Patent Grant
10464198
Not Applicable.
Not Applicable.
The present invention relates to striking tools, and more particularly to light weight hammer handles that are made of layered composite materials.
Hammers are well known for driving and prying nails and are used both commercially by framers, roofers and construction workers as well as in non-commercial settings for various uses. Generally, hammers are made up a head attached to the end of a handle which can be grasped by a user and swung to hit and drive a nail, stake, or similar fastener into a desired position. Accordingly, the functionality of hammers has largely remained unchanged where the earliest hammers satisfactorily accomplished the intended job. However, there exists a problem in the industries where tradespeople repeatedly use hammers at their worksites; traditional hammers result in repetitive stress injuries to approximately 30% of the workers (ref. Werner R A, Franzblau A, Gell N, et al. Predictors of persistent elbow tendonitis among auto assembly workers. J. Occup. Rehabil. 2005; 15(3):393-400). Contact stress and force are known concerns for workers (ref. Occupational Safety and Health Administration, US Department of Labor. Computer Workstations eTool, Contact Stress, Force. Accessed Nov. 29, 2012—www.osha.gov/SLTC/etools/computerworkstations/more.html). One of the injuries suffered by these tradespeople is lateral epicondylitis, also called tennis or carpenter's elbow, and this injury is caused by the repeated shock caused by the transference of energy from the handle to the worker's hand, wrist and elbow during the hammering motion, especially the shock at the end of the hammering motion when the head of the hammer strikes the head of a nail. Accordingly, there exists a need in the art for a handle capable of reducing the amount of shock to the worker's hand, wrist and elbow at the end of the hammering motion.
There have been a number of modifications made to traditional hammers in an effort to reduce the shock imparted to the worker. For example, regardless of the type of material being used for handles, many manufacturers have added one or more layers of a resilient, dampening material over the gripping portion of the handle's base section where the worker would grasp and swing the hammer for the most forceful head strikes. While these layers may be effective in reducing vibrations, the vibrations tend to be either so small in amplitude or high enough in frequency that they are simply absorbed by the skin in the hand and do not cause tendon injuries. Accordingly, eliminating the sinusoidal oscillations of the handle after impact is an ineffective answer to the wrong problem. Different from vibration is a mechanism called impact shock or recoil shock, where a single high velocity object must be stopped quickly. The transfer of momentum from the moving object to the stopping object is impact shock. In the case of hammers, the moving object is the handle immediately after impact with the nail, and the stopping object is the user's hand, wrist, forearm, elbow and upper arm. As will become evident from the description of the present invention, the addition of this material at the distal end of the handle could actually be more counterproductive to reducing stress because of the increased weight that the material adds to the handle as well as the corresponding movement of the hammer's center of gravity further away from the head toward the base of the handle.
Hammer manufacturers have also used different handle materials, including hickory (or other wood), steel, aluminum, fiberglass, polycarbonate and other plastics, composites, and even titanium. Some manufacturers suggest that the materials of their handles provide better shock protection. For example, a manufacturer of titanium tools advertises that its hammers with titanium handles have ten (10) times less recoil shock than steel hammers. It may be true that titanium dampens vibrations ten (10) times greater than high carbon steel, but this does not necessarily result in an equivalent reduction in recoil shock as felt by the worker. As will become evident from the description of the present invention, it is the mass in the handle that must be stopped by the user's hand and the mass is independent of the material from which it comes. Other manufacturers have varied the weight of the hammer head, some increasing the head weight to provide a greater impact force while others have reduced the head weight to change the hammer's weight distribution to make the hammer less top heavy and allow for increased swing speed to increase kinetic energy, such as explained in U.S. Pat. No. 8,534,643, and manufacturers have changed the weight of the handle to varying degrees. Some of these changes in weights may reduce the shock imparted to the worker and may alleviate the repeated stress injuries, but no prior art hammer design has been optimized based on the operation of the hammer as the head impacts a nail head. To perform such an optimization, the problem of recoil shock is rethought from a different perspective, keeping the same or better the impact energy at the head while minimizing the energy transferred from the handle to the worker's hand during the impact, and what results can be a very different picture of the hammer's design.
The head is at the end of the hammer away from the worker's hand on the grip of the handle, and the center of gravity (CG) of the hammer is typically located away from the grip toward the head between approximately three-quarters (¾) and four-fifths (⅘) of the total length of the hammer. In operation, the head of a hammer stops very quickly on the head of the nail, but the handle is only constrained from further movement by the worker's hand. Therefore, the further away from the head that the CG is located towards the base of the handle, the more shock will be felt by the worker because, although the head stops on the nail head, the handle still has kinetic energy that must be stopped by the worker's hand, and this energy is transferred through the handle to the worker's hand. High speed videography shows the shock applied to a worker's hand following the head strike: the head is stopped and the handle's momentum carries it in the direction of the swing after the impact causing the handle to rotate around the impact point on the nail head. There is a resulting yank or jerking applied to the worker's hand by the handle because of the inertia of the handle's mass, and the further away that the CG is from the head, the more shock will be felt by the worker. Additionally, even without linear kinetic motion the effect of CG location is substantial. For example, if the hammer swing is purely rotational around the user's hand the hammer will impact the fastener causing the head to stop. However, the CG still has momentum which is transferred to the base of the handle and subsequently into the user's arm as the hammer pivots around the contact point.
