Abstract:
An improved rotary cutting tool overcomes the disadvantages and limitations of known constructions through the use of least one primary flute defining a low-angle cutting surface, and at least one secondary flute defining a high-angle cutting surface. The primary and secondary flutes intersect to form a compound cutting surface having a continuous cutting edge including a leading cutting edge formed along at least a portion of the low-angle cutting surface, and a trailing cutting edge formed along at least a portion of the high-angle cutting surface. The invention may further include a cooling channel and at least one aperture exiting out of the main body portion to provide a cooling fluid to one of more of the cutting edges. In a different embodiment, the leading cutting edge begins from a leading point and the trailing edge terminates in a trailing point, and one or both of the leading and trailing points are eased to reduce scoring. Optionally, the region of intersection between the primary and secondary flutes may be truncated or radiused, and one or more additional flutes may be used to provide the truncation or radius. According to yet a further configuration, a volume of material may be removed distally with respect to one or more of the leading edges to reduce the clearance angle associated therewith and improve chip removal.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a continuation-in-part application of U.S. patent application Ser. No. 09/416,347, filed Oct. 12, 1999, which is a continuation of U.S. patent application Ser. No. 08/798,324, filed Feb. 10, 1997 now U.S. Pat. No. 6,007,276, which is a continuation-in-part of U.S. patent application Ser. No. 08/238,864, filed May 6, 1994, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     In general, the present invention relates to machining of a workpiece. More particularly, the present invention relates to end-mill tools for milling a workpiece and a related method. 
     BACKGROUND OF THE INVENTION 
     Rotary cutting end-mill tools are used for various machining operations on workpieces. Such machine operations are generically referred to as milling operations and include the forming of slots, keyways, pockets, and the like. Several considerations related to end-mill tool design include time for completing a machining operation, amount of material removed in a cut, quality of the: cut, and wear on the tool itself during the milling operation. 
     The various machining operations performed with an end-mill tool can be performed in a “roughing” mode (rough cutting) and a “finishing” mode (finishing cutting). During roughing, material is removed from a workpiece at a relatively high rate (e.g., depth of cut), but with a relatively rough surface finish. Finishing involves the removal of material from a workpiece at a relatively low rate, but with a relatively smooth surface finish. Generally, these two operations (roughing and finishing) are antithetical to one another, and require two operations with two different end-mills. 
     End-mill tools are formed from materials such as tungsten carbide, high speed steel, ceramic, and other advanced materials and coatings and typically include a “shank” portion, a “body” portion and a “point”. The shank portion is located towards one end of the end-mill tool and is generally cylindrical (but may be tapered) for engagement by a spindle of a milling machine. In use, the milling machine rotatably drives the end-mill tool about its longitudinal axis. The body portion of the end-mill tool is located between the shank and the point. The point is formed at an opposite end of the tool from the shank portion, and typically includes one or more cutting edges. 
     To manufacture an end-mill tool, a grinder is typically used to grind a flute face and a corresponding cutting edge on the body of the end-mill tool. The grind (grinding operation) typically starts from a position adjacent an end of the body portion and continues to a point at or near the interface of the body portion and the shank portion, commonly referred to as an “inception location”. The grind forms a desired helical flute face and/or helical cutting edge. Prior art end-mills typically have continuous helical flutes with continuous cutting edges helically extending from the inception location to the point (or vice-versa). The flutes function primarily for chip removal, in a manner similar to the helical flutes found on an ordinary drill bit. 
     An end-mill tool representative of the end-mill tools of the prior art is illustrated in FIGS. 1A and 1B and identified with reference numeral  100 . The tool  100  has been formed of cylindrical rod stock which has been ground to form distinctive portions. At one end of the tool  100  is a shank portion  102 , suitable for chucking to the spindle of a milling machine (not shown) for rotating and advancing the tool  100 . At an other end of the tool  100  is a point  104  which is provided with flat cutting edges  114  and  116 . Between the shank portion  102  and the point  104  is a body portion  106  which is helically ground to have a number of flutes  110  and  112 . A “boundary” between the body portion  106  and the shank portion  102  is designated  108  in the drawing. 
