GB2053771A

GB2053771A - Handle for percussive tools with vibration damping means

Info

Publication number: GB2053771A
Application number: GB8021318A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-07-11
Filing date: 1980-06-30
Publication date: 1981-02-11
Also published as: DE3025997A1; FR2460760A1; AU6015780A; JPS5621791A

Abstract

The shank of a hammer is made of a multiplicity of vertebra members 20 that are assembled into a column. Aligned passages 30, 34 in the vertebra members provide three elongated passages in one embodiment that extend from the handle 22 to the head 12. Pultruded shafts 38 extend through two of these passages and are fixedly connected at each end to the head and the handle. The third passage 30, which is spaced toward the impact surface of the head from the other two passages, has a shaft 36 of spring-tempered tool steel extending through it that is fixedly connected to the head but slidably received in the handle. This arrangement provides a flexible shank that damps the shock produced on impact. However, the flexibility is only afforded in one direction so as not to interfere with the use of the claw portion of the head. Alternate embodiments have different numbers of shafts, and one is flexible in both directions. <IMAGE>

Description

SPECIFICATION handle for percussive tools with vibration damping means The present invention relates to the field of hand impact tools. The most common example of this type of tool is the hammer. Although it is a relatively simple instrument, the hammer has been continually improved, and the standard wood-shanked, steel-headed hammer has long since lost dominance to improved versions.

The improvements in the hammer have been directed to various aspects, the most obvious, of course, being the connection of the head to the shank. I However, there is another area in which room for improvement exists. This is in the amount of shock transmitted by the hammer to the hand. The shock transmitted to the hand as a result of occasional, irregular use is not ordinarily a matter of great concern to the user, it does affect his comfort to an extent. On the other hand, one who uses the hammer for extended intervals on a day-to-day basis may consider reductions in transmitted shock to be quite important.

Accordingly, the minimization of this transfer of energy from the impact head to the hand is desirable.

It has been found that the type of shank that the hammer has can make a great difference in the amount of shock experienced by the user; it can be expected, for instance, that a steel-handled hammer will afford a substantial reduction in shock over the wood-handled version. Furthermore, there are fiberglass-handled hammers in existence in which the shock is reduced in many cases from steel-handled hammers of the same size.

It is the object of the present invention to further reduce the shock transmitted to the user of a hand impact tool. It is a further object to afford this reduction through the use of a handle that is flexible but can be adapted to provided a proper lever arm if necessary for the use of a claw portion on a hammer head.

A hand impact tool according to the invention includes an elongated spine assembly. The spine assembly has a multiplicity of vertebra members assembled to provide an elongated column, and each of the vertebra members has a passage extending through it longitudinally of the column to provide an elongated passage through the column. A resiliently deflectable shaft extends through the elongated passage and beyond at least one end of the column of vertebra members. The spine assembly also has means spaced from the shaft for preventing relative rotation among the vertebra members about the shaft. An impact tool head is fixedly connected to the one end of the resiliently deflectable shaft, the impact tool head thereby being biased to a quiescent position relative to the end of the column of vertebra members remote from the head.The head is nonetheless permitted upon deflection of the shaft to undergo a change in position relative to the remote end of the column vertebra members.

Each of the vertebra members may include a second passage extending longitudinally through it.

Together, these provide a second elongated passage through the column. The means for preventing rotation may include a second deflectable shaft extending through the second elongated passage. The second shaft prevents relative rotation between the vertebra members about the first shaft. The second shaft is preferably resiliently deflectable and fixedly connected to the impact tool head, and it could conveniently be polygonal in cross section.

In the preferred embodiment, the first-mentioned shaft is a shug fit in the first elongated passage.

The first shaft typically extends through the other end of the column of vertebra members, and the hand impact tool further includes a handle member fixedly connected to the end of the first shaft remote from the impact tool head. The second shaft is fixedly connected either to the hand or the impact-tool head and is slidably received in the other. Rotation of the vertebra members relative to the handle is thereby prevented while motion of the head relative to the handle is permitted. In the preferred embodiment, the second shaft is fixedly connected to the impact-tool head and is slidably received in the handle.

