Magnetic bit holder and hand tool incorporating same

A hand tool has an elongated shank with a handle at one end and a bit holder at the other end, the bit holder including a cylindrical body having a distal end surface and an axis, the body having an axial bore formed in the end surface of non-circular transverse cross section and terminating at an inner end surface. A neodymium permanent magnet is freely received in the bore and retained against the inner end surface by a thin circular retainer, formed of metal or plastic, which is interference-fitted in the bore. Both flat, disk-like and concave, bowl-shaped retainers are disclosed. A shock-absorbing cushion may be disposed between the magnet and the inner end surface of the bore. A bit formed of magnetizable material is mateably received in a socket portion of the bore and retained in place by the magnet. The portion of the bore receiving the magnet may have a different cross section from the socket portion. The magnet may be disposed in an encapsulation which interference fits in the bore.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to hand tools and, in particular, to tools incorporating a bit holder for receiving interchangeable bits, such as screwdriver bits or the like. The invention has particular application to tools in which bits are magnetically retained in a bit holder.

2. Description of the Prior Art

Typical current magnetic bit holders include a cylindrical body having a socket formed axially in one end thereof for mateably receiving an associated bit. The inner end surface of the socket has further formed therein an axial hole of reduced cross section receiving an associated magnet to retain the bit in place in the socket. A suitable permanent magnet is press-fitted or crimped into the magnet hole for magnetically retaining the associated bit in place. The magnet is commonly formed of a material such as Alnico and has considerable mass, typically being approximately one inch long and approximately one-quarter inch in diameter.

Other permanent magnet materials, such as neodymium, have been provided which can afford greater magnetic holding power with significantly reduced magnet mass. However, neodymium magnets are extremely brittle and cannot be press fit or crimped, nor can they be impacted in use by a bit, since such handling may cause the magnet to fracture and separate from the tool.

SUMMARY OF THE INVENTION

It is a general object of the invention to provide an improved magnetic bit holder which avoids the disadvantages of prior bit holders while affording additional structural and operating advantages.

An important feature of the invention is the provision of a magnetic bit holder which obviates the drilling of a separate hole for retention of a permanent magnet.

A further feature of the invention is the provision of a bit holder of the type set forth, which can effectively use a neodymium magnet.

Yet another feature of the invention is the provision of a bit holder of the type set forth which can effectively retain a neodymium magnet in place, minimizing the risk of fracture thereof and assuring adequate retention even in the event of fracture.

Yet another feature of the invention is the provision of a hand tool incorporating a bit holder of the type set forth.

These and other features of the invention are attained by providing a bit holder comprising: a cylindrical body having a distal end surface and an axis, the body having formed in the end surface an axial bore terminating at an inner end surface, a permanent magnet received in the bore and having an outer surface, and retaining structure in contact with the outer surface of the magnet and interference fitted in the bore to retain the magnet in the bore, the bore having a portion of non-circular transverse cross section outboard of the retaining structure defining a bit-receiving socket.

The invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring toFIG. 1, there is illustrated a hand tool10having an elongated shank11, provided at one end thereof with an enlarged handle12and provided at the other end thereof with a substantially cylindrical bit holder20. The shank11and the bit holder20are preferably of unitary, one-piece construction, being formed of a suitable metal, while the handle12may be formed of any desirable material, such as wood, plastic or the like. The handle12may have an axial bore to receive the adjacent end of the shank11or, alternately, may be formed around the handle end of the shank11, as by a suitable molding process, all in a known manner.

Referring also toFIG. 2, the bit holder20includes a circularly cylindrical body21having a distal end surface22in which is formed an axial bore23, which has a transverse cross-sectional shape which is non-circular, such as polygonal. Preferably, the bore23is hexagonal in transverse cross section. The bore23terminates at an inner end surface24.

A permanent magnet25is freely received in the bore23, the magnet25preferably being formed of a strong magnetic material, such as neodymium. The magnet25is preferably cylindrical in shape, having a diameter smaller than the across-sides width of the bore23. It will be appreciated that the size of the magnet25shown in the drawing is simply for purposes of illustration and that the magnet may actually be quite small and still provide sufficient holding force to retain an associated bit.

In order to retain the magnet25in place, there is also provided a retainer26which is in the shape of a flat, circular disk, and may be formed of a suitable metal. The retainer26is dimensioned to be interference-fitted in the bore23against the outer surface of the magnet25. Thus, it will be appreciated that the retainer26serves to effectively retain the magnet25in place against the inner end surface24. The retainer26is as thin as possible, preferably 0.005 inch or less, so as to maximize the magnetic coupling force between the permanent magnet25and the associated bit. A shock-absorbing cushion27, formed of rubber or other suitable shock-absorbing material, may be provided between the magnet25and the inner end surface24of the bore23. This serves to cushion the brittle neodymium magnet25against shock. While the cushion27is preferably provided, it is not essential and could be dispensed with.