     In the embodiment illustrated, the formation of flutes in the body portion  106  generally involves the grinding of two channels, or flutes  110  and  112 , which form two diametrically-opposed positions at the point  104  towards the shank portion  102 . The grinding is discontinued at the boundary  108  of the body portion  106  and the shank portion  102 . It will be appreciated that the direction of the grind could, of course, be reversed. In a known variation referred to as a three-flute end-mill, three flutes wind helically around the body portion of the tool and terminating in three cutting edges. The flutes  110  and  112  are formed at a helix angle which “winds” around the cylindrical body portion. 
     Generally, the location of the flat cuffing edges  114  and  116  is determined by the location of the flutes  110  and  112  at the, point  104  of the tool  100 . The end-mill tool  100  illustrated in FIG. 1A has two cutting edges  114  and  116  at the point  104 . The number and location of the cutting edges  114  and  116  is determined by the flutes  110  and  112 . FIG. 1B shows the cutting edges  114  and  116  of the tool  100  in greater detail. 
     It is known in the art to form flutes at a low helix angle or a high helix angle. A “low helix” (or low helical flute) is a flute that helically “winds” around a cylinder at an angle of no more than 45° (forty-five degrees). A “super” low-helical flute would be a flute that winds around a cylinder at an angle of at no more than 150. A “high helix” (or high helical flute) is a flute that helically winds around a cylinder at an angle of greater than 45°. A “super” high-helical flute would be a flute that winds around a cylinder at an angle of at least 65°. Low helix angle flutes are typically employed for rough cutting while high helix angle flutes are employed for finish cutting. 
     Returning to FIG. 1A, the tool  100  is illustrated to include two cutting edges  120  and  122 . Each of the cutting edges  120  and  122  is helical and follows one of the flutes  110  and  112  helically around the body portion  106 . A notable feature of these cutting edges  120  and  122  is that they are “continuous”—in other words, they helically extend continuously from the point  104  to the shank  102 . These cutting edges  120  and  122  function to remove material in the linear direction of travel of the end-mill  100  (e.g., from right-to-left, as viewed in FIG. 1A) during a machining operation when the end-mill is “buried” into a workpiece. Material removed from the workpiece will tend to be in the form of an elongated helical (curlicue) chip, and will be guided away from the workpiece by the channels formed by the flutes  110  and  112 . 
     By way of further definition, the edges  114  and  116  at the point  104  of the tool  100  can be considered to be “flat” cutting edges, and the cutting edges  120  and  122  along the body  106  of the tool  100  can be considered to be “helical” cutting edges. 
     The following U.S. patents are further instructive of the prior art: U.S. Pat. Nos. 4,610,581; 5,049,009; 4,721,421; and 4,963,059. These patents are incorporated by reference as if fully set forth herein. 
     Numerous variations of the grind (e.g., flute angle) have been attempted for end-mill tool design. Prior advancements relating to material removal and feed rate of end-mill cutters have been accomplished by (1) varying the spiral lead angle; (2) increasing the depth of the flutes in the body portion of the end-mill. (3) changing the radial rake; (4) changing the clearance angles of the cutting edges; and (5) forming chip splitting grooves in the flutes. While such variations have proven successful in various applications, they are also associated with disadvantages and limitations. For example, such variations may weaken the core diameter of the end-mill cutter, thereby weakening the tool. Additionally, such noted variations are not suitable for particular applications (e.g., regarding milling time, rough cut, finish cut, etc.). Furthermore, known end-mills are not efficient for both rough cutting and finish cutting. 
     It is often advantageous when performing an end-mill machining operation to create many small chips, rather than fewer elongated curlicue chips. This allows, for example, rapid rate of removal of material from a workpiece without undue heating of the end-mill tool. Heat is generally anathema to tools, particularly end-mill tools. To the end of reducing heat, it is known to use coolants. Dry machining (sans coolant) offers an advantage of simplicity. Generally, the end-mill of the present invention provides for increased rate of removal without sacrificing tool life and&#39;strength, and may not require flowing coolant onto the workpiece or tool. 
     SUMMARY OF THE INVENTION 
     It is therefore a principal object of the present invention to provide an improved rotary cutting tool which overcomes the disadvantages and limitations of known constructions, including but not limited to those discussed above. 