In accordance with another aspect of the invention, the hand impact tool includes the impact-tool head which has first and second ends. The elongated first shaft has an end fixedly connected to the impact-tool head intermediate its ends and is resiliently deflectable but substantially unexpandable longitudinally. The handle is fixedly connected to the end of the shaft remote from the head, the shaft thereby biasing the impact-tool head to a quiescent position relative to the handle. A brace means extends, when the head is in the quiescent position, between the handle and the head to engage the handle and to engage the head between the shaft and the first end but permit motion away from the handle of the part of the head engaged by the brace means.The brace means is substantially incompressible and thereby prevents motion from the quiescent position toward the handle of the part of the head engaged by the brace means. The shaft and the brace means thereby cooperate to permit the head to be tilted from the quiescent position in the direction of the second end of the head but prevent it from being tilted from the quiescent position in the direction of the first end of the head.

The brace means may conveniently include the multiplicity of vertebra members assembled to provide the elongated column of substantially incompressible vertebra members. The column thereby includes first and second end vertebra members on the ends of the column. Each of the vertebra members has a passage extending through it longitudinally of the column to provide an elongated passage through the column. The shaft portion extends through the elongated passage. The first end vertebra member abuts the handle and the second end vertebra member, when the head portion is in the quiescent position, abuts the head at least between the shaft and the first end of the head to thereby provide the engagement of the head by the brace means.The second shaft inn the preferred embodiment consists essentially of spring-tempered tool steel, and there are two first shafts spaced apart in the direction substantially perpendicular to an imaginary line extending between the ends of the head.

The teachings of the present invention may be employed in a hand impact tool that has the impact-tool head with the first and second ends, the handle, the elongated deflectable first shaft with one end fixedly connected to the impact-tool head intermediate its ends and the other end fixedly connected to the handle, the elongated deflectable second shaft extending from the handle to the impact-tool head between the first shaft and the first end of the head and being slidably received in either one or both of the handle and the head, and the multiplicity of vertebra members assembled to provide an elongaged column extending from the head to the handle with each of the vertebra members having first and second passages extending through it longitudinally of the column to provide elongated first and second passage% respectively, through which the first and second shafts extend, and in which hand impact tool at least one of the first shaft and the second shaft is resiliently deflectable.

These and further features and advantages of the present invention are described in connection with the attached drawings, in which; Figure 1 is a vertical elevation, partially in section, of a hammer exhibiting the teachings of the present invention; Figure 2 is an exploded view showing parts of an exemplary spine assembly that follows the teachings of the present invention; Figure 3 is a cross-sectional view taken at line 3-3 of Figure 1; Figure 4 is a cross-sectional view taken at line 4-4 of Figure 1; Figure 5 is a vertical elevation of a handle of another embodiment of the present invention; Figure 6 is a plan view of the handle in Figure 5; Figures 7, 8, and 9 are plan views of alternative embodiments of vertebra members.

Figure 10 is a side elevation of the vertebra member shown in Figure 9; A claw hammer that follows the teachings of the present invention is shown in Figure 1. It has a largely conventional head 12 with the usual impact surface 10 at one end and a claw portion 14 at the other end. As is also conventional, a shank portion 18 is provided between the ends to connect the head to a handle 22.

However, the shank portion 18 of the hammer differs markedly from prior-art devices in that it is provided by a spine assembly that is flexible to reduce shock transmission. It nonetheless permits proper use of the claw portion of the head.

According to an embodiment of the present invention, shank 18 includes multiplicity of vertebra members 18 that are assembled to form a colum extending from handle 22 to head 12. The construction of the spinal assembly is illustrated in Figure 2, in which two vertebra members 20 are shown, one being assembled on shafts 36 and 38. vertebra members 20 are substantially incompressible and are typically molded from any of a number of tough plastics such as polyamides, polycarbonates, polyacetals, polyethylene, polypropylene, or acrylonitrile/butadienelstyrene terpolymers. Specifically, satisfactory results have been achieved with vertebra molded members molded from 20% glass-filled polyamide resin. As Figure 2 shows, several openings are formed in each vertebra member 20.Irregularly shaped holes 32 serve no particular function in the finished product but would typically be provided to afford the relatively uniform thickness in the molded product that those skilled in the art of molding will recognize to be desirable. A pasage 30 of square cross section is provided toward the side of the vertebra member closest to impact surface 10. Two further passages 34 are provided toward the claw side of the vertebra member, and when the vertebra members are assembled, these passages are aligned to provide three elongated passages.

