HK40080884A - Impact tool with tapered anvil wing design - Google Patents

Description

Impact tool with tapered anvil wing design

Cross Reference to Related Applications

This application claims the benefit of U.S. provisional patent application No. 63/220,325, filed on 9/7/2021 and the benefit of U.S. patent application No. 17/841,221, filed on 15/6/2022, the contents of which are incorporated herein by reference in their entirety.

Technical Field

The present invention relates generally to impact tools for driving fasteners, and more particularly to anvils for impact tools having a tapered anvil wing design.

Background

Various wrenches and tools are commonly used to apply torque to a workpiece, such as a threaded fastener. Such tools, known as impact wrenches, screwdrivers, drills or tools, are designed to deliver a high torque output by storing energy in a rotating mass, which is then abruptly transferred to an output shaft. In operation, a rotating mass, known as a hammer, is accelerated by a motor, stores energy, and then is abruptly connected to an output shaft via an anvil, producing a high torque impact. The hammer mechanism is designed so that after the impact force is transmitted, the hammer is allowed to rotate freely and not remain locked. In this way, the only reaction force applied to the tool body is that of the motor accelerating the hammer block, so the operator feels very little torque even though very high peak torques are transmitted. Conventional hammer block designs require a certain minimum torque before allowing the hammer block to rotate separately from the anvil, thereby stopping the tool from hammering, while driving the fastener smoothly with only a low torque required, thereby rapidly rotating the fastener.

Conventional impact tools are designed to impact the mating surfaces of the hammer block and anvil, assuming that the hammer block and anvil rotate on the same central axis. The assembly clearances and wear cause the surfaces to contact the straight flat face of the hammer block and the straight wing of the anvil at tool-specific locations. With conventional designs, high stresses are applied at the location where the anvil wings of the anvil transition to the anvil shaft. As a result, the internal components of the impact tool (e.g., the hammer block, anvil, and shaft) may be subjected to undesirable stresses that would reduce the efficiency and useful life of the tool.

Disclosure of Invention

The present invention generally relates to an anvil for an impact mechanism, wherein the anvil includes wings that taper at a taper angle of about 5 degrees to about 30 degrees. The anvil may also include a shaft extending from the wing and a drive end adapted to transmit and apply torque to the workpiece. The wing of the anvil also includes a wing impact surface that receives the rotational impact force from the hammer block. For example, the impact mechanism may further include a hammer block rotatable about a central axis and having a hammer block impact surface or lug. The hammer lugs contact the wings of the anvil and apply a torque or rotational force thereto.

During operation, the wings of the anvil will be subjected to high stresses at the intersection of the wings and the axis of the anvil. At this intersection, the principal bending stresses at the wings are converted to torsional stresses in the shaft. By incorporating a taper angle of about 5 degrees to about 30 degrees, the section modulus of the anvil at the intersection of the wing and the shaft can be increased without increasing the overall cross-section of the wing, without sacrificing the stroke range of the hammer block. The taper angle also provides a larger contact area between the lugs of the hammer block and the wings of the anvil, reducing the contact pressure, and the reduced stiffness of the wings along the length of the wings (due to the taper angle) improves the stress distribution and stress at the lugs of the hammer block.

In one embodiment, the present invention generally relates to an anvil for an impact mechanism of an impact tool. The anvil comprises: a base; a wing extending radially outward from the base and tapering at an angle of about 5 degrees to about 30 degrees; and a shaft extending axially from the base.

Drawings

For the purpose of facilitating an understanding of the subject matter sought to be protected, there are shown in the drawings embodiments which, by way of inspection of these embodiments, will be readily understood and appreciated as the subject matter sought to be protected, its construction and operation, and many of its advantages, when considered in connection with the following description.

Fig. 1 is a side view of an impact tool according to an embodiment of the present invention.

Fig. 2 is a perspective view of an impact mechanism according to an embodiment of the present invention.

FIG. 3A is a perspective end view of an anvil of an impact mechanism according to an embodiment of the present invention.

FIG. 3B is a side perspective view of the anvil of FIG. 3A.

FIG. 4A is a perspective end view of an anvil of an impact mechanism according to an embodiment of the present invention.

Fig. 4B is a side perspective view of the anvil of fig. 4A.

FIG. 5A is a perspective end view of an anvil of an impact mechanism according to an embodiment of the present invention.

Fig. 5B is a side perspective view of the anvil of fig. 5A.

FIG. 6A is a perspective end view of an anvil of an impact mechanism according to an embodiment of the present invention.

Fig. 6B is a side perspective view of the anvil of fig. 6A.

FIG. 7A is a perspective end view of an anvil of an impact mechanism according to an embodiment of the present invention.

FIG. 7B is a side perspective view of the anvil of FIG. 7A.

FIG. 8A is a perspective end view of an anvil of an impact mechanism according to an embodiment of the present invention.

Fig. 8B is a side perspective view of the anvil of fig. 8A.

FIG. 9A is a perspective end view of an anvil of an impact mechanism according to an embodiment of the present invention.

Fig. 9B is a side perspective view of the anvil of fig. 9A.

Detailed Description

While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail embodiments of the invention (including preferred embodiments), with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to any one or more of the embodiments illustrated herein. As used herein, the term "present invention" is not intended to limit the scope of the claimed invention, but is merely used to discuss exemplary embodiments of the invention for illustrative purposes.

The present invention generally relates to an anvil for an impact mechanism, wherein the anvil includes wings that taper at a taper angle of about 5 degrees to about 30 degrees. The anvil may also include a shaft extending from the wing and a drive end adapted to transmit and apply torque to a workpiece. The wing of the anvil also includes a wing impact surface that receives the rotational impact force from the hammer block. For example, the impact mechanism may further include a ram rotatable about a central axis and having a ram impact surface or lug. The hammer lugs contact the wings of the anvil and apply a torque or rotational force thereto.

During operation, the wings of the anvil will be subjected to high stresses at the intersection of the wings and the anvil shaft. At this intersection, the principal bending stresses at the wings are converted to torsional stresses in the shaft. By incorporating a taper angle of about 5 degrees to about 30 degrees, the section modulus of the anvil at the intersection of the wing and shaft can be increased without increasing the overall cross-section of the wing, without sacrificing the range of travel of the hammer block. The taper angle also provides a larger contact area between the lugs of the hammer block and the wings of the anvil, reducing the contact pressure, and the reduction in stiffness of the wings along the length of the wings (due to the taper angle) improves stress distribution and stress at the lugs of the hammer block.

Referring to FIG. 1, an exemplary impact tool 100 is shown in accordance with an embodiment of the present invention. The impact tool 100 may have a housing 102, the housing 102 including a main housing portion 104 and a handle portion 106. The motor 108 and impact mechanism 110 may be disposed in the main housing portion 104. The impact mechanism 110 may include a hammer block 112 and an anvil 114, and the anvil 114 may include or be coupled to an output drive 116. The drive portion 116 is adapted to apply torque to a workpiece, such as a fastener (e.g., a wheel flange nut or bolt), via an adapter (bit or sleeve) coupled to the drive portion 116. As shown, the drive portion 116 is a "male" connector (e.g., a drive lug, which may include a square or other polygonal cross-sectional shape) designed to fit into or matingly engage with a female counterpart. However, the drive portion 116 may alternatively include a "female" connector designed to matingly engage a male counterpart. The drive portion 116 may also be configured to directly engage a workpiece without coupling to an adapter (drill bit or sleeve). The drive portion 116 is operatively coupled to the motor 108 (which may be a pneumatic motor, or a brushed or brushless motor) via the impact mechanism 110 and is driven by the motor 108.

A trigger 118 for controlling operation of the motor 108 is operatively coupled to the motor 108 and is disposed in the housing 102. The selector lever 120 may also be operably coupled to the trigger 118 and/or the motor 108 to allow selection or control of the rotational drive direction (e.g., clockwise or counterclockwise). The motor 108 may be operatively coupled to a power source 122 (e.g., a battery or other power source), a motor speed circuit, and/or a controller via a trigger 118 (housed in the housing 102) and to the drive portion 116 to provide torque to the tool 100 and, in turn, to the drive portion 116 via the impact mechanism 110 in a known manner. The motor 108 may be a brushless or brushed type motor, a pneumatic motor, or any other suitable motor.

The trigger 118 may be adapted to selectively turn power to the motor 108 on and off, or to cause power/voltage to flow from the power source 122 to the motor 108 or to stop power/voltage from flowing from the power source 122 to the motor 108. The trigger 118 may be biased to an OFF position such that the trigger 118 is actuated or depressed inwardly relative to the housing 102 to move the trigger 118 to an ON (ON) position to operate the tool 100, and releasing the trigger 118 moves the trigger 118 to an OFF position to stop operation of the tool 100 via the biasing characteristics of the trigger 118. The flip-flop 118 may also be a variable speed flip-flop. In this regard, the relative actuation of the trigger 118 causes the motor 108 to operate at a variably increasing speed the further the trigger 118 is actuated.

During operation, the motor 108 selectively rotates the hammer block 112 in either of a first rotational drive direction and a second rotational drive direction (e.g., clockwise or counterclockwise), which rotates the anvil 114 and the drive portion 116 to apply torque to a workpiece. Under high torque conditions, the hammer block 112 is disengaged from the anvil 114 and the motor 108 rotates the hammer block 112 independently of the anvil 114. To apply a high torque output, the hammer block 112 engages and transmits the high torque output to the anvil 114, thereby generating a high torque impact. The impact mechanism 110 is designed such that after the impact force is transmitted, the hammer block 112 is separated from the anvil 114 and allowed to rotate freely. Thus, the only reaction force applied to the body of the tool 100 is that of the motor 108 accelerating the hammer block 112, so the operator feels very little torque or impact force even though a very high peak torque is being transmitted. The impact mechanism 110 typically requires a predetermined amount of minimum torque to separate (or decouple) the hammer block 112 from the anvil 114 after impact. Under low-drag torque operating conditions, the predetermined torque requirement allows the hammer block 112 to remain engaged with the anvil 114 and rotate with the anvil 114, thereby stopping the hammering or impacting of the tool 100, but driving the workpiece smoothly and rotating it quickly.

Referring to fig. 1 and 2, in an embodiment, the hammer block 112 of the impact mechanism 110 may include a hammer block base 124 and one or more hammer block lugs 126, and the hammer block 112 may rotate (via operation of the motor 108) about a central axis of the hammer block 112. As shown, the ram lugs 126 project from the ram base 124 and project radially inward toward the central axis of the ram 112. Each hammer lug 126 defines a hammer impact surface 128 that contacts the anvil 114 (e.g., anvil wings 134 on an anvil impact surface 138 described below) during an impact operation. The ram 112 may include or be coupled to a drive shaft 130, the drive shaft 130 being axially aligned with the ram center and receiving rotational force from the motor 108.

Referring to fig. 2, 3A, and 3B, in an embodiment, anvil 114 of impact mechanism 110 may include an anvil base 132, one or more anvil wings 134 extending radially outward from anvil base 132, an anvil shaft 136 extending axially from anvil base 132, and a drive portion 116 proximate an end of anvil shaft 136. The anvil 114 is rotatable about a central axis of the anvil 114 (via operation of the motor 108 and hammer block 112). Each anvil wing 134 defines an anvil impact surface 138, the anvil impact surface 138 being in contact with the corresponding hammer impact surface 128 during an impact operation. Each anvil wing 134 may also taper at a taper angle (θ) of about 5 degrees to about 30 degrees, which also provides an anvil impact surface 138 that tapers at the taper angle (θ). As shown in fig. 3, the drive portion is a 3/4 inch square drive lug and the taper angle (θ) is about 15 degrees. The anvil 114 may also include an undercut or recessed portion 140 that extends circumferentially around the anvil shaft 136. The outer diameter of the recessed portion 140 is smaller than the outer diameter of the anvil shaft 136. For example, the outer diameter of groove 140 may be about 25% to about 100% of the outer diameter of anvil shaft 136, may be about 25% to about 75% of the outer diameter of anvil shaft 136, and/or may be about 25% to about 50% of the outer diameter of anvil shaft 136. The recessed portion 140 may help reduce inertia (i.e., the mass of the anvil 114) and increase the spring effect on the anvil shaft 136, which helps reduce stress at the transition from the anvil shaft 136 to the drive portion 116.

The highest stress on anvil wing 134 occurs at the intersection of anvil wing 134 and anvil base 132. At this intersection, the primary bending stresses at the anvil wings 134 are converted into torsional stresses in the anvil shaft 136. A larger anvil shaft 136 or anvil base 132 may be added to connect anvil wings 134 and anvil shaft 136 to provide an intermediate transition to reduce eruptions at the transition from bending stresses to torsional stresses. At the intersection of anvil wing 134 and anvil base 132, a radius (R) may be provided to provide a smooth geometric transition from anvil base 132 to anvil wing 134. Radius (R) also increases the section modulus at the intersection of anvil wing 134 and anvil base 132, thereby reducing bending stresses. However, a larger radius will result in a smaller wing contact area or anvil impact surface 138. The anvil wings 134 may be extended to increase the contact area, but this will reduce the output torque due to the higher inertia of the anvil from the additional wing material. In one example, radius (R) is about 100% to about 150% of the radius of anvil base 132. Radius R of anvil wing 134 _W It may also be about 100% to about 250% of the radius of anvil base 132, and more specifically may be about 150% to about 200% of the radius of anvil base 132.

The hammer block 112 and anvil 114 also provide an angle (β) between the centerline of the hammer lugs 126 and the centerline of the anvil wings 134. Minimizing the overlap angle (2 β) provides additional clearance for the hammer block 112 to rotate (hammer block travel range =180 ° -overlap angle), mitigating potential impact (also known as pinching) on the underside of the anvil wings 134 during operation. In one example, the angle (β) is about 20 degrees to about 40 degrees. This range provides sufficient material cross-section in the anvil wings 134 and hammer lugs 126 to withstand impact stresses and allow a wide range of hammer rotation without binding.

By tapering the anvil wings 134 at a taper angle (θ), the section modulus of the anvil 114 at the intersection of the anvil wings 134 and the anvil base 132 will increase without increasing the overall cross-section of the anvil wings 134. Conventional straight wings with the same section modulus at the intersection result in a very high anvil inertia and therefore lower output torque due to the additional material at the wing tip. Also, by tapering the anvil wings 134 at a taper angle (θ), the section modulus of the anvil at critical locations can be increased without sacrificing the range of travel of the hammer block.

Further, the resulting area with the tapered anvil wings 134A larger contact area is provided between the ram lugs 126 and the anvil wings 134, thereby reducing the contact pressure. The contact area of each anvil wing surface (e.g., anvil impact surface 138) may be about 0.01 square inches to about 0.2 square inches, and more specifically, about 0.02 square inches to about 0.1 square inches. When two anvil wings 134 (e.g., anvil impact surfaces 138) are simultaneously in contact with the ram lobes 126 (e.g., at the ram impact surfaces 128), the total system contact area during operation is twice the contact area per anvil wing surface. By varying the taper angle (θ), a gradual reduction in stiffness of the anvil wings 134 along the length may be achieved to improve stress distribution and stress at the root of the hammer lugs 126. A taper angle (θ) of about 5 degrees to about 30 degrees provides a minimum overlap angle and improves stress distribution at the hammer lugs 126 and anvil wings 134.

Referring to fig. 4A and 4B, an embodiment of an anvil 414 is shown. The anvil 414 is similar to the anvil 114 and may include one or more features of the anvil 114. For example, the anvil 414 may include an anvil base 432, one or more anvil wings 434 having an anvil impact surface 438 extending radially outward from the anvil base 432, an anvil shaft 436 extending axially from the anvil base 432, and a drive portion 416 proximate an end of the anvil shaft 436. Anvil 414 may also include an undercut or grooved portion (not shown) extending circumferentially around anvil shaft 436.

In this example, the drive portion 416 is a 3/4 inch square drive lug, and each anvil wing 434 may also taper at a taper angle (θ) of about 5 degrees to about 30 degrees, more specifically about 10 degrees. Radius (R) may be about 0.7 inches to about 0.8 inches, and more specifically may be about 0.75 inches, radius R of the anvil wing _W May be about 1 inch, anAnd the impact (contact) surface area on each anvil impact surface 438 may be about 0.06 square inches to about 0.08 square inches, and more particularly may be about 0.07 square inches.

Referring to fig. 5A and 5B, an anvil 514 is depicted. The anvil 514 is similar to the anvil 114 and may include one or more features of the anvil 114. For example, the anvil 514 may include an anvil base 532, one or more anvil wings 534 having anvil impact surfaces 538 extending radially outward from the anvil base 532, an anvil shaft 536 extending axially from the anvil base 532, and a drive portion 516 proximate an end of the anvil shaft 536. The anvil 514 may also include an undercut or recessed portion 540 extending circumferentially about the anvil shaft 536.

In this example, drive portion 516 is a 3/4 inch square drive lug, and each anvil wing 534 may also taper at a taper angle (θ) of about 5 degrees to about 30 degrees, more specifically about 12 degrees. The radius (R) may be about 0.575 to about 0.65 inches, and more specifically may be about 0.625 inches, the radius R of the anvil wing _W May be about 1 inch and the impact (contact) surface area on each anvil impact surface 538 may be about 0.05 square inches to about 0.07 square inches and more particularly may be about 0.06 square inches.

Referring to fig. 6A and 6B, another embodiment of an anvil 614 is depicted. The anvil 614 is similar to the anvil 114 and may include one or more features of the anvil 114. For example, the anvil 614 can include an anvil base 632, one or more anvil wings 634 having an anvil impact surface 638 extending radially outward from the anvil base 632, an anvil shaft 636 extending axially from the anvil base 632, and a drive portion 616 proximate an end of the anvil shaft 636. Anvil 614 may also include an undercut or recessed portion (not shown) extending circumferentially about anvil shaft 636.

In this example, drive portion 616 is a 3/8 inch square drive lug, and each anvil wing 634 may also taper at a taper angle (θ) of about 5 degrees to about 30 degrees, more specifically about 7.5 degrees. Radius (R) may be about 0.5 inches to about 0.6 inches, and more specifically may be about 0.55 inches, radius R of the anvil wing _W May be about 0.6 inches to about 0.7 inches, and more particularly may be about 0.68 inches, and the impact (contact) surface area on each anvil impact surface 638 may be about 0.02 square inches to about 0.04 square inches, and more particularly may be about 0.03 square inches.

Referring to fig. 7A and 7B, another embodiment of the anvil 714 is shown. The anvil 714 is similar to the anvil 114 and may include one or more features of the anvil 114. For example, the anvil 714 may include an anvil base 732, one or more anvil wings 734 extending radially outward from the anvil base 732 with anvil impact surfaces 738, an anvil shaft 736 extending axially from the anvil base 732, and a drive portion 716 near an end of the anvil shaft 736. The anvil 714 may also include an undercut or grooved portion (not shown) that extends circumferentially around the anvil shaft 736. The anvil 714 may include an additional base portion 742 extending circumferentially around the anvil shaft 736 between the anvil shaft 736 and the anvil wings 734. This additional base 742 may help provide an intermediate stress transition from the anvil wings 734 to the anvil shaft 736. Additional base 742 may also be incorporated into any of the other anvil designs described herein (e.g., anvil 114, anvil 414, anvil 514, anvil 614, anvil 814, and/or anvil 914).

In this example, drive portion 716 is a 1/2 inch square drive lug, and each anvil wing 734 may also taper at a taper angle (θ) of about 5 degrees to about 30 degrees, more specifically about 5 degrees. Radius (R) may be about 0.475 inches to about 0.6 inches, and more particularly may be about 0.525 inches, radius R of the anvil wing _W May be about 1 inch and the impact (contact) surface area on each anvil impact surface 738 may be about 0.03 square inches to about 0.05 square inches and more particularly may be about 0.04 square inches.

Referring to fig. 8A and 8B, another embodiment of an anvil 814 is shown. The anvil 814 is similar to the anvil 114 and may include one or more features of the anvil 114. For example, the anvil 814 can include an anvil base 832, one or more anvil wings 834 having an anvil impact surface 838 extending radially outward from the anvil base 832, an anvil shaft 836 extending axially from the anvil base 832, and a driving portion 816 proximate an end of the anvil shaft 836. The anvil 814 may also include an undercut or recessed portion (not shown) that extends circumferentially around the anvil shaft 836. The anvil 814 may include additional bases (not shown), such as additional bases 742 that extend circumferentially around the anvil shaft 836.

In this example, drive portion 816 is a 1/2 inch square drive lug, and each anvil wing 834 can also taper at a taper angle (θ) of about 5 degrees to about 30 degrees, more specifically about 12.5 degrees. Radius (R) may be about 0.5 inches to about 0.7 inches, and more specifically may be about 0.6 inches, radius R of the anvil wing _W May be about 1 inch and the impact (contact) surface area on each anvil impact surface 838 may be about 0.05 square inches to about 0.07 square inches, and more particularly may be about 0.06 square inches.

Referring to fig. 9A and 9B, another embodiment of an anvil 914 is illustrated. The anvil 914 is similar to the anvil 114 and may include one or more features of the anvil 114. For example, anvil 914 may include an anvil base 932, one or more anvil wings 934 having an anvil impact surface 938 extending radially outward from anvil base 932, an anvil shaft 936 extending axially from anvil base 932, and a drive 916 proximate an end of anvil shaft 936. The anvil 914 may also include an undercut or recessed portion (not shown) extending circumferentially about the anvil shaft 936. The anvil 914 may include additional bases (not shown), such as additional bases 742 that extend circumferentially around the anvil shaft 936.

In this example, drive portion 916 is a 1/2 inch square drive lug, and each anvil wing 934 may also taper at a taper angle (θ) of about 5 degrees to about 30 degrees, more specifically about 21 degrees. The radius (R) may be infinite, the radius R of the anvil wing _W May be about 1 inch and the impact (contact) surface area on each anvil impact surface 938 may be about 0.03 square inches to about 0.05 square inches, and more particularly may be about 0.04 square inches.

As described herein, the anvil includes anvil wings that taper at a taper angle of about 5 degrees to about 30 degrees. The taper angle helps to increase the section modulus of the anvil at the intersection of the wing and the shaft without increasing the overall cross-section of the wing, without sacrificing the stroke range of the hammer block. The taper angle also provides a larger contact area between the lugs of the hammer block and the wings of the anvil, reducing the contact pressure, and the reduction in stiffness of the wings along the length of the wings (due to the taper angle) improves stress distribution and stress at the lugs of the hammer block.

As used herein, the term "coupled" may refer to any physical, electrical, magnetic, or other direct or indirect connection between two or more components or parts. The term "coupled" is not limited to a fixed direct coupling between components or parts.

The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. While particular embodiments have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects. The actual scope of the protection sought is to be defined in the claims appended hereto, when viewed in their proper perspective on the basis of the prior art.

Claims (20)

1. An anvil for an impact mechanism of an impact tool, comprising:

a base;

a wing extending radially outward from the base and tapering at an angle of about 5 degrees to about 30 degrees; and

a shaft extending axially from the base.

2. The anvil of claim 1, further comprising: a drive section proximate an end of the shaft.

3. The anvil of claim 2, wherein said driver portion has a square cross-sectional shape.

4. The anvil of claim 1, wherein said angle is approximately 15 degrees.

5. The anvil of claim 1, further comprising: a groove portion extending circumferentially around the shaft.

6. The anvil of claim 5, wherein said recessed portion has a recess outer diameter and said shaft has a shaft outer diameter, wherein said recess outer diameter is smaller than said shaft outer diameter.

7. The anvil of claim 6, wherein the pocket outer diameter is about 25% to about 75% of the shaft outer diameter.

8. The anvil of claim 6, wherein the pocket outer diameter is about 25% to about 50% of the shaft outer diameter.

9. The anvil of claim 1, wherein an intersection of said wing and said base includes a radius providing a transition from said base to said wing.

10. The anvil of claim 9, wherein said radius is about 100% to about 150% of a base radius of said base.

11. The anvil of claim 1, wherein the wing comprises a contact area of about 0.01 square inches to about 0.2 square inches adapted to contact a hammer lug.

12. An impact mechanism for an impact tool, comprising:

an anvil, the anvil comprising:

an anvil base;

a wing extending radially outward from the anvil base and tapering at an angle of about 5 degrees to about 30 degrees; and

a shaft extending axially from the anvil base; and

a ram, the ram comprising:

a hammer body base; and

a ram lug protruding from the ram base and adapted to impact the wing at a contact region of the wing.

13. The impact mechanism of claim 12, wherein the anvil further comprises: a drive section proximate an end of the shaft.

14. The impact mechanism of claim 13, wherein said drive portion has a square cross-sectional shape.

15. The impact mechanism of claim 12, wherein the anvil further comprises: a groove portion extending circumferentially around the shaft.

16. The impact mechanism of claim 15, wherein the groove portion has a groove outer diameter and the shaft has a shaft outer diameter, wherein the groove outer diameter is about 25% to about 75% of the shaft outer diameter.

17. The impact mechanism of claim 16, wherein the groove outer diameter is about 25% to about 50% of the shaft outer diameter.

18. The impact mechanism of claim 12, wherein the intersection of the wing and the anvil base includes a radius that provides a transition from the anvil base to the wing.

19. The impact mechanism of claim 18, wherein the radius is about 100% to about 150% of a base radius of the anvil base.

20. The impact mechanism of claim 12, wherein the contact area is about 0.01 square inches to about 0.2 square inches.