SHOCK ABSORBING HAMMER

Abstract: A shock absorbing hammer, comprising an elongated shaft (2) and a hammer head (1). An end portion (2a) of the shaft is obliquely oriented in a somewhat wider recess (6) in the hammer head (1) so as to permit a limited pivotal movement in one angular direction, the movement being damped by a shock absorbing material in said recess.

Description: Shock Absorbing Hammer FIELD OF THE INVENTION The present invention concerns a shock absorbing hammer, comprising a shaft and a hammer head being provided with a shock absorbing material, e.g. in the form of a rubber material, a hydraulic cushioning material or the like, the purpose being to dampen the rebound force and vibrations imparted to the shaft when the hammer head hits an object during a swinging motion of the hammer. PRIOR ART There are many examples of hammers of this general kind, see e.g. US 2,451,217, US 3,172,438, US 4,085,784 and SE-B-462,616. The last-mentioned document discloses a hammer, wherein an end portion of the shaft is mounted in a recess in the hammer head so as to permit a limited pivotal movement, being damped by a shock absorbing material, in one angular direction from a rest position when the hammer head strikes an object during a swinging motion of the hammer, whereas mutual movement in the opposite angular direction from said rest position is inhibited. Accordingly, the hammer can either be used in the normal way for striking an object, e.g. a nail, with the hammer head or, alternatively, for withdrawing a fastener, e.g. a nail, by means of a claw portion at the back of the hammer head. However, this known hammer is relatively complicated in its structure, namely with radially projecting lugs formed at the shaft end portion in order to ensure a direct surface contact between the shaft and the hammer head inside the recess, the latter being substantially parallel to but wider than the shaft end portion. In some embodiments there are also internal, especially adapted recess portions, in addition to a simple cylindrical bore in the hammer head, which make the production thereof even more complicated and expensive. SUMMARY OF THE INVENTION A primary object of the present invention is to accomplish a shock absorbing hammer of the kind defined in the preamble of claim 1 which has a simple structure and is inexpensive to manufacture and which provides an effective shock absorbtion. This object is achieved in that the shaft end portion and the recess in the hammer head are both cylindrical, the cylindrical recess in the hammer head being obliquely inclined in relation to the cylindrical shaft end portion, so as to provide wedge¬ like upper and lower recess portions, which accommodate the shock absorbing material and permit a limited pivotal movement in one angular direction, and in that, in the rest position, the shaft end portion is in surface contact with the inside wall of the obliquely inclined cylindrical recess at diagonally opposite locations directly, i.e., without the intermediary of said shock absorbing material, whereby mutual movement in the opposite angular direction is inhibited. The manufacture of a hammer according to the invention is simple. Thus, it is sufficient to make a downwardly inclined bore hole in the hammer head, as seen from the side of the shaft, and to insert the cylindrical shaft end portion, which has a smaller diameter, into the bore horisontally, so that the shaft end portion makes direct contact with the walls of the bore adjacent to the front end of the shaft, normally near the bottom of the hole, and adjacent to the opening of the bore, whereby the shaft end portion, and the central axis thereof, will extend at an angle, normally 3°-10°, preferably about 4°, relative to the bore axis. In this way, there will remain a lower recess portion with increasing vertical thickness from the location of contact near the opening of the hole to the bottom thereof, and an upper recess portion with increasing thickness in the opposite direction. These recess portions are shaped somewhat like a wedge, at least as seen in a vertical section, and are filled with a shock absorbing material. Ξecause of this wedge-like configuration, the dampening and shock absorbing power of the shock absorbing material will be uniform and effective along the full length of the shaft portion inserted into the cylindrical bore in the hammer head. Preferably, the cylindrical bore in the hammer head is lined internally by a cylindrical sleeve, fitted tightly in the bore, so that the interior of the sleeve constitutes the recess into which the shaft end portion is inserted. Advantageously, the sleeve is made of metal and is provided with deformed portions near its ends, at the upper side near the bottom of the bore and at the lower side near the opening of the bore, these deformed portions extending radially inwards so as to provide the desired surface contact between the recess and the shaft end portion. These and other optional features are stated in the dependant claims and will also appear from the detailed description below. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described further with reference to the appended drawing illustrating a preferred embodiment. Fig. 1 is a sectional view of the hammer head and the shaft end portion of a hammer according to the invention; Fig. 2 shows a sleeve separately in longitudinal section along the line A-A in fig. 3, the sleeve forming a part of the connection between the shaft and the hammer head; and Fig. 3 shows an end view of the sleeve of fig. 2. DESCRIPTION OF A PREFERRED EMBODIMENT The illustrated hammer comprises a conventional hammer head 1 which is resiliently connected to an end portion 2a of a tubular shaft 2, e.g. made of metal or a reinforced plastic material. The other end of the shaft (not shown in fig. 1) is provided with a gripping handle, as is well-known in the art of hand tools of this kind. The hammer head has a lower striking surface 3 and an upper claw portion 4, the latter being used for withdrawing nails or the like. A mid-portion of the hammer head 1 includes a substantially cylindrical portion 5 projecting backwards in parallel to the axis S of the shaft 2, to the right in fig. 1, to provide a secure connection with the shaft 2. A cylindrical bore 6, the diameter of which is somewhat larger than the external diameter of the tubular shaft 2, is made at a small angle α, about 4° in the illustrated embodiment, so that the bore axis B is slightly inclined downwards towards the front end, to the left in Fig. 1, relative to the horisontal axis S of the shaf 2 and the hammer head portion 5. A bushing or sleeve 7 (compare figs. 2 and 3), made of a metal material, preferably steel, is press-fitted into the bore 6, so that the interior of the sleeve constitutes a cylindrical recess firmly integrated with the hammer head 1. The shaft 2 is inserted with its end portion 2a into this recess, the axis S thereof being oriented horisontally or in parallel to the cylindrical, backwardly projecting portion 5 of the hammer head 1. Consequently, the forward, upper end of the shaft end portion 2a makes direct contact with the innermost end 7a of the sleeve 7 and the rear, lower end of the shaft end portion 2a makes direct contact with the outer end 7b of the sleeve. This contact is well-defined and distributed over a surface area by means of inwardly deformed material portions 8 and 9, respectively, at each location. Because of the inclinational angle α between the sleeve 6 and the shaft end portion 2a, there are formed wedge-like recess portions 10 and 11 between the inside of the sleeve 7 and the outside of the shaft end portion 2a, the thickness increasing towards the bottom of the recess at the lower side (10) and in the opposite direction at the upper side (11) . Of course, in che circumferential direction, the thickness of these recess portions will increase downwards at the front end 7a of the sleeve and upwards at the rear end 7b of the sleeve 7. The recess portions 10 and 11 are filled with a shock absorbing material, e.g. of rubber, foam, an elastically resilient plastic material or the like, which secures a permanent connection between the hammer head 1 and the shaft 2, on one hand, and provides the desired shock absorbing effect therebetween, on the other hand. During use in the normal way, when the hammer strikes an object such as a nail, the hammer head 1 will be retarded and bounce back upwards, whereas the shaft 2, which is held in the hand of the user, still has a momentum directed downwards. The mutual movement is such that the hammer head 1 will impart an upwardly directed force onto the shaft end portion 2a at the location of direct surface contact with the deformed material portion 9, at the rear end of the shaft end portion 2a. Because of the relative upward movement of the hammer head 1, the latter will perform a pivotal movement around the last-mentioned location of direct contact. This relative pivotal movement will be effectively damped and retarded by the shock absorbing material in the wedge-like recess portion 10. During this process, a large part of the kinetic energy will be absorbed and be transformed into thermal energy. Therefore, the shock impact onto the shaft and handle of the hammer will be considerably reduced. The structure of the hammer according to the invention may be modified by those skilled in the art within the scope of the appended claims. For example, the "cylindrical" shape of the hammer head recess and the shaft end portion includes also non- circular cross-sectional configurations, e.g. a rectangular cross-section. The crucial feature is the obliquely inclined orientation of the shaft end portion within the hammer head recess.