As Figure 2 shows, shaft 36 extends through the elongated passage formed by individual passages 30, while shafts 38 extend through the elongated passages provided by individual passages 34. Shafts 38 are preferably pultruded members of glass, carbon, or boron fibers in a suitable resin such as polyester, epoxy, or silicone and would accordingly resemble the material used in modern fishing rods. Shafts made of continuous glass fibers in polyester resin have proved to be quite workable. Shaft 36 in the preferred embodiment is made of spring-tempered tool steel. It will be appreciated that all three shafts are resiliently deflectable.

The connection of the head and the handle to the spine assembly 18 can be understood by reference to Figures 3 and 4 in conjunction with Figures 1 and 2. Figure 3 is a cross section taken at line 3through a fiberglass insert 17 that meets and an end vertebra member 20 but has the cross-sectional shape seen in Figure 3. The pultruded shafts 38 are bonded into recesses in insert 17. Shaft 36 is bonded in another recess.

Although not seen in the drawings, shaft 36 would typically be knurled at that end to enhance the effectiveness of the bonding.

Handle 22 is seen in Figures 1 and 4 to have a relatively conventional shape, but it is provided with recesses 24 and 26 (Figure 1) to receive shafts 36 and 38. Although all three shafts are received in handle 22, only shafts 38 are bonded to it. Shaft 36 is only slidably received in handle 22. In fact, it may be desired to lubricate recess 36 to enhance the freedom of motion of shaft 36 within the handle.

As seen in Figure 1, a space 28 is left at the end of recess 26 to receive excess bonding medium.

In operation, the impact surface 10 strikes the nail or other target in the normal manner. However, the resiliently deflectable shafts 36 and 38 of the spine assembly permit motion of head 12 relative to handle 22.

In moving, head 12 is tilted to the position shown by reference numeral 16. In this position, one end of head 12 has moved slightly away from handle 22 while the other end has moved toward it. If shaft 36 were fixedly connected to the handle, such tilting would not be permitted; although they are deflectable, none of the shafts is significantly compressible or expandable longitudinally. However, as was indicated above, shaft 36 is only slidably received in handle 22, so it slides relative to handle 22 upon impact and permits the tilting motion suggested by reference numeral 16.

Although it is not certain by what mechanism the arrangement described in Figures 1 through 4 reduces vibration, it is fairly clear that some initial shock is avoided due to the flexing of spine assembly 18. This energy, of course, is stored to an extend in resiliently deflectable shafts 36 and 38, but it is thought that the motion required of vertebra members 20 relative to each other probably accounts for the dissipation of some energy. Furthermore, it is noted that the shafts fit relatively snugly in the vertebra members 20, and some inelastic bending is probably experienced at the interface of the shaft and the vertebra member as the vertebra member is being deflected. Finally, there is some relative motion between shaft 36 and the vertebra members, which may contribute to frictional losses. Most probably, the damping effect is afforded by a combination of these factors.

Whatever the reason for the damping effect may be, tests have shown that the shock experienced by users of the present invention is significantly less than that received by users of prior-art hammers. Tests have been conducted in which hammers similar to that shown in Figures 1 through 4 were compared with wood-, steel-, and fiberglass-handled hammers. In one test a 16-ounce hammer of each type was placed in a pendulum with an accelerometer attached to its handle, and the accelerometer recorded the amount of shock experienced at the handle end. The same test was repeated with 22 ounce hammers. The test results are listed below: Present Fiberglass Invention Handle Steel Handle Wood Handle Impact No.Shock (G's) Shock (G's) Shock (G's) Shock (G's) 1 8 18 22 49 2 10 18 20 45 3 10 17 23 45 4 8 17 23 45 5 9 18 25 40 6 9 18 28 50 7 9 17 20 55 8 11 17 23 45 9 7 17 21 54 10 7 17 23 56 Average 8.8 G's 17.4 G's 22.8 G's 48.4 g's Present Fiberglass Invention Handle Steel Handle Wood Handle Impact No. Shock (G's) Shock (G's) Shock (G's) Shock (G's) 1 25 35 57 72 2 27 30 57 69 3 25 32 50 68 4 20 31 50 71 5 19 30 53 70 6 19 33 54 71 7 20 31 65 72 8 20 30 68 69 9 20 32 57 68 10 21 31 69 67 Average 21.6 G's 31.5 G's 58.0 G's 69.7 G's It is clear from these results that a marked reduction in shock is afforded by hammers that incorporate the teachings of the present invention.