     It is another object of the present invention to provide a rotary cutting tool wherein a low and high flute angle cutting surfaces intersect to define one or more compound yet continuous cutting surfaces. 
     It is further object of the present invention to provide a rotary cutting tool which provides for a higher rate of chip removal. 
     It is a related object of the present invention to provide an end-mill tool suitable for both roughing and finishing of a workpiece. 
     In meeting these and other objectives, the invention provides a rotary cutting tool having a main body portion extending proximally from the distal end of a shank. At least one primary flute is formed on the main body portion defining a low-angle cutting surface, and at least one secondary flute formed on the main body portion defining a high-angle cutting surface. The primary and secondary flutes intersect to form a compound cutting surface having a continuous cutting edge including a leading cutting edge formed along at least a portion of the low-angle cutting surface, and a trailing cutting edge formed along at least a portion of the high-angle cutting surface. 
     In one embodiment, the invention further includes a cooling channel extending longitudinally through a least a portion of the shank, and at least one aperture in fluid communication with the cooling channel, the aperture exiting out of the main body portion to provide a cooling fluid to one of more of the cutting edges. The cooling channel may stop short of the distal end of the tool, or may extend therethrough, exiting out the distal end. Preferably, a plurality of apertures are provided, each exiting out of the main body portion of the tool at a point proximate to a leading cutting edge. In addition, when a plurality of apertures are used, they are spaced apart along the length of the main body portion, with the diameter of the apertures becoming increasingly larger toward the distal end of the tool to provide uniform fluid distribution. 
     In a different embodiment, the leading cutting edge begins from a leading point and the trailing edge terminates in a trailing point, and one or both of the leading and trailing points are eased to reduce scoring. Optionally, the region of intersection between the primary and secondary flutes may be truncated or radiused, and one or more additional flutes may be used to provide the truncation or: radius. According to yet a further configuration, a volume of material may be removed distally with respect to one or more of the leading edges to reduce the clearance angle associated there with and improve chip removal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further objects, features and advantages of the present invention will become apparent from analysis of the following written specification and accompanying drawings and the appended claims in which: 
     FIG. 1A is a side view of an end-mill tool, representative of the prior art; 
     FIG. 1B is an end view of the end-mill tool of FIG. 1A; 
     FIG. 2 is a side view of an end-mill constructed in accordance with a first preferred embodiment of the present invention, detailing the helical flute face of the end-mill; 
     FIG. 3 is a side view of the end-mill of the first preferred embodiment of the present invention, from a different perspective than the view of FIG. 2, detailing the helical cutting edge of the end-mill; 
     FIG. 4 is an end view of the end-mill of FIG. 2; 
     FIG. 5A is a partial plan view taken in the direction  5 — 5  of FIG. 2; 
     FIG. 5B is a cross-sectional view taken along the time  5 B— 5 B of FIG. 5A; 
     FIG. 6 is an enlarged side view of a portion of the end-mill of FIG. 2; 
     FIG. 7 is an enlarged simplified view of four vertically adjacent lands of the end-mill of the first preferred embodiment. 
     FIGS. 8 and 9 are simplified end views, illustrating alternate constructions of the first preferred embodiment of the end-mill of the present invention; 
     FIG. 10 is a side view of an end-mill constructed in accordance with a second preferred embodiment of the present invention, detailing the helical flute face of the end-mill; 
     FIG. 11 is a side view of the end-mill of the second preferred embodiment of the present invention, from a different perspective than the view of FIG. 10, detailing the helical cutting edge of the end-mill; 
     FIG. 12 is an enlarged simplified view similar to FIG. 7, illustrating four vertically adjacent lands of the second preferred embodiment and showing the right stagger of the lands; and 
     FIG. 13 is another enlarged simplified view similar to FIG. 7, illustrating an alternative arrangement to the second preferred embodiment having a left stagger of adjacent lands. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings in which preferred embodiments are shown. It will be appreciated, however, that the present invention may be embodied in many other forms and should not be construed as limited to the embodiments set forth herein. For purposes of clarity, the same reference numerals are used throughout the drawings to consistently identify identical or equivalent elements. In the discussion that follows, it will be understood that no priority of function is meant to be attributed to the terms “primary” and “secondary”. In this regard, these terms are used for identification purposes only. 
