Abstract:
An improved expandable broadhead with rear deploying blades. The rear deploying blades deploy reliably upon impact of the blades with a target. The expandable broadhead resists deflection by the target regardless of the angle of entry. Consequently, the present expandable broadhead maximizes kinetic energy on impact and increases the probability of substantial penetration into the target.

Description:
The present application claims the benefit of U.S. Provisional Application No. 60/822,873 entitled Expandable Broadhead with Rear Deploying Blades, filed Aug. 18, 2006. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an improved expandable broadhead with rear deploying blades. The rear deploying blades have an in-flight retracted configuration and an expanded deployed configuration upon striking a target. 
     BACKGROUND OF THE INVENTION 
     In the archery industry, many manufacturers have attempted to simultaneously achieve an arrowhead that has aerodynamic properties similar to those associated with non-bladed arrowheads known as field points or nib points, while also achieving effective cutting areas provided by bladed arrowheads, which are often referred to as broadheads. Broadhead blades which are exposed during flight often result in undesirable steering of the front portion of the arrow, causing the arrow to deviate from a perfect flight path that coincides with a longitudinal axis of the arrow shaft, when loaded or drawn within an archery bow. 
     By reducing the surface area of a broadhead blade, the undesirable steering effects can be reduced. However, by reducing the surface area of a blade, the cutting area within a target or game is also reduced, resulting in a less effective entrance and exit wound. 
     Conventional blade-opening arrowheads have been designed so that a substantial portion of the blade is hidden within the body of the arrowhead, such as during flight of the arrow. Upon impact, such blades are designed to open and thereby expose a cutting surface or sharp edge of the blade. When the blades of such conventional arrowheads are closed and substantially hidden within the body, the exposed surface area is reduced and thus produces relatively less undesirable steering effects. 
     Many of such conventional blade-opening arrowheads rely upon complex mechanisms, some of which fail to open reliably because of a significant holding or closing force that must be overcome, and others that open prematurely because of structural deficiencies within the blade carrying body that fail upon impact, resulting in non-penetration of the arrow. With such relatively complex mechanisms, dirt or other materials that may enter such conventional arrowheads can affect the reliability of the arrowhead, particularly after prolonged use. Examples of such mechanisms are disclosed in U.S. Pat. Nos. 5,112,063, 4,998,738 and 5,082,292. The deployable cutting blades are connected by pivot features to a plunger. The cutting blades pivot between an open cutting position and a closed non-barbed position. U.S. Pat. No. 5,102,147 discloses a ballistic broadhead assembly that has blades pivotally mounted on an actuating plunger. Upon impact, the actuating plunger thrusts the blades outwardly and forwardly. 
     Other conventional broadheads which have blades partially hidden within the body use annular retaining rings, such as O-rings, wraps, bands and the like, in order to maintain the blades in a closed position during flight. Upon impact, such annular retaining rings are designed to sheer or roll back along the opening blades, in order to allow the blades to move to an open position. Quite often, such conventional annular retaining rings are prone to cracking, particularly when the elastomer material dries out. Upon release of a bowstring, the rapid acceleration and thus significant opening forces move the blades in an opening direction. The conventional annular retaining rings counteract such opening forces. However, when the ring material dries out, cracks or is otherwise damaged, the blades may open prematurely, resulting in significant danger or injury to the archer. 
     Many of the annular retaining rings are designed for one use and thus must be replaced after each use. In addition to the cost involved with supplying such consumable item, the annular retaining rings are difficult and time-consuming to install, such as when hunting, particularly during inclement weather. Furthermore, the material properties of such conventional annular retaining rings can be affected by temperature changes, thereby resulting in different bias forces that cause the blade to open prematurely or to not open when desired. 
     One class of mechanical broadheads deploy the blades in an over-the-top motion, such as disclosed in U.S. Pat. No. 5,090,709. The extendable blades are pivotally connected to a body near the rear of the broadhead body. A ring releasably holds the extendable blades within corresponding slots within the body. 
     High-speed photography of over-the-top broadheads shows that the blades often do not fully open until after the blades enter the target. Consequently, the full cutting diameter of an over-the-top broadhead is often not available through the depth of the target. Also, as illustrated in  FIG. 1 , an angled hit with over-the-top broadhead  20  can also result in one of the blades  22 A engaging the target  24  before the other blade  22 B, potentially applying a deflection force  26  on the broadhead  20 . Both the deflection force  26  and blade deployment  22 A,  22 B during entry of the over-the-top broadhead  20  can dramatically reduce kinetic energy of the arrow. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is directed to an improved expandable broadhead with rear deploying blades. The rear deploying blades deploy reliably upon impact of the blades with the target. The present expandable broadhead resists deflection by the target regardless of the angle of entry. Consequently, the present expandable broadhead maximizes kinetic energy on impact and increases the probability of substantial penetration into the target. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a prior art over-the-top expandable broadhead impacting a target. 
         FIG. 2  is a perspective view of a two-blade expandable broadhead in a retracted configuration in accordance with an embodiment of the present invention. 
         FIG. 3  is a side view of a rear deploying blade illustrated in  FIG. 2 . 
         FIG. 4A  is a side sectional view of the two-blade expandable broadhead of  FIG. 2  in a retracted configuration in accordance with an embodiment of the present invention. 
         FIG. 4B  is a side sectional view of the two-blade expandable broadhead of  FIG. 2  in a partially deployed configuration in accordance with an embodiment of the present invention. 
         FIG. 4C  is a side sectional view of the two-blade expandable broadhead of  FIG. 2  in a deployed configuration in accordance with an embodiment of the present invention. 
         FIG. 5A  is a side sectional view of an alternate expandable broadhead with engagement features on blades in accordance with an embodiment of the present invention. 
