorporating a variable radius gash geometry  1002 , according to one or more embodiments of the present disclosure. As illustrated, the variable radius gash geometry  1002  includes a plurality of gashes  1004  arranged at an axial end  1006  of the cutting tool  1000 . A plurality of end cutting edges  1008  are formed at the axial end  1006 , with each of the end cutting edges  1008  corresponding with one of the gashes  1004 . Also, each gash  1004  includes a gash surface  1016 , with an axial rake face  1010  extending from the end cutting edge  1008  into a first side of the gash surface  1016  and a clearance face  1012  extending from an opposite second side of the gash surface  1016 , away from the axial rake face  1010  and towards a neighboring end cutting edge  1008 . Here, the gash surface  1016  includes a continuous curvature of constant radius, with the gash surfaces  1016  of the different gashes  1004  having unique or different radii. However, one or more of the gash surfaces  1016  may have a flat portion. Thus, grinding each of the gashes  1004  into a cutting face at the axial end  1006  of the cutting tool  1000  develops a corresponding one of the plurality of end cutting edges  1008 , as well as the gash surfaces  1016  and the corresponding axial rake face  1010  and the corresponding clearance face  1012  of the gash  1004 . 
       FIG. 11  is detailed side view of the variable radius gash geometry  1002  of  FIG. 10 . As illustrated, the gashes  1004  each include (or, are each defined by) a radius R. In particular, each of the gashes  1004  is a full radius gash, defined by its radius R, such that the gash  1004  is tangent to the axial rake face  1010  and the clearance face  1012  associated therewith. Grinding the gash  1004  as a full radius gash adds strength to a corner  1014  of the cutting tool  1000 . Also, the radius R for each of the gashes  1004  is unique or different from the radii of the other gashes  1004 , thereby providing the cutting tool  100  with the variable radius gash geometry  1002  and equalizing the lengths of the end cutting edges  1008  formed when grinding the gashes  1004 . In the illustrated examples, the gash surface  1016  is ground with radius R that is tangent to the axial rake face  1010  and the clearance face  1012  surrounding the gash surface  1016 . 
       FIGS. 12-13  illustrate how providing the gashes  1004 , each with a unique size or radius and tangent to its corresponding axial rake and clearance faces, equalizes the lengths of the end cutting edges  1008 .  FIGS. 12 and 13  are end views of the cutting tool  1000  of  FIGS. 10 and 11  configured with unequal indexing, and illustrate how the variable radius gash geometry  1002  equalizes the lengths of the end cutting edges  1008  formed by the gash  1004  grinds. In particular,  FIG. 12  illustrates an example of the cutting tool  1000  having unequal flute indexing and  FIG. 13  illustrates how grinding (or forming) grinding the variable radius gash geometry  1002  forms the end cutting edges  1008  with equal lengths a′, b′, c′, d′, e′. Here, the cutting tool  1000  incorporates unequal flute indexing such that the flutes are arranged at different index angles a°, b°, c°, d°, e° ( FIG. 12 ), and grinding the gashes  1004 , each with a unique and full radius R that is tangent to the axial rake face  1010  and the clearance face  1012 , results in the end cutting edges  1008  having equal lengths a′, b′, c′, d′, e′ (i.e., a′=b′=c′=d′=e′). 
       FIGS. 14-15  are various perspective views of the cutting tool  1000  having the variable radius gash geometry  1002  of  FIGS. 10-11 , whereas  FIG. 16  is a top view thereof. As illustrated, the gashes  1004  are each a full radius R, tangent to the axial rake face  1010  and the clearance face  1012 , and the full radius R of each of the gashes  1004  is unique (or different) from the other gashes  1004 . This results in the end cutting edges  1008  having equal lengths, which adds strength and durability to the corners  1014 . 
     Also disclosed herein are various methods associated with the variable radius gash geometry. For example, this disclosure includes methods for forming a variable radius gash geometry, methods for manufacturing a rotary cutting tool having a variable radius gash geometry on a cutting face of the rotary cutting tool, methods for equalizing end cutting edges of a rotary cutting tool having variable flute indexing, etc. Such methods generally include generating a variable radius form for each of the variable radius gashes via use of a single form grinding wheel. Here, for example, the single form grinding wheel may be plunged into a cutting face (to form one variable radius gash at a time) and then walked along a radius tool path (corresponding with the unique radius of the particular gash being ground) to grind the radius form of each variable radius gash. For example, a CNC grinding program may control the single form grinding wheel to cut with multi-axis movements the cutting face (axial rake face), the radius in the bottom of the gash, and the clearance face. Thus, the axial rake face, the radius of the gash, and clearance face may all be formed during the radius gash grinding However, such methods may instead generally include plunging a plurality of grinding wheels into a cutting face of a rotary cutting tool, one at a time or two or in groups of two or more at the same time, where each grinding wheel has a unique or different radius to form gash grinds having corresponding unique or different radii and to develop end cutting edges having the same length (i.e., to equalize length of the end cutting edges). 