As described above, following the head striking the nail head, the worker's hand, wrist, and elbow stops the rotation of the handle. Since the handle is in motion, the worker's hand must apply a force to the handle to decelerate it; force is dependent on the mass and the deceleration (F=ma). To reduce the force, the deceleration of the handle can be slowed or the mass of the handle can be reduced. Practically, reducing the deceleration is counter-productive because the hammer would be swung with less velocity which reduces the effectiveness of the head strike and then requires more swings and strikes. Accordingly, for a given head weight, a lighter mass handle could be installed; a lighter handle would have an additional benefit of shifting the CG away from distal end of the handle where the worker grips the hammer toward the head of the hammer. Since the head is stopped on the nail head following the strike and the handle's momentum produces the rotation around the nail head, there is a torque with the nail head acting as a fulcrum, and moving the location of the CG towards the head increases the lever arm, thereby increasing the mechanical advantage of the handle and decreasing the force required to stop the handle.
In currently manufactured hammers, the handles are heavy relative to the head of the hammer and typically weigh between nearly one half (½) and three quarters (¾) of the weight of the head, with some handles weighing as much as or more than the head. Accordingly, hammers have handle weights that account for approximately one quarter (¼) of the hammer weight, and typically account for more than one third (⅓) of the total hammer weight and may even be around one half (½) of the total weight. For a given head weight, the larger the weight of the handle relative to the head, the higher the shock to the worker following the impact of the head. Once the relationship between the operation of the hammer and the shock to the worker is recognized, with the continued momentum and torque of the handle around the nail head where the hammer head is stopped, it can then be recognized that there is a significant benefit to reducing the weight of the handle for a given head weight so that the energy transferred to the worker's hand following the head strike and corresponding shock is reduced.
Some current hammers are designed to have a lighter weight handle. However, current handle weights are still too heavy to effectively reduce the shock and repetitive stress injuries caused by the amount of energy transferred from the handle to the worker's hand. As described in the present invention, even the lightest weight handles are more than twice as heavy as they should be to effectively reduce the energy being transferred. Even with the most recent, innovative hammer designs, the designers are following the same practices of adding weight to the handle section for one reason or another. For example, in the '643 Patent referred to above, it is suggested that a softer material should be placed over the gripping portion, and according to the weight distribution design of this hammer, the handle weighs nearly as much as the head or weighs more than the head. Other designs that use hollow metal shells, such as in US Pat. Pub. No. 2014/0238201, result in handle weights that are less than the weight of the head but are at best equivalent to standard hickory handles. As another example, U.S. Pat. No. 8,104,379 and as related patent, U.S. Pat. No. 8,833,207, disclose hammers with a composite handle, but the handle also includes a titanium plate that spans the entire length of the handle in order to improve strength, resist torque, and reduce vibrations. Accordingly, the '379 Patent and the '207 Patent are additional examples of innovative hammer designs that still distribute the weight in the traditional manner, with the handles weighing between nearly one half (½) and three quarters (¾) of the weight of the head. Numerous other hammers have disclosed various shock absorbing structures to help reduce the shock imparted to the worker swinging the hammer. Although there have been efforts to reduce the vibrations and shock imparted to a worker, no prior art hammer has sought to reduce the handle weight sufficiently relative to the head weight and move the CG sufficiently close to the head that the shock imparted to the worker is significantly reduced. Instead, current hammer designs, even those that are innovative, maintain the traditional distribution of weight between the head and handle. Additionally, it is desirable to have a hammer that is as light as possible to lighten the load of a worker's tool belt when the hammer is not being used.
Other types of tools may have a head at the end of an elongated handle which is grasped with two hands such as shovels, rakes, hoes, spades and forks. As compared with the single-handed grasp of a hammer handle or other tool designed for striking, the handles of these double-handed tools are designed for actions other than striking. Accordingly, these double-handed tools are not typically concerned with the weight of the handle or any shock imparted to the worker through the handle and are primarily concerned with the strength of the handle. An example of a double-handed handle is disclosed in U.S. Pat. No. 5,211,669 and includes a composite handle with support-bearing core, preferably wood, but may also be a foam or a shaped honeycomb material. There are some types of hammers that have very large heads, such as sledgehammers, and some sledgehammers can have short handles which may result in a CG location that is relatively close to the head. However, these sledgehammers do not have the smaller diameter striking face that is required by hammers which must have accuracy in striking nail heads without bending the nails or damaging the material into which the nails are being driven. These nails may also be driven in very confined geometries such as tie connectors or certain framing and remodeling applications that would not fit a sledgehammer. Additionally, sledgehammers are not typically swung with the repetitiveness of nail-striking hammers so there had been no reason to consider the relative CG location in striking hammers as compared with the CG location in sledgehammers.