Claims: CLAIMS 1. Shock absorbing hammer, comprising an elongated shaft (2) and a hammer head (1) , an end portion (2a) of the shaft being mounted in a recess (6) in the hammer head so as to permit a limited pivotal movement, being damped by a shock absorbing material, in one angular direction from a rest position when the hammer head strikes an object during a swinging motion of the hammer, whereas mutual movement in the opposite angular direction from said rest position is inhibited, c h a r a c ¬ t e r i z e d i n that the shaft end portion (2a) and said recess (6) in the hammer head (1) are both cylindrical, the cylindrical recess (6) in the hammer head being obliquely inclined in relation to the cylindrical shaft end portion (2a) , so as to provide wedge-like upper and lower recess portions (11,10), which accommodate said shock absorbing material and permit said limited pivotal movement in said one angular direction, and in that, in said rest position, the cylindrical shaft end portion (2a) is in surface contact with the inside wall (7) of the obliquely inclined cylindrical recess (6,7) at diagonally opposite locations (7a, 8,7b, 9) directly, i.e., without the intermediary of said shock absorbing material, whereby mutual movement in the opposite angular direction is inhibited. 2. Shock absorbing hammer as defined in claim 1, wherein a cylindrical sleeve (7) of a hard and wear-resistant material is inserted radially between the cylindrical shaft end portion (2a) and a cylindrical bore (6) in the hammer head (1) , said sleeve (7) having radially protruding portions (8,9) adjacent to its ends (7a,7b) providing said surface contact locations. 3. Shock absorbing hammer as defined in claim 2, wherein said cylindrical sleeve (7) is fitted tightly in said cylindrical bore (6), the interior of said sleeve constituting said cvlindrical recess. 4. Shock absorbing hammer as defined in claim 3, wherein said protrusions (8,9) extend radially inwards. 5. Shock absorbing hammer as defined in any one of claims 2-4, wherein said protrusions are constituted by deformed portions (8,9) of the sleeve material (7). 6. Shock absorbing hammer as defined in any one of claims 2-5, wherein said cylindrical sleeve (7) is made of metal. 7. Shock absorbing hammer as defined in any one of claims 1-6, wherein the shaft (2) is constituted by a cylindrical member of a strong material. 8. Shock absorbing hammer as defined in claim 7, wherein the cylindrical shaft (2) member is tubular.

Inventors: BROK HANS, HEDELIN JOAKIM, BROK, HANS, HEDELIN, JOAKIM
Applicants: BROK HANS, HEDELIN JOAKIM, HULTAFORS AB, BROK, HANS, HEDELIN, JOAKIM
Application year: 1996
Main classification: B25D1
IPC codes: B25D1, B25G1, B25G3