     Referring generally to FIGS. 2 through 7 of the drawings, an end-mill tool constructed in accordance with the first preferred embodiment is identified with reference numeral  200 . FIGS. 2 and 3 illustrate two side views of the end-mill  200  of the present invention, taken ninety (circumferential) degrees from one another. FIG. 4 is an end view of the end-mill of FIGS. 2 and 3. FIGS. 5,  6  and  7  further show details of the end-mill  200 . As will become evident, this embodiment is termed a “2×4” embodiment, since it has two primary flutes and four secondary flutes. 
     The end-mill tool  200  is shown to generally include a shank portion  202 , a point  204  and a body portion  206 . The end-mill has two primary flutes  210  and  212  extending from the point towards the shank portion  202 . Only one of the flutes  210  is visible in the view of FIG.  2 . In all embodiments of the invention, a coolant channel such as  209  may be added which communicates from the butt end  201  of the tool to apertures such as  211 ,  211 ′ and  211 ″, preferably exiting out through at least the main, high-angle flute. Though alternative exit holes may be used, including within the secondary flutes, points closest to the initial cutting edges of the lands described below are preferably used to distribute coolant to the cutting surfaces on an efficient basis. In addition, as a further novel feature, the size of the apertures may be made larger toward the distal tip of the tool, to ensure that coolant is distributed where it is needed the most. That is, aperture  211  would be smaller than aperture  211 ′, which would be smaller than aperture  211 ″. The central bore may, or may not, extend all the way through and past the distal tip of the tool, but may fall short thereof, depending upon the type of tool and the end application. 
     The primary flutes  210  and  212  are formed at a relatively shallow helix angle Δ. In the embodiment illustrated, the helix angle β is preferably approximately  15 ° which, according to the definitions set forth above is a super low-helix angle. At the point  204  of the tool  200 , the two primary flutes  210  and  212  terminate and define a pair of flat cutting edges  214  and  216 , commonly referred to as end teeth cutting edges. In forming the end teeth cutting edges, a clearance angle, Δ, is generally machined at an angle of approximately 7 degrees. In forming the high- and low-angle flutes according to the invention, the clearance angles associated with the distally oriented surfaces of the lands are greater, typically on the order of 25 degrees, as shown with angle Δ′. As an option, then, an additional grinding step may be used to remove material such as that shown in regions  229 , thereby creating a shallower clearance angle, preferably on the order of the clearance angle Δ used at the end of the tool. Among other advantages, the use of this additional grinding operation removes a volume of material which assists in chip funneling and removal. 
     Further, in the embodiment illustrated, the end-mill has four secondary flutes  220 ,  222 ,  224  and  226  which helically wind around the body portion  206  at a helix angle Θ which is different than the helix angle β. It will be appreciated by those skilled in the art that the specific number of secondary flutes  220 - 226  is largely a matter of design choice and subject to variation. The four secondary flutes  220 - 226  originate from four evenly-spaced virtual points (not shown) around the circumference of the point  204 , and terminate at four evenly-spaced virtual points (not specifically shown) around the circumference of the body portion  206  (e.g., at the intersection of the body portion and the shank portion  202 ). Preferably, the secondary flutes  220 - 226  are all formed along the same helix angle Θ. However, the secondary flutes  220 - 226  can alternatively be formed at different angles relative to one another. 
     The two primary flutes  210  and  212  and the four secondary flutes  220 - 226  intersect and cooperatively define a plurality of Compound helical cutting surfaces or lands  228 . A side view of one of the lands  228  is shown in FIG.  6 . The simplified side view of FIG. 7 illustrates the relative orientation of four axially adjacent lands  228 . For purposes of illustration, each of the lands  228  is shown to be equal in size and shape. As shown particularly in FIG. 2, depending on its location, a particular land  228  (e.g. the uppermost land  228 ) may only be partially formed. The lands  228  illustrated in FIG. 7 are generally disposed radially between the first and second primary flutes  210  and  212 . It will be understood that a corresponding number of lands  228 , which are substantially identical in shape and form, are formed on a circumferentially opposing side of the tool  200 . 