         FIG. 5B  is a side sectional view of an alternate expandable broadhead with blades contacting a broadhead body in a deployed configuration in accordance with an embodiment of the present invention. 
         FIG. 6A  is a side sectional view of an expandable broadhead with a non-cylindrical pivot feature in a retracted configuration in accordance with an embodiment of the present invention. 
         FIG. 6B  is a side sectional view of the expandable broadhead of  FIG. 6A  in the deployed configuration. 
         FIGS. 7A-7F  illustrate a sequence of blade movement from a retracted configuration to an expanded configuration in an expandable broadhead in accordance with an embodiment of the present invention. 
         FIG. 8  is a side view of an expandable broadhead penetrating an object in accordance with an embodiment of the present invention. 
         FIG. 9  is a perspective view of a three-blade expandable broadhead in a retracted configuration in accordance with an embodiment of the present invention. 
         FIG. 10  is a perspective view of the expandable broadhead of  FIG. 9  in a deployed configuration. 
         FIG. 11  is a side view of a rear deploying blade illustrated in  FIG. 9 . 
         FIGS. 12-18  illustrate alternate blades for use in the present expandable broadhead with camming edges and slots that provide different deployment profiles in accordance with an embodiment of the present invention. 
         FIG. 19  illustrates an alternate expandable broadhead in accordance with an embodiment of the present invention. 
         FIGS. 20 and 21  illustrate blades with alternate cutting edges in accordance with an embodiment of the present invention. 
         FIG. 22  illustrates a practice broadhead in accordance with an embodiment of the present invention. 
         FIG. 23  is a side view of an alternate expandable broadhead in the retracted configuration with a broadhead body made of a polymeric material in accordance with an embodiment of the present invention. 
         FIG. 24  is a cross-sectional view of the expandable broadhead of  FIG. 23 . 
         FIG. 25  is a side view of the expandable broadhead of  FIG. 23  in the deployed configuration in accordance with an embodiment of the present invention. 
         FIG. 26  is a cross-sectional view of the expandable broadhead of  FIG. 25 . 
         FIG. 27A  is a side view of an alternate expandable broadhead in the retracted configuration with quick release cutting blades in accordance with an embodiment of the present invention. 
         FIG. 27B  is a side view of the expandable broadhead of  FIG. 27A  in the deployed configuration in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 2  is a perspective view of an expandable broadhead  50  in accordance with an embodiment of the present invention. The expandable broadhead  50  includes a broadhead body  52  with a penetrating end  54  and a rear end  56 . 
     The rear end  56  preferably includes threads  58  that couple with a conventional arrow shaft. In the illustrated embodiment, the penetrating end  54  includes a tip blade  60  attached to the broadhead body  52  by fastener  62 . The illustrated fastener  62  is adapted to receive a hex-shaped tool, that can optionally be provided to permit easy replacement of the tip blade  60 , such as for example the tools disclosed in U.S. Pat. No. 6,684,741, which is hereby incorporated by reference. 
     In an alternate embodiment, the penetrating end may take a variety of other forms, such as for example conical, faceted, or a straight tapered structure, with or without the tip blade  60 . In another embodiment, the penetrating end  54  is formed with the broadhead body  52  as a unitary structure. 
     The penetrating end  54  of the broadhead body  52  preferably includes a plurality of facets or flat regions  64 . In the illustrated embodiment, the broadhead body  52  includes six facets  64 . It is believed that the facets  64  increase the aerodynamic stability of the expandable broadhead  50  during flight. The number of facets  64  can vary with broadhead design and other factors. 
     The broadhead body  52  includes one or more slots  70  adapted to receive one or more rear deploying blades  72 A,  72 B (referred to collectively as “ 72 ”). The rear deploying blades of the present invention can also be referred to generically as cutting blades, as distinguished from a tip blade. In the illustrated embodiment, a single slot  70  receives both of the rear deploying blades  72 . The rear deploying blades  72  are slidably engaged with the broadhead body  52 . In the preferred embodiment, the blades  72  are pivotally attached to the broadhead body  52  by pivot feature  76 , such as the pin illustrated in  FIG. 4 . The pivot feature  76  is preferably a threaded fastener, such as the hex fastener  62  illustrated in  FIG. 2  that can be removed to permit blade replacement. A hex-shaped tool or other tool suitable for removing the pivot feature  76  is preferably provided with the present expandable broadheads to permit easy blade replacement. 
     As used herein, “rear deploying” means rearward translation of blades generally along a longitudinal axis of a broadhead body and outward movement of a rear portion of the blade way from the longitudinal axis. The rearward translation can be linear, curvilinear, rotational or a combination thereof. 
     In a rear deploying system the rear portion of the blade typically remains on the same side of a blade pivot axis in both the retracted and deployed configurations. An example of the movement of a rear deploying blade is illustrated in  FIGS. 7A-7F . Prior expandable broadheads with rear deploying blades are disclosed in U.S. Pat. Nos. 6,517,454 (Barrie et al.); 6,626,776 (Barrie et al.); and 6,910,979 (Barrie et al.), which are hereby incorporated by reference. 
     In the embodiment of  FIG. 2 , the blades  72  are generally parallel to longitudinal axis  120 . In an alternate embodiment, the blades  72  may be offset or oriented a slight angle with respect to the longitudinal axis, causing rotation of the broadhead  50  during flight, such as disclosed in U.S. patent Ser. No. 11/037,413 entitled Broadhead with Reversible Offset Blades, which is hereby incorporated by reference. 
     The tip blade  60  has maximum width  61 , which is typically less than maximum width  63  of the blades  72  in the retracted configuration  80 . In one embodiment, the maximum width  61  is greater than the maximum width  63 . In the illustrated embodiment, the maximum width  63  of the blades  72  is near the rear portion  94 , but may be in other locations, such as for example near the penetrating edges  82 . 