Hammers are also used by many different types of tradespeople and certain handle shapes are more conducive to particular uses. Many framers favor a curved, axe handle shape that puts the extension of the center axis of the grip well behind the head/handle joint. This is extremely useful when hammering nails sideways at your feet with tremendous force, as is common in modern stick building construction. Additionally, a straight handle is preferred for light carpentry, siding installation, finishing applications, and precision work since the centerline of the grip aligns with the head/handle joint or is slightly forward thereof in a third embodiment. Accordingly, there is a problem in the art where a tradesperson needs multiple hammers for each particular job. For example, there are no known hammers that combine an axe handle, straight handle, and precision handle. Conventional axe handles are sometimes called a curved handle or hatchet handle and have a curved section and a straight section, such as described in '201 Patent Application referred to above. However, the straight section is at a position proximate to the hammer head rather than the handle base. Accordingly, the effective length of the handle is shortened because the user is required to grip the straight section closer to the head, and the hammer becomes less efficient. Since a conventional handle is mostly straight and then curves down into the axe shape, the curved part can hit the wall that the user is nailing. Given this problem, there is also need in the art for a single hammer that has multiple gripping sections with different angles relative to longitudinal axis of the handle, capable of being effectively used for different jobs.
Known hammers also have improved striking faces, including malleable striking faces that partially deform when striking a surface. In fact, in the early days of copper and bronze tools all hammers had malleable striking faces. Only with hardened steel striking faces have traditional hammers moved away from malleable striking faces. But even with the advance of technology, malleable striking faces still have a place in the hammer repertoire. However, these malleable striking faces are not typically used to absorb shock but instead are used to prevent a sparking oxidation reaction when the hammer is used in environments where sparks could prove dangerous. Additionally, many deformable materials used in striking faces, like silicon bronze and aluminum bronze are slippery enough that they are also used as a bearing material in other inventions.
Accordingly, these deformable materials are not typically used as a solution to preventing nails from slipping off the striking face of a hammer head primarily because a malleable surface works best in a very narrow range of parameters, namely a very hard blow substantially in line with the axis of the nail. For impacts that fall within this range of parameters the striking surface material deforms and prevents the hammer from slipping off the nail. Additionally, the deformation process keeps the hammer in contact with the nail slightly longer, which delivers more energy to the nail. However, if the blow is at an angle, the slippery material causes the hammer to slide off the nail. For this reason, a machined surface on the striking face, sometimes called a milled face, or a waffle face, is universally more popular for preventing hammer slip. However, these machined faces have some substantial disadvantages as they tend to wear out and become less effective until they eventually have to be replaced. For most hammers, this means replacing the entire hammer or simply using the hammer in an ineffective condition. Additionally, the machining leaves obvious imprints on the wood when a nail is either missed or sunk flush with the wood. Although this may not be a disadvantage in framing hammers since framing wood is typically not exposed, it does limit the applicability of the hammer where the builder must switch hammers when working on materials that might be visible. Accordingly, there exists a desire in the art to have a long lasting, universally applicable malleable striking face that does not leave impact imprints and is capable of keeping the striking face on the nail head longer while overcoming the slipping problem if the hammer is not swung with enough force.
Of course, a higher amount of energy is transferred to the nail if the striking face stays in contact with the nail for a longer period of time during impact. This effect is used successfully in the golf industry with deforming, “spring face” technology on driver faces. Although there is an equivalent idea with a hammer striking face, the different impact forces make applying an appropriate spring face to hammers difficult. For example, nail setting is a much softer blow than nail driving. Similarly, sinking a 16d nail in 2×4 construction lumber in a production setting calls for tremendous force but installing siding with a 10d nail takes a more subtle touch. Another limitation is that the deforming face spring effect only works when the nail is struck very nearly dead center on the striking face as off center hits significantly reduce the effectiveness of a deforming spring face. Accordingly, there is a desire in the art to have a hammer that effectively uses a spring face to promote more efficient transfer of energy between the impact face and nail.
Another aspect commonly seen in hammers are nail pulling features like a claw on the opposite end of the head as the striking face. Additionally, other hammers have nail pull features on the side of the hammer head. However, there is still a desire in the art to have a hammer head with a nail pull feature that offers a significant mechanical advantage over existing hammers. Additionally, there is a desire in the art for a nail pull feature capable of removing longer nails that traditional claws and singular nail pulls have trouble removing.
A hammer having a head connected to a handle that may be grasped and swung by a user to drive a nail, stake or similar fastener and made from a strong and lightweight composite material like polymer reinforced composite fiber, carbon fiber, fiberglass, Kevlar, and aramid weaves. The hammer head has a striking face used for striking the fastener, a claw end opposite the striking face and an end face separating the two. The handle is attached to the head at a position opposite the end face and extends away from the end face of the head to a handle base. Accordingly, the first longitudinal axis of the head extends the head length between the circular striking face and the end of the hammer's claw and is perpendicular to the second longitudinal axis of the handle extending between the base of the handle and the end face of the head. Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
An aspect of the hammer invention is a center of gravity that is proximate to the end face of the head. The center of gravity is separated from the base of the handle by 85%-95% of the total hammer length, measured between the base of the handle and the end face of the head. Because the center of gravity is proximate to the head, the majority of the weight of the hammer is targeted to the striking face which promotes easier use and better striking.