     In one example, a method includes a step of providing a rotary cutting tool having a cylindrical body that extends along a longitudinal axis towards an axial end, wherein the rotary cutting tool further includes a cutting face at the axial end. This method may also include a step of providing a single form grinding wheel (or other cutting tool). This method may also include a step of plunging the grinding wheel into the cutting face, axially along the longitudinal axis, and then walking the grinding wheel along a first radius path, so as to form a first gash grind having a first unique (or different) radius that is tangent to the axial rake face and the clearance face associated therewith. This method then includes a step of plunging the grinding wheel into the cutting face, axially along the longitudinal axis, and then walking the grinding wheel along a second radius path, so as to form a second gash grind having a second unique (or different) radius that is tangent to the axial rake face and the clearance face associated therewith. It will be appreciated that this step of forming the unique gash grinds may be repeated “n” number of times, where the number “n” corresponds with the number of flutes present on the cutting tool. Thus, for a tool having seven ( 7 ) flutes, this method may then include a step of plunging the grinding wheel into the cutting face as described above, so as to form a third gash grind having a third unique radius, a fourth gash grind having a fourth unique radius, a fifth gash grind having a fifth unique radius, a sixth gash grind having a sixth unique radius, and a seventh gash grind having a seventh unique radius. Accordingly, this method may be utilized with rotary cutting tools having any number of flutes. By plunging the grinding wheel into the cutting face when forming each uniquely dimensioned gash grind, the grinding wheel enters the cutting face so as to form or develop a gash grind having a radius that is tangent to the axial rake face and the clearance face, and wherein the grinding wheel follows a unique radius tool path when forming each gash such that the radii of the gash grinds are different from each other (i.e., unique). This method may also include a step of removing or withdrawing each of the plurality of grinding wheels from the cutting face, one at a time or simultaneously. 
     In this method, the step of plunging the grinding wheel into the cutting face may include forming either the axial face or the clearance face of the gash, and then continuing along the radius tool path to form the gash surface tangent to the previously formed axial face or the clearance face, and then forming the other of the clearance face or axial face of the gash tangent to the unique radius of the radius tool path. Thus, when forming the axial face and the clearance face, the grinding tool may follow a linear tool path either when plunging into the cutting face or when being retracted therefrom. Thus, the method may include forming the gash surface of the gash, together with forming the axial rake race and clearance thereof that are tangent to a radius defining the gash surface. 
     In another example, a method includes a step of providing a rotary cutting tool having a cylindrical body that extends along a longitudinal axis towards an axial end, wherein the rotary cutting tool further includes a cutting face at the axial end. This method may also include a step of providing a plurality of grinding wheels (or other cutting tools) that each have a unique or different radius. This method may also include a step of plunging each of the plurality of grinding wheels into the cutting face, axially along the longitudinal axis, so as to form a plurality of gash grinds that each have a unique (or different) radius that is tangent to the axial rake face and the clearance face. By plunging the grinding wheels into the cutting face, each grinding wheel enters the cutting face so as to form or develop a gash grind having a radius that is tangent to the axial rake face and the clearance face, wherein the radii of the gash grinds are different from each other (i.e., unique). The grinding wheels may be plunged into the cutting face one at a time, or two or more of the grinding wheels may be plunged into the cutting face simultaneously. This method may also include a step of removing or withdrawing each of the plurality of grinding wheels from the cutting face, one at a time or simultaneously. 
     Therefore, the disclosed systems and methods are well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the teachings of the present disclosure may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered, combined, or modified and all such variations are considered within the scope of the present disclosure. The systems and methods illustratively disclosed herein may suitably be practiced in the absence of any element that is not specifically disclosed herein and/or any optional element disclosed herein. While compositions and methods are described in terms of “comprising,” “containing,” or “including” various components or steps, the compositions and methods can also “consist essentially of” or “consist of” the various components and steps. All numbers and ranges disclosed above may vary by some amount. Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles “a” or “an,” as used in the claims, are defined herein to mean one or more than one of the elements that it introduces. If there is any conflict in the usages of a word or term in this specification and one or more patent or other documents that may be incorporated herein by reference, the definitions that are consistent with this specification should be adopted. 
     The use of directional terms such as above, below, upper, lower, upward, downward, left, right, and the like are used in relation to the illustrative embodiments as they are depicted in the figures, the upward or upper direction being toward the top of the corresponding figure and the downward or lower direction being toward the bottom of the corresponding figure. 
     As used herein, the phrase “at least one of” preceding a series of items, with the terms “and” or “or” to separate any of the items, modifies the list as a whole, rather than each member of the list (i.e., each item). The phrase “at least one of” allows a meaning that includes at least one of any one of the items, and/or at least one of any combination of the items, and/or at least one of each of the items. By way of example, the phrases “at least one of A, B, and C” or “at least one of A, B, or C” each refer to only A, only B, or only C; any combination of A, B, and C; and/or at least one of each of A, B, and C.