       FIG. 2  illustrates the expandable broadhead  50  with the rear deploying blades  72  in the retracted configuration  80 . In the retracted configuration  80 , impact edges  82 A,  82 B (referred to collectively as “ 82 ”) of the rear deploying blades  72 A,  72 B, respectively, are positioned exterior to the broadhead body  52 . As will be discussed in greater detail below, retainer  86  assists in retaining the rear deploying blades  72  in the retracted configuration  80 . 
     In one embodiment, the broadhead body  52  optionally includes one or more elongated features  146 . The elongated features  146  can be either concave, convex, or a combination thereof. In one embodiment, the features  146  are grooves or depressions arranged generally parallel to the longitudinal axis  120 . In another embodiment, the features  150  are ridges or protrusions. The features  146  are believed to provide a number of functions, such as aerodynamics, stability of the expandable broadhead  50  as it penetrates a target, and the release of fluid pressure that may accumulate in front of the expandable broadhead  50 . As will be illustrated in  FIGS. 4-6 , the blades  72  may optionally include elongated features as well. 
       FIG. 3  is a side view of one embodiment of the rear deploying blades  72  in accordance with an embodiment of the present invention. In the illustrated embodiment, the rear deploying blades  72  are same. In an alternate embodiment, the blades  72  may have different configurations, such as to have asymmetrical deployment profiles. 
     The rear deploying blades  72  of  FIG. 3  include the impact edge  82 , a cutting edge  90 , a camming edge  92 , and a rear portion  94 . Notch  96  is preferably located between the camming edge  92  and the rear portion  94 . Camming edge  92  includes a transition region  126  adjacent to a deployment region  98 . In the illustrated embodiment, the transition region  126  is a step or drop-off to a deployment region  98 . The deployment region  98  optionally includes a protrusion. Alternatively, the deployment region  98  can include a recess, such as for example a recess shaped to couple with the retainer  86 . 
     In the illustrated embodiment, the rear deploying blades  72  include slot  100  that extends proximate the impact edge  82  towards the camming edge  92 . The slot  100  includes first end  102 , a center portion  108 , and second end  104 . In the embodiment illustrated in  FIG. 3 , the first and second ends  102 ,  104  have a diameter  106  (or shape) that corresponds closely to the diameter (or shape) of the pivot feature  76 . It will be appreciated that a recess could be substituted for slot  100  and that the term “slot” is used generically herein to include a cut-out through extending completely through the blade, a single recess on one side of the blades or recesses on both sides of the blades. 
     Center portion  108  of the slot  100  preferably has a width  110  greater than the diameter  106 , and hence, the width  110  is greater than the maximum diameter of the pivot feature  76 . The width  110  preferably defines a free floating region  109  that the pivot feature  76  can theoretically traverse without contacting sidewalls  111  of the slot  100 . The free floating region  109  minimizes friction and deflection forces during deployment of the blades  72 . As used herein, “free floating region” refers to a portion of a slot/pivot feature interface in which the gap between the pivot feature and side walls of the slot is greater than the gap between the pivot feature and at least one end of the slot. In the embodiments in which the pivot feature has a non-circular cross-section, the maximum cross-sectional dimension of the pivot feature is substituted for diameter. 
     The rear deploying blades  72  of  FIG. 3  optionally include one or more cutouts  112 . The cutouts  112  optionally serve to reduce the weight of the blades  72 , to increase the strength and/or flexibility of the blades  72 , or a variety of other functions. 
     In the illustrated embodiment, the camming edge  92  has a slightly concave curvature  114  and length  116 . Alternate camming edge configurations are discussed below. The length  116  of the camming edge  92  is corresponds to length  118  of slot  100 . In one embodiment, the length  116  of the camming edge  92  plus the diameter of the pivot feature  76  is approximately equal to the length  118  of the slot  100 . Alternatively, the travel distance of the pivot feature  76  in the slot  100  is approximately equal to the length of the camming edge  92 . 
     In the preferred embodiment, during blade deployment the retainer  86  reaches the transition region  126  just before the pivot feature  76  engages the first end  102  of the slot  100 . The retainer passes the transition region  126  and enters the deployment region  98  when the pivot feature  76  engages the first end  102  of the slot  100 . This configuration releasably secured in the blade  72  in the deployed configuration  130  by simultaneous engagement of the pivot feature  76  with the first end  102  of the slot  100  and the engagement of the deployment region  98  with the retainer  86 . 
     As will be discussed in detail below, the shape of the curvature  114  and the shape of the slot  100  determine the rate and angle at which the blades  72  move from the retracted configuration  80  to the deployed configuration  130 . Consequently, the shape of the slot  100  and the camming edge  92  can be engineered to create a variety of deployment profiles. As used herein, “deployment profile” refers to the path traversed by a blade from a retracted configuration to a deployed configuration. 
       FIG. 4A  is a cross-sectional view of the expandable broadhead  50  in the retracted configuration  80 . Rear deploying blades  72  are partially retained in slot  70 . The pivot feature  76  is positioned in the second ends  104  of the slots  100 . The pivot feature  76  has a diameter corresponding generally to the diameters of the second ends  104 , limiting lateral movement of the blades  72  along the axes  119 . The notches  96  are coupled to retainer  86 , thus retaining the blades  72  close to the longitudinal axis  120 . The combination of the pivot feature  76  engaged with the second ends  104  and the notches  96  engaged with the retainer  86  secure the blades  72  in the retracted configuration  80 . 
     Upon impact, the penetrating end  54  proceeds into the object. As the retractable broadhead  50  advances into the object, the impact edges  82  also contact the object. Because the impact edges  82  extend beyond the perimeter of the broadhead body  52 , movement of the expandable broadhead  50  into the object causes generally oppositely directed forces  124  to act on the impact edges  82 . 