Despite the flexibility of the spinal assembly of the present invention, claw portion 14 of head 12 can still be used in the normal manner. This is because the column of vertebra members acts as a brace to prevent tilting of the head in the direction of impact surface 10. Head 12 is allowed to tilt in the direction of the claw-the front end of the hammer is allowed to move away from the handle-because shaft 36 is only slidably received in handle 22. But the column of vertebra members, which are made of a substantially incompressible material, prevents the head from moving to any great degree toward the handle. Shafts 36, which are fixedly connected to both handle 22 and head 12, prevent the side of the head toward claw 14from moving away from handle 22.Accordingly, head portion 12 is prevented from tilting forward, and claw portion 14 may therefore be employed in the normal manner.

Although the teachings of the present invention have so far been illustrated by reference to an exemplary embodiment that has been tested and found to afford the significant advantages outlined above, it will be apparent to those skilled in the art that these teachings can be adapted to different situations and still afford many of the advantages-described above. In particular, it should be apparent that it is not necessary to provide two shafts that are fixed at both ends. Figures 5 and 6 illustrate a handle portion that suggests another embodiment, in which there is only one shaft fixed at both ends. Recess 26 for the pultruded shaft is illustrated as being deeper than recess 24. This is not required, of course, but it is thought that it would be desirable to have a relatively long bonding surface for-the fixed shaft.

It will also be appreciated that the shape of the vertebra members may be changed considerably, and Figure 7 shows a possible alternative shape. In this arrangement of the hammer, the fixed shaft is square in cross section, as its passage 34 suggests. Figure 7 also shows that the openings 32 can vary in shape, too.

Figure 8 gives a further aiternative, with corresponding reference numerals again referring to corresponding parts.

It should be recalled at this point that the teachings of the present invention are not restricted merely to the typicai claw hammer, or even to hammers in general. It is apparent that any hand impact tool, such as a pick or an ax, can also benefit from the teachings set out here. Furthermore, it is not necessary that the feature of one-way deflection be provided in order to obtain the shock-absorption benefits. As an example, Figures 9 and lOillustrateavertebra memberthatcan be used in aball peen hammerwith impact surfaces on both ends of the head. As in the previous drawings, reference numeral 30 refers to a passage through which a sliding shaft passes, while recess 34 receives the fixed shaft.The hammer that employs this arrangement is intended to be tilted in both directions, and this is achieved by the provision of slightly tapered surfaces 40 on vertebra members 20. With this arrangement, the vertebra members perform most of their normal functions but do not act as a brace. The faces 40 of each vertebra member converge toward either end. The resulting clearances between vertebra members allow the vertebra column to be squeezed on either side while being expanded on the other. The shock-absorption effects are still afforded, but deflection is now permitted in two directions rather than only one.

The question may arise in connection with Figure 10 as to why the sliding shafts provided in passages 30 are required at all. The answer is that they are not absolutely required in any of the embodiments, but they add a measure of stiffness that prevents the spine assembly from being excessively flexible; the slidable shaft members would normally be resiliently deflectable and as a result would tend to add to the stiffness of the spinal assembly. Nonetheless, a single resiliently deflectable shaft of the proper dimensions could afford the proper stiffness. The use of a second shaft also prevents relative rotation among the individual vertebra members and between the vertebra column and the head. Small amounts of rotational movement would probably not be a functional problem, but it is thought that the user would normally find this movement somewhat annoying.