     The secondary flutes  220 - 226  are formed in the body portion  206  of the tool  200  at a relatively high helix angle Θ. Preferably the helix angle Θ of the secondary flutes  220 - 226  is approximately 65°, which, according to the definitions set forth above is a super high-helix angle. The secondary flutes  220 - 226  preferably intersect the primary flutes  210  and  212  at an angle of at least 45°. In the exemplary embodiment illustrated, the primary flutes  210  and  212  intersect the secondary flutes  220 - 226  at an angle of approximately 50° (i.e. the difference between the high helix angle Θ (65°) and the low helix angle β (15°)). 
     With specific reference to FIG. 6, each of the compound helical cutting surfaces  228  is formed to include a continuous cutting edge  230 . These cutting edges  230  each includes a leading portion  232  and a trailing portion  234 . The leading portions  232  are disposed at the intersection of the secondary flutes  220 - 226  and the primary flute  210 , and are disposed at the low-helix angle β (e.g., 15°) which is determined by the helix angle β of the primary flutes  210 . Inasmuch as the angle of the leading portions  232  of the cutting edges  230  is determined by the primary flute  210 , they are considered to be “low-helical” cutting edges. As shown in the simplified view of FIG. 7, the leading portions  232  of the cutting edges  230  are aligned along a straight line  233 . 
     Each trailing portion  234  of the cutting edges  230  originates from the top of a respective leading portion  232  and helically winds around a portion of the body portion  206 . These trailing portions  234  are located at the interface of the compound surface  228  and a respective secondary flute  220 - 226 , and are disposed at the high-helix angle Θ (e.g., 65°) which is determined by the helix angle Θ of the secondary flutes  220 - 226 . Inasmuch as the angle of the trailing portions  234  is determined by the secondary flutes  220 - 226 , they are considered to be “high-helical” cutting edges. 
     With continued reference to FIG. 6, adjacent pairs of leading portions  232  and trailing portions  234  are provided with a common cutting relief  236  and a common clearance relief  238  behind the cutting relief  236 . The cutting relief  236  includes a leading portion  236   a  adjacent the leading portion  232  and a trailing portion  236   b  adjacent the trailing portion  234  of the cutting edge  234 . Similarly, the clearance relief  238  includes a leading portion  238   a  adjacent the leading portion of the cutting relief  236  and a trailing portion  238   b  adjacent the trailing portion  236   b  of the cutting relief  236 . The cutting relief  236  allows for radial clearance during milling operation. 
     An important feature of the present invention is that the leading portion  236   a  of the cutting relief  236  “runs into” (intersects, and is continuous with) the trailing portion  236   b  of the cutting relief  236 . Likewise, the leading portion  238   a  and trailing portions  238   b  of the clearance relief  238  run into one another. 
     In the embodiment illustrated, the trailing portions  234  of the cutting edges  230  have an axial dimension (as measured along the longitudinal axis of the tool  200 ), from a one edge to the next, of a dimension L 2 . The axial (vis-a-vis the longitudinal axis of the tool  200 ) extent of each of the leading portions  232  is each of a dimension L 1 . These dimensions L 1 , and L 2  are of particular interest and are discussed in greater detail hereinbelow. 
     As mentioned above, the helix angle β of the primary flutes  210  and  212  is preferably low, on the order of 15°, and the helix angle Θ of the secondary flutes is preferably high, on the order of 65°. An important feature of the invention is that the leading portion  232  and associated (e.g., on the same flute surface) trailing portion  234  form a contiguous cutting edge  230  of dimension L 1 +L 2  for improved chip removal. Although the leading most point  231  of leading portion  232 , and trailing most point  235  of trailing portion  234  are shown as sharp and discontinuous, they do not have to be, and in fact, they may be truncated or radiused to prevent scoring. More particularly, due to manufacturing imperfections, point  231  or point  235  may be slightly proud with respect to the outside diameter of the tool, thereby creating a line as the tool is moved laterally within a workpiece. Placing a slight radius on points  231  and  235 , preferably smaller than perceivable with the unaided eye, would assist in avoiding such score marks. 