     In the illustrated embodiment, the impact edges  82  are angled slightly backward relative to axis  119  perpendicular to longitudinal axis  120 . Consequently, forces  124  applied to the impact edges  82  generate torque  134  on the blades  72  that assists in releasing the notches  96  from the retainer  86 . In an alternate embodiment, the impact edges  82  extend perpendicular to the longitudinal axis  120 . The forces  124  acting on the impact edges  82  at a distance from the longitudinal axis  120  is sufficient to deploy the blades  72 . 
     As best illustrated in  FIG. 4B , once the notches  96  are released from the retainer  86 , the camming edges  92  ride along the retainer  86  towards the deployed configuration. Since the widths  110  of the slots  100  in the center region  108  between the first and second ends  102 ,  104  are greater than the diameter of the pivot feature  76 , the blades  72  move relatively freely in the free floating region  109 . 
       FIG. 4C  is a sectional view of the expandable broadhead  50  in the deployed configuration  130  in accordance with an embodiment of the present invention. The first ends  102  of the slots  100  are engaged with the pivot feature  76 . The transition regions  126  on the blades  72  have moved past the retainer  86 , retaining the blades  72  in the deployed configuration  130 . The tight tolerances between the second ends  102  and the pivot feature  76  aids in stabilizing the position of the rear deploying blades  72  and provide more uniform force distribution between the pivot feature  76  and the second ends  102 . As a result, blade failure on deployment is reduced. 
     The retainer  86  is positioned in between the deployment regions  98  located along the rear edges of the blades  72  and the broadhead body  52 . In the preferred embodiment, the retainer  86  is a resilient or elastomeric material that absorbs some of the impact force between the blades  72  and the broadhead body  52  in the deployed configuration  130  illustrated in  FIG. 6 . The shock absorbing properties of the retainer  86  reduces blade failure in the deployed configuration  130 . In another embodiment, the retainer  86  plastically deforms upon impact of the blades  72 . 
     The retainer  86 , broadhead body  52  and blades  72  can be made from a variety of materials, such as polymeric materials, metals, ceramics, and composites thereof. The Durometer of the retainer  86  can be selected based on the degree of impact absorption required, the configuration of the blades  72 , and the like. For example, the retainer  86  can be constructed as a metal snap ring made from a softer metal than the blades  72 . In another embodiment, the retainer  86  is constructed from a low surface friction material, such as for example nylon, to facilitate blade deployment. 
     The blades  72  of  FIGS. 4A-4C  optionally include one or more elongated features  150 . The elongated features  150  can be either concave, convex, or a combination thereof. In one embodiment, the elongated features  150  are grooves or depressions arranged generally parallel to the longitudinal axis  120  when the blades  72  are in the deployed configuration  130 . In another embodiment, the elongated features  150  are ridges or protrusions. The elongated features  150  are believed to serve a number of functions, such as facilitating deployment of the blades  72 , stability of the expandable broadhead  50  as it penetrates a target, and the release of fluid pressure that may accumulate in front of the expandable broadhead  50 . 
       FIG. 5A  is a cross-sectional view of an alternate expandable broadhead  50 ′ in the retracted configuration  80 ′. The impact edges  82 ′ have curved profiles  83 ′ to provide a more aerodynamic profile. Protrusions  85 ′ are located at the base of the curved profiles  83 ′ to engage with the target and promote blade deployment. The location of the protrusions  85 ′ generate increased torque  134 ′ on the blades  72 ′ that assists in releasing the notch  96 ′ from the retainer  86 ′. The blades  72 ′ of  FIG. 5A  are particularly well suited for use with retainers  86 ′ made of metal or other stiff materials. 
       FIG. 5B  illustrates another alternate embodiment of a expandable broadhead  50  where the camming edges  92  ride on the broadhead body  52  rather than the retainer  86  (see e.g.,  FIG. 4B ). The retainer  86  is preferably positioned closer to the longitudinal axis  120  so as to not engage the blades  72  during deployment. In the embodiment of  FIG. 5B , the retainer  76  may still absorb impact between the blades  72  and the broadhead body  52  at the deployed configuration  130 . For purposes of the present invention, the blades may ride or slide on either the broadhead body or the retainer and the disclosed embodiments should be interpreted to have either configuration. 
     The blades  72  of  FIG. 5A  optionally include one or more curved elongated features  150 . The curved elongated features  150  can be either concave or convex. The curved shape of the features  150  is particularly well suited to facilitate deployment of the blades  72 . In the preferred embodiment, the shape of the elongated features corresponds generally to the deployment profile of the blades  72 . 
       FIG. 6A  is a sectional view of an alternate expandable broadhead  700  in the retracted configuration  702  in accordance with an embodiment of the present invention. First ends  704  of slots  706  are non-cylindrical. In the illustrated embodiment, the non-cylindrical first ends  704  are square, but could be triangular, rectangular, hexagonal, an irregular shape, or a variety of other non-cylindrical shapes. The pivot feature  708  is also non-cylindrical. In the illustrated embodiment, the pivot feature  708  has a square cross-section with a diagonal dimension that is less than the width of the slot  706  providing a free floating region  724 . The free floating region  724  permits the blades  714  to rotate freely during movement from the retracted configuration  702  to the deployed configuration  710 . (See  FIG. 6B .) As used herein, the term “pivot feature” is not limited to a particular cross-sectional shape. 
       FIG. 6B  is a sectional view of the expandable broadhead  700  of  FIG. 6A  in the deployed configuration  710 . The first ends  704  of the slots  706  are engaged with the non-cylindrical pivot feature  708  in the deployed configuration  710 . The tight tolerances between the first end  704  and the pivot feature  708  provide more uniform force distribution between the pivot feature  708  and the first end  704 . 