The portion of the bore23outboard of the retainer26defines a socket or cavity for receiving an associated bit30. More specifically, the bit30has a working end31, which may be in the nature of a screwdriver bit, such as a cross-tip bit, a flat blade bit or the like, and also includes a hexagonal end32shaped and dimensioned for mating engagement in the bore23for driven engagement therewith. As can be seen inFIG. 2, the hex end32of the bit30bottoms against the retainer26and is magnetically retained in place therein by the magnetic holding force of the permanent magnet25.

It will be understood that, even in the event that the permanent magnet25should fracture with use, the retainer26will effectively serve to retain the magnet25in place and prevent escape of any magnet parts from the bore23. It will be also understood that a significant aspect of the invention0is that it obviates the drilling of an additional magnet-retaining hole in the body21of the bit holder20, thereby reducing the fabrication costs.

Referring now also toFIGS. 4 and 5, there is illustrated an alternative form of retainer, generally designated by the numeral35, which is a generally bowl-shaped, circular retainer, which is preferably oriented in use with its convex side facing the magnet25and is also dimensioned to be press-fitted in the bore23. The retainer35is illustrated as being formed of a suitable plastic material. It will be appreciated, however, that either of the retainers26or35could be formed or either metal or plastic. The bowl-shaped configuration of the retainer26also affords a certain flexible resilience, which can provide an additional cushioning effect to reduce the shock forces applied to the permanent magnet25.

Referring toFIG. 6, there is illustrated an alternative bit holder generally designated by the numeral40, which is similar to the bit holder20, described above, except for the nature of the bore therein. More specifically, the bit holder40has a cylindrical body41in which is formed an axial bore43terminating at an inner end surface44. The bore43may have any desired cross-sectional configuration, but is preferably circularly cylindrical. The bore43is provided with an enlarged cross section counterbore45which is non-circular in transverse cross section, preferably being hexagonal.

In this embodiment, the magnet25is dimensioned to fit freely in the bore43and, again, the cushion27may or may not be provided. The retainer26(or the retainer35) is then mounted in the counterbore45in the same manner as was described above in connection withFIG. 2, for retaining the magnet25in place.

Referring now toFIG. 7, there is illustrated another embodiment of the invention, utilizing an encapsulated magnet50. More specifically, the magnet25is completely surrounded with an encapsulation51. The thickness of the encapsulation51along the side of the magnet25is such as to provide an interference fit in the bore23, so that the magnet may be retained in place without the use of the retainers26or35. The thickness of the encapsulation51along the outer surface of the magnet25is such as to provide the necessary protection of the magnet25from shock as a result of contact with the bit30. Also, it will be appreciated that, in the event that the magnet25is fractured, the encapsulation51will prevent the escape of any pieces of the magnet25.

In the embodiment illustrated inFIG. 7, the encapsulation of the magnet is in the nature of a settable adhesive which may be deposited in liquid form around the magnet25in the bore. Thus, a thin layer of adhesive could first be deposited in the bore and the magnet set thereon and then the remainder of the adhesive flowed around the sides and outer surface of the magnet. Alternatively, the magnet could be set on the end surface of the bore and then adhesive flowed around the magnet in the manner described above. After the adhesive has set, it serves not only to retain the magnet in the bore23of the bit holder20or the bore43of the bit holder40, but would also provide a buffering protective layer between the magnet and the associated bit30.

While, in the embodiment ofFIG. 7, the encapsulation of the magnet is provided in situ in the bore, it will be appreciated that the encapsulation could be provided before the magnet is inserted in the bore of the bit holder. Referring toFIG. 8, there is illustrated another embodiment of an encapsulated magnet55, wherein the magnet25is completely surrounded with an encapsulation56, which may be formed of any suitable material, including plastic, rubber, brass or the like, but for purposes of illustration is shown as having a metal encapsulation. The dimensions of the encapsulation56may be similar to that of the encapsulation51of FIG.7and for the same reasons. In this case, the prefabricated encapsulated magnet55is press-fitted into the bore23, the encapsulation56protecting the magnet25from fracture during the press-fitted insertion.

Referring toFIG. 9, there is an alternative embodiment of the encapsulated magnet, generally designated by the numeral60, which utilizes encapsulation61covering only the outer and side surfaces of the magnet25. If desired, any of the magnets50,55or60could be used together with the cushion27between the magnet and the end surface of the bore. Also, while the encapsulated magnet has been illustrated as mounted in the bore23of the bit holder20, it will be appreciated that it could also be disposed in the bore43of the bit holder40.

From the foregoing, it can be seen that there has been provided an improved bit holder and a hand tool incorporating same, which afford the improved magnetic holding ability of a neodymium magnet, while at the same time minimizing risk of fracture of the magnet, and assuring retention of the magnet in place, even in the event of fracture.