     Additionally, although the transition to  240  between leading portion  232  and trailing portion  234  is shown as a sharp discontinuity, which may be beneficial in terms of chip splitting, this corner may also be truncated or radiused, as shown with broken line  233  to avoid fatigue due to excessive corner wear. The segment  233  may either be ground smoothly from cutting edge to cutting edge or alternatively one or more mid-angle helixes may be used, thereby providing additional cutting surfaces. 
     Provided that the rotational speed of the tool  200  is sufficient, the chips removed from the workpiece by the leading and trailing portions  232  and  234  of the cutting edges  230  will correspond in length to their respective axial lengths L 1  or L 2 . More particularly, a single chip is formed by the continuous cutting edge  230 . Splitting of the chip will occur at an intersection  240 , or corner, of the leading portion  232  and the trailing portion  234 . Chips cut from the trailing portion  234  will “flow” through the respective adjacent secondary flute (e.g.,  220 - 226 ). Chips cut from the leading portion  232  will flow through the associated low helical flute (e.g.,  210  or  212 ). 
     In certain applications, the leading and trailing portions  232  and  234  will remove one chip (without chip splitting) having a! length corresponding to the sum of their axial dimensions (L 1 +L 2 ). For example, if the rotational speed of the tool  200  is not sufficient, the splitting of the chips at the intersection  240  may not occur. The required rotational speed depends primarily upon the material of the workpiece and the amount of material being removed from the workpiece. Therefore, it may be desirable to incorporate additional chip splitting (breaking) structures (not shown, such as grooves) on the trailing portions  234  for machining under such circumstances. Such structures include grooves (not shown) and the like, and are well known in the art. 
     The present invention contemplates a range of helix angles for the primary flutes  210  and  212  and for the secondary flutes  220 - 226  in addition to the low and high helix angles β and Θ set forth hereinabove. Evidently, it is important that the primary and secondary sets of flutes intersect one another. The present invention further contemplates: 
     primary flute helix angles β of at least 0°, but preferably no more than 45°, although primary flutes having helix angles greater than 45° are possible; and 
     secondary flute helix angles Θ of no more than 65°, although secondary flutes having helix angles greater than 65° is possible. 
     It is also within the scope of the present invention that the primary flutes  210  and  212  are angled in a different direction relative to the secondary flutes  220 - 226  in which case, for example, the two helix angles β and Θ could be equal in magnitude but different in direction. For example, a set of primary flutes  210  and  212  may have a left-hand helix angle of 30°, and a set of secondary flutes  220 - 226  may have a right-hand helix angle of 30°. These angles, although equal in magnitude, are different (in direction) than one another, which will cause the primary flutes  210  and  212  and the secondary flutes  220 - 226  to intersect one another on the body portion  206  of the tool  200 . 
     The helix angles can be modified over a wide range. For example, specific applications may include, but by no means are limited to, the following: 
     primary flutes  210  and  212  at 15°, secondary flutes  220 - 226  at 65°; 
     primary flutes  210  and  212  at 30°, secondary flutes  220 - 226  at 60°; and 
     primary flutes  210  and  212  at 50°, secondary flutes  220 - 226  at 80°. 
     The method of forming the tool  200  of the present invention generally includes the following steps: 
     1. providing a generally cylindrical tool blank (not shown); 
     2. grinding the primary flute  210  at the low helix angle β into the body portion  206 ; 
     3. grinding the second primary flute  212  at the low helix angle β into the body portion  206 ; 
     4. grinding the first secondary flute  220  at the high helix angle Θ into the body portion  206 ; 
     5. grinding the second secondary flute  222  at the high helix angle Θ into the body portion  206 ; 
     6. grinding the third secondary flute  224  at the high helix angle Θ into the body portion  206 ; 
     7. grinding the fourth secondary flute  226  at the high helix angle Θ into the body portion  206 ; 
     8. grinding continuous cutting reliefs  236  on each of the compound helical cutting surfaces  228  by following the low helix angle β until the intersection point  240  and following the high helix angle Θ thereafter; 
     9. grinding continuous clearance reliefs  238  on each of the compound helical cutting surfaces  228  by following the low helix angle β until the intersection point  240  and following the high helix angle Θ thereafter; 
     10. grinding reliefs and clearances at the point  204  to form the cutting edges  214 - 216 . 