     In the illustrated embodiment, the non-cylindrical pivot feature  708  holds the blades  714  in the deployed configuration  710  without direct contact with the retainer  716  or the broadhead body  718 . The deployed configuration  710  includes gap  722  between the blades  714  and the retainer  716 . The cantilevered configuration illustrated in  FIG. 6B  permits the blades  714  to flex in directions  720 . In one embodiment, the blades  714  flex into and out of contact with the retainer  716 . 
     In another embodiment of the broadhead  700 , blades  714  engage with retainer  716  in the deployed configuration  710 , such as illustrated in  FIG. 6 . The retainer  716  preferably operates as a shock absorber. 
       FIGS. 7A through 7F  illustrate the expandable broadhead  50  as the blades  72  move between the retracted configuration  80  illustrated in  FIG. 7A  and the deployed configuration  130  illustrated in  FIG. 7F .  FIG. 7B  illustrates the forces  124  acting on the expandable broadhead  50  upon impact with an object. In the illustrated embodiment, the forces  124  acting on the impact edges  82  at a distance from the longitudinal axis  120  generates torque  134  that causes the blades  72  to rotate slightly, thereby releasing the notches  96  from the retainer  86 . 
       FIGS. 7C through 7E  illustrate further rearward movement of the blades  72  along the longitudinal axis  120 . As the blades  72  continue to move toward the rear of the expandable broadhead  50 , the rear ends  94  of the blades move away from the longitudinal axis  120 . As the blades  72  move rearward, the camming edges  92  force the rear ends  94  of the blades  72  further away from the longitudinal axis. As illustrated in  FIG. 7F , the transition regions  126  on the blades  72  have moved past the retainer  86  to assist in maintaining the blades  72  in the deployed configuration  130 . 
       FIG. 8  is a schematic illustration of the expandable broadhead  140  in accordance with an embodiment of the present invention penetrating object  141 . The penetrating end  142  makes contact with the object  141  before the impact edges  143 A,  143 B of the blades  144 A,  144 B, respectively. Consequently, the penetrating end  142  acts to secure the expandable broadhead  140  to the object  141  sufficiently to resist any lateral forces, such as when the impact edge  143 A contacts the object  140  before the impact edge  143 B. Therefore, impact with the object  141  causes minimal or no deflection of the expandable broadhead  140  from its original trajectory  145 . This straight-line motion along trajectory  145  maximizes the kinetic energy of the arrow  146  into and through the object  141 . 
       FIG. 9  is perspective views of a three-blade expandable broadhead  250  in retracted configuration  280  in accordance with an embodiment of the present invention.  FIG. 10  illustrates the expandable broadhead  250  with the rear deploying blades  272  in the deployed configuration  330 . As discussed above, the expandable broadhead  250  includes a broadhead body  252  with a penetrating end  254  and a rear end  256 . While the penetrating end  254  includes a tip blade  260  attached to the broadhead body  252  by fastener  262 , the penetrating end  254  may take a variety of other forms. The broadhead body  252  preferably includes a plurality of facets or flat regions  264  that increase the aerodynamic stability of the expandable broadhead  250  during flight. 
     The broadhead body  252  of  FIGS. 9 and 10  include three slots  270 A,  270 B,  270 C (referred to collectively as “ 270 ”) adapted to receive one or more rear deploying blades  272 A,  272 B,  272 C (referred to collectively as “ 272 ”). Each of the rear deploying blades  272  are slidably attached to the broadhead body  52  by separate pivot features  276 A,  276 B,  276 C. 
     In the retracted configuration  280 , impact edges  282 A,  282 B,  282 C (referred to collectively as “ 282 ”) of the rear deploying blades  272 , respectively, are positioned exterior to the broadhead body  252 . Retainer  286  assisted retaining the rear deploying blades  272  in the retracted configuration  280 . 
     In the illustrated embodiment, broadhead body  252  optionally includes elongated features  346  arranged in a helix or coil configuration around the broadhead body  52 . The elongated features  346  can be either concave, convex, or a combination thereof. 
       FIG. 11  is a side view of the rear deploying blades  272  illustrated in  FIGS. 9 and 10 . In the illustrated embodiment, the rear deploying blades  272  may have the same or different configurations. The rear deploying blades  272  include the impact edge  282 , a cutting edge  290 , a camming edge  292 , and a rear portion  294 . Notch  296  is preferably located between the camming edge  292  and the rear portion  294 . Transition region  326  is located at the end of the camming edge  292 . Deployment region  298  is located between the transition region  326  and the impact edge  282 . 
     In the illustrated embodiment, the rear deploying blades  272  include slot  300  that extends proximate the impact edge  282  towards the camming edge  292 . The slot  300  includes first end  302 , center portion  308 , and second end  304 . In the embodiment illustrated in  FIG. 10 , the first and second ends  302 ,  304  have a radius  306  that corresponds to the diameter of the pivot feature  276 . The center portion  308  of the slot  300  has a width  310  greater than the diameter  306 . The width  310  of the center portion  308  is preferably large enough to form a free floating region  320 . 
     The camming edge  292  has a slightly concave curvature  314  and a length  316 . The shape of the curvature  314  and the shape of the slot  300  determine the rate and angle at which the blades  272  move from the retracted configuration  280  to the deployed configuration  330 . Alternate examples of camming edges are discussed below. In order to fit the three blades  272  in the broadhead body  252  without exceeding optimal weight, the blades  272  and the broadhead body  254  are typically shorter than the blades  72 . The length  316  of the camming edge  292  is also shorter than the camming edge  116  illustrated in  FIG. 3 . 