Another aspect of the present invention is a handle weight (WTHA) that is at most 20% of total hammer weight (WTTOT) but is preferably between 10%-20%. Because the weight of the handle is lighter relative to the entire weight of the hammer, the center of gravity is closer to the head. Conversely, traditional hammers have handle weights that makeup greater than 25% of total hammer weight. Accordingly, the heavier handles contribute to greater shock and prevent the center of gravity of the hammer from being within 85%-95% of the total hammer length from the base of the handle while maintaining a comfortable head weight (WTHD) between fourteen ounces (14 oz.≈396 g) and twenty-five ounces (25 oz.≈708 g). The light weight handle is made from a single layer of composite material that may be reinforced with additional composite material layers in areas that experience high stress when the hammer is swung and impacts a surface. Additionally, these composite layers are formed around an internal core that is preferably made of foam. However, the core itself is does not provide any strength or structural support once the composite is hardened, thus the internal core may be hollow or made from some other non-structural material.
Another aspect of the present invention is a handle having an inflection point proximate to the base of the handle to provide multiple gripping sections. In effect, the inflection point allows a user to grip the handle in different locations and at different gripping angles that move relative to the longitudinal axis of the hammer. The inflection point is intended to be within 5 diameters of the striking face from the base of the handle. Accordingly, the multiple gripping positions and axes are proximate to the base of the handle. Thus, the user does not necessarily need to grip the handle at a position significantly closer to the head, and thereby sacrifice leverage when accomplishing varying tasks, as seen in the prior art.
Another aspect of the invention is the interface between the mounting end of the handle and the head. In the preferred embodiment, the head and handle are attached through the set screw and the reinforcing block. The set screw extends through a threaded hole in the front plate of the head and embeds in at least a portion of the front side of the composite handle's mounting end. Additionally, the reinforcing block is held within the mounting end of the handle and provides support to the thin carbon fiber layer into which the set screw compresses.
Another aspect of the head of the present invention is a double nail-pull made up of a pair of notches on opposite sidewalls of the head, slightly offset from the side of the handle. The first notch engages the head of the nail and a user may rotate a portion of the nail of out the wall, board or similar surface to first position. Subsequently, the head of the hammer can be repositioned into a second position where the second notch engages the head of the nail and the first notch engages the shank of the nail. Accordingly, the hammer can again be rotated about the nail-pull and the nail can be completely pulled out of the wall, board or similar surface. This is particularly useful for fully removing the long nails typically used in framing at high levels of mechanical advantage.
Another aspect of the head of the present invention is a malleable striking face imbedded with the grit materials. This striking face is made up of a plug made from a deformable metal into which hard particles are embedded. In operation, when the striking face hits a fastener, like the head of a nail, with sufficient force the striking face will deform around the struck surface and thereby prevent the striking face from sliding off. Additionally, repeated impacts on the deformable material kneads the surface of the striking face, burying some of the hard particles and exposing others which provide a textured striking face that further prevents nail slide.
The present invention will become more fully understood from the detailed description and the accompanying drawings. The drawings constitute a part of this specification and include exemplary embodiments of the invention, which may be embodied in various forms. It is to be understood that in some instances, various aspects of the invention may be shown exaggerated or enlarged to facilitate an understanding of the invention; therefore the drawings are not necessarily to scale. In addition, in the embodiments depicted herein, like reference numerals in the various drawings refer to identical or near identical structural elements.
The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
As illustrated in
The head 12 is connected to the handle 14 at a side opposite the end face 48 through the head void 94 and in the preferred embodiment houses at least a portion of the handles mounting end 74a as shown in
An aspect of the hammer 10 invention is a center of gravity (CG) 18 that is proximate to the end face 46a of the head 12. The CG is located away from the base 56 of the handle 14 by a distance that is 85%-95% of the total hammer length 20 (LTot), measured between the base of the handle and the end face of the head. Because the CG is proximate to the head, the majority of the weight of the hammer is targeted to the striking face 16 which promotes easier use and better striking. The inventive hammer's CG is closer to the head than previously considered by or possible in the prior art, and by positioning the hammer's CG even closer to the head and further away from the base of the handle, the inventive hammer reduces the amount of shock delivered down the entire handle, ultimately reducing the chance of injury to the user.
As shown in
Another aspect of the present invention is a handle weight (WtHa) that is less than 20% of total hammer weight (WtTot), preferably between 10%-20%. Because the weight of the handle is lighter relative to the entire weight of the hammer, the center of gravity 18 is closer to the head 12. Conversely, traditional hammers have handle weights that makeup greater than 25% of total hammer weight. These heavier handles contribute to greater shock and prevent the center of gravity of the hammer from being located as close to the head as in the present invention while maintaining a comfortable head weight (WtHd) between fourteen (14 oz.≈396 g) and twenty-five ounces (25 oz.≈708 g). Examples of prior art hammers and their centers of gravity can be seen in
In the present invention, the effective weight of the handle is further reduced where the heaviest part of the handle is held within the head when mounted. Accordingly, the center of gravity 18 of the entire hammer 10 is moved closer to the head 12. The lightweight handle is made from layers of composite material 26, including the internal layer or layers 26a, that preferably extend the entire length of the handle, the external layer or layers 26b that also extend the entire length of the handle, with reinforcing in intermediate layers 26c in areas that experience high stress when the hammer is swung and impacted. Additionally, these composite layers are formed around a non-structural internal core 32 that is preferably made of foam 32a. However, the core itself does not provide any strength or structural support once the composite is hardened, thus the internal core 32 may be hollow 32b or made from some other non-structural material. Conversely, internal cores described in the prior art are designed to provide structural support, such as the support-bearing core disclosed in U.S. Pat. No. 5,211,669. In the present handle, the internal core is not a support-bearing core, providing insufficient tensile strength or impact strength to serve as a hammer handle without the composite layers surrounding the core. Accordingly, in the handle of the present invention, the handle support is produced by the multiple composite layers and not by the core. Accordingly, the handle 14 is designed to maximize strength and stiffness while reducing mass. The carbon fiber and Kevlar layers, and possibly alternative layers such as fiberglass, are the only structural components and are designed to provide adequate strength during use so that other materials such as aluminum, metal, plastic, titanium or wood are not needed.
Another aspect of the present invention is an inflection point 24 in the handle 14 proximate to the base 56 of the handle to provide multiple gripping sections 96. In effect, the inflection point 24 allows a user to grip the handle in different locations and at different gripping angles 98 that rotate relative to the longitudinal axis 50 of the hammer as shown in
In addition to the light weight handle, the head 12 includes a number of inventive features. The preferred head uses a welded box construction with a head void 94 and has replaceable striking faces 16 that attach to a set screw 36a which also holds the handle 14 onto the head 12 as described below in the preferred embodiment. Both the handle and striking face can be easily replaced in the field with common tools and a variety of striking faces can be attached to the hammer head for different building applications. For example, a textured face can be used for framing and heavy construction, a smooth face can be used for lighter, finish carpentry, while a plastic face can be used for non-marring or non-sparking applications. Additionally, the head has a traditional rip claw 86 for pulling nails and prying boards, but also features a double nail-pull 38 with two notches 76a, 76b on opposite sidewalls 78 for high-leverage nail pulling.
As generally explained above, in the present invention, the hammer's CG 18 is very close to the end face 46a of the head 12 and may actually be within the head section. In particular, the CG is located away from the base of the handle 56 by approximately 85%-95% of the total hammer length 20. To shift the CG closer to the head 12, it is an aspect of the present invention to have a hammer handle 14 significantly lighter than the prior art such that the handle itself is between 10%-20% of the total hammer weight. Additionally, the ratio between the head weight and handle weight of the present invention is greater than the highest ratio found in the prior art. Table I below and
For the data in Table I above, the total weight of the hammers were measured on a single scale and are displayed in grams. In regards to the head weight, some of the prior art hammers did not have removable heads and were made of materials that did not easily facilitate the removal the head of the hammer from the handle. Accordingly, the head weights are followed by an “A” indicating that manufacturer's advertised head weight was used. For example, the Husky 21 hickory handle has an advertised head weight of twenty-one ounces (21 oz.≈595 g), as indicated in Table I above. Conversely, heads easily separable from the handle were individually weighed and indicated in Table I with an “M.” Additionally, the “A*” indicates the DeWalt 20 steel hammer having an advertised head weight of twenty ounces (20 oz.≈567 g) but an estimated head weight of fourteen ounces (14 oz.≈400 g). This estimate is based on DeWalt's advertised claim that this hammer is an “Optimal Weight Distribution” hammer which is defined in Black & Decker's U.S. Pat. No. 8,534,643 as a weight distribution spread almost equally between the head and the handle of the hammer. Accordingly, the estimated head weight of 400 grams gives a weight distribution between the head weight and handle weight of approximately 1:1, matching the optimal weight distribution as advertised and indicated with “A*”. Subsequently, the handle weight was calculated by subtracting the head weight from the total weight and the hammer length was measured from the top face of the head to the base of the handle in centimeters. Lastly, the location of the CG for each hammer was determined and is reflected in Table I as a percentage of the entire length measured from the base of the handle.
As illustrated in
To have a center of gravity proximate to the head, the weight of the handle is reduced to 10%-20% of the total weight of the hammer. Accordingly, the head weighs substantially more than the handle, and the CG consequently is shifted closer to the head and further away from the handle base. Hammers of the type documented in Table I have a total weight under 1.5 kg, with most being between 0.75 kg and 1.0 kg, with the present invention having a total hammer weight under 0.75 kg due to the lightweight handle. According to the present invention, the handle weight may vary between 0.075 kg and 0.15 kg depending on the length of the handle and the types of materials that are used. In comparison, the handles of the prior art hammers are all over 0.2 kg, with most handles weighing between 0.3 kg and 0.5 kg. Accordingly, the handle of the present invention is not only substantially lighter than the prior art handles, it contributes a smaller percentage to the overall weight of the hammer and ultimately results in an overall lighter hammer with the same head weight as the prior art hammers.