If it were desired to maintain alignment of the vertebra members without using a second shaft, the embodiment illustrated in Figures 11 and 12 could be employed. As before, similar reference numerals in Figures 11 and 12 identify similar portions of the structure, but a new reference numeral 50 is used to refer to a J-shaped shaft, which is the only shaft in the embodiment of Figures 11 and 12. Figure 11 shows the handle 22 as having an elongated recess 44 in which J-shaped shaft 50 is received. A rivet whose head is indicated by reference numeral 46 fits in handle 22 with its post 48 in the hooked portion of the J-shaped shaft to keep shaft 50 in position in handle 22. As before, the shaft extends into an insert 17, to which it is fixedly connected to hold the head in place.In this embodiment, the single shaft, which is fixedly connected at both ends, would typically be made of spring-tempered tool steel instead of the pultruded plastic of the fixed shafts in the other embodiments. Of course, the fixed shafts in the other embodiments could have been made of steel, and the sliding shafts could have been made of the pultruded plastic. In the embodiment of Figures 11 and 12, however, steel has been selected because the bulk of the stiffness of the shank of the hammer must be supplied by single shaft 50 itself, and it is thought that this characteristic is more readily afforded in a steel shaft.

Rotation of the vertebra members relative to each other and relative to the handle and head is prevented in this embodiment not by a second shaft but by the provision of rib portions 42 on the upper surface of the handle 22 and of the vertebra members 20. These ribs 42 fit in complementary slots 43 on the bottom surfaces of the vertebra members, and it can be appreciated that this arrangement prevents relative rotation.

Thus, the provision of ribs or other protuberances and complementary slots or other recesses can be employed to avoid the use of more than one shaft. Of course, in some applications two shafts may be found desirable from the point of view of stiffness or of the security of the attachment of the head, but in those situations in which the use of one shaft is practical, the arrangement of Figures 11 and 12 is a simple apparatus that affords the advantages of the present invention.

Figures 11 and 12 illustrate another feature that may be included in any of the emobdiments illustrated. A clearance 52 can be seen in Figure 12 between shaft 50 and the wall of the passage through which it extends.

Shaft 50 actually fits snugly in the passage, as can be seen in Figure 11, but the passage diverges toward either end. Since the vertebra members are in many cases intended to be essentially incompressible so that they can act as brace means, it may be found that the snug fit of the shaft throughout the length of the passage may contribute more stiffness to the shank than is actually desired. Accordingly, the arrangement shown in Figures 11 and 12 affords a snug fit that insures relative motion among the vertebra members and friction between the shaft and the vertebra member but does not interfere excessively with the deflection of the shaft.Of course, this shape of the cross section of the passages is not required, and its use will depend on a variety of factors, such as the shaft material, the vertebra-member material, and whether or not the column of vertebra members is to be used as a brace means. Other factors, such as the mass of the head or the length of the shank, can also be expected to have an effect on the desirability of the passage arrangement shown in Figures 11 and 12.

From the foregoing it can be appreciated that a truly novel arrangement for a hand impact tool has been provided that represents quite a significant advance in the art. Both the amplitude and the duration of shock experienced with hammers built according to the teachings of the present invention are reduced by the flexibility and damping characteristics that are inherent in the present invention. Furthermore, this flexibility can be afforded in a claw hammer without sacrificing the effectiveness of the claw function.

Claims

1. A hand impact tool comprising: a. an elongated spine assembly including: i) a multiplicity of vertebra members assembled to provide an elongated column, each of said vertebra members having a passage extending therethrough longitudinally of said column to provide an elongated passage through said column; ii) a resiliently deflectable shaft extending through said elongated passage and beyond at least one end of said column of vertebra members; iii) means spaced from said shaft for preventing relative rotation among said vertebra members about said shaft; and b. an impact-tool head fixedly connected to said one end of said resiliently deflectable shaft, said impact-tool head thereby being biased to a quiescent position relative to the end of said column of vertebra members remote from said head but being permitted upon deflection of said shaft to undergo a change in position relative to said remote end of said column of vertebra members.

2. The hand impact tool of Claim 1 wherein each of said vertebra members includes a second passage extending Iongitudinallytherethrough to provide a second elongated passage through said column, said means for preventing rotation including a second deflectable shaft extending through said second elongated passage.

3. The hand impact tool of Claim 2 wherein said second shaft is resiliently deflectable and fixedly connected to said impact-tool head.

4. The hand impact tool of claim 2 wherein said second shaft is polygonal in cross section.

5. The hand impact tool of Claim 1 or 2 wherein said first-mentioned shaft is snugly fit in said first-mentioned elongated passage.