     Deployment Profile 
     As discussed above, the shape of the slots of the camming edges can be modified to change the angle of blade deployment and the rate of blade deployment.  FIGS. 12-18  relate to variations in the blades that permit different deployment profiles, preferably using the same broadhead body. It will be appreciated that the various features on the blades disclosed in  FIGS. 12-18  can be combined with each other in a variety of other ways. Therefore, all of the possible permutations are not disclosed herein. 
     The various blade slots illustrated in  FIGS. 12-18  preferably have first and second ends with diameters that correspond closely to the diameter or shape of the pivot features and a free floating region in between. In an alternate embodiment, the free floating region extends into one or both of the ends of the slots. 
     Generally, longer camming edges and corresponding longer slots result in a deployment profile where the blades more closely follows the longitudinal axis of the broadhead body before moving outward away from the longitudinal axis. Alternatively, shorter camming edges and shorter slots result in a deployment profile where the blades move outward away from the longitudinal axis more quickly. Expandable broadheads with longer slots are generally less likely to fail during deployment. Essentially infinite variation is possible. 
       FIG. 12  illustrates an alternate blade  400  with a shortened camming edge  402  and a correspondingly shortened slot  404 . The camming edge  402  is preferably sized so that the retainer or broadhead body (not shown) reaches transition region  406  just before the pivot feature (not shown) reaches the first end  408  pf the slot  404 . The slot  404  preferably includes a free floating region  414 . By reducing length  410  of the camming edge and length  412  of the slot  404 , the blade  400  deploys outward from the longitudinal axis (see  FIG. 2 ) more quickly than a blade with a longer camming edge and slot. The blade  400  exhibits an accelerated deployment profile relative to the blade  272  in  FIG. 11 . 
       FIG. 13  illustrates an alternate blade  420  with a convex camming edge  422 . The camming edge  422  initially contacts the broadhead body (not shown) adjacent to notch  424 . The upward sloping portion  426  of the convex camming edge  422  from the notch  424  to the high point  428  results in faster blade deployment than on the downward sloping portion  430  of the convex camming edge  422  from the high point  428  to the transition region  432 . Consequently, the blade  420  exhibits an uneven deployment profile. 
       FIG. 14  illustrates an alternate blade  450  with a camming edge  452  having a concave first portion  454  and a convex second portion  456 . Consequently, the blade  450  exhibits an irregular deployment profile. 
       FIG. 15  illustrates an alternate blade  470  with an upwardly angled slot  472 .  FIG. 16  illustrates an alternate blade  480  with a downwardly angled slot  482 .  FIG. 17  illustrates an alternate blade  490  with an upwardly curved slot  492 .  FIG. 18  illustrates an alternate blade  500  with a slot  502  that is both angled and curved. Each of these blades will exhibit a different deployment profile. 
       FIG. 19  illustrates the expandable broadhead  500  with the rear deploying blades  502  in the retracted configuration  504 . The expandable broadhead  500  includes a broadhead body  506  with penetrating end  508  and rear end  510 . The rear end  510  is coupled to arrow shaft  512  by threads  514 . In the illustrated embodiment, the penetrating end  508  includes a tip blade  516  attached to the broadhead body  506  by fastener  518 . The penetrating end  508  of the broadhead body  506  preferably includes a plurality of facets or flat regions (see e.g.,  FIG. 2 ). 
     The broadhead body  506  includes one or more generally T-shaped slots  520  adapted to receive the rear deploying blades  502 .  FIG. 19  illustrates one of the slots  520  without a blade  502  for illustration purposes only. The rear deploying blades  502  are slidably engaged with the generally T-shaped slot  520  by boss or protrusion  524 . The protrusion  524  can be integrally formed with the blades  502  or a separate component attached to the blades  502 . In one embodiment, the protrusion  524  has an elongated shape to limit rotation of the blades  502  during deployment. In this alternate embodiment, the deployment profile is determined primarily by the shape and angle of the slot  520 . The general concept of a boss or protrusion on a blade that slidably engages with a slot in a broadhead body is discussed in U.S. Pat. No. 6,935,976 (Grace, Jr. et al.), which is hereby incorporated by reference. 
     In the retracted configuration  504 , impact edge  530  is positioned exterior to the broadhead body  506 . Notch  532  on the blade  522  is releasably coupled to retainer  534  to retain the rear deploying blade  522  in the retracted configuration  504 . When the impact edge  530  contacts an object, the notch  532  releases from the retainer  534  and the blades  502  are displaced rearward generally in direction  536 . As the blades  502  move rearward, camming edge  538  rides on the retainer  534 , causing the blades  502  to move from the retracted configuration  504  to a deployed configuration. 
     The pivot feature  524  preferably has a diameter close to width  540  of the first end  542  of the slot  520 . The slots  520  preferably include a free floating region  544 . The second end  546  optionally includes the same width  540  as the first end  542 . 
     The camming edge  538  and the location of the protrusion  524  can be changed to modify the deployment profile of the blade  502 , as discussed herein. In the preferred embodiment, the retainer  534  is a resilient or elastomeric material that absorbs some of the impact force that occurs during deployment of the blades  502 . The blades  502  are replaced by removing the broadhead body  506  from the arrow shaft  512 , thereby exposing the second ends  546  of the slots  520 . 
     Different deployment profiles are desirable for a variety of reasons, such as for example the nature of the target or game being hunted. The threaded fastener preferably used as the pivot feature on the present expandable broadheads permit quick and easy substitution of blades having different deployment profiles. An alternate blade substitution system is illustrated in  FIGS. 27A and 27B . Consequently, a user can be provided a kit including a broadhead body and a plurality of interchangeable blades having different deployment profiles, different length cutting edges, different materials, and the like. For some applications it may be advantageous to attach blades having different deployment profiles to a single broadhead body. 