As explained above and shown in
As documented in Table II below, the handle weight of the present invention is below 20% of the total weight of the handle. This relative weight of the handle to the total weight of the hammer is plotted relative to the total length of the hammer in
While the total weight of the inventive hammer is comparable to the prior art hammer weights, inasmuch as they are all significantly less than the weight of sledgehammers and are typically more than a specialty lightweight tacking hammers, the lightweight handle of the present invention clearly results in a hammer with a weight that heretofore has not been achieved or even considered. According to the present invention, the total hammer weight is lighter than the prior art hammers by a measure that is equal to the differential in the weights of the handles as shown in Table I and illustrated in
Additionally, it is another aspect of the present invention to have a head weight to handle weight ratio above 3:1. As evident from Table II above, prior art hammers have a head to handle weight ratio that is less than 3:1, with most prior art hammers having a ratio between 1 and 2. Conversely, embodiments of the present invention have a head to handle weight ratio that is greater than 4:1. Accordingly, it is another aspect of the present invention to have a ratio of head weight to handle weight that is above 4:1 while maintaining the preferred length between 35 and 47 centimeters and a total weight between 600 and 1200 grams as plotted in
Another aspect of the present invention is an apparent handle weight less than 10% of the total hammer weight when the hammer is measured in the fully assembled configuration. The apparent weight of the head and handle of the hammer has a significant effect on the performance and comfort of the tool for the worker. The apparent weight is measured by placing the head of the hammer on a first scale and the base of the handle on a second scale. The head is positioned on one scale such that the head rests on the edge of the striking face proximate to the handle and the base of the handle rests on the second scale that is separated from the head scale by the length of the hammer. Accordingly, the weight reading shown on the scale under the head is the apparent head weight and the weight reading shown on the scale under the handle is the apparent handle weight. In some embodiments, the apparent handle weight can actually be 0% of the total weight such as when the hammer CG is so far towards the opposite end of the base that it is not only located within the head, it is located within the lateral projection of the striking face (i.e. within the diameter extending perpendicular to the striking face sitting on one scale—along the axis of the head) so that the hammer can actually balance on the striking face. Hammers with lighter apparent handle weights have less impact shock and the weight distribution of the present invention results in apparent weights of head and handle that are significantly different than any hammer in the prior art, as described in Table III below.
Additionally, the apparent head weight and handle weight further illustrate how the weight of the present invention is targeted towards the head of the hammer. As shown in
Another aspect of the handle of the present invention is the proximity of the inflection point 24 to the handle's base 56 on the handle's front side 64 that faces the striking surface 16. The inflection point 24 is situated between a concave shape 66 closest to the base and a convex shape 68 as shown in
The variations in the concave shape 66 and convex shape 68 relative to the curvature on the handle's backside 100 result in different gripping axes 98 relative to the overall longitudinal axis 50 of the handle. Accordingly, the variations in the gripping axes 98 in different sections of the handle provide for different gripping positions 96 in these handle sections. As shown
As shown in
Accordingly, the inflection point 24 provides three separate and unique gripping sections 96 that allow a user to complete multiple jobs, including framing work and finishing work, without necessarily switching hammers. Additionally, the inflection point allows a user to effectively and ergonomically use the hammer 10 in multiple positions without sacrificing leverage since all three gripping sections 96 are proximate to the base of the handle 56. Yet, the relatively straight overall profile of the entire handle 14 does not interfere with the work surface compared to the axe handles seen in the prior art. When gripped with the middle two fingers at the inflection point, the natural gripping axis is rotated towards the striking face relative to the longitudinal axis of the handle which can be seen in
Another aspect of the handle are the multiple composite layers that collectively form the handle 14 as shown in
The carbon fiber layers of the handle 14 provide increased stiffness which increases the handle's natural frequency of vibration. Some conventional hammer handles are more flexible and have low vibration frequencies that can cause tendon problems. In comparison, the higher vibration frequencies of the stiffer carbon fiber handle, without any titanium spar or other plate along the length of the handle, are much more effectively absorbed by the skin and flesh of the worker's hand. Another benefit of the handle's increased stiffness is that the user perceives the hammer as more effective and accurate, which increases the user's confidence in the tool. Additionally, because impacts with the present invention have so little shock on the user's hand, the user is naturally encouraged to swing the tool harder. Conversely, conventional hammers with conventional weight distribution discourage forceful swings as the user subconsciously protects their hand from extreme shock. Additionally, carbon fiber handles do not have the failure modes associated with fatigue as found in wood, aluminum, titanium, and steel handles. For example, hammers with steel handles are subject to “pinging” caused by stress fractures within the structure of the handle.
At impact, as depicted in
The intermediate composite layers 26c of carbon fiber are positioned around the inner layer 26a proximate to head 12 of the hammer which then extends a length 72 towards the base 56. However, the length 72 of the intermediate layer 26c is shorter than the handle length 54. Accordingly, it is an aspect of the intermediate layers 26c to only extend across parts of the handle 14 that experience high stress when the hammer is swung and impacted. For example and as discussed in the hump design 102 above, the backside 100 of the handle directly below the head may have multiple layers of composite material as this is a point of high stress, as shown in
It is another aspect of the handle of the present invention to have an external layer 26b that covers the inner layer 26a and extends the entire length of the handle 54. Accordingly, the intermediate layers 26c are sandwiched between the inner layer 26a and external layer 26b as depicted in
In another aspect of the preferred embodiment of the present invention, the internal core 32 is made up of a foam core 32a and a reinforcing block 34 embedded within the layers of composite at the mounting end 74 of the handle 14. Examples of the internal core 32 and reinforcing block 34 can be seen in
As described above, the composite layers are formed around the internal core 32. However, once the composite layers have been set, the internal core does not provide structural support or strength. To protect the composite shell at the base of the handle, a protective plug 106 made from resin, plastic, rubber or similar material is inserted inside the shell connected to the core 32 and is held in place by the composite layers once they have cured. Additionally, the plug has a vent hole 108 for expanding foam. In the preferred embodiment the foam core 32a extends from the plug 106 at the base 56 of the handle to the reinforcing block 34 held within the mounting end 74 of the handle attached to the head 12. Accordingly, the composite layers may be formed around the foam core 32a, reinforcing block 34, and plug 106 which together form the internal core in the preferred embodiment. In another embodiment, the foam core may not be used at all and the internal core 32 can be comprised of a protective plug 106, a hollow core 32b and the reinforcing block 34. Regardless of the embodiment, when the reinforcing block is used at least one of the foam core, hollow core, or other core material extends from the reinforcing block to the protective plug at the base of the handle. Accordingly, it is an aspect of the core to be lightweight and only provide shape to the composite layers as they are being laid and formed, which is described below.
In another aspect of the preferred hammer, the reinforcing block is held within the internal core 32 at a position opposite the base, which defines the mounting end 74. At least a portion of the mounting end 74a of the handle is inserted into the head void 94 substantially perpendicular to the end face 46a of the head, as shown in
In another embodiment the handle 14 does not have the reinforcing block 34 and the set screw 36a extends through the front side 64 of the handles 14 mounting end 74 and compresses into the composite layers of the backside 100 or extends completely through a hole 114b on the back side of the handle 100, as shown in
In another embodiment, the handle 14 is mounted to the head 12 by securing the head within the handle with an adhesive 36f. As is traditionally done with polycarbonate and other plastic handles, an epoxy or glue may be used. Although inexpensive, using an adhesive 36f to attach the head to the handle makes the handle difficult to replace. Accordingly, the preferred adhesive is an epoxy resin that can be baked out by a user allowing the handle or head to be subsequently replaced. Additionally, an adhesive can also be used in combination with the other embodiments shown in
In the embodiment depicted in
In another embodiment, the handle is mounted to the head by two opposing wedge fasteners 36c that lock the handle into the head void 94, which can be seen in
In the embodiment depicted in
In another embodiment, the handle is attached to the head using a wedging system, shown in
In addition to the light weight handle in the preferred embodiment the hammer 10 has a number of new usability features while maximizing strength and durability. The striking face 16 is field replaceable simply by screwing a new striking face onto the head 12. This way, the same hammer can be used for both framing and finish applications. In the preferred embodiment, the striking face 16 is secured to the head by the end of the set screw 36a opposite that attaching the head and handle. The front plate 110 of the head consists of the hole 110 through which the set screw passes 36a, shown in
Additionally, the front plate 110 consists of an overstrike portion 126 extending below the head 12 along the front side of the handle 64. The overstrike portion 126 is no greater than one striking face diameter 60 away from the longitudinal axis of the head 42. Additionally, the overstrike portion 126 is wide enough to protect the composite handle from damage resulting from miss hits. In the preferred embodiment, the overstrike portion 126 is an extension of the front plate 110 towards the base of the handle 56. However, in another embodiment the overstrike portion may be a protective metal plate embedded under the external layer of composite material on the handle. Regardless of the embodiment, the overstrike portion is designed to protect the composite handle proximate to the head of the hammer.
An aspect of the striking face shown in
In operation, when the malleable striking surface 88a hits a fastener, like the head of a nail 80, with sufficient force the striking face will deform around the struck surface and thereby prevent the striking face from sliding off. Additionally, the repeated nail impacts on the deformable material knead the surface of the striking face 88a, burying some of the grit 90a particles and exposing others. After multiple strikes, the malleable material may mushroom over the edges of the steel striking face 88a, but hammering the mushroomed material on the side of the striking face will fold the deformable material back onto the striking surface 88a. Additionally, as a user is unlikely to strike a nail at the same position on the striking face each swing, the malleable striking surface 88a remains reasonably flat causing neither miss-hits nor flush setting blows to leave unsightly imprints on the surface the user is striking. Additionally, if the hammer is not swung with enough force to deform the malleable material, the embedded grit 90a provides a textured surface to prevent slipping. In addition to lighter blows, the malleable surface may deform if the hammer is swung at an angle and the striking face does not have a flush impact with the nail head or other surface being struck.