     Alternative constructions to the first preferred embodiment of the end-mill  200  of the present invention are provided in the simplified end views of FIGS. 8 and 9. For example, FIG. 8 illustrates a simplified end view of an embodiment of an end-mill  300  having three primary flutes  302 ,  304 , and  306  which are visible in an end view looking onto the point of the end-mill  300 . With three secondary flutes (not shown), this would be termed a “3×3” end-mill. FIG. 9 illustrates an embodiment of an end-mill  350 , the invention having four primary flutes  352 ,  354 ,  356 , and  358  which are visible in an end view looking onto the point of the end-mill. With four secondary flutes (not shown), this would be termed a “4×4” end-mill. 
     Various embodiments of an end-mill may be fabricated according to the techniques set forth hereinabove by varying parameters such as helix angles β and Θ, spacing of a plurality of discrete low-helical leading portions  232 , and the like. Further alternative embodiments from the previously-described embodiments principally in the number of primary and secondary flutes formed. Generally, since each one-or-more (“N”) primary flute is typically intersected at least once by each one-or-more (“M”) secondary flute, various end-mills can be fabricated having “N×M” configurations. It will be readily appreciated that the present invention is not limited to any particular number of flutes or discrete low-helix angle cutting edges. 
     With reference now to FIGS. 10 through 12, an end-mill tool  400  constructed in accordance with a second preferred embodiment of the present invention is illustrated. The reference numerals used for the first preferred embodiment have been applied to drawings for the second preferred embodiment to identify identical or equivalent elements. 
     The first and second preferred embodiments differ only in that the cutting edges  232  of the second preferred embodiment are staggered to the right progressing from the point  204  to the shank  202  (e.g., a staggered right hand spiral). This is specifically shown in FIG. 12 by the right stagger of the line  233 . As a result, the cutting edges  232  engage the workpiece at different times, thereby advantageously lessening tool pressure. In certain applications, such an arrangement may further facilitate chip removal. 
     Turning now to FIG. 13, a simplified side view of the adjacent lands  228  similar to FIG. 12 illustrating an alternative construction of the second preferred embodiment of the present invention is shown. In this alternative construction, the cutting edges  232  are staggered to the left progressing from the point  204  to the shaft  202  (e.g., a staggered left hand spiral). 
     The specific method of the present invention contemplates use of one of the above-described embodiments or alternatives thereto and includes the step of rotating the end-mill tool (e.g.,  200 ) about its longitudinally axis. The method further includes the steps of removing a first plurality of chips from the workpiece through the primary flute and removing a second plurality of chips from the workpiece through the secondary flutes. In the preferred method, the chips of the first plurality of chips each have a length which is substantially equivalent to the axial length L 1  of the leading portion  232  and the chips of the second plurality of chips each are substantially equivalent in length to the axial length L 2  of the trailing portion  234  of the cutting edge  230 . 
     The preferred embodiments and alternatives discussed above all assume that the primary and secondary flutes each are formed along right hand helix. In certain applications, it may be desired to incorporate a left hand helix. For example, such an orientation may be desired where downward transfer of removed chips is preferred. 
     The above, and other objects, features, advantages and embodiments of the invention, including other embodiments of the techniques discussed above may become apparent to one having ordinary skill in the art to which this invention most nearly pertains, and such other and additional embodiments are deemed to be within the spirit and scope of the present invention. For example, the compound helical cutting surfaces which are described as being integrally formed with the tool may alternatively be provided on removable inserts. In certain applications, carbide inserts maybe braised to a steel body or alternatively mounted to the steel body with suitable fasteners. In addition, although the invention has been described with a substantially transverse end face, other tip arrangements may be used, including ball-nose ends, conical twist-drill shapes, and so forth, with the cutting surfaces associated with one side of the tool transitioning to cutting surfaces elsewhere around the tool, as appropriate, to enhance cutting or plunging operations, as the case may be. It will also be apparent to one of skill in the art that tools manufactured in accordance with this invention are applicable to both ferrous and non-ferrous workpieces.