     In addition to engineering the deployment profiles, the manufacturing techniques discussed herein permit an infinite variety of cutting edge shapes on the blades.  FIGS. 20 and 21  illustrate two exemplary variations of cutting edge shapes.  FIG. 20  illustrates a blade  600  with a generally convex curvilinear cutting edge  602 .  FIG. 21  illustrates a blade  610  with a generally concave curvilinear cutting edge  612 . In addition to altering the cutting profile of the blades  600 ,  610 , the curvilinear cutting edges  602 ,  612  will change the resistance of the blades to fracture. 
       FIG. 22  is a perspective view of a practice broadhead  650  in accordance with an embodiment of the present invention. The aerodynamics and flight characteristics of the practice broadhead  650  are substantially the same as the expandable broadhead  50  illustrated in  FIG. 2 , except the blades  652 ,  654  and the broadhead body  656  are molded as a single unitary structure in the retracted configuration  668  using one of the manufacturing methods discussed below. In the preferred embodiment, the blades  652 ,  654  and broadhead body  656  are molded from plastic and metal blade tip  658  is attached with fastener  660 . In the preferred embodiment, duplicating similar aerodynamic flight characteristics is typically achieved by creating a practice broadhead with the substantially the same physical characteristics, such as for example shape, weight distribution, air resistance, and the like. It is possible, however, to duplicate similar flight characteristics with a physically different structure. 
     Because the blades  652 ,  654  do not deploy, the practice broadhead  650  is easy to remove from a practice target. Wear and tear on the actual expandable broadhead  50  is avoided. The flight characteristics of the practice broadhead  650 , however, are substantially the same as the expandable broadhead  50 . Consequently, the user can gain experience using the practice broadhead  650  that directly corresponds to use of the expandable broadhead  50 . While a molded version of the practice broadhead  650  may not be identical in shape to the expandable broadhead  50 , the flight characteristics and weight are substantially the same. 
     In another embodiment, the practice broadhead  650  is the broadhead  50  illustrated in  FIG. 2 , except that the blades  652 ,  654  are secured in the retracted configuration  668  to the broadhead body  656  with an adhesive, fasteners, and the like. Regardless of how the blades are secured, the weight distribution and shape of the practice broadhead  650  are preferably substantially the same as the expandable broadhead  50 . Practice broadheads can be made for any expandable broadhead, including the embodiments disclosed herein. 
     In yet another embodiment, fastener  662  is engaged with broadhead body  656  to secure the blades  652 ,  654  in the retracted configuration  668  in a practice broadhead mode. Once the fastener  662  is removed, the practice broadhead  650  operates in a rear deploying mode as discussed in connection with the expandable broadhead  50 . Consequently, a single structure can be switched from the practice broadhead  650  to the expandable broadhead  50  simply by inserting or removing the fastener  662 . 
       FIG. 23  is a side view of an alternate expandable broadhead  800  in the retracted configuration  80  with a broadhead body  802  made of a polymeric material in accordance with an embodiment of the present invention.  FIG. 24  is a cross-sectional view of the expandable broadhead  800  of  FIG. 23 . 
     In the illustrated embodiment, the broadhead body  802  is molded around tip blade  804 . Tip blade  804  preferably includes one or more features  806 , such as for example cut-out. The polymer preferably flows through the cut-out  806  during the injection molding process to strengthen the attachment to the broadhead body  802 . In an alternate embodiment, the features  806  can be a raised structure or protrusion around which the polymeric material flows during molding. Tip blade  804  is preferably made from metal, such as for example stainless steel. Although the present application is directed primarily to expandable broadheads with rear deploying blades, the present broadhead body  802  molded around tip blade  804  is applicable to any type of fixed or expandable broadhead, such as for example the broadheads illustrated in U.S. Pat. Nos. 6,306,053 and 6,743,128 (Liechty). 
     As best illustrated in  FIG. 24 , a feature  808  is formed in the broadhead body  802  to engage with slot  810 A on the blade  812 A in the retracted configuration  80 . In the two-blade expandable broadhead  800  of  FIGS. 23 and 24 , a similar feature  808  is formed on the other half of the broadhead body  802  to engage with slot  810 B of the blade  812 B. The feature  808  can be a protrusion, detent or other convex structure that penetrates into the slots  810  in the retracted configuration  80 . The feature  808  can be integrally molded with the broadhead body  802  or a separate attached feature. The feature  808  is optionally elastically or plastically deformable. It will be appreciated that the blade retaining system of  FIGS. 23 and 24  can be used with broadheads made of materials other than polymeric materials, such as for example metal or ceramic. 
     As illustrated in  FIG. 24 , the blades  812  engaged with the pivot feature  814 , the surface  816  and the feature  808  in the retracted configuration  80 . This three-point system secures the blades  812  until impact edge  830  strikes an object. 
     The surface  816  preferably extends along a portion of the broadhead body  802  and onto member  818 . The member  818  is preferably a metal ring that protects the arrow shaft (see  FIG. 8 ) from the impact of the blades  812  on deployment. In another embodiment, the member  818  can be a plastic or elastomeric material that absorbs some of the impact of the blades  812 . In one embodiment, the broadhead body  802  plastically deforms as the location  816  upon blade deployment. 
       FIG. 25  is a side view of the expandable broadhead  800  in the deployed configuration  130  in accordance with an embodiment of the present invention.  FIG. 26  is a cross-sectional view of the expandable broadhead  800  of  FIG. 25 . During deployment, camming edges  820  of the blades  812  travel along surfaces  816 . In the illustrated embodiment, deployment regions  822  are a recess engaged with surfaces  816 . 