6. The hand impact tool of Claim 2 wherein said first-mentioned shaft extends through the other end of said column of vertebra members, said hand impact tool further including a handle member fixedly connected to the end of said first shaft remote from said impact-tool head, said second shaft being fixedly connected to one of said handle and said impact-tool head and being slidably received in the other of said impact-tool head and said handle, rotation of said vertebra members relative to said handle thereby being prevented while motion of said head relative to said handle is permitted.

7. The hand impact tool of Claim 6 wherein said second shaft is fixedly connected to said impact-tool head and is slidably received in said handle.

8. The hand impact tool of Claim 6 or 7 wherein said second shaft is resiliently deflectable.

9. The hand impact tool of Claim 2 wherein said first shaft is pultruded from a material consisting essentially of continuous glass fibers in a polyester resin, said second shaft consists essentially of spring-tempered tool steel, and said vertebra members are molded from a material consisting essentially of a glass-filled polyamide resin.

10. A hand impact tool comprising: a. an impact-tool head having first and second ends; b. an elongated shaft having an end fixedly connected to said impact-tool head intermediate its ends, said shaft being resiliently deflectable but substantially unexpandable longitudinally; c. a handle fixedly connected to the end of said shaft remote from said head, said shaft thereby biasing said impact-tool head to a quiescent position relative to said handle; and d. brace means extending, when said head is in said quiescent position, between said handle and said head to engage said handle and to engage said head between said shaft and said first end but permit motion away from said handle of the part of said head engaged by said brace means, said brace means being substantially incompressible and thereby preventing motion from said quiescent position toward said handle of the part of said head engaged by said brace means, said shaft and said brace means thereby cooperating to permit said head to be tilted from said quiescent position in the direction of said second end of said head but prevented it from being tilted from said quiescent position in the direction of said first end of said head.

11. The hand impact tool of Claim 10 wherein said brace means includes a multiplicity of vertebra members assembled to provide an elongated column of substantially incompressible vertebra members, said column thereby including first and second end vertebra members on the ends of said column, each of said vertebra members having a passage extending therethrough longitudinally of said column to provide an elongated passage through said column, said shaft portion extending through said elongated passage, said first end vertebra member abutting said handle, said second end vertebra member, when said head portion is in said quiescent position, abutting said head at least between said shaft and said first end of said head to thereby provide said engagement of said head by said brace means.

12. The hand impact tool of Claim 11 wherein each of said vertebra members includes a second passage extending therethrough longitudinally of said column to provide a second elongated passage through said column, said hand impact tool further including a second deflectable shaft extending throuqh said second elongated passage, said second shaft thereby preventing rotation of said vertebra members relative to each other about said first shaft.

13. The hand impact tool of Claim 12 wherein said second shaft is fixedly connected to one of said handle and said head and slidably received in the other of said handle and said head.

14. The hand impact tool of Claim 13 wherein said second shaft is fixedly connected to said head and slidably received in said handle.

15. The hand impact tool of Claim 12, 13, or 14 wherein said second shaft is resiliently deflectable.

16. | The hand impact tool of Claim 15 wherein said second shaft consists essentially of spring-tempered tool steel.

17. The hand impact tool of Claim 16 in which there are two first shafts spaced apart in the direction substantially perpendicular to an imaginary line extending between said ends of said head.

18. A hand impact tool comprising: a. an impact-tool head having first and second ends; b. a handle; c. an elongated deflectable first shaft having one end fixedly connected to said impact-tool head intermediate its ends and having its other end fixedly connected to said handle; d. an elongated deflectable second shaft extending from said handle to said impact-tool head between said first shaft and said first end of said head, said second shaft being slidably received in at least one of said handle and said head, at least one of said first shaft and said second shaft being resiliently deflectable; ; e. a multiplicity of vertebra members assembled to provide an elongated column extending from said head to said handle, each of said vertebra members having first and second passages extending therethrough longitudinally of said column to provide elongated first and second passages, respectively, said first and second shafts extending through said first and second elongated passages, respectively.

19. A hand impact tool substantially as herein described with reference to and as illustrated in the accompanying drawings.