In another embodiment, shown in
Another aspect of the head of the present invention is a double nail-pull 38 made up of a pair of notches 76a,76b on opposite sidewalls 78a,78b of the head, slightly off-center from the side of the handle which can be seen in
Another aspect of the head of the present invention is a magnet insert 40 affixed within at least one of the side walls 78 of the head, as shown in
During the preferred method of manufacturing of the handle, the reinforcing block 34 is machined to the desired dimensions. Though the design can vary, all reinforcing blocks have dimensions matching the mounting end of the handle and receiving feature on the head. Additionally, the reinforcing block is machined to compensate precisely for the thickness of the composite fiber layers. The blocks are machined at 90 degrees to ensure that the finished head is properly aligned with the handle. Also, the undercut section 104 is machined for set screw contact. Next, a foam handle blank is cast and the reinforcing block 34 and protective plug 106 are placed at opposite end of a female mold made from a master handle. A two-part expanding foam is poured into the mold and allowed to expand until the foam expands to the proper shape and bonds to the reinforcing block and protective plug.
Once the foam has expanded and bonded to the reinforcing block the internal core 32 is complete and removed from the mold where it is covered with the inner composite layer 26a, extending the entire length of the internal core. The inner composite layer is wetted with epoxy and the intermediate composite layer 26c is laid over the inner layer first—but this section only extends from the reinforcing block 34 to the top of the precision gripping section. As discussed above, the intermediate layer extends from the head side of the internal core towards the base. In the preferred embodiment the intermediate layer is approximately eight inches (20 cm) long. Another intermediate layer is laid which is approximately fourteen inches (36 cm) long and reaches just to the neutral section of the handle, proximate to the inflection point. Then, another intermediate layer 26c is laid which is approximately fifteen inches (38 cm) long. However, the number and length of the intermediate layers may be altered to change the stiffness and natural flex points of the handle. Finally, the full length external layer 26b of Kevlar is laid on the handle. Each new layer of composite is wetted with epoxy and the excess is wiped off.
Once all the layers have been formed, the handle 14 assembly is inserted into a specially treated heat shrink tubing. A heat gun or oven is then used to shrink the tubing to compress the layers of composite material and epoxy while the handle cures. After 24 hours, the shrink wrap is removed from the handle, and the excess carbon composite layers are cut from both ends with a diamond saw. The grip end of the handle proximate the base 56 is dipped in a low durometer rubber or a shrinkable rubber section is applied to the outside of the grip end to provide a tacky, satisfying grip.
A second embodiment of the handle manufacture is to use no internal structure at all. By using a two piece mold and an inflatable bladder, layers of composite are wrapped around the inflatable bladder. The bladder and carbon are then inserted into a hard-shell female mold. The bladder is then inflated, compressing the carbon and Kevlar layers against the outside of the mold until the polymer has cured sufficiently.
The head 12, shown in
In the preferred embodiment, the head is made from several individual pieces of flat metal stock like high carbon steel, stainless steel or similar materials. These pieces are cut from a single sheet of metal using a plasma cutter and template, a CNC plasma cutter or water jet and a nut with a female internal thread or other threaded fastener is welded to the front flat plate 110 of the head proximate to the striking face 16. In the preferred embodiment, the internal threaded nut 112 is M16×2 mm, but it should be appreciated that other sized threads can be used. Additionally, for a front plate with sufficient thickness, the front hole 114a can be threaded. Then the end plate 46 is bent over a precision form to match the curve of the side walls 78. The head is then welded together using a TIG welding process and depending on application, the TIG filler rod may be silicon bronze or a metal rod that matches the chemistry of the flat plates more precisely. Lastly, the M16 female threaded screw nut 112 is welded to the front of the front plate 110 which receives the set screw when the head is attached to the handle. This piece can be a conventional nut, a round bar with a drilled hole that is threaded or any other threaded fastener. In another embodiment, the head could be manufactured by creating a male and female die set. The metal plates would be then cut out, but left attached with additional margin to accommodate the bend. This blank would then be bent by a male and female die that forms the near-final head shape.
A final grinding operation removes excess weld material from the sides and sharpens the claw. The fully assembled heads are then heat treated to ensure that the metal has the ideal physical characteristics of hardness and pliability. Finally, the heat treated heads are tumbled in a vibratory tumbler with ceramic media to give the piece a pleasing, consistent finish. The heat treated heads may also be surface ground, wire brushed or finished with an abrasive pad. Subsequently, the entire hammer is ready to be assembled and a handle is inserted into the head and the set screw is tightened onto the handle. Lastly, a striking face is then tightened onto the exposed section of the set screw.
The embodiments were chosen and described to best explain the principles of the invention and its practical application to persons who are skilled in the art. As various modifications could be made to the exemplary embodiments, as described above with reference to the corresponding illustrations, without departing from the scope of the invention, it is intended that all matter contained in the foregoing description and shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.
This application claims priority to U.S. Provisional Patent Application Ser. No. 62/304,223 filed on Mar. 6, 2016, which is hereby incorporated by reference.
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| Number | Date | Country | |
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| 62304223 | Mar 2016 | US |