       FIG. 27A  is a side sectional view of an alternate expandable broadhead  900  in the retracted configuration  902  in accordance with an embodiment of the present invention. Slots  906  on blades  908  include cut-outs  910  near the second ends  904 . Cut-outs  910  permit the blades  908  to be manually rotated in direction  912  to a position between pivot feature  914  and penetrating end  916 . The blades  908  are then disengaged from the pivot feature  914  and removed from the broadhead body  918 . The embodiment of  FIGS. 27A and 27B  permits the blades  908  to be removed and alternate blades substituted without removing the pivot feature  914 . 
     In an alternate embodiment, the pivot feature  914  has a diameter greater than the width of cut-outs  910 . The portions of the blades  908  on either side of the cut-out  910  preferably flex to permit the pivot feature  914  to be engaged with, and disengaged from, the slot  906 . In another embodiment, pivot feature  914  has a non-cylindrical cross-sectional shape (see e.g.,  FIGS. 6A and 6B ) that permits the blades  908  to be removed only when the blades  908  are positioned in a specific oriented relative to the broadhead body  918 , such as for example the blades  908  oriented generally perpendicular to the broadhead body  918 . 
     In the retracted configuration  902 , pivot feature  914  is preferably located closer to penetrating end  916  than the cut-out  910  to minimize interference between the cut-out  910  and the pivot feature  914  during deployment. In the illustrated embodiment, notches  920  on the blades  908  engage with retainer  922 . Upon impact with an object, impact edges  924  force the blades  908  rearward in direction  926 . The pivot feature  914  slides freely generally in the direction  926  in the slot  906 . The slot  906  preferably includes a free-floating region. 
       FIG. 27B  is a sectional view of the expandable broadhead  900  of  FIG. 27A  in the deployed configuration  924 . The first ends  926  of the slots  906  are engaged with the pivot feature  914  in the deployed configuration  924 . In the illustrated embodiment, deployment regions  930  on the blades  908  engage with the retainer  922 . In one embodiment, cantilever portions  932  near the camming edges  934  flex in direction  936  against the retainer  922  and/or the broadhead body  918 . In another embodiment, the cantilever portions  932  plastically deform against the broadhead body  918  on impact with an object. 
     Manufacturing precision blades for expandable broadheads has traditionally been a time consuming and expensive process. The present invention contemplates flexible manufacturing techniques that permits a wide variety of blade shapes and deployment profiles at low cost. In one embodiment, the blades are cut from a sheet or blank of blade stock material. In one preferred embodiment, the blade stock material is a strip of pre-sharpened and/or pre-tempered material, reducing or eliminating the need to sharpen the blade blanks. The blades are preferably made from the blade stock material by laser cutting, electro-discharge machining, water-jet cutting, and other similar techniques that are adaptable to computer control. These computer controlled processes permit the blade shape to be changed essentially instantaneously. 
     The blade stock material can be made from various different steels, including tool steels; M-2, S-7 &amp; D-2, stainless steels; such as 301, 304, 410, 416, 420, 440A, 440B, 440C, 17-4 PH, 17-7 PH, 13C26, 19C27, G1N4, &amp; other razor blade stainless steels, high speed steel, carbon steels, carbides, titanium alloys, tungsten alloys, tungsten carbides, as well as other metals, ceramics, zirconia ceramics, organic polymers, organic polymer containing materials, plastics, glass, silicone containing compounds, composites, or any other suitable material that a cutting blade or equivalent could be fabricated from, or could be at least in part fabricated from. Various blade manufacturing techniques are disclosed in U.S. Pat. Nos. 6,743,128 (Liechty) and 6,939,258 (Muller), which are hereby incorporated by reference. 
     In one embodiment, the broadhead body or practice broadhead is a unitary molded or machined structure that includes various slots, facets, threads and the like. In an alternate embodiment, the broadhead body or practice broadhead may include a plurality of components that are assembled. 
     The practice broadhead and the components of the present expandable broadhead can be manufactured using a variety of techniques. In one embodiment, the practice broadhead, broadhead body and/or the rear deploying blades are made using metal injection molding (hereinafter “MIM”) techniques, such as disclosed in U.S. Pat. Nos. 6,290,903 (Grace et al.); 6,595,881 (Grace et al.); and 6,939,258 (Muller), which are hereby incorporated by reference. In another embodiment, the practice broadhead, broadhead body and/or the rear deploying blades are made using powder injection molding (hereinafter “PIM”) techniques, such as disclosed in U.S. Pat. No. 6,749,801 (Grace et al.), which is hereby incorporated by reference. The powder mixtures used in either the MIM or PIM processes can include metals, ceramics, thermoset or thermoplastic resins, and composites thereof. Reinforcing fibers can optionally be added to the powder mixture. 
     In another embodiment, the practice broadhead, broadhead body and/or the rear deploying blades are made using other molding techniques, such as injection molding and the methods disclosed in U.S. Pat. Nos. 5,137,282 (Segar et al.) and 6,739,991 (Wardropper), which are hereby incorporated by reference. The molding materials can include metals, ceramics, thermoset or thermoplastic resins, and composites thereof. In one embodiment, the broadhead body is molded from the polymers IXEF or AMODEL available from Solvay Advanced Polymers, reinforced by about 30% to about 60% by volume glass or carbon fibers. 
     Reinforcing fibers can optionally be added to the molding mixture. In one embodiment, the practice broadhead and/or broadhead body are made of carbon fiber reinforced polymers. 
     Reinforcing fibers can optionally be added to the mixture. Suitable reinforcing fibers include glass fibers, natural fibers, carbon fibers, metal fibers, ceramic fibers, synthetic or polymeric fibers, composite fibers (including one or more components of glass, natural materials, metal, ceramic, carbon, and/or synthetic components), or a combination thereof. In another embodiment, the reinforcing fibers include at least one polymeric component. 
     The particular embodiments disclosed above are illustrative only, as the invention 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